Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. LATE QUATERNARY VOLCANIC STRATIGRAPHY WITHIN A PORTION OF THE NORTHEASTERN TONGARIRO VOLCANIC CENTRE A thesis presented as partial fulfi lment of the requirements for the degree of Doctor of Philosophy in Soil Science By Shane Jason Cronin Massey University Palmerston North New Zealand 1 996 Mount Ruapehu viewed from the east, July 1996. Fresh tephra covers snow on the northern sector of the volcano. ii ACKNOWLEDEGMENTS I thank Vince Neal l , Bob Stewart and Alan Palmer for al l their help during the course of this study. The enthusiasm and passion they have for their science has taught me that geology is not just a job, nor a discipline, but a lifelong process of d iscovery. I n particu lar I thank Vince for "letting me loose" on this project, even if it seemed that I was heading in the wrong direction at times. Cleland Wallace, John Kirkman, Brent Alloway and David Lowe have all provided valuable and h ighly appreciated input into various parts of this work, as have journal reviewers l isted within the thesis. I was the grateful benefactor of funding from the New Zealand Vice Chancellors Committee, the Helen E. Akers Scholarship fund (twice!) , the Massey University Graduate Research Fund and the Tongariro Natural History Society. Travel funding from the Royal Society of New Zealand (Young Scientists' Fund), Massey University Research Fund, and the New Zealand Vice Chancellors Committee (Ciaude McCarthy Fellowship) enabled me to attend two international conferences, which has greatly enhanced my Ph.D. experience. I am grateful to Justlands, the Department of Conservation and the Rangipo Forest Trust for access into parts of the study area. I thank al l my contemporaries in the Department of Soil Science for making it such a relaxed and "down to earth" place to work, particularly John (pH) Morrell and Shivaraj (Bucket) Gurung. Last but not least, I thank my family and I ris for their patient support during this work. iii ABSTRACT I nvestigation of the Late Quaternary volcanic stratigraphy within the andesitic Tongariro Volcanic Centre has elucidated the h istory of construction of the northeastern Ruapehu and eastern Tongariro ring plains and provided a lahar record for the Tongariro catchment. Volcaniclastic ring-plain sequences were correlated and dated using rhyolitic and andesitic marker tephras. The identification of d istal rhyolitic tephras in the area was improved by the application of d iscriminant function analysis (DFA) to their electron microprobe? determined g lass chemistry. The Okaia, Omataroa and Hauparu Tephras and the Rotoehu Ash were identified for the first time in this area, providing a chronology for pre- 22.6 ka ring-plain sequences not previously investigated . DFA of ferromagnesian mineral chemistry proved useful for d iscrimination of andesitic tephras, with titanomagnetite being the most useful phase. Development of an andesitic tephrostratigraphy in pre-22.6 ka sequences was aided by clustering analysis and DFA. Seven andesitic marker tephras were identified using a range of parameters to supplement the rhyolitic tephrostratigraphy. Using the tephrochronologic framework, 1 5 packages of lahar deposits were identified on the northeastern Ruapehu ring plain (from >64 to c. 5.2 ka) and six on the eastern Tongariro ring plain (from >22.6 to 1 1 .9 ka). Lahar deposition on both ring plains was most voluminous and widespread during the last (Ohakean) and antepenultimate (Porewan) stadials of the last glacial (Otiran). Holocene lahars were restricted to a narrow sector of the northeastern Ruapehu ring plain. They appear to have been triggered mostly in response to large-scale tephra eruptions of Ruapehu and Tongariro, and mostly occurred a long the path of the Mangatoetoenui Stream. Lahar deposits and surfaces beside the Tongariro River were mapped in eight lahar hazard zones, with lahar recurrence intervals ranging from 1 in > 1 5 000 years to 1 in 35 years. The largest number and volume of lahars in this catchment occurred in the period from 1 4.7 to 1 0 ka. The greatest population risk identified in the Tongariro catchment is part of Turangi, built within a 1 in 1 000 year lahar-hazard zone. Other property and infrastructure at greater risk include the State Highway 1 bridge across the Mangatoetoenui Stream and the Rangipo Dam and Power Station, with in a 1 in 35 year hazard zone. The landscape of the northeastern Ruapehu and eastern Tongariro ring plains has developed in relation to late Quaternary climate changes in addition to volcanic activity. During the last and antepenultimate stadials of the last glacial , major ring-plain aggradation by lahars and streams occurred. This was probably in response to greater physica l weathering and g lacier action on the volcanic cones provid ing abundant sediment for lahars. During the warmer interstadials of the last glacia l , soi l development within andesitic ring plain material was greatest, particu larly when the rate of soil accretion was low. iv TABLE OF CONTENTS PREFACE Frontispiece . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Acknowledgements iii Abstract iv r Table of contents V l tl?HH??J;:s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ? CHAPTER ONE: INTRODUCTION, OBJECTIVES, OUTLINE OF STUDY AREA AND PREVIOUS WORK - 1.1 1.2 1.3 - 1.4 -1.5 -1.6 -1.7 1.8 -1.9 1.10 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Objectives of study 1 Methods 1 Geography of the study area 2 Cl imate, soils and land use 4 Regional geologic setting 6 Tongariro Volcanic Centre 10 Previous work in and around the study area 1 0 Summary and conclusions from previous work 15 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 CHAPTER 2: RHYOLITIC TEPHROCHRONOLOGY 2.1 2.2 .... 2.3 2.4 2.5 2.6 2.7 2.8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Additional methodology and notes 22 Methods of identifying late Quaternary rhyol itic tephras on the ring 22 plains of Ruapehu and Tongariro volcanoes, New Zealand Keywords Introduction Setting Methods 2.7.1 Sample preparation and analysis 2.7.2 Statistical methods - 2.7.3 Tephra classification methodology Results 2.8.1 Ferromagnesian assemblages 2.8.2 Glass chemistry and similarity coefficients 1 0-22 ka tephras 22-65 ka tephras 2.8.3 Canonical d iscriminant function analyses of glass analyses 10-22 ka tephras discriminant model Classification of 1 0-22 ka unknown tephras 22-65 ka tephras discriminant model Classification of 22-65 ka unknown tephras V CHAPTER 3: ANDESITIC TEPHROCHRONOLOGY 3.1 I ntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3.1.1 Photographs of the Upper Waikato Stream sequence 41 3.2 Contributions of co-authors 44 3.3 Sourcing and identifying andesitic tephras using major oxide 45 titanomagnetite and hornblende chemistry, Egmont volcano and Tongariro Volcanic Centre, New Zealand 3.3.1 I ntroduction 45 3.3.2 Methods 48 3.3.3 Statistical methods 48 3.3.4 Discrimination between sources 49 Titanomagnetite 49 Hornblende 50 3.3.5 Discrimination of individual Egmont volcano-sourced tephras 52 Titanomagnetite 52 Hornblende 53 3.3.6 Summary and conclusions 55 3.3. 7 Acknowledgements 56 3.4 A multiple-parameter approach to andesitic tephra correlation, 56 Ruapehu volcano, New Zealand - 3.4.1 I ntroduction 57 3.4.2 Setting 57 3.4.3 Methods 59 3.4.4 Statistical methods 59 3.4.5 Stratigraphy and distribution of 23-75 ka andesitic tephras 61 3.4.6 Physical properties and mineralogy of 23-75 ka andesitic tephras 63 3.4.7 Mineralogy 64 3.4.8 Mineral chemistry of 23-75 ka andesitic tephras 66 3.4.9 Titanomagnetite (discrimination of Marker Units 1, 2 and 6) 67 3.4.1 0 Hornblende (discrimination of Marker Unit 4) 71 3.4.11 Olivine (discrimination of Marker Unit 5) 73 - 3.4.12 Other phases 74 "' 3.4.13 Conclusions 75 3.4.14 Acknowledgements 76 3.5 Combined reference list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 CHAPTER 4: PALEOSOL DEVELOPMENT AND PALEOCLIMATIC INVESTIGATIONS OF THE RING PLAIN SEQUENCE 4.1 4.2 4.3 4.4 4.5 -4.6 4.7 4.8 4.9 - 4.10 I ntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 I nvestigation of an aggrading paleosol developed into andesitic ring 82 plain deposits, Ruapehu volcano, New Zealand. I ntroduction 82 Setting 83 Stratigraphy 83 Physical description 84 Mineralogy of ash grade material 86 M??s M Results and discussion 88 4.9.1 Primary ash mineralogy 88 4.9.2 Sil iceous phases 88 4.9.3 Secondary minerals 90 Relationship of Ruapehu ring-plain sequence to climate record for 94 southern North Island vi 4. 1 1 Conclusions 96 4 . 1 2 Acknowledgements 97 4. 1 3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 CHAPTER 5: THE LAHAR RECORD AND CONSTRUCTION OF THE NORTHEASTERN RUAPEHU AND EASTERN TONGARIRO RING PLAINS 5 . 1 5 .2 5 .3 5 .4 5 .5 5.6 5 .7 5 .8 ?.9 5. 1 0 5. 1 1 . 1 2 - 5. 1 3 , 5. 1 4 5. 1 5 5 . 1 6 I ntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A late Quaternary stratigraphic framework for the northeastern Ruapehu and eastern Tongariro ring plains, New Zealand Keywords Introduction Setting Time control Terminology and identification of ring plain deposits Present channel geography Group 1 - Northeastern Ruapehu streams Group 2 - Streams drain ing both volcanoes Group 3 - Eastern and northeastern Tongariro streams Lahar d istribution on the eastern ring-plain sectors from 23 ka to the present Source and generation of lahars Summary and conclusions Acknowledgements References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 1 1 02 1 02 1 02 1 03 1 03 1 03 1 06 1 07 1 1 0 1 1 1 1 1 3 1 1 8 1 22 1 22 1 23 CHAPTER 6: LAHAR HISTORY AND LAHAR HAZARD OF THE TONGARIRO RIVER 6 . 1 6 .2 6 .3 6 .4 6 .5 6 .6 > 6.7 6 .8 6 .9 6 . 1 0 6 . 1 1 6 . 1 2 6 . 1 3 6 . 14 I ntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lahar history and lahar hazard of the Tongariro River, northeastern Tongariro Volcanic Centre, New Zealand Keywords Introduction Setting Terminology Hazards of lahars Methods Lahar h istory of the Tongariro River 6 .9 . 1 Stratigraphic record within the tributary streams 6.9 .2 Stratigraphic record with in the Tongariro River val ley 6.9.2A Highest surface 6.9.28 Lower surfaces Lahar hazards in the Tongariro River 6 . 1 0 . 1 1 in > 1 5 000 yea r zone 6 . 1 0 .2 1 in 12 000 yea r zone 6 . 1 0 .3 1 in 1 0 000 yea r zone 6 . 1 0.4 1 in 5 000 year zone 6 . 1 0 .5 1 in 2 000 year zone 6 . 1 0.6 1 in 1 000 year zone 6 . 1 0 .7 1 in 1 00 year zone 6 . 1 0 .8 1 in 35 year zone Discussion 6. 1 1 . 1 M itigation of hazards Conclusions Acknowledgements References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 1 25 1 26 1 26 1 26 1 27 1 27 1 29 1 30 1 30 1 30 1 31 1 3 1 1 34 1 36 1 37 1 37 1 37 1 39 1 39 1 39 1 39 14 1 14 1 1 42 1 43 1 44 1 44 CHAPTER 7: GEOLOGY AND LANDSCAPE DEVELOPMENT OF THE NORTHEASTERN TONGARIRO VOLCANIC CENTRE - 7 . 1 I ntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 47 - 7.2 Surficial geologic map of the northeastern Tongariro Volcanic Centre 1 47 7.2. 1 Methods 1 47 7 .2.2 Laharic surfaces 15 0 7.2.2A Ruapehu-derived lahar surfaces 15 0 7.2.28 Tonga riro-derived lahar surfaces 15 1 7.2.3 Lavas 15 1 7.2.3A Ruapehu-derived lavas 15 1 7.2.38 Tongariro-derived la va s 15 3 7 .2.4 Moraines 15 4 7 .3 Geological history of the northeastern ring plain of Ruapehu volcano, 15 4 New Zealand - 7.3. 1 I ntroduction 155 - 7.3.2 Geologic setting 155 I' 7.3 .3 Site of study 15 6 7 .3 .4 Stratigraphy 15 6 7.3.4A Age 15 6 7.3.48 Sequence 15 7 7 .3 .5 Lithology 1 60 7.3.5 A Diamictons 1 60 - 7.3.5 8 Andesitic tephra 1 61 7.3.6 Interpretation of geological history 1 62 7.3.7 Discussion and conclusions 1 66 7.3.8 Acknowledgements 1 66 7.3.9 Subsequent comments on the paper 1 67 7.4 Summary geological synthesis of the northeastern Tongariro 1 67 Volcanic Centre 7.4 . 1 c. 75 000 - 64 000 years ago 1 67 7.4.2 64 000 - 36 000 years ago 1 68 7.4.3 36 000 - 23 000 years ago 1 69 7.4.4 23 000 - 15 000 years ago 1 69 7.4.5 15 000 - 9 700 years ago 1 70 7.4.6 9 700 - 2 5 00 years ago 1 71 7.4.7 25 00 - present 1 71 7.5 Combined references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 71 CHAPTER 8: CONCLUSIONS 8 . 1 Fulfi lment of study objectives - Tephrochronology groundwork . . . . . . . . . . . 1 75 8.2 Fulfi lment of study objectives - Specific objectives 1 76 8.2 . 1 An improved assessment of the lahar hazards from Ruapehu 1 76 volcano 8.2.2 An a ssessment of the lahar hazards on the eastern Ton ga riro 1 76 ring plain and the Tonga riro Rive r - 8.2.3 A better understanding of the eruptive history (pa rticula rly 1 76 that of tephra eruptives) of the two volcanoes 8.2.4 An overall synthesis of the landscape development of the 1 77 northeastern Ruapehu and eastern Ton ga riro ring plains 8.3 Additional contributions made by this study 1 77 8 .3 .1 Rhyo/itic tephra identification 1 77 8.3.2 Andesitic tephra discrimination 1 78 viii 8.3.3 Halloysite/allophane formation in andesitic te phra s 1 78 8.3.4 Relationship of rin g plain construction to late Quaternary 1 79 climate change 8.4 Potential future work 1 79 8 .5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 80 APPENDICES APPENDIX 1 : SAS PROGRAMS USED IN THIS STUDY 1 . 1 Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 1 1 .2 Reference A3 APPENDIX 2: RHYOLITIC GLASS ANALYSES . . . . . . . . . . . . . . . . . . . . . . . . . . . A4 APPENDIX 3: ANDESITIC TEPHRAS 3 . 1 Ferromagnesian mineral assemblages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A 1 1 3.2 Hornblende analyses A 1 3 3.3 Olivine analyses A 1 5 3.4 Titanomagnetite analyses A 1 8 3 .5 Analyses of other phases A24 3.5. 1 Chromite A24 3.5 .2 Clinopyroxene A24 3.5 .3 Orthopyroxene A24 3.5.4 Andesitic g lass A25 3.5 .5 Plagioclase A26 3.5.6 l lmenite A26 3.5.7 Spine! A26 APPENDIX 4: SELECTED FIELD SECTION DESCRIPTIONS . . . . . . . . . . . . A27-A71 ix j LIST OF TABLES Table 1 . 1 Stratigraphy of Tongariro Subgroup tephras and interbedded tephras 1 3 described by Topping ( 1 973, 1 974) and Topping and Kohn ( 1 973). 1 .2 Stratigraphy of lahar formations on the SE Ruapehu ring plain, 1 5 from Oonoghue ( 1 99 1 ) and Purves ( 1 9 9 1 ) . 1 .3 Stratigraphy of andesitic and rhyolitic tephras on the SE Ruapehu 1 6 ring plain, from Oonoghue et al. ( 1 995). 2.1 Ages and sources of rhyolitic tephras with in the two discriminant 27 models used in this study. 2.2 Ferromagnesian mineral assemblages (modal %) and location 28 unknown tephra samples on the Ruapehu ring plain. 2.3 Correlation matrix of similarity coefficients, comparing glass major 29 oxide chemistry of rhyolitic tephras found in this study with published g lass chemistry (Stokes et al., 1 992) from potential correlative tephras aged 1 0-22 ka. 2.4 Correlation matrix of similarity coefficients, comparing glass major 30 oxide chemistry of rhyolitic tephras found in this study with published g lass chemistry from potential correlative tephras aged 22-65 ka. 2.5 Mean electron microprobe glass compositions of tephras used 3 1 in the initial 1 0-22 ka discriminant model . 2.6 02 values and classification efficiencies of the in itial d iscriminant 33 model for the 1 0-22 ka tephras. 2.7 Probabilities of classification of unknown tephras in the 1 0-22 ka 33 range with their potential correlatives, using the initial 1 0-22 ka tephra d iscriminant model . 2.8 02 values and classification efficiencies of the updated d iscriminant 34 model for the 1 0-22 ka tephras. 2.9 Probabil ities of classification of unknown tephras (that were poorly 35 classified by the in itial model) in the 1 0-22 ka range with their potential correlatives, using the updated 1 0-22 ka tephra discriminant model . 2.10 Mean electron microprobe compositions of tephras used in the 35 23-65 ka discriminant model . 2.1 1 02 values and classification efficiencies of the discriminant model 36 for the 22. 5-65 ka tephras. 2.12 Probabilities of classification of unknown tephras in the 22.5-65 ka 36 range with their potential correlatives, using the 22.5-65 ka tephra discriminant model. 3.1 Average titanomagnetite and hornblende chemistry from the two 49 tephra sources. 3.2 Classification efficiency of the between-source discriminant functions. 52 3.3 Egmont-sourced tephras used in the discrimination study. 53 3.4 Classification efficiencies of the d iscriminant function analyses for 53 the ind ividual Egmont-sourced tephras. 3.5 Rhyolitic tephras identified within the eastern ring plain sequence, 6 1 Ruapehu. 3.6 Mean electron microprobe analyses of final titanomagnetite, 66 hornblende and olivine groupings. 3.7 02 values between titanomagnetite groupings. 69 3.8 02 values between hornblende groupings. 73 X 3.9 02 values between olivine groupings. 3.1 0 Summary of the criteria for identification of andesite marker tephras in this study. 4.1 Rhyolitic tephra identified within the north-eastern ring plain sequence. 4.2 Soil physical properties of selected ash samples. 5.1 Tephra coverbeds used in this study. 5.2 Sedimentary features of ring plain deposits and their inferred mode of deposition . 5.3 Summary of the eruptive activity of Ruapehu and Tongariro volcanoes for the last 75 ka based on the ring plain tephra record (Topping, 1 973; Donoghue et al., 1 995; Cronin et al. , 1 996(a)). 6.2 Number and timing of lahars in tributary catchments of the Tongariro River, based on the exposed stratigraphic record in each catchment (Cronin and Neall , in press). 7.1 Mineralogy and locations of lava sampled from the northeastern Tongariro Volcanic Centre. 7.2 Rhyolitic tephra identified within the northeastern ring-plain sequence, Ruapehu . 7.3 Surface-flow sediment l ithotypes with in the northeastern Ruapehu ring plain area, with their characteristic properties and inferred mode of deposition. LIST OF PLATES Plate 1 .1 1 .2 3.1 3.2 3.3 3.4 View of the eastern flanks of Ruapehu volcano across its ring plain . View of Tongariro volcano from the southeast. Part of the Upper Waikato Stream sequence located at T20/4681 02 and represented in Figs. 3.6, 4 . 1 and 5.3. Marker Unit 1 tephra at T20/464098. Marker Unit 2 tephra at T20/4691 00. Marker Unit 3 tephra at T20/4681 02. LIST OF FIGURES 74 75 84 86 1 05 1 06 1 1 9 1 32 1 52 1 56 1 61 1 1 1 1 42 42 43 43 Figure 1 .1 Location of the study area (shaded) within the Tongariro Volcanic 3 Centre, central North Island, New Zealand . 1 .2 I nfrastructure and land ownership within the studied area. 5 1 .3 Soi ls of the study area. 5 1 .4 Vegetation/land use with in study area. 7 1 .5 Major elements of the Pacific- lndo-Australian Plate boundary through 7 New Zealand and the positions of the Taupe Volcanic Zone and the Tongariro Volcanic Centre. 1 .6 Sketch map of the geology of the region surrounding the study area, 9 adapted from Grindley ( 1 960) and Hay ( 1 967). 1 . 7 General ised geologic map of Ruapehu and related vents, adapted 1 4 from Hackett ( 1 985). xi 2.1 Location map of the eastern ring plains of Tongariro and Ruapehu 25 volcanoes. 2.2 (A) Plot of the first two canonical variates (Can 1 and Can 2) for 32 tephras comprising the in itial 1 0-22 ka rhyolitic glass discrimination model. (B) Plot of FeO vs. CaO weight % with in the rhyolitic g lass of the 32 tephras comprising the initial 1 0-22 ka discriminant model. (C) Plot of the first two canonical variates (Can 1 and Can 2) for 32 tephras comprising the updated 1 0-22 ka rhyolitic glass discriminant model. 2.3 Plot of the first two canonical variates (Can1 and Can2) for tephras 32 comprising the 22-65 ka rhyolitic glass discriminant model. 3.1 North Island of New Zealand with locations of Egmont volcano and 46 Tongariro Volcanic Centre. 3.2 Plots of the first and second canonical variates (Can1 and Can 2) 51 for titanomagnetite data, together with 02 values between source groups. (A) Sample mean data with al l oxide variables, (B) sample mean data excluding Cr203, (C) al l individual analyses using al l oxides. 3.3 Plots of the first and second canonical variates (Can1 and Can2) 51 for hornblende data together with 02 values between source groups. (A) Sample mean data, (B) al l individual analyses. 3.4 Plots of the first and second canonical variates (Can1 and Can2) for 54 Egmont-sourced tephras together with 02 values between tephra groups. (A) Using titanomagnetite data, (B) using hornblende data. 3.5 Location map of the eastern ring plains of Tongariro and Ruapehu 58 volcanoes. 3.6 Composite stratigraphic sequence from principal reference sections 62 observed in the Upper Waikato Stream area, with positions of andesitic and rhyol itic marker tephras shown . 3.7 Partial andesitic tephra isopach maps, (A) Marker Unit 1 , 65 (B) Marker Unit 3. 3.8 Plot of Ti02 wt% vs. FeO(recalculated) wt% of titanomagnetite data. 65 3.9 Plots of the first and second canonical variates (Can1 and Can2) 70 for titanomagnetite data. (A) Cluster-defined groupings, (B) mineralogical groupings, (C) mineralogical groupings with reduced variables (Cr203 omitted), (D) chemically defined groupings. 3.1 0 Plots of the first and second canonical variates (Can1 and Can2) 72 for hornblende data. (A) Cluster defined groupings, (B) refined cluster-defined groups. 3.1 1 Plots of the first and second canonical variates (Can1 and Can2) 72 for olivine data. (A) Cluster defined groupings, (B) mineralogical groupings, (C) mineralogical groupings with reduced variables . 4.1 Stratigraphic column of part of the northeastern Ruapehu ring-plain 85 sequence with paleosol development and its position with in the overall ring plain sequence. 4.2 Grain-size d istribution with in the fine ash materials assessed using 89 the methods of Alloway et al. (1 992). 4.3 Selected mineralogy of the fine ash sequence. 92 xii 4.4 The relationship of the northeastern Ruapehu ring-plain sequence 95 with deep sea 8018 isotope record , and southern North Island loess stratigraphy from the Rangitikei val ley, Wanganui and Taranaki. 5.1 Location of Tongariro Volcanic Centre including Mts. Tongariro 1 04 Ngauruhoe and Ruapehu and the streams dissecting the eastern Ruapehu and Tongariro ring plains. 5.2 A sequence of selected measured sections in the d i rection of 1 08 stream flow in the Mangatoetoenui Stream. 5.3 Composite stratigraphic sections for Group 1 streams draining 1 09 the northeastern flanks of Ruapehu . 5.4 Stratigraphy of lahar deposition episodes on the northeastern 1 1 1 Ruapehu and eastern Tongariro ring plains. 5.5 Composite stratigraphic sections for Group 2 streams draining 1 1 2 the northeastern flanks of Ruapehu and southeastern flanks of Tongariro. 5.6 Composite stratigraphic sections for Group 3 streams draining 1 1 4 the eastern flanks of Tongariro. 5.7 Distribution of deposits from lahar episodes: (A) R1 1 /T4, (B) R1 0 , 1 1 5 (C) R09/T3 and the Hinuera Formation , (D) T2. 5.8 Distribution of deposits from lahar episodes: (A) R08/T1 , (B) R07 1 1 6 and R06, (C) R05, (D) R04. 5.9 Distribution of deposits from lahar episodes: (A) R03 and R01 , 1 1 7 (B) R02. 6.1 Location of the Tongariro catchment, draining the northeastern 1 28 Tongariro Volcanic Centre in the central North Island of New Zealand. 6.2 Stratigraphy of sections preserved through the h ighest laharic 1 33 surface beside the Tongariro River. 6.3 Stratigraphy of sections through the lower laharic surfaces alongside 135 the Tongari ro River. 6.4 Lahar hazard map of the Tongariro River catchment. 1 38 6.5 Enlargement of lahar hazard map for Turangi and its surrounds. 1 40 7.1 Map of the surficial geology of a portion of the northeastern 1 48 Tongariro Volcanic Centre. 7.2 Legend of geologic un its mapped in Fig . 7. 1 with their relationship 1 49 to previously mapped formations and tephra marker beds. 7.3 Location of the Tongariro Volcanic Centre including Mts. Tongariro, 1 58 Ngauruhoe and Ruapehu, and the streams dissecting the eastern Ruapehu and Tongariro ring plains. 7.4 Composite stratigraphic columns of the northeastern Ruapehu ring- 1 59 plain sequence below the regional marker horizon of the Kawakawa Tephra . 7.5 Comparison of the northeastern Ruapehu ring-plain landscape events 1 64 with deep sea 8018 isotope record , rhyolitic tephra marker beds, and southern North Island loess stratigraphy from the Rangitikei val ley, Wanganui and Taranaki. 7.6 Summary diagram of the estimated rate (per ka) of lapil l i-producing 1 68 sub-plinian eruptions of Ruapehu and Tongariro volcanoes for the last 75 ka. xiii CHAPTER 1 : INTRODUCTION, OBJECTIVES, OUTLINE OF STUDY AREA AND PREVIOUS WORK 1 .1 Introduction Ruapehu and Tongariro are the two largest and youngest Quaternary volcanoes of the Tongariro Volcanic Centre in the central North Island of New Zealand. Both volcanoes are surrounded by ring plains composed dominantly of volcaniclastic deposits and lava flows. The ring plains are volumetrical ly as large or larger than the cone they surround. The ring plains provide arguably the best geologic record of the activity of the two volcanoes, because the cone itself is generally exposed to more severe physical weathering leading to greater erosion and loss of the stratigraphic record, and also older deposits tend to be buried by later erupted lavas. Of human importance, the geologic record contained with in the ring plains provides information on the rates and magnitudes of tephra eruptives and lahars from the two volcanoes which are of the greatest threat to l ife and property. 1 .2 Objectives of study The manifold objectives of this study all branched from the main aim of establishing a stratigraphy for the northeastern Ruapehu and eastern Tongariro ring plains. Once this stratigraphy was developed , investigations were made into the chronology and rates of tephra eruptions, lahars, lava flows and also soil development and landscape stabil ity. Prior to this study the last detailed work in this area of the ring plains was that of Topping ( 1 973, and 1 974). Topping's study was limited to the younger part of the stratigraphic record (<22.5 ka B .P . ) and mostly to the Tongariro ring plain . The outcomes of this study were to be; ( 1 ) an improved assessment of the lahar hazards from Ruapehu volcano in conjunction with the previous studies of Purves ( 1 990), Donoghue ( 1 991 ) and Hodgson ( 1 993) on other sectors of the volcano, (2) an assessment of the lahar hazards on the eastern Tongariro ring plain and the Tongariro River, (3) a better understanding of the eruptive history (particu larly that of pre-22.5 ka tephra eruptives) from the two volcanoes, and (4) an overall synthesis of the landscape development of the NE Ruapehu and E Tongariro ring plains. 1 .3 Methods The initial part of the study was carried out in the field . The ring-plain areas were traversed and detailed section descriptions taken of al l important exposures found. Effort was concentrated on the channels of rivers and streams which incise into the ring-plain deposits, affording the best exposure of the ring plain stratigraphy. Aerial photography was used where possible in conjunction with the field information to map deposits and/or surfaces using their coverbed stratigraphy. Previously dated tephra layers, both rhyolitic 1 and andesitic, were quickly found to be the most useful means of dating surfaces and deposits . Laboratory studies concentrated on the identification of these tephras and also on finding new marker tephra layers, particularly andesitic tephras. Laboratory studies involved analysing the mineralogy of tephras as well as major element mineral and glass chemistry using the electron microprobe technique. Statistical methods were developed and used for both rhyolitic and andesitic tephra identification from the chemical analyses. Further laboratory studies were also conducted on buried soil materials to investigate former soil-forming, landscape and paleoclimatic conditions. 1 .4 Geography of the study area This study was confined to the NE Ruapehu and E Tongariro ring plains and is effectively the volcanic portion of the Tongariro River catchment (Fig. 1 . 1 ). The southern extent of the area lies along the watershed boundary between the Whangaehu River to the south and the Tongariro River to the north. Donoghue ( 1 991 ) studied the Ruapehu ring plain in detai l south of this boundary. The studied area encompasses the full eastern extent of the two ring plains which terminate against footh i l ls of the Kaimanawa Mountains in the approximate position of the Tongariro River channel. The Round-the-Mountain Track on Ruapehu and a similar altitude (ea. 1 300 m) on Tongariro marks the western boundary of study. North of State H ighway 47A the study area narrowed to the general vicinity of the Tongariro River and its terraces. The town of Turangi is the largest population centre within the area with a population of 4239 in 1 991 (Department of Statistics, 1 992). In addition, two smaller settlements, Rangipo and Tokaanu, and the Rangipo Prison l ie within the study area. These settlements and other scattered dwellings are confined to the northern part of the area, while in the southern portion there are no permanent dwell ings (Fig. 1 .2) . The Turangi-Tokaanu area has been occupied by Maori of the Ngati Tuwharetoa tribe since the 1 6th century and European settlement began in the Tokaanu area as trout were released into the Tongariro River in the early 1 900s (Ciarke and Smith, 1 986). Prior to 1 964 less than 500 people lived in Turangi. The population swelled up to 7000 during the period of construction of the Tongariro Power Development from 1 964 to 1 983 (Mercer, 1 973). Following completion of the Tongariro Power Development the population has dwindled and the town has become a service centre for a developing tourist industry. In addition, the town services extensive exotic forestry planting and the surrounding farming industry. The southern part of the study area contains a large portion of the Tongariro National Park, while other parts of the area are Ngati Tuwharetoa tribal lands, Justice Department land and also Kaimanawa State Forest Park (Fig. 1 .2). A major arterial transport route, State H ighway 1 , runs through the centre of the area as wel l as three sets of high voltage electricity transmission l ines. Parts of the major Tongariro power development are also contained within the area. 2 I 1 75?30' Mt. Tongariro .... Mt. Ngauruhoe .... 0 5 1 0 km - - - - Main Trunk railway l ine - State Highways (SH) Figure 1 .1 . Location of the study area (shaded) within the Tongariro Volcanic Centre, central North Island, New Zealand 3 I n this hydroelectric power scheme water is d iverted from the southern tributaries of Ruapehu through an underground aqueduct into Lake Moawhango. Subsequently the water travels via a tunnel to the Rangipo Dam within the Tongariro River channel ; water from the Wahianoa River is a lso diverted into the dam (Ministry of Works and Development, 1 97 4 ). Water is then taken from the dam into the underground Rangipo Power station before being returned to the Tongariro River. A short d istance downstream a variable proportion of the water is d iverted through the Poutu Tunnel and Canal into Lake Rotoaira . A further tunnel is used to transfer water from Lake Rotoaira to the Tokaanu Power Station and eventually Lake Taupo via the Tokaanu Tai lrace Canal (Fig. 1 .2) . This power development produces not only 1 1 82 GWh of electricity from the two stations per annum, but adds extra water to Lake Taupo which in turn increases power generation at eight further hydroelectric power stations a long the Waikato River. At the time of writing, the Rangipo Power Station is generating at only half of its capacity, because one of its two turbines needs to be replaced due to abrasion suffered from sediment in the water sourced from tephra and lahars from Ruapehu eruptions during September-November 1 995. 1 .5 Cl imate, soils and land use The area studied ranges widely in physiography and altitude from the steep slopes of Ruapehu and Tongariro Volcanoes at ea. 1 400 m to the flat surfaces of Turangi and surrounds at 360 m. There is a corresponding range in climatic conditions within this area. Turangi has a mean annual temperature of 1 2 oc with a relatively large range between the average dai ly maximum and minimum temperatures of 1 7-6.9 oc {Thompson, 1 984). Away from the influence of the ocean, Turangi tends to have warm summer days and very cool winter evenings. The incidence of both ground and air frosts is high and the area is wel l sheltered from the prevai l ing westerly wind. Mean annual ra infal l is in the order of 1 600 mm (N.Z. Meteorological Service, 1 980) with maximum falls in the late autumn and winter months and lower falls in the summe?months. This produces a summer soil moisture deficit, while in winter runoff occurs (Tho?pson, 1 984 ). I n the higher a ltitude areas of Ruapehu and Tongariro rainfal l is on average h igher, up to 5000 mm, gale-force winds are common and temperatures are much lower. At 1 500 m altitude the mean annual maximum to minimum temperature range is 9.4 to 2 .3 oc. Heavy snow falls are common in the alpine areas and the winter snowline descends to the 1 400-1 500 m level . Four main groups of soils occur with in the study area (Fig. 1 .3) a l l of which are azonal and intrazonal soils (Staff of Soil Bureau , 1 968; Water and Soils Division, Ministry of Works and Development, 1 979). I n the areas close to the volcanoes the soils are typically recent soils developed from andesitic tephra erupted from Ruapehu and Tongariro volcanoes since the Taupo Tephra ( 1 850 years B .P . ; Froggatt and Lowe, 1 990). These soils are known as the Ngauruhoe series and have l imited production potential due to the harsh climatic conditions in which they occur. 4 .............. High voltage lines - State Highways --- Tunnels (for water) -- Rivers and streams = Canals - Study area boundaries A A Ngati Tuwharetoa land 1 I I from I Lake Moawhango Figure 1 .2 . Infrastructure and land ownership within the studied area. Tokaanu series (organic soils) recent soils from alluvium Hinemaiaia series (YBPS) Turangi series (YBPS) Rangipo series (YBPS) Ngauruhoe series (recent soils from volcanic ash) [36l bare rock and Ngauruhoe series Mt. Tongariro A Mt. Ngauruhoe A 0 5km I I 39? Figure 1 .3. Soils of the study area. Data from; Staff of Soil Bureau ( 1 968) and Water and Soils Division , M.W. and Development (1 979). Higher on the flanks of the volcanoes where the degree of erosion is higher areas of bare rock and scree occur. Northeast of the two volcanoes the andesitic tephra covering on top of the Taupo lgnimbrite becomes thinner and the soils are yellow-brown pumice soi ls, developed directly into the Taupo lgnimbrite. Closer to the volcanoes the soils are Rangipo soils and further north and lower in altitude Turangi soils occur. Both of these soil series have potential for pastoral or exotic forestry use, while the Turangi series with more favourable climatic conditions can a lso be used for fodder cropping. With in the low-lying area of the Tongariro River delta there is a mixture of recent soils from alluvium in areas near the present river course and organic soils in the swampy areas further away. The al luvium is composed in some cases of reworked Taupo Tephra and gives rise to another type of weakly developed yel low-brown pumice soil , the H inemaiaia series. These soils are of low ferti l ity and have few potential land uses, aside from low producing pastures. The whole area between Turangi and Lake Taupo is low lying and swampy and much of it is covered in peat in which is developed the Tokaanu series, an organic soi l . This area has little potential agricultural use as there is d ifficulty in its drainage and very low gradient to the Lake, so i t is best left as conservation reserve. The actual land use in this area depends not only on the soils but also the land ownership or status. Much of the study area, particularly the southern part is undeveloped agricultural ly (Fig. 1 .4). Portions are within Tongariro National Park and Kaimanawa State Forest Park, and in addition parts of the Ngati Tuwharetoa land is undeveloped . In the northern part of the study area there are large areas of exotic forestry planting (Radiata Pine and Douglas Fir) on the NW slopes of Tongariro and also alongside the Tongariro River. Well developed pastoral lands are restricted to the Rangipo Prison farm and surrounds, and smaller areas near Turangi . Much of the swampy low-lying area between Lake Taupo and Turangi and Tokaanu is either poorly developed pasture or remains as undeveloped wetlands with a high conservation value. 1 .6 Regional geologic setting The current geological setting of New Zealand is dominated by the boundary between the lndo-Austral ian and Pacific plates which occurs through most of the length of the country (Fig. 1 .5). The oblique angle of convergence of the two plates, the type of the crust along the boundary and the geometry of the plate boundary through New Zealand causes variations in the nature of the boundary (Cole and Lewis, 1 981 ; Cole, 1 986; Kamp, 1 992). To the NE of New Zealand oceanic crust of the Pacific Plate is being subducted beneath the Austral ian Plate, forming the Tonga-Kermadec Island arc system which includes the Kermadec volcanoes. Farther south the angle of convergence between the two plates and subduction becomes more oblique through the central North Island of New Zealand. 6 -....! Swamp vegetation ! Urban areas Pasture Tokaanu ? Exotic Forest ? >9 Native or reverting to native tussock, shrub and forest lands Mt. Tongariro .. , , , , ' ' ' I I I I I I I ' ' , ' Bare: .6. rock areas Mt. Ngauruhoe 0 5 km I I Figure 1 .4. Vegatationllanduse within study area. D Taupo Volcanic Zone - Plate Boundary -- Major Fault l ines ? Subduction in the direction of the arrows 40? 5 Ol..c: llJ 0 Ill c: >-e er? lndo-Australian Plate llJ .?I I ll: I If) llJ I -?1 ?;;:I ll:r !J I ::ll .,_Q er' .m r ? ti rj r ??'lt ? I I 175 ? I I I I I I I llJ ,' ?: ? .-B> I ?I .rj ?EI?ItJ:: I I 0 .:jl.fl? "?I;! I! (j I I c..; I I ? I I fi c: lE };:. 0 -8 117 I I I I ,,,. .., g <:J---60 ? mmtyr ? <1-= 50 o'>OJ mm/yr . "'? ?? .s-tti ? 40 ?1"1'1'1{ Pacific Plate 0 150 km I I Figure 1 .5. Major elements of the Pacific/lndo-Australian Plate boundary through New Zealand , and the positions of the Taupo Volcanic Zone and the Tongariro Volcanic Centre. Adapted from Cole and Lewis (1 98 1 ). Subduction is expressed in the central North Island by the development of a frontal ridge in E North Island; a volcanic front, including the andesitic and dacitic volcanoes of Ruapehu, Tongariro, Tauhara , Edgecumbe and White Island ; and an ensialic marginal basin behind the volcanic front (Cole, 1 990). Crustal spreading in the marginal basin has produced the voluminous Taupe Volcanic Zone (TVZ) rhyolitic volcanism in the Central North Island throughout the Quaternary (Wilson, et al. , 1 984; Wilson et al., 1 986). TVZ volcanism appears to have begun at around 1 .6 Ma (Pringle et al., 1 992; Soengkono et al. , 1 992), reflecting the inception of the current orientation of the plate boundary. The southern l imit of subduction volcanism is marked approximately by Ruapehu volcano; from this latitude southward the decreasing angle of convergence of the two plates eventually g ives rise to largely strike-sl ip motion between the two plates in the South Island (Fig. 1 .5). Strike slip motion is taken up along a series of faults in Hawkes Bay and Wairarapa in the North Island and in the Hope Fault zone and Alpine Fault in the South Island. The component of convergence between the two plates in the South Island is represented by the uplift of the Southern Alps along the Alpine Fault Zone where there is continental-continental crust collision (Kamp et al. , 1 989; Kamp and Tippett, 1 993). In the general vicin ity of the study area there are three geologically d istinct groups of rocks (Gregg , 1 960). These are: (1 ) indurated Triassic-Jurassic greywacke/arg i l l ite rocks and their low grade (semi-schist) metamorphic equivalents; (2) weakly indurated Tertiary (Miocene-Piiocene) marine sediments; and (3) Quaternary volcanic rocks and deposits with associated volcaniclastic sediments. The Triassic-Jurassic greywacke and argi l l ite rocks make up the Kaimanawa Mountains in the eastern part of the area and are the basement of the volcanic terrain (Fig. 1 .6). These rocks are equivalent to the Torlesse Terrane, an important and widely d istributed basement terrane throughout New Zealand (Korsch and Wellman, 1 988). These highly indurated and relatively unfossil iferous sedimentary rocks were orig inally deposited by turbid ity currents in a deep ancestral basin and were sourced from a granitic continental mass. The sediments were then scraped from a subducting crustal slab to be accumulated as an accretionary wedge. Later deformation and metamorphism occurred in the late Mesozoic when the rocks were metamorphosed up to semi-schist grade in places. They have been uplifted to their present position over the last 2 mi l l ion years during the Kaikoura Orogeny, relating to the propagation of the present boundary between the Pacific and lndo-Austral ian Plates through New Zealand. Tertiary marine sediments within the area (Fig 1 .6) were deposited on top of an eroded surface of the Mesozoic greywacke/argi l l ite basement (Fieming, 1 953; Gregg, 1 960; Grindley, 1 960; Will iams, 1 994). These sediments were deposited in the M iocene and Pliocene and include fossil iferous sandstone and siltstone with lenses of sub? bituminous coal , calcic sandstone and l imestone units. They represent the encroachment and presence of a shal low sea over the region during Miocene and Pl iocene times. 8 Recent alluvium Pumice alluvium of Taupe Tephra Recent lahars of Whangaehu River Waimarino Lahars l Murimotu Lahars late Huatapu lahars Pleistocene Rangipo Lahars Kawakawa Tephra Ruapehu Andesite ] Tongariro Andesite Quaternary Pihanga Andesite Kakaramea Andesite Pliocene marine sediments Miocene marine sediments Triassic greywake/argillite Triassic Kaimanawa Schist Main Trunk railway line State Highways (SH) Figure 1 .6. Sketch map of the geology of the region surrounding the study area (adapted from Grind ley ( 1 960) and Hay ( 1 967). 9 Quaternary volcanic rocks cap the eroded remnants of these late Tertiary sediments (Fig. 1 .6) and mostly consist of a series of andesitic stratovolcanoes of the Tongariro Volcanic Centre which are surrounded by aprons of volcaniclastic sediment and tephras. In addition, rhyol itic ignimbrites and reworked ignimbrite material from the Taupe volcano cover the northern part of the region (Fig. 1 .6) . 1 .7 Tongariro Volcanic Centre The Tongariro Volcanic Centre (TgVC) comprises four main volcanoes which l ie at the southern terminus of the Taupe Volcanic Zone (Fig. 1 .5 and 1 .6 ; Plates 1 and 2). I n addition to the four large andesitic volcanoes of Ruapehu , Tongariro, Kakaramea-Tihia and Pihanga ( in order of descending size) there are several smaller outlying centres. The eruptives of TgVC are mostly calcalkaline medium-K basic and acid andesites with minor amounts of basalt and dacite (Cole et al., 1 986; Graham and Hackett, 1 987). Within the porphyritic lavas the most common phenocrysts are plagioclase, hypersthene and augite, with minor amounts of hornblende and olivine. The TgVC eruptives are typical erogenic andesites consistent with the upper surface of the subducted Pacific Plate slab being 80 km below (Gamble et al., 1 990). The oldest radiometrical ly dated lava from the TgVC is 0 .27 ? 0.02 Ma (Hobden et al., 1 996); however, pebbles of TgVC lithology have been found in Lower Pleistocene conglomerates in the Wanganui region to the south (Fieming, 1 953). Activity continues into the historic record for both Tongariro and Ruapehu volcanoes with the most recent eruptions being those of Ruapehu volcano in 1 995-1 996. The pre-50 ka eruptive centres in the TgVC are aligned in a NW orientation, while the post-50 ka centres trend NNE, cross-cutting the old NW al ignment (Hackett, 1 985; Cole et al., 1 986). The eruptives from these two apparent sets of volcanism are petrological ly d istinct; the younger rocks are lower si l ica andesites than the older series and they contain more olivine-bearing lavas. The NNE trending vents are al igned with the young andesitic volcanoes of Mt. Edgecumbe, Whale Island and White Island and the orientation of the present subduction system, whereas the older NW trending system may represent an earlier orientation of subduction . 1 .8 Previous work in and around the study area The first mapping of the Tongariro region was carried out by Grange et al., ( 1 938). This reconnaissance mapping outlined the main components of the regional geology and the main volcanic features. Gregg ( 1 960) described early geologic observations and records of the volcanic activity and provided a description of the volcanic and non-volcanic geology of the area including the Grange et al. ( 1 938) maps. Later work by Grindley ( 1 960) d istinguished in greater detail several lava and lahar formations on and around Ruapehu. The Ruapehu ring plain was mapped as dominantly Waimarino Lahars (Fig. 1 .6) determined to be of Last Glacial age. 1 0 Plate 1 .1 : View of the eastern flanks of Ruapehu volcano across its ring plain . Plate 1 .2 View of Tongariro volcano from the south-east. The large cone on the left is the most recently active vent, Ngauruhoe. 1 1 Two further lahar formations, the Hautapu, and Murimotu Lahars which form terraces in the Whangaehu val ley were correlated to stadials of the Last Glacial and recent lahars were mapped in the Whangaehu Val ley. Hay ( 1 967) also mapped Murimotu Lahars on the NW flanks of Ruapehu. This deposit has been subsequently described as a 9 .5 ka debris-avalanche deposit (Palmer and Neall , 1 989). Mathews ( 1 967) mapped and described the Tongariro massif as being a multiple volcano, made up of several small overlapping volcanic cones of varying age. Mathews also mapped paired Last Glacial moraines beside the Waihohonu Val ley as well as in two valleys on the eastern flanks of the volcano. The first detailed work on the stratigraphy of the Tongariro and Ruapehu ring plains was carried out by Topping (1 974). Topping established a detailed chronology of late Pleistocene and Holocene distal rhyolitic tephras erupted from the TVZ calderas to the north which were interbedded with in the andesitic ring plain sequence (Topping and Kohn, 1 973). Using these tephra layers as time planes Topping developed a stratigraphy of andesitic tephras erupted from Tongariro and Ruapehu volcano from 1 3.8 ka B .P . to the present (Table 1 . 1 ) and mapped their d istributions (Topping, 1 973). The Tongariro Subgroup was defined to include al l of these described tephra formations. Topping also noted the presence of Hinuera Formation gravels containing reworked Kawakawa Tephra and ranging in age from 22.59 ka B.P. to ea. 1 0 ka. Hackett ( 1 985) carried out a detailed study of Ruapehu and described four formations of lavas and associated volcaniclastic rocks which comprise the massif (Fig 1 .7). Each of these formations represents a cone-building episode of Ruapehu . The Te Herenga Formation is the remnants of the oldest cone-building episode, the vents for which are thought to lie in the N-NW of Ruapehu (Hackett, 1 985; Hackett and Houghton, 1 989). The source vents for the next youngest, Wahianoa Formation are thought to l ie in the SE of the present cone. Both the Te Herenga and Wahianoa Formations are of andesitic composition. The Mangawhero Formation occupies the present summit of Ruapehu and is of basaltic to dacitic composition . The lavas erupted in the post-glacial period belong to the Whakapapa Formation which includes eruptives from the present summit vents as well as several flank vents spread widely over the volcano. The lavas of Ruapehu and the other volcanoes of the TgVC were further subdivided on the basis of petrology and geochemistry by Cole et al. ( 1 986) and Graham and Hackett ( 1 987). They defined six lava types on the volcano and its related vents characterised by their phenocryst species and geochemical similarities. Prior to the present study the most recent work on the eastern ring plains was that of Donoghue ( 1 991 ) who studied in detail the lahar and tephra stratigraphy of the Ruapehu ring plain to the south of the area investigated in this study. Purves ( 1 990), in a landscape ecology study on the Rangipo Desert area of the SE Ruapehu ring plain also contributed to elucidating the lahar stratigraphy of the area. Donoghue ( 1 991 ) and Purves ( 1 990) significantly revised the lahar stratigraphy from the early mapping of Grindley ( 1 960) and defined five new lahar formations dating from > 22.6 ka B .P to the present (Table 1 .2). 1 2 Table 1 .1 . Stratigraphy of Tongariro Subgroup tephras and interbedded rhyolitic tephras described by Topping ( 1 973, 1 974) and Topping and Kohn ( 1 973). Tephra ages are those currently accepted . Formation* Ngauruhoe Tephra Taupo Tephra (Unit Y) Mangatawai Tephra unnamed andesitic ash Whakaipo Tephra unnamed andesitic ash Waimahia Tephra (Unit S) Papakai Tephra Hinemaiaia Tephra Papakai Tephra Rotoma Ash Papakai Tephra Opepe Tephra (Unit E ) Papakai Tephra Mangamate Tephra Poronu i Tephra (Unit C) Mangamate Tephra Karapiti Tephra (Unit B ) Okupata Tephra unnamed andesitic ash ?Rotorua Tephra unnamed andesitic ash Puketarata Ash unnamed andesitic ash Rotoaira Tephra unnamed andesitic ash Rerewhakaaitu Tephra unnamed andesitic ash Kawakawa Tephra Members Poutu Lapi l l i Wharepu Tephra Ohinepango Tephra Waihohonu Lapi l l i Oturere Lapi l l i Oruanui lgnimbrite and Aokautere Ash Source t Age ka Reference to age TgVC ea . 1 .8-01 Taupo 1 .852 Froggatt and Lowe (1 990) Tongariro 2 .5-1 .852 Taupo TgVC Taupo TgVC Taupo 5.2-3.952 Wilson ( 1 993) TgVC Oakataina 8 .532 Froggatt and Lowe (1 990) TgVC Taupo 9.052 TgVC Tongariro Taupo Tongariro Taupo Ruapehu TgVC Okataina TgVC Maroa TgVC Tongariro TgVC Okataina Tongariro Taupo ea . 9.71 Topping ( 1 973) ea . 9 .71 9.8 1 2 Froggatt and Lowe (1 990) ea . 9.71 Topping ( 1 973) ea . 9 .71 9.782 1 0. 1 2 Wilson (1 993) >9.792 Topping ( 1 973) 1 3.082 Froggatt and Lowe (1 990) 1 3.82 Topping ( 1 973) 14 .72 Froggatt and Lowe (1 990) Wilson et al. , ( 1 988) * Taupo Volcanic Centre Unit nomenclature from Wilson (1 993) . t TgVC = Tongariro and Ruapehu volcanoes, Tongariro includes the vent of Ngauruhoe. 1 Estimated ages. 2 Average or single 14C ages on old (Libby) half l ife basis. 1 3 National Park Mt. Ngauruhoe ? ? Vents less than or equal to 30 ka 0 S km Ruapehu Group Whakapapa Formation N.Z. Stages K-Ar ages (Stipp, 1 968) Aranuian - - - - ?unconformity - - - - -.1-===-=-=i--- - - - - - - - Mangawhero Formation Otiran Wahianoa Formation Oturian Te Herenga Formation Terangian 24 ka 36 ka 230 ka Figure 1 .7. General ised geologic map of Ruapehu volcano and related vents, adapted from Hackett (1 985), with additions from Donoghue et a/ ( 1 988) and Lecointre et a/ ( 1 994). 1 4 Table 1 .2. Stratigraphy of lahar formations on the SE Ruapehu ring plain, from Donoghue ( 1 99 1 ) and Purves (1 990). Lahar formation Onetapu Formation Manutahi Formation Mangaio Formation 1 Manutahi Formation Tangatu Formation Te Heuheu Formation Age range (ka B .P . ) 1 .85 - present 3.28 - 4.60 4.60 4.60 - 5.43 5.43 - 14 .7 1 4.7 - > 22.6 Tephra boundary marker beds Taupo Tephra Waimahia Tephra Motutere Tephra Rerewhakaaitu Tephra no lower l imit defined 1 Mangaio Formation represents the deposits of a single event or a closely spaced series of events dated at 4.6 ka B.P . by Donoghue ( 1991 ) . The other formations span the presented time ranges and include multiple events. Based on the defined and mapped lahar formations Donoghue ( 1 991 ) and Hodgson ( 1 993) produced lahar hazard maps for the SE Ruapehu ring plain and the Whangaehu catchment. Do nog hue ( 1 991 ) and Donoghue et al. (1 995) a lso added to and revised the previously established rhyol itic and andesitic tephrostratigraphy developed by Topping ( 1 973, 1 974) and Topping and Kohn ( 1 973) extending the stratigraphy to 22.6 ka B.P. Donoghue e t al. ( 1 995) revised the base of the Tongariro Subgroup from ea . 14 ka B .P . to ea. 1 0 ka B .P. and defined the Tukino Subgroup to include tephras aged between 1 0 and 22.6 ka B .P. They group al l tephras erupted from the Tongariro Volcanic Centre since 22.6 ka B .P. into seven formations (Table 1 .3). The major additions to the existing stratigraphy were the newly defined Tufa Trig and Bul let Formations. The Tufa Trig Formation with 1 8 members and the Bul let Formation with 23 lapi l l i members record the activity of Ruapehu volcano over the last 1 .85 ka B.P. and the period 1 0 to 22.6 ka B .P . respectively. The definition of these two formations and mapping of the tephras within them contributed significantly to knowledge of the eruptive history of Ruapehu volcano. 1 .9 Summary and conclusions from previous work Geologic mapping of the study area and the surrounding region until the 1 970's was concentrated on the volcanic cones with only reconnaissance work carried out on the ring plains. The ring plains of Ruapehu and Tongariro volcanoes were mapped as mostly Waimarino and Rangipo Lahars respectively. The Ruapehu ring plain also had smaller areas mapped in more detai l . Topping ( 1 973 and 1 974) and Topping and Kohn ( 1 974) constructed the first detai led late Pleistocene and Holocene andesitic and rhyolitic tephrostratigraphy of the area, defining the Tongariro Subgroup. 1 5 Table 1 .3. Stratigraphy of andesitic and rhyolitic tephras on the SE Ruapehu ring plain, from Donoghue (1 991 ) and Donoghue et al. (1 995). Subgroup Formation Members Source Age (ka) I nterbedded rhyolitic te hras Ngauruhoe Formation Tongariro ea. 1 .85 - 01 Kaharoa Tephra Tufa Trig Formation Tf1 8 - Tf1 Ruapehu ea. 1 .85 - 01 Kaharoa Tephra 1 .852 Taupo Tephra Mangatawai Tephra Tongariro 2.5 - 1 .852 Mapara Tephra Papakai Formation TgVC 2.5 - 9.71 Waimahia Tephra Hinemaiaia Tephra Whakatane Tephra Motutere Tephra Tongariro Mangamate Poutu Lapilli Tongariro ea. 9.71 Subgroup Formation Wharepu Tephra 9.81 2 Poronui Tephra Ohinepango Tephra Waihohonu Lapilli Oturere Lapilli T e Rato Lapilli 9 .782 unnamed tephra TgVC 1 0Y Karapiti Tephra unnamed tephra TgVC Pahoka T ephra Tongariro ea. 1 0-9.81 Bullot Formation Ruapehu ea. 1 01 (upper) " Ngamatea Lapilli-2 Ngamatea Lapi ll i-1 Pourahu Member L 18 - L1 7 Tu ino Shawcroft Subgroup Lapill i L 16 1 1 .852 Waiohau Tephra L 1 5 - L8 1 3.082 ? Rotorua T ephra Rotoaira Lapilli Tongariro 1 3 .82 Bullot Formation L 1 5 - L8 Ruapehu (upper) 1 4.72 Rerewhakaaitu Tephra Bul lot Formation L7b - L4 (middle) ea. 1 8.01 Okareka Tephra3 Bullot Formation L3 - L 1 (lower) 22.62 Kawakawa Tephra 1 Estimated ages, references to ages the same as Table 1 . 1 . 2 Average or single 14C ages on old (Libby) half life basis, references as for Table 1 . 1 . 3 Age from Nairn (1 992). 1 6 Hackett ( 1 985) described the stratigraphy of the Ruapehu cone and with Cole et al. (1 986) and Graham and Hackett ( 1 987) subdivided the lavas of TgVC on the basis of their mineralogy and geochemistry. Later work by Donoghue ( 1 991 ) and Purves ( 1 990) constructed a more detailed lahar stratigraphy of the SE Ruapehu ring plain with 5 lahar formations defined by dated tephra interbeds. Donoghue ( 1 991 ) and Hodgson ( 1 993) then were able to produce lahar hazard maps of the SE Ruapehu ring plain and Whangaehu River based on the lahar stratigraphy. Donoghue ( 1 99 1 ) and Donoghue et al. ( 1 995) revised and added to the existing tephrostratigraphy, adding the Tukino Subgroup to extend the stratigraphy to 22.6 ka B .P . Donoghue and eo-workers also added a new stratigraphy of Ruapehu-sourced eruptives on the SE Ruapehu ring plain. I n conclusion, there are four areas in which geological investigations in the study area can add to that which has previously been carried out: ( 1 ) The NE Ruapehu lahar and tephra stratigraphy up to 22.5 ka B.P. can be mapped using the framework established on the SE Ruapehu ring plain . (2) The ring plain record older than 22.5 ka B .P . can be investigated to extend the existing lahar and tephra stratigraphy and the eruptive h istory of Ruapehu volcano. Both of these first two areas of investigation can contribute to a synthesis of the construction of the NE Ruapehu ring plain . (3) The E Tongariro ring plain has not been investigated since the reconnaissance mapping of Grindley ( 1 960) in which the entire area was mapped as the Rangipo Lahars. An investigation of the lahar and tephra stratigraphy in this area can potentially provide further information on the eruptive history of Tongariro volcano. (4) By mapping the lahar stratigraphy on the NE Ruapehu and E Tongariro ring plains as well as along the Tongariro River a lahar hazard map for these areas can be constructed. I n particular, knowledge of the lahar history of the Tongariro River, one of the most important dra inage channels from TgVC is necessary because the town of Turangi (ea. 4200 population) is located on low surfaces beside the river. I n addition the river is used for the Tongariro Power Development and al l of its tributaries draining the volcanoes are crossed by the main transport arterial route of State H ighway 1 . The relevance of this issue is demonstrated by the generation of at least two lahars in the Mangatoetoenui Stream in 1 995 which entered the Tongariro River. These lahars have seriously impacted on the Tongariro Power development by causing abrasion of turbines in the Rangipo Power Station necessitating the replacement of one of the two turbines, and also debris has accumulated behind the Rangipo Dam severely reducing its storage capacity. Serious effects on trout (a major tourist attraction and source of revenue for Turangi) also occurred and continue to occur at the time of writing due to much additional fine sediment remaining in the river system. 1 7 1 .1 0 References Clarke, C. and Smith , M . , 1 986. Turangi town centre, where to now? Taupe County Council Special Report, 1 5 . Cole, J .W. , 1 986. Distribution and tectonic setting of late Cenozoic volcanism in New Zealand. Royal Soc. of N.Z. Bul l . , 23: 7-20. Cole, J .W. , 1 990. Structural control and origin of volcanism in the Taupe Volcanic Zone, New Zealand. Bull. Volcanol . , 52: 445-492. Cole, J .W. and Lewis, K.B . , 1 981 . Evolution of the Taupo-Hikurangi subduction system. Tectonophysics, 72; 1 -21 . Cole, J .W. , Graham, I . J . , Hackett, W.R. , Houghton , B .F . , 1 986. Volcanology and petrology of the Quaternary composite volcanoes of Tongariro Volcanic Centre, Taupe Volcanic Zone. Royal Soc. of N.Z. Bul l . , 23: 224-250. Department of Statistics, 1 992. 1 991 Census of Population and Dwell ings, Waikato/Bay of Plenty Regional Report. Department of Statistics, Wel lington, N .Z. Donoghue, S .L . , Neal l , V .E . , Palmer, A.S. , 1 988. Holocene geology of the upper Whangaehu River, Mt. Ruapehu . Geological Soc. of N .Z. Mise. Publ. 41 a : 6 1 . Donoghue, S .L . , 1 991 . Late Quaternary volcanic stratigraphy of the south-eastern sector of Mount Ruapehu ring plain, New Zealand . Unpub. PhD. thesis, Massey University, Palmerston North , N. Z. Donoghue, S.L . , Neal l , V.E . , Palmer, A.S., 1 995. Stratigraphy and chronology of late Quaternary andesitic tephra deposits, Tongariro Volcanic Centre, New Zealand. J . Ray. Soc. of N.Z., 25: 1 1 5-206. Fleming, C.A. , 1 953. The Geology of Wanganui Subdivision. N .Z. Geological Survey Bul l . , 52: 362 pp. Froggatt, P .C. and Lowe, D. J. , 1 990. A review of late Quaternary si l icic and some other tephra formations from New Zealand : their stratigraphy, nomenclature , d istribution, volume and age. N .Z. J . Geol. and Geophys . , 33 : 89-1 09. Gamble, J .A. , Smith , I . E .M . , Graham, I . J . , Kokelaar, B .P . , Cole, J .W. , Houghton, B .F . , Wilson , C.J .N . , 1 990. The petrology, phase relations and tectonic setting of basalts from the Taupe Volcanic Zone, New Zealand, and Kermadec Island Arc? Havre Trough, SW Pacific. J . Volcano!. and Geotherm. Res . , 54: 265-290. Graham, I . J . , Hackett, W.R. , 1 987. Petrology of calc-alkaline lavas from Ruapehu volcano and related vents, Taupe Volcanic Zone, New Zealand. J. of Petrology, 28: 531 -567. Grange, L. l . , Wil l iamson , J .H . , Hurst, J .A. , 1 938. Geological maps of Tongariro Subdivision , to accompany, N .Z. Geological Survey Bul l , 40: 4 sheets. Gregg, D .R . , 1 960. The geology of Tongariro Subdivision. N.Z. Geological Survey Bull . , 40: 1 52pp. Grindley, G .W. , 1 960. Geological map of New Zealand, 1 st ed . , 1 : 250 000, Sheet 8, Taupe. D.S. I .R . , Well ington. 1 8 Hackett, W.R. , 1 985. Geology and petrology of Ruapehu volcano and related vents. Unpub. thesis Victoria University of Well ington: 31 2 pp. Hackett, W.R. , Houghton, B.F. , 1 989. A facies model for a Quaternary andesitic composite volcano: Ruapehu , New Zealand. Bull . Volcano! . , 5 1 : 51 -68. Hay, R,F . , 1 967. Geological map of New Zealand, 1 st ed . , 1 : 250 000, Sheet 7, Taranaki. D.S . I .R . , Well ington. Hobden, B.J . , Houghton, B. F., Lanphere , M.A. , Nairn, I .A. , 1 996. Growth of the Tongariro volcanic complex: new evidence from K-Ar age determinations. N .Z. J. Geol . and Geophys. , 39: 1 5 1 -1 54. Hodgson, K.A. , 1 993. Late Quaternary lahars from Mount Ruapehu in the Whangaehu River val ley. Unpub. PhD. thesis, Massey University, Palmerston North, N. Z. Kamp, P.J .J . , 1 992. Tectonic architecture of New Zealand . In Soons, J .M . and Selby, M.J . (eds). Landforms of New Zealand, 2nd Edition , Longman Paul , Auckland : 1 - 30. Kamp, P.J . J . , Green. P .F . , White , S .H. , 1 989. Fission track analysis reveals character of coll isional tectonics in New Zealand. Tectonics, 8: 1 69-1 95. Kamp, P.J .J , Tippett, J .M . , 1 993. Dynamics of Pacific Plate crust in the South Island (New Zealand) zone of oblique continent-continent convergence. J. Geophys. Res . , 98(B9): 1 6 1 05-1 6 1 1 8. Korsch, R.J . , Wellman, H .W. , 1 988. The geological evolution of New Zealand and the New Zealand region. In Nairn, A.E.M . , Stehl i , F .G. , Uyeda, S. (eds). The Ocean Basins and margins, Vol . 7B: 41 1 -481 . Plenium Publishing Corporation. Lecointre, J .A. , Neal l , V.E . , Palmer, A.S . , 1 994. A new lava field from the southwestern quadrant of the Ruapehu ring plain. Geological Soc. of N .Z. Mise. Publ. BOA: 1 1 1 . Mathews, W.H . , 1 967. A contribution to the geology of the Mount Tongari ro massif, North Island, New Zealand. N.Z. J . Geol. and Geophys. , 1 0: 1 027-1 038. Mercer, E.V. , (ed), 1 973. Turangi "the town of the future". Papers from the Lions symposium 1 2-1 3 May 1 973. Turangi Lions Club Inc., Turangi. Ministry of Works and Development, 1 974. New Zealand's latest power story, Tongariro Power Development. Ministry of Works and Development, Wellington, N .Z. Nairn, I .A. , 1 992. The Te Rere and Okareka eruptive episodes - Okataina Volcanic Centre, Taupo Volcanic Zone, New Zealand . N.Z. J . Geol. and Geophys. , 35: 93- 1 08 . New Zealand Meteorological Service, 1 980. Summary of climatological observations to 1 980. New Zealand Meteorological Service Mise. Publ . , 1 77. Palmer, B.A. , Neal l , V.E . , 1 989. The Murimotu Formation - 9500 year old deposits of a debris avalanche and associated lahars, Mount Ruapehu , North Island, New Zealand. N .Z. J. Geol. and Geophys. , 32: 477-486. Pringle, M .S. , McWil l iams, M . , Houghton, B .F . , Lanphere , M .A. , Wilson, C.J .N . , 1 992. 40Arf9Ar dating of Quaternary feldspar: Examples from the Taupo Volcan ic Zone, New Zealand. Geology, 20: 531 -534. 1 9 Purves, A.M . , 1 990. Landscape ecology of the Rangipo Desert. Unpub. MSc. Thesis. Massey University, Palmerston North, N .Z. Soengkono, S., Hochstein , M .P . , Smith , I .E .M . , ltaya, T. , 1 992. Geophysical evidence for widespread reversely magnetised pyroclastics in the western Taupe Volcanic Zone (New Zealand). N.Z. J . of Geol. and Geophys. , 35: 47-55. Staff of Soil Bureau, 1 968. Soils of New Zealand, Part 1 . N .Z. Soil Bureau Bul l . 26 (1 ) . Stipp, J .J . , 1 968. The geochronology and petrogenesis of the Cenozoic volcanics of the North Island of New Zealand . Unpub. Ph .D . Thesis. Austra l ian National University, Canberra. Thompson, C .S . , 1 984. The weather and climate of the Tongari ro Region. N . Z. Meteorological Service Mise. Publ . , 1 1 5(1 4): 35pp. Topping, W.W. , 1 973. Tephrostratigraphy and chronology of late Quaternary eruptives from the Tongariro Volcanic Centre, New Zealand . N. Z. J. Geol. and Geophys. , 1 6 : 397-423. Topping, W.W. , 1 974. Some aspects of Quaternary history of Tongariro Volcanic Centre. Unpub. PhD. thesis, Victoria University of Well ington N. Z. Topping, W.W. , Kohn , B.P. , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island , New Zealand . N.Z. J . Geol. and Geophys . , 1 6 : 375-395. Water and Soils Division , Ministry of Works and Development, 1 979. N. Z. Land Resource Inventory Worksheets, N 1 02 Tokaanu and N 1 1 2 Ngauruhoe and Bay of Plenty - Volcanic Region Landuse Capabil ity Extended Legend ( 1 2pp). National Water and Soil Conservation Organisation, Ministry of Works and Development, Well ington , N.Z. Wil l iams, J .K . , 1 994. Some aspects of the Cenozoic geology of the Moawhango River region, in the army training area, Waiouru , North Island, New Zealand. Unpub. MSc. Thesis. Massey University, Palmerston North , N .Z. Wilson, C.J .N . , Rogan, A.M . , Smith , I .E .M . , Northey, D .J . , Nairn, I .A. , Houghton, B .F . , 1 984. Caldera volcanoes of the Taupe Volcanic Zone, New Zealand. J . Geophys. Res . , 89(B1 0): 8463-8484. Wilson, C .J .N , Houghton, B .F . , Lloyd , E .F . , 1 986. Volcanic history and evolution of the Maroa-Taupo area, central North Island. Royal Soc. of N .Z. Bul l . , 23: 1 94-223. Wilson , C.J .N . , Switzur, R.V. , Ward , A.P . , 1 988. A new 14C age for the Oruanui (Wairakei) eruption, New Zealand. Geol. Mag . , 1 25: 297-300. Wi lson, C.J .N . , 1 993. Stratigraphy, chronology, styles and dynamics of late Quaternary eruptions from Taupe Volcano, New Zealand. Phi l . Trans. Roy. Soc. London A 343: 205-306. 20 CHAPTER 2: RHYOLITIC TEPHROCHRONOLOGY 2.1 Introduction Rhyolitic tephra layers have played a key role in previous stratigraphic studies of the Tongariro and Ruapehu ring plains. I n particular, Topping and Kohn ( 1 973) and Donoghue et al. (1 995) demonstrated the use of dated rhyolitic tephra layers to establish a stratigraphy of andesitic tephra layers and lahar deposits. In this study, one of the first approaches to establishing a stratigraphy on the NE Ruapehu and E Tongariro ring plains was to find and identify rhyolitic tephras in described sequences. In situations where the stratigraphy of a site was otherwise unclear, identification of a rhyolitic tephra layer within the sequence was an invaluable method of dating the sequence. In addition, in the older part of the ring plain sequences (> 40 ka B.P. ) , radiocarbon dating is impossible and identifying a rhyolitic tephra with in a sequence became even more crucial . The major problem encountered with using rhyolitic tephra layers was establ ishing their identity with confidence. Previous methods of rhyolitic tephra identification on the Tongariro and Ruapehu ring plains were based on stratigraphy, mineralogy and numerical comparisons of glass chemistry (Topping and Kohn , 1 973; Donoghue, 1 991 ). However, in many instances these methods were found to be insufficient to uniquely identify a particular tephra . Usually the existing methods could only narrow the field of possibi l ities, resulting in the necessity for a subjective decision of the tephras identity. In this study, methods of improving the unique identification of rhyolitic tephras within the ring plain sequence were investigated . In particu lar the statistical analysis of major oxide glass chemistry was attempted. These studies form the paper below which is in press in the New Zealand Journal of Geology and Geophysics (Vol. 40 No. 2 , 1 997). The paper has multiple authors and the following l ists each author's contribution to the work: S. J. Cron in: Principal investigator Carried out a l l : field description and sampling, laboratory preparation of samples, optical microscopy work, electron microprobe analysis, statistical programming and analysis, manuscript preparation and writing V.E. Neal l, A.S. Palmer, R.B. Stewart: Advisers Aided the study by: discussing results and methodology with SJC editing and d iscussion of the manuscript 21 2.2 Additional methodology and notes The problem of statistical closure discussed in the manuscript is due to the nature of compositional data; the component proportions (in this case, oxide weight proportions) must sum to unity (or close to unity) in compositional data. This is termed the constant sum constraint and causes a high degree of correlation or interdependence between the individual variables making up a composition (Aitchison, 1 983 and 1 986). However, d iscriminant function analysis (DFA) requires variables to be independent of one another. To remove the high correlation between the variables the log ratio transformation was developed by Aitchison ( 1 983). The formula: Yi = log(xi I xd ) describes the transformation, where xd is the score of the oxide chosen arbitrarily as the d ivisor, X; some raw oxide score and Y; the transformed score (i can take values 1 to d-1 ) . Not only does this procedure remove the statistical closure it reduces al l of the composition variables to the same order of magnitude. The SAS programs used for the D ISCRIM , CANDISC and STEPDISC statistical analyses in the following study are presented in Appendix 1 . A l isting of al l electron microprobe analyses of rhyolitic tephra samples carried out in this study comprises Appendix 2 . 2.3 METHODS OF IDENTIFYING LATE QUATERNARY RHYOLITIC TEPHRAS ON THE RING PLAINS OF RUAPEHU AND TONGARIRO VOLCANOES, NEW ZEALAND Shane J . Cronin, V.E. Neal l , A.S. Palmer and R.B. Stewart Department of Soil Science, Massey University, Private Bag 1 1 222, Palmerston North, New Zealand. New Zealand Journal of Geology and Geophysics 40, No. 2, in press. Abstract On the ring plains of Ruapehu and Tongariro volcanoes, d istal rhyolitic marker tephras provide a valuable stratigraphic framework. However, identification of many of these tephras has been imprecise. Here we provide a quantitative approach for identifying tephras with in the ring-plain sequences. We extend from simple canonical discriminant function models of glass chemistry to show how these, in conjunction with other geological information, can be used in a practical field-based study. In two stratigraphically distinguishable groups ( 1 0-22 ka and 22-65 ka), we established d iscriminant models for possible tephra correlatives from standard glass analyses. Testing analyses from unknown tephras against the models classified 34 of the 41 samples with probabi lities > 0. 75 to tephras that were consistent with mineralogical and stratigraphic evidence. Unknowns with lower probabil ities of classification had several possible correlatives. Some of these were improved when the tephras classified with > 0.75 probabil ity, and which were consistent with stratigraphic and other evidence, were 22 added to the discriminant models. The improved classifications were due to an increased number of samples for each tephra and also because the added analyses were produced by the same EMP operator under the same instrument conditions. Classifications of other unknowns were improved by considering them as mixed tephras. In addition to more rigorously correlating several tephras previously identified in this area, four tephras have been identified in the area for the first time, the Okaia, Omataroa and Hauparu Tephras and the Rotoehu Ash. These occur as microscopic accumulations of rhyol itic g lass shards with in weathered andesitic tephra deposits . 2.4 Keywords Ruapehu volcano, Tongariro volcano, ring plain, stratigraphy, rhyolitic tephra correlation, d iscriminant function analysis, Okaia Tephra, Omataroa Tephra , Hauparu Tephra , Rotoehu Ash . 2.5 I ntroduction Tephra layers play an important part in stratigraphic studies throughout New Zealand and the surrounding sea floor. The most voluminous and best studied tephra layers are the rhyolitic eruptives from calderas of the Taupo Volcanic Zone in the central North Island of New Zealand. Over 30 dated, widespread, rhyol itic tephras have erupted over the last c. 65 ka and most have well-constrained radiocarbon ages (Vucetich and Pullar, 1 969; 1 973; Howorth, 1 975; Vucetich and Howorth , 1 976; Froggatt and Lowe, 1 990). Primary tephra layers enable isochronous time horizons to be established in a wide range of depositional environments. In studies of the ring plains of andesitic volcanoes within the Tongariro Volcanic Centre, rhyolitic tephras enable relative ages to be assigned to andesitic tephras and lahar deposits in order to provide a basis for calculating eruption and volcanic hazard frequencies (Cronin et al. , 1 996a; Cronin and Neall , in press). The tephras a lso are used for investigating the construction of the ring plains (Cronin et al., 1 996b) and for investigations of soil development on ring plain materials (Cronin et al., 1 996c). Methods of rhyol itic tephra identification have become increasingly sophisticated over time as the need arose for identification of tephras in distal areas, where field criteria are less usefu l . Methods appl ied have involved mineralogical studies (e.g. Ewart, 1 963; Randle et al. , 1 97 1 ; Lowe, 1 988) and chemical stud ies (e .g . Smith and Westgate, 1 969; Kahn, 1 970; Borchardt et al. , 1 97 1 ; Froggatt, 1 983; Stokes et al. , 1 992). Chemical techniques have concentrated on g lass and titanomagnetite, and in New Zealand, g lass chemistry has assumed the greatest importance for chemical characterisation of tephras (e.g . Froggatt, 1 983; Stokes et al. , 1 992). Stokes and Lowe ( 1 988) introduced the use of canonical d iscriminant functions (DFA) with g lass chemistry to New Zealand tephras and showed a theoretical discrimination of tephras from different volcanic sources. Stokes et al. ( 1 992) went on to show a theoretical discrimination of several ind ividual rhyolitic tephras from Okataina and 23 Taupe sources. Shane and Froggatt ( 1 994) again demonstrated a theoretical d iscrim ination of six rhyolitic tephras of widely varying ages from the Taupe Volcanic Zone. Al l of these studies have shown the potential of the DFA method to d iscriminate New Zealand rhyolitic tephras but d id not go on to show these techniques used in a practical situation . The Shane and Froggatt ( 1 994) study in particu lar, a lthough providing a further demonstration of the statistical techniques, used tephras which ranged in age from 1 .85 ka to 1 .63 Ma that are unl ikely to be confused stratigraphically. Eighteen distal rhyolitic tephras have been identified on the ring plains of Tongariro and Ruapehu volcanoes ranging in age from ea. 0 .8 to 22 ka. (Topping and Kohn , 1 973; Donoghue et al. , 1 995). In this study we focus on the time range between 1 0 and 65 ka and provide a practical demonstration of the use of d iscriminant function analysis (DFA) to identify the rhyol itic tephras present. We extend from the initial construction of DFA models by testing unknown tephras against the models and attempt d ifferent means of improving their classification performance. 2.6 Setting Ruapehu volcano within the Tongariro Volcan ic Centre, is a large, active, andesitic composite volcano, and forms the highest point in the North Island at 2797 m (Fig. 2. 1 ). The current massif comprises a 1 1 0 km3 cone with a volcaniclastic ring plain of similar volume surrounding it (Hackett and Houghton, 1 989). Tongariro volcano is a slightly smaller andesitic massif made up of several coalescing volcanic cones (Mathews, 1 967), the largest of which is the recently active cone of Ngauruhoe. The ring plains of Ruapehu and Tongariro volcanoes are confined to the east by the Kaimanawa Mountains, and the Tongariro River is the approximate boundary of the eastern ring plains. The section local ities where rhyolitic tephras were found in this study are shown in Fig. 2 . 1 . 2.7 Methods 2. 7.1 Sample Preparation and analysis Rhyolitic tephra samples from macroscopic layers were cleaned in water using an u ltrasonic probe; it was unnecessary to concentrate further glass. When tephra samples were scattered within fine andesitic ash or soil material they were cleaned in 0.2 M acid? oxalate reagent to disperse them and to remove short-range order and organic constituents (Biakemore et al. , 1 987; Alloway et al., 1 992). G lass was then concentrated using a sodium polytungstate solution at a density of 2 .45 Mg/m3. Ferromagnesian minerals were concentrated from al l samples using a Frantz lsodynamic Separator. Grain mounts of ferromagnesian minerals were prepared and assemblages described by point counting. Glass grains were mounted in epoxy resin plugs, which were ground to expose the grains and pol ished . 24 Mt. Tongari ro ... Mt. Ngauruhoe ... 39? 1 0 I Mt. Ruapehu ... - State Highways Waihohonu Stream 41 1 75? 45' 0 5 km Figure 2.1 . Location map of the eastern ring plains of Tongari ro and Ruapehu volcanoes. Numbered dots ind icate locations of sections where the rhyolitic tephras of this study were sampled ; grid references are given in Table 2.2. 25 The major element chemistry was determined for polished ind ividual grains on a JEOL- 733 electron microprobe following the procedures and analytical conditions of Froggatt ( 1 983). A 20 )lm beam diameter was used when possible, otherwise a 1 0 llm beam was used with a beam current of 8 nA at an accelerating voltage of 1 5 kV. For each tephra sample at least 1 0 individual g lass shards were analysed . The glass chemistry was compared with published g lass analyses carried out under the same analytical conditions and on the same instrument (AIIoway, 1 989; Oonoghue, 1 991 ; Froggatt, 1 982; 1 983; Froggatt and Sol loway, 1 986; Froggatt and Rogers, 1 990; Lowe, 1 988; Pi l lans and Wright, 1 992; Stokes et al. , 1 992; Pi l lans et al. , 1 993; Shane and Froggatt, 1 994; Carter et al. . 1 995). Simi larity coefficients , and coefficients of variation (Borchardt et al. , 1 971 ) , were calculated to compare the unknown samples with large volume tephra units in the same general time frame. However, these often provided two or three possible correlatives for a sample, even after their position in the stratigraphic column was considered , leaving the difficulty of choosing the most l ikely correlative. To improve on this correlation, canonical OFA was used . 2.7.2 Statistical Methods Canonical OFA is a technique related to principal component analysis, which reduces the d imensionality of data such as compositional data which has a large number of independent variables. Canonical OFA produces a small number of l inear combinations of the quantitative variables which best discriminate pre-defined groups of observations or analyses. This means that instead of working with ten oxide scores to d iscriminate groups of samples, one or two canonical variables contain the information . A reference set of analyses with pre-defined groupings must first be set up and canonica l OFA is used to produce a d iscriminant model which can be used to classify unknown observations or analyses. The theory of OFA is outlined in many texts on multivariate analysis (e.g. Srivastava and Carter, 1 983; Johnson and Wichern, 1 992). The 02 or Mahalanobis d istance statistic is produced within the results of canonical OFA, and indicates the multivariate spacing between data groups in multi-d imensions (Srivastava and Carter, 1 983). The 02 statistic is therefore a useful measure of the separation of groups of samples (Stokes et al. , 1 992) in place of the coefficients of variation and similarity coefficients fi rst used with volcanic glass by Borchardt et al. ( 1 971 ) . The studies of Beaudoin and King (1 986) and Stokes and Lowe ( 1 988), introduced the use of stepwise OFA methods which selected variables that had the greatest discriminating power. Stepwise OFA is further described by Srivastava and Carter ( 1 983). In this study the SAS system programs O ISCRIM, STEPOISC and CANOISC were used (SAS Institute I nc. , 1 989). Prior to statistical analysis the data used in this study were transformed fol lowing the log-ratio procedure of Aitchison (1 983, 1 986) and Stokes and Lowe ( 1 988) to avoid statistical closure, inherent in compositional data. We used MgO as the oxide d ivisor for this study, because of its moderate content and relatively low with in , and between sample variance (Shane and Froggatt, 1 994 ). 26 2.7.3 Tephra classification methodology From the overall time interval of 1 0-65 ka, separate data bases were establ ished for two stratigraphically d istinct groups of tephras (Table 2. 1 ) ; those above and below the regional marker horizon of the Kawakawa Tephra (22.6 ka B.P. , Wilson et a/., 1 988). This enables two simpler discriminant models to be created rather than a single very complex model . All known tephras of sign ificant volume within each time interval were included. Database 1 contained g lass analyses of Karapiti, Waiohau , Rotorua , Rerewhakaaitu, Okareka and Te Rere Tephras. Database 2 contained analyses of Kawakawa, Okaia, Tihoi, Omataroa, Mangaone and Hauparu Tephras, and Rotoehu Ash . Analyses of Maketu Tephra were unavailable. The analyses were from published sources listed previously and unpublished data of SJC. Discriminant models were then created for each of these reference sets using the D ISCRIM program. Analyses of samples from the two stratigraphic intervals collected from the Ruapehu and Tongariro ring plains were tested against the discriminant functions calculated from the models. To improve any poor classifications resulting from this first model two further approaches were used . Firstly, unknown tephras that were correctly classified were added to the initial model to attempt to improve its performance in classifying the remaining unknowns. To satisfy the 'correctly classified' precondition, the overal l probabil ity of classification of a g iven sample with a particular tephra had to be high (>0.75), and this had to be consistent with all other evidence from stratigraphy, field observations and mineralogy. Secondly, in some cases where it appeared the sample was of a mixed origin , each component of the mixture was treated as a separate tephra for classification. Once again, any classifications made had to be consistent with other l ines of evidence. Table 2.1 Ages and sources of rhyolitic tephras within the two discriminant models used in this study. Tephra name Source* Database 1, 10-22 ka tephras Karapiti Tephra TVC Waiohau Tephra OVC Rotorua Tephra OVC Rerewhakaaitu Tephra OVC Okareka Tephra OVC Te Rere Tephra OVC Database 2, 22.5-65 ka tephras Kawakawa Tephra TVC Okaia T ephra TVC Omataroa Tephra OVC Mangaone Tephra OVC Hauparu Tephra OVC Tihoi Tephra TVC Rotoehu Ash OVC Symbol Kp Wh Rr Rk Ok Te Kk 0 Om Mn Hp T Re Age (Yrs B.P.) 9820 ? sot 1 1 850 ? 60t 1 3080 ? sot 1 4700 ?1 1 0t c. 1 8000* 21 1 00 ? 320t 22590 ? 230t c. 23000* 28220 ? 630t 27730 ? 350t 35870 ? 1 270t c. 46000* 64000 ? 4000? * TVC - Taupo Volcanic Centre; OVC = Okataina Volcanic Centre. t Denotes 14C ages on old half l ife basis. * Estimated stratigraphic age. s Whole rock K-Ar age. 27 Reference for age Froggatt & Lowe (1 990) Wilson et al. ( 1 988) Froggatt & Lowe (1 990) Wilson et al. ( 1 992) 2.8 Results 2.8.1 Ferromagnesian Assemblages Table 2.2 Ferromagnesian mineral assemblages (modal %) and location of unknown tephra samples on the Ruapehu ring plain. Ferromagnesian mineralogy Sample number Section number 10-22 ka tephras 93.5 93.6 93.7 93.8 93.9 93.32 93.59 94.7 94.9 94.21 94.24 94.27 94.28 94.29 94.37 94.47 94.51 94.58 94.71 94.74 94.79 95.2 95.3 95.6 95.9 95. 1 3 20 22 1 07 26 29 7 68 20 30 55 57 58 59 59 62 66 67 68 70 7 1 73 81 81 82 83 96 22. 5-65 ka tephras 93. 1 1 93.3 3 93. 1 7 4 1 93.33 7 7 .37 7 7 .36 7 9.37 9 9.36 9 9.35 9 9.33 9 9 .25 9 9.22 9 9.21 9 1 4.23 1 4 1 4.22 1 4 Abbreviations: opx Grid Ref. NZMS 260 T20/4651 27 T20/453 1 29 T20/430 1 27 T20/435 1 29 T20/498 1 57 T20/4691 00 T1 9/505248 T20/4651 27 T20/468 1 62 T1 9/48 1 2 1 1 T1 9/4862 1 1 T1 9/485221 T1 9/495220 T1 9/495220 T1 9/485238 T1 9/496238 T1 9/504237 T1 9/505248 T1 9/488242 T1 9/499247 T1 9/364544 T1 9/430238 T1 9/430238 T1 9/423339 T1 9/448326 T1 9/549328 T20/455088 T20/465095 T20/461 1 70 T20/469 1 00 T20/468 1 02 T20/4771 1 2 opx 52 54 49 43 54 53 69 48 50 58 57 69 4 1 46 61 53 56 73 53 68 67 61 53 51 63 59 30 53 35 32 58 66 63 66 68 59 79 75 78 77 79 cpx 4 1 40 37 53 25 22 24 1 6 30 40 29 27 1 6 34 35 23 40 20 34 26 1 5 37 35 4 1 32 32 44 37 1 8 1 5 39 28 27 23 20 35 1 9 21 18 1 9 1 9 hb 5 2 1 2 2 5 3 tr 1 5 1 tr 2 37 4 3 1 8 3 2 1 2 2 6 1 8 4 2 1 1 8 2 33 37 6 4 1 0 3 2 2 2 1 1 orthopyroxene, cpx = clinopyroxene, hb curnrningtonite, tm = titanomagnetite; tr = trace quantities ( < 1 %). bi tr 1 8 tr tr cu tr tr 1 tr tr tm 2 4 2 2 1 5 3 7 2 1 1 9 2 1 4 2 6 1 6 1 6 1 5 1 4 2 1 4 4 3 8 8 8 1 4 1 6 3 6 4 7 2 3 tr 2 2 3 1 hornblende, bi = biotite, cu The ferromagnesian assemblages for tephra samples studied are given in Table 2.2. These can be compared to the dominant mineral assemblages summarised by Froggatt 28 and Lowe ( 1 990). The ferromagnesian assemblage is often useful to narrow down the possible correlatives of a tephra sample, but was rarely able to identify it un iquely. The assemblages are also found to be highly variable due to winnowing effects in d istal localities and the common contamination of samples with andesitic tephra minerals. This contamination is evidenced by the presence of abundant clinopyroxene in many of the samples. 2.8.2 Glass chemistry and similarity coefficients 1 0-22 ka tephras A correlation matrix with the similarity coefficients for the tephra samples from Ruapehu and Tongariro ring plain deposits in the 1 0-22 ka period with their potential correlatives is presented in Table 2.3. l t has been reported that similarity coefficients for replicate analyses under the same microprobe operating conditions can deviate by around 1 0 % from the expected ideal value of 1 .0 (Froggatt and Solloway, 1 986; Stokes et al., 1 992). When different beam diameters are used , replicate analyses can have similarity coefficients as low as 0.88 (Pil lans and Wright, 1 992). Table 2.3 Correlation matrix of similarity coefficients , comparing glass major oxide chemistry of rhyolitic tephras found in this study with published g lass chemistry (Stokes et al., 1 992) from potential correlative tephras aged 1 0-22 ka. Tephra abbreviations from Table 2 . 1 . Sample Kp Wh Rr Rk Ok Te 93.5 0.76 0.85 0.81 0.81 0.78 0.80 93.6 0.84 0.91 0.91 0.85 0.82 0.93 93.7 0.78 0.87 0.86 0.82 0.80 0.86 93.8 0.77 0.81 0.82 0.78 0.75 0.82 93.9 0.78 0.92 0.83 0.88 0.87 0.86 93.32 0.80 0.93 0.88 0.88 0.79 0.69 93.59 0.80 0.92 0.88 0.88 0.85 0.88 94.7 0.85 0.94 0.90 0.87 0.84 0.94 94.9 0.94 0.81 0.92 0.75 0.72 0.88 94.21 0.86 0.91 0.93 0.85 0.82 0.94 94.24 0.91 0.77 0.88 0.72 0.70 0.84 94.27 0.80 0.94 0.84 0.94 0.91 0.88 94.28 0.79 0.92 0.84 0.94 0.92 0.86 94.29 0.82 0.90 0.84 0.92 0.91 0.86 94.37 0.86 0.93 0.90 0.87 0.84 0.95 94.47 0.74 0.84 0.77 0.85 0.84 0.81 94.51 0.84 0.94 0.90 0.87 0.84 0.93 94.58 0.81 0.90 0.86 0.87 0.86 0.89 94.71 0.79 0.95 0.84 0.93 0.90 0.87 94.74 0.84 0.93 0.90 0.86 0.83 0.92 94.79 0.85 0.70 0.80 0.67 0.65 0.77 95.2 0.84 0.93 091 0.87 0.84 0.93 95.3 0.79 0.93 0.84 0.93 0.91 0.88 95.6 0.88 0.91 0.93 0.85 0.82 0.96 95.9 0.84 0.90 0.93 0.85 0.81 0.93 95. 13 0.86 0.93 0.91 0.87 0.83 0.94 Kp 0.81 0.89 0.76 0.75 0.91 Wh 0.86 0.92 0.89 0.89 Rr 0.80 0.78 0.93 Rk 0.97 0.84 Ok 0.81 29 Most of the tephra samples from this study in the 1 0-22 ka interval have simi larity coefficients of 2:: 0.90 with published data for two or more of their possible correlatives. Simi larity coefficients comparing published analyses of tephras in the 1 0-22 ka age range (Table 2.3) show a very high degree of correlation between almost all of the possible tephra combinations especially those from the same volcanic centre. The high degree of similarity between the glass chemistry of the tephras of this age range renders the similarity coefficient comparison technique ineffectual and a unique correlation can not be made for each unknown sample. 22-65 ka tephras A correlation matrix of similarity coefficients for tephra samples from Ruapehu and Tongariro ring plain deposits in the 22-65 ka period with their potential correlatives is presented in Table 2.4. Again , most of the samples have more than one potential correlative with the similarity coefficient comparisons. In a comparison of published g lass chemistry of the tephras in this time frame (Table 2.4), similarity coefficients indicate a high degree of correlation between al l of these tephra combinations with the exception of Hauparu Tephra , which is d istinctive. The high degree of similarity between most of the tephra units in this time frame render the simi larity coefficient comparisons virtually unusable. This is particularly true for the study area, in which the stratigraphy beneath the Kawakawa tephra was completely unknown prior to this study. Table 2.4 Correlation matrix of simi larity coefficients, comparing glass major oxide chemistry of rhyolitic tephras found in this study with published glass chemistry from potential correlative tephras aged 22-65 ka. Tephra abbreviations from Table 2. 1 . Sam[!le Kk* ot om? Mn* H[!* rt Re* 95. 1 0.82 0.83 0.82 0.79 0.76 0.78 0.78 93.3 0.90 0.90 0.92 0.89 0.72 0.83 0.85 93. 1 7 0.88 0.88 0.93 0.89 0.73 0.81 0.82 93.33 0.86 0.87 0.88 0.87 0.74 0.82 0.82 7.37 0.85 0.85 0.83 0.82 0.72 0.80 0.81 7.36 0.92 0.90 0.89 0.81 0.70 0.69 0.87 9.37 0.83 0.85 0.83 0.81 0.72 0.78 0.82 9.36 0.92 0.92 0.90 0.81 0.68 0.76 0.87 9.35 0.87 0.87 0.87 0.84 0.75 0.85 0.83 9.33 0.90 0.90 0.89 0.86 0.70 0.87 0.87 9.25 0.73 0.73 0.73 0.74 0.86 0.67 0.69 9.22 0.73 0.75 0.80 0.80 0.85 0.68 0.68 9.21 0.95 0.95 0.93 0.88 0.68 0.87 0.91 14.23 0.77 0.79 0.82 0.83 0.85 0.71 0.72 14.22 0.91 0.93 0.90 0.85 0.68 0.87 0.90 Kk 0.97 0.89 0.85 0.68 0.90 0.90 0 0.91 0.87 0.69 0.87 0.88 Om 0.93 0.73 0.84 0.85 Mm 0.77 0.79 0.80 Hp 0.64 0.63 T 0.91 Source of analyses: ? Pillans & Wright ( 1992); t Froggatt (1 982). 30 2.8.3 Canonical discriminant function analyses of glass analyses In both models the transformed oxide values of Si02, Ti02 , Al203 , FeO, CaO, Na20 and K20 within the glasses were used . 1 0-22 ka tephras discrimination model The initial d iscriminant model for the six 1 0-22 ka interval tephras comprises 1 85 glass analyses. This model can be represented as a plot of the first two (of five) canonical variates calcu lated from the log-transformed glass analyses (Fig. 2 .2A). The mean compositions of each tephra group in the model are presented in Table 2 . 5 . The D2 statistics indicate good separation between each tephra group with values ranging between 8.9 and 1 02 (Table 2.6). The classification efficiencies (proportion of correctly identified g lass shards based on reclassifying the original data with the calculated discriminant function) of this discriminant model are al l high (Table 2 . 7 ) ; the lowest classification efficiency of 89 % is for the Rerewhakaaitu Tephra. Stepwise DFA was attempted for the discriminant model to assess the oxides with the greatest discriminating power. All of the transformed oxides were h ighly d iscriminating, in the order of: K20, CaO, Na20, FeO, Si02 , Al203 and Ti02? The choice of K20 , CaO and FeO near the top of the list of d iscriminating variables reflect their use by some workers in bivariate or trivariate plots to d istinguish TVC and OVC sourced eruptives (e.g . , Froggatt and Rogers, 1 990; Pil lans and Wright, 1 992). However, five further oxides also provided discrimination according to STEPDISC, showing that much information is lost when only a subset of the available composition data is used ; e.g. compare the plot of CaO vs. FeO for the analyses of the 1 0-22 ka tephras in Fig. 2.28 to the plot of the first two canonical variates in Fig. 2 .2A. Table 2.5 Mean electron microprobe glass compositions of tephras used in the initial 1 0- 22 ka d iscriminant model. Kara?iti Waiohau Rotorua Rerewhakaaitu Okareka Te Rere Si02 76.31 (1 .08) 78.31 (0.70) 77.72 (0.40) 77.99 (0.33) 78.29 (0.27) 77.36 (0.26) Ti02 0.20 (0.06) 0 . 1 4 (0.05) 0.20 (0.04) 0.09 (0.03) 0 . 1 2 (0.03) 0 . 1 4 (0.04) Al203 1 2.98 (0.38) 1 2 . 1 0 (0.27) 1 2.46 (0. 1 6) 1 2.45 (0.24) 1 2 . 1 4 (0. 1 3) 1 2.44 (0. 1 4) FeO 1 .67 (0.24) 0.91 (0. 1 3) 1 . 1 7 (0. 1 5) 0.85 (0.1 1 ) 0.90 (0. 1 0) 1 . 1 9 (0.1 1 ) M gO 0 . 1 7 (0.03) 0 . 1 4 (0.03) 0.20 (0.03) 0.08 (0.02) 0. 1 0 (0.03) 0 . 1 9 (0.02) CaO 1 .39 (0. 1 4) 0 .89 (0. 1 2) 1 . 1 3 (0. 1 4 ) 0.68 (0. 1 1 ) 0.83 (0.08) 1 .05 (0.1 1 ) Na20 3.99 (0.33) 3.99 (0.43) 3.45 (0.26) 3.64 (0. 1 5) 3 .60 (0. 1 7) 3.6 1 (0. 1 3) K20 3.06 (0.24) 3.38 (0.2 1 ) 3 .50 (0.40) 4 . 1 2 (0.29) 3.89 (0.36) 3 .85 (0.33) n 45 52 1 3 27 33 1 5 3 1 ? -6 -6 -4 -2 4 c N 0 -2 ? -4 -6 -4 I I 0 2 Can 1 -2 0 Can 1 4 6 8 2 4 6 4.---------??--------------? N !ii -2 (.) ? ?() ? ? ? -4 ? -6 -6 -3 ? I I I I I ... 0 Can 1 3 - - - - + + + 6 9 32 2.0 .-----------------, B 1 .5 "#. -.I: C> -? 1 .0 0 ro (.) + 0.5 0.0 L.----1---...1...-----L----1------l 0.0 0 .5 1 .0 1 .5 2 .0 FeO weight % Symbol Key 2.5 ?= Kp ?= Wh o = Rr O = Rk + = Ok ? = Te Figure 2.2 A: Plot of the first two canonical variates (Can 1 and Can 2) for tephras comprising the initial 1 0-22 ka rhyolitic g lass discriminant model; 02 values between groups are g iven in Table 2.6. 8: Plot of FeO vs, CaO weight % within the rhyolitic glass of the tephras comprising the the initial 1 0-22 ka discri minant model . C: Plot of the first two canonical variates (Can 1 and Can 2) for teph ras comprising the updated 1 0-22 ka rhyolitic glass discriminant model; 02 values between tephra groups are given in Table 2.8. Symbol Key O = Kk ? = O D= Om + = Hu + = Mg ? = T ? = Re Figure 2.3 Plot of the first two canon ical variates (Can 1 and Can 2) for tephras comprising the 22-65 ka rhyolitic g lass discriminant model; 02 values between tephra groups are given in table 2 .1 1 . Table 2.6 02 values and classification efficiencies of the initial discriminant model for the 1 0-22 ka tephras. Kp Wh Rr Rk Ok T e 02 values between groups Kp 55 Wh Rr Rk Ok % correctly reclassified by model 1 7 24 98 1 00 1 00 1 02 29 65 89 83 1 8 42 8.9 97 43 20 1 5 33 14 93 Table 2. 7 Probabilities of classification of unknown tephras in the 1 0-22 ka range with their potential correlatives, using the initial 1 0-22 ka tephra d iscriminant model. Sample n Overall 12robabili? of classification Kf2 Wh Rr Rk Ok Te Well classified samples 93.5 8 0.79 0.04 0 . 1 7 93.6 1 1 0.98 0.01 0.01 93.7 9 0.83 0 . 1 0 0.07 93.32 9 0.88 0 . 1 2 94.7 9 0.78 0.09 0 . 1 3 94.9 1 0 0.87 0 . 1 3 94.21 9 0.79 0.03 0.08 0.05 0.05 94.24 1 0 1 .00 94.37 1 0 0.85 0. 1 4 0.01 94.47 1 1 0.93 0.07 94.51 9 0.94 0.05 0.01 94.58 8 0.91 0.09 94.74 1 0 0.99 0.01 94.79 6 1 .00 95.2 9 0.98 0.02 95.3 9 0 . 1 4 0.82 0.04 95.6 1 0 0.89 0.09 0.02 95.9 1 0 0.95 0.04 0.01 95. 1 3 9 0.81 0 .1 9 Poorly classified samples 93.8 1 4 0.07 0.35 0.26 0.09 0.23 93.9 1 1 0.61 0.37 0.01 0.01 93.59 1 0 0 . 1 0 0.27 0.09 0.44 0.06 0.04 94.27 9 0.64 0.02 0.23 0 . 1 0 0.01 94.28 1 0 0.01 0 . 1 8 0 . 1 5 0.30 0.31 0.05 94.29 8 0.01 0.09 0.30 0.29 0.31 94.71 1 0 0.38 0 . 1 1 0.33 0 . 1 8 n = number of analyses. Classification of 1 0-22 ka unknown tephras Twenty-six unknown tephra samples in this time range were tested against the initial discrimination model, 1 9 were classified with a particu lar tephra with overal l (averaged over the number of analyses for each sample) probabilities exceeding 0 . 78 (Table 2 .7). All of the 1 9 classifications were consistent with field, stratigraphic and minera logical evidence. The remaining seven tephra samples had lower overall probabil ities of classification to any one potential tephra correlative. 33 An updated discriminant model based on 3 5 1 analyses was constructed, with the addition of analyses from the 1 9 classified tephras to the in itial model (Fig. 2 . 2C). The D2 distances between tephra groups remained high, between 8.7 and 72 (Table 2.8), and so too did the classification efficiencies for each tephra . However, the improvement of this model over the in itial one was with its classification of the remaining unknown tephras. This is because the updated model contained more analyses, and thus comprised better samples of the component tephra populations. Also the analyses added to form the updated model were carried out at the same time, by the same operator (SJC) as the remaining unknown samples awaiting classification . This was expected to reduce operator and instrument condition differences which may occur between the unknown analyses and those in the published l iterature or analysed at an earlier time. Small classification improvements were made with the seven formerly poorly classified tephra samples using the updated model (Table 2 . 9 ) . Two tephras were wel l classified, while the remaining five were still poorly classified . The next approach was to examine the possibi l ity of mixed glass populations in the remaining unknown samples by classifying ind ividual shards within each sample. lt appears that each of the five poorly classified tephras contained two glass populations. One population was wel l classified whilst the other remained poorly classified (Table 2 . 9 ) . The poorly classified population was later correlated with the Kawakawa Tephra using the 22-65 ka database. The presence of large volumes of Kawakawa Tephra and associated H inuera Formation (Topping, 1 97 4) in the study region provides a ready source of Kawakawa glass for admixing with these tephras. Table 2.8 D2 values and classification efficiencies of the updated d iscriminant model for the 1 0-22 ka tephras. Kp Wh 02 values between groups Kp 29 Wh Rr Rk Ok % correctly reclassified by model Rr 1 4 1 8 Rk 72 27 55 96 97 1 00 84 22-65 ka tephras discriminant model Ok Te 57 29 20 1 7 33 1 4 8.7 28 1 1 97 93 The in itial d iscriminant model for seven of the largest volume tephras in this age range comprised 1 1 0 glass analyses (Fig. 2 . 3 ) . The mean compositions of each tephra group in the model are presented in Table 2 . 1 0 . The D2 values between tephra groups range between 7 . 3 and 262 indicating good group separation (Table 2 . 1 1 ). The closest groups are the Kawakawa and the Okaia Tephras which were erupted from the same volcano with in a short space of time (Froggatt and Lowe, 1 990). The classification efficiencies of this d iscriminant model are high for all of the tephra groups; the lowest value of 93% is for the Kawakawa Tephra (Table 2. 1 1 ) . 34 Stepwise DFA of the analyses of this age group ind icated that al l of the transformed oxides were h ighly discriminating. The order in which the oxides were chosen was: K20, FeO, Al203 , CaO, Ti02, Si02 and Na20. Table 2.9 Probabil ities of classification of unknown tephras (that were poorly classified by the in itial model) in the 1 0-22 ka range with their potential correlatives, using the updated 1 0-22 ka tephra discriminant model . Sample n Overall probability of classification Kp Wh Rr Rk Ok Samples with improved classifications 93.9 1 1 0.95 94.27 9 0.98 0.01 Mixed samples* 93.8 1 4 0.07 93.8a 8 93.8b 6 0 . 1 0 93.59 1 0 0 . 1 3 93.59a 5 93.59b 5 0.33 94.28 1 0 0.01 94.28a 6 94.28b 4 0 . 1 0 94.29 8 94.29a 4 94.29b 4 94.71 1 0 94.71 a 5 94. 7 1 b 5 n = number of analyses. 0.35 0.02 0 . 1 5 0.29 0.47 0 . 1 8 0 . 1 0 0.44 0.01 0.06 0.03 0.38 0.01 0.46 0.26 0.28 0.04 0. 1 1 0 . 1 5 0.02 0.05 0.09 0 . 1 7 0.28 0 . 1 2 0.05 0.01 0.09 0.97 0 . 1 3 0.47 0.95 0.30 0.06 0.35 0.30 0.36 0 . 1 1 0.07 0.23 * For mixed samples, the first line is for all shards, (a) denotes the classified subset, and (b) the remaining unclassified subset. 0.01 0.04 0.05 0.31 0.77 0.01 0.29 0.32 0.33 0.78 0 . 1 0 Te 0.23 0.34 0.03 0.09 0.05 0.05 0.05 0.31 0.77 0.01 0 . 1 8 0 . 1 4 0.09 Table 2 .10 Mean electron microprobe compositions of tephras used in the 23-65 ka discriminant model . Kawakawa Okaia Omataroa Mangaone Hauparu Tihoi Rotoehu Si02 78.36 (0.47) 78.48 (0. 1 6) 78. 1 7 (0. 1 7) 78.36 (0. 1 3) 76.05 (0.27) 78.47 (0.20) 78.87 (0.49) Ti02 0 . 1 4 (0.02) 0. 1 1 (0.03) 0 . 1 5 (0.0 1 ) 0 . 1 7 (0.01 ) 0.33 (0.04) 0.09 (0.04) 0 . 1 3 (0.0 1 ) Al203 1 2.24 (0. 1 6) 1 2.55 (0.09) 1 2.30 (0.36) 1 2.76 (0.05) 1 3.09 (0.2 1 ) 1 2.53 (0. 1 0) 1 2.08 (0. 1 9) FeO 1 . 1 9 (0.06) 1 . 1 5 (0.04) 1 . 1 4 (0.05) 1 . 1 2 (0.0 1 ) 1 .75 (0.08) 1 .01 (0.09) 0.92 (0.04) MgO 0 . 1 3 (0.02) 0 .1 5 (0 .0 1 ) 0 . 1 5 (0.02) 0 . 1 9 (0.02) 0.35 (0.05) 0 . 1 0 (0.02) 0 . 1 2 (0.02) CaO 1 .07 (0.07) 1 .08 (0.05) 1 .07 (0.02) 1 . 1 4 (0.04) 1 .73 (0. 1 2) 0.79 (0.07) 0.77 (0.06) Na20 3.50 (0.39) 3.45 (0. 1 3) 3.84 (0.09) 3.80 (0. 1 4) 4 .09 (0. 1 2) 3 .34 (0.26) 3.46 (0.37) K20 3 . 1 2 (0. 1 7) 3.00 (0.20) 3.04 (0.2 1 ) 2.37 (0.20) 2.50 (0.33) 3.60 (0. 1 3) 3.51 (0.29) n* 68 5 4 4 8 6 1 5 * each of the averaged analyses is itself a mean of usually 1 0 analyses. 35 Classification of the 22-65 ka unknown tephras Fifteen unknown tephras were tested against the discriminant model as well as the sub? populations of the five mixed tephras mentioned previously from the 1 0-22 ka unknowns. All 1 5 of the unknown tephras were classified with probabil ities of 0. 7 or better (Table 2 . 1 2 ) . All of the tephra samples older than the Kawakawa Tephra were microscopic g lass accumulations with in weathered andesitic tephras, thus l ittle other corroborating evidence for these correlations was avai lable. However, the correlations produced using the model were in the correct stratigraphic order considering the sampling positions. Table 2.1 1 02 values and classification efficiencies of the d iscriminant model for the 22.5- 65 ka tephras. Kk 0 Om Mg Hu T Re 02 values between groups Kk 7.3 25 77 98 45 64 0 1 8 59 1 06 40 6 1 Om 30 1 23 50 30 Mg 1 26 1 1 8 85 Hu 262 245 T 35 % correctly reclassified by model 93 1 00 1 00 1 00 1 00 100 1 00 Table 2.1 2 Probabil ities of classification of unknown tephras in the 22.5-65 ka range with their potential correlatives, using the 22.5-65 ka tephra discriminant model. Sample n Overall probabil ity of classification Kk 0 Om Mg Hu 22.5-65 ka unknown tephra samples 93.1 1 0 1 .00 93.3 1 0 1 .00 93. 1 7 1 1 0.99 0.01 93.33 1 1 1 .00 7 .37 8 0. 1 1 0.89 7.36 6 0.20 0.80 9 .37 1 0 0.71 0.29 9 .36 6 0.70 0.30 9 .35 1 0 0.06 0.94 9 .33 9 0 . 14 0.86 9.25 1 .00 9.22 1 .00 9.21 1 4.23 1 .00 14.22 Unclassified subsets of mixed 10-22 ka group samples 93.8b 6 1 .00 93.59b 5 0.98 0.02 94.28b 4 0.73 94.29b 4 1 .00 94.71 b 5 0 .70 0.30 n = number of analyses. T Re 0 . 1 9 0.81 0 . 1 0 0 .90 0 .27 The unknown analyses not classified by the 1 0-22 ka model in the five mixed tephras were classified as Kawakawa Tephra with probabil ities >0.7. This indicates that the five 36 mixed tephras were contaminated by reworked Kawakawa Tephra shortly after their deposition. The tephras were being deposited between 2 1 . 1 and 1 4 .7 ka B .P . , during a period when the climate was cool, dry and stormy (McGione and Topping, 1 983). Much erosion and deposition of ring plain deposits (including the Oruanui lgnimbrite member of the Kawakawa Tephra) by lahars and fluvial activity was occurring at this time on the ring plain (Cronin and Neal l , in press). These conditions probably led to much Kawakawa Tephra g lass being transported aerial ly and fluvially to contaminate the tephras and other ring plain deposits of this age. 2.9 Conclusions I n this study we have extended the scope of past DFA work and show a practical example of these statistical methods in action . From this work we have reached the following conclusions: 1 ) The creation of canonical discriminant models for potential tephra correlatives in two clearly defined stratigraphic intervals offers a considerable improvement on other methods for the identification of the tephras in this study. 2 ) Most unknown tephras in the two stratigraphic groups were classified using the initial d iscriminant models based on past analyses of the potential correlative tephras. However, small improvements in classification of unknown tephras were achieved by including correctly classified tephras into the model. This should only be done where al l other corroborating evidence supports the statistical classification. The improvements were probably due to larger sample sizes in the updated model, and a reduction of d ifferences in operators and instrument conditions between the unknown tephras being tested and the past analyses making up the in itial model . 3 ) DFA enables the use of al l of the g lass analyses of a particular unknown tephra to be used to classify or identify it. We have shown this to be of great value for identifying mixed tephras in samples containing mixed glass populations. This approach will be especially practical when examining tephras which occur as microscopic concentrations in slowly accumulating sediments such as loess and aggrading soils. In these sediments there is a common mixing upwards of g lass grains so that younger tephras need to be separated from a background of older shards into which they are mixed (Eden et al., 1 992). 4) I n this study we have identified four previously undiscovered rhyolitic tephras in this area from glass concentrations with in buried soil and andesitic ash . These are the Okaia, Omataroa and Hauparu Tephras and the Rotoehu Ash; they assist sign ificantly in establishing a chronology for andesitic tephras and diamictons older than 22.6 ka B.P. 2.1 0 Acknowledgements SJC gratefu lly acknowledges funding from the New Zealand Vice-Chancellor's Committee, Massey University Graduate Research Fund , the Helen E. Akers Scholarship 37 Fund, and the Department of Soil Science of Massey University. Ken Palmer (Victoria University of Wel l ington) is thanked for his introduction to the operation of the electron microprobe. Comments from two journal reviewers helped us to clarify our arguments, for which we are gratefu l . 2.1 1 References Aitchison , J . , 1 983. Principal component analysis of compositional data. Biometrika 70: 57-65. Aitch ison, J . , 1 986. The statistical analysis of compositional data . Monographs on Statistics and Applied Probabil ity. Chapman and Hal l , London. Alloway, B.V. , 1 989. Late Quaternary cover-bed stratigraphy and tephrochronology of north-eastern and central Taranaki , New Zealand. Unpublished Ph.D. thesis, Massey University, Palmerston North. Alloway, B.V. ; Neall , V.E . ; Vucetich , C.G . , 1 992. Particle size analyses of Late Quaternary al lophane-dominated andesitic deposits from New Zealand. Quat. Inter. 1 3/14 : 1 67-1 74. Beaudoin, A.B . ; King , R .H . , 1 986. Using discriminant function analysis to identify Holocene tephras based on magnetite composition: a case study from the Sunwapta Pass area, Jasper National Park. Canadian J . of Earth Sci. 23: 804- 8 1 2. Blakemore, L .C. ; Searle, P .L . ; Daly, B .K . , 1 987. Methods for chemical analysis of soils. N . Z. Soil Bureau Scientific Rep. 80: 1 03pp. Borchardt, G.A .. ; Harward , M .E . ; Schmitt, R.A. , 1 971 . Correlation of ash deposits by activation analysis of g lass separates. Quat. Res. 1 : 24 7-260. Carter, L . ; Nelson, C .S . ; Nei l , H .L. ; Froggatt, P .C . , 1 995. Correlation , d ispersal , and preservation of the Kawakawa Tephra and other late Quaternary tephra layers in the Southwest Pacific Ocean. N. Z. J . of Geol. and Geophys. 38: 29-46. Cronin , S.J . ; Neall , V.E . , in press. A Late Quaternary stratigraphic framework for the northeastern Ruapehu and eastern Tongariro ring plains, New Zea land . N. Z. J. of Geol. and Geophys. 40. Cronin, S.J . ; Neall , V .E . : Palmer, A.S. , 1 996b. Geological history of the northeastern ring plain of Ruapehu volcano, New Zealand . Quat. I nter. 34-36: 21 -28. Cronin, S.J . ; Neall , V .E . , Palmer, A.S . , 1 996c. I nvestigation of an aggrading paleosol developed into andesitic ring-plain deposits, Ruapehu volcano, New Zealand. Geoderma 69: 1 1 9-1 35. Cronin , S.J . ; Neall , V.E . ; Stewart, R .B . ; Palmer, A.S . , 1 996a. A multiple-parameter approach to andesitic tephra correlation , Ruapehu volcano, New Zealand. J . Volcano!. and Geotherm. Res. , 72: 1 99-21 5. Donoghue, S .L . , 1 991 . Late Quaternary volcanic stratigraphy of the southeastern sector of Mount Ruapehu ring plain, New Zealand. Unpub. Ph .D . thesis, Massey University, Palmerston North . 38 Donoghue, S .L . ; Neal l , V.E . ; Palmer, A.S. , 1 995. Stratigraphy and chronology of late Quaternary andesitic tephra deposits , Tongariro Volcanic Centre, New Zealand. J . Roy. Soc. N. Z. 25: 1 1 5-206. Eden, D .N . ; Froggatt, P .C . ; Mclntosh , P .D . , 1 992. The distribution and composition of volcanic g lass in late Quaternary loess deposits of southern South Island, New Zealand , and some possible correlations. N. Z. J. of Geol. and Geophys. 35: 69- 79. Ewart, A. , 1 963. Petrology and petrogenesis of the Quaternary pumice ash in the Taupo area, New Zealand. J . Petrology 4: 392-431 . Froggatt, P .C . , 1 982. A study of some aspects of the volcanic history of the Lake Taupo area, North Island, New Zealand. Unpub. Ph .D. thesis, Victoria University of Well ington, Wel l ington. Froggatt, P .C. , 1 983. Towards a comprehensive Upper Quaternary tephra and ignimbrite stratigraphy in New Zealand using electron microprobe analysis of g lass shards. Quat. Res. 1 9 : 1 88-200. Froggatt, P .C. ; Solloway, G.J . , 1 986. Correlation of Papanetu Tephra to Karapiti Tephra, central North Island, New Zealand. N . Z. J . of Geol. and Geophys.29: 303-3 1 3. Froggatt, P .C . ; Lowe, D .J . , 1 990. A review of late Quaternary sil icic and some other tephra formations from New Zealand: their stratigraphy, nomenclature , distribution , volume, and age. N . Z. J . of Geol. and Geophys. 33 : 89-1 09. Froggatt, P .C . ; Rogers, G .M . , 1 990. Tephrostratigraphy of high altitude peat bogs along the axial ranges, North Island, New Zealand . N . Z. J . of Geol. and Geophys. 33: 1 1 1 -1 24. Hackett, W.R. ; Houghton, B.F. , 1 989. A facies model for a Quaternary andesitic composite volcano: Ruapehu, New Zealand . Bul l . Volcano! . 51 : 51 -68. Howorth, R . , 1 975. New formations of Late Pleistocene tephras from Okataina Volcanic Centre, New Zealand. N . Z. J . of Geol. and Geophys. 1 8: 683-71 2. Johnson , R.A. ; Wichern, D.W. , 1 992. Applied multivariate statistical analysis (3rd Edition). Prentice-Hal l lnc. , New Jersey. Kohn , B .P . , 1 970. Identification of New Zealand tephra layers by emission spectrographic analysis of their titanomagnetites. Lithos 3: 361 -368. Lowe, D .J . , 1 988. Stratigraphy, age, composition, and correlation of late Quaternary tephras interbedded with organic sediments in Waikato lakes, North Island, New Zealand. N. Z. J. of Geol. and Geophys. 31 : 1 25-1 65. Mathews, W.H . , 1 967. A contribution to the geology of the Mount Tongariro massif, North Island, New Zealand. N. Z. J . of Geol. and Geophys. 1 0 : 1 027-1 038. McGione, M .S . ; Topping, W.W. , 1 983. Late Quaternary vegetation, Tongariro region, central North Island, New Zealand. N . Z. J . of Botany 21 : 53-76. Pil lans, B.J . ; Wright, I . , 1 992. Late Quaternary tephrostratigraphy from the southern Havre Trough - Bay of Plenty, northeast New Zealand. N. Z. J. of Geol. and Geophys. 35: 1 29-143 . 39 Pil lans, B . , McGione, M . , Palmer, A. , Mildenhall , D . , Alloway, B. ; Berger, G . , 1 993. The Last Glacial Maximum in central and southern North Island: a paleoenvironmental reconstruction using the Kawakawa tephra formation as a chronostratigraphic marker. Palaeo. , Palaeo . , Palaeo. 1 0 1 : 283-304. Randle, K. ; Gorton, G .G . ; Kittleman, L .R. , 1 97 1 . Geochemical and petrological characterisation of ash samples from Cascade Range volcanoes. Quat. Res. 1 : 26 1 -282. SAS Institute I nc. , 1 989. SAS users guide: statistics. Version 6 Edition. Cary N .C . , SAS Institute I nc. , 1 028 pp. Shane, P.A.R. , Froggatt, P .C. , 1 994. Discriminant function analysis of g lass chemistry of New Zealand and North American tephra deposits . Quat. Res. 4 1 : 70-8 1 . Smith , D . G . W. ; Westgate, J .A. , 1 969. Electron probe technique for characterising pyroclastic deposits. Earth Planet. Sci . Lett. 5: 31 3-3 1 9. Srivastiva, M .S . ; Carter, E .M . , 1 983. An introduction to applied multivariate statistics. Elsevier Science Publishing Co. I nc. , New York. Stokes, S . : Lowe, D.J . , 1 988. Discriminant function analysis of late Quaternary tephras from five volcanoes in New Zealand using glass shard major e lement chemistry. Quat. Res. 30: 270-283. Stokes, S . ; Lowe, D .J . ; Froggatt, P .C. , 1 992. Discriminant function analysis and correlation of Late Quaternary rhyolitic tephra deposits from Taupe and Okataina volcanoes, New Zealand , using glass shard major element composition. Quat. l nter. 1 3/1 4: 1 03-1 1 7 . Topping, W.W. , 1 974. Some aspects of the Quaternary history of the Tongariro Volcanic Centre, New Zealand. Unpub. Ph .D . thesis, Victoria University of Wellington, Wellington. Topping, W.W. ; Kohn, B.P. , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island, New Zealand. N. Z. J. of Geol . and Geophys. 1 6 : 375-395. Vucetich, C .G . ; Pul lar, W.A. , 1 969. Stratigraphy and chronology of late Pleistocene volcanic ash beds in central North Island, New Zealand. N. Z. J . of Geol. and Geophys. 1 2 : 784-837. Vucetich, C .G . ; Pullar, W.A. , 1 973. Holocene tephra formations erupted in the Taupe area and interbedded tephras from other volcanic sources. N . Z. J. of Geol. and Geophys. 1 6 : 745-780. Vucetich, C .G . ; Howorth , R . , 1 976. Late Pleistocene tephrostratigraphy in the Taupe district, New Zealand. N . Z. J . of Geol . and Geophys. 1 9 : 5 1 -69. Wilson, C.J .N . ; Switzur, R.V. ; Ward , A.P. , 1 988. A new 14C age for the Oruanui (Wairakei) eruption, New Zealand. Geol . Mag. 1 25: 297-300. Wilson, C.J .N . ; Houghton, B .F . ; Lanphere, M .A. ; Weaver, S .D . , 1 992. A new radiometric age estimate for the Rotoehu Ash from Mayor Island volcano, New Zealand. N. Z. J . of Geol. and Geophys. 35: 371 -374. 40 CHAPTER 3. ANDESTIC TEPHROCHRONOLOGY 3.1 Introduction The work of Topping ( 1 973, 1 974) and Donoghue et al. ( 1 995) has resulted in a well defined stratigraphy of Ruapehu- and Tongariro-sourced tephras since 22.6 ka B.P (Chapter 1 : Table 1 .3). The identification of these tephras in the ring p la in area relies mostly on their physical appearance in conjunction with their stratigraphic position . I n more d istal areas the identification of TgVC-sourced tephras relies on other features such as characteristic mineralogy as well as chemistry of g lass or phenocryst minerals (e.g. Lowe, 1 988a; Donoghue et al., 1 991 ) . There were two ways in which this study was intended to add to previous andesitic tephrochronology work in the study area as well as to andesitic tephrochronolgy as a whole. The first contribution was to attempt additional methods of andesitic tephra identification such as the use of the major oxide chemistry of ferromagnesian phenocryst minerals within the tephras. To compare the chemical compositions of the tephras in this study, statistical methods similar to those used for the rhyolitic tephras in Chapter 2 were used. The second contribution of this study was to investigate the pre-22.6 ka B .P . andesitic tephrochronology of the NE Ruapehu and E Tongari ro ring plains. These two contributions have been written up as the fol lowing two papers . In the first study, the major oxide chemistry of hornblende and titanomagnetite phenocrysts of TgVC- and Egmont volcano (EV)-sourced tephras were used to test and develop the canonical d iscriminant function analysis (DFA) method . Once it was determined whether this method was able to distinguish between tephras from the two sources, discrimination between individual tephras from the same source was attempted . A wel l controlled sequence of EV-sourced tephras was chosen for this trial . The second study involved combining many parameters to correlate the pre-22.6 ka B .P. sequence of andesitic tephras on the NE Ruapehu ring plain . Physical appearance, mineralogy and mineral chemistry were all used in combination to correlate this sequence. A statistical clustering method was used to establish tephra groupings which could then be discriminated using the DFA methods developed in the first study. A l isting of al l electron microprobe analyses used in these studies comprises Appendix 3. The SAS programs used in the two studies are included in Appendix 1 . 3. 1 . 1 Photographs of the Upper Waikato Stream sequence The fol lowing plates display part of the Upper Waikato Stream sequence and three of the marker units described on the basis of their appearance in Section 3.4. These plates were not included in either of the papers comprising this chapter. 41 P l ate 3.1 . Part of the Upper Waikato Stream sequence located at T20/4681 02 and represented in Figs. 3.6, 4.1 and 5.3. The exposure is ea. 30 m high. position of Kawakawa Tephra R1 1 lahar deposits (Fig. 5.3) position of Marker Un it 2 (Fig. 3.6) R12 lahar deposits (Fig. 5.3) Marker Unit 3 (Fig. 3.6) ind icated by arrow on the left of photograph. P l ate 3.2. Marker Unit 1 tephra at T20/464098, see Fig. 3.6 for stratigraphic position and Section 3.4.6 for description . Lens cap is 50 mm in diameter. 42 Plate 3.3. Marker Unit 2 tephra at T20/4691 00; see Fig. 3.6 for stratigraphic position and Section 3.4.6 for description . Lens cap is 50 mm in d iameter. Plate 3.4. Marker Unit 3 tephra at T20/4681 02; see Fig. 3.6 for stratigraphic position and Section 3.4.6 for description. Lens cap is 50 mm in d iameter. 43 3.2 Contributions of co-authors Sourcing and identifying andesitic tephras using major oxide titanomagnetite and hornblende chemistry, Egmont volcano and Tongariro Volcanic Centre, New Zealand Bulletin of Volcanology, 58: 33-40 ( 1 996). S.J. Cronin : Principal investigator Carried out: sampling and laboratory preparation of TgVC tephras electron microprobe analysis of TgVC tephras al l statistical programming and analysis manuscript preparation and writing R.C. Wallace: Go-investigator Carried out: sampling and laboratory preparation of EV tephras electron microprobe analysis of EV tephras V.E. Neal l : Adviser: editing and discussion of the manuscript aided the study by discussing results and methodology as well as editing and d iscussion of the manuscript. A multiple-parameter approach to andesitic tephra correlation, Ruapehu volcano, New Zealand Journal of Volcanology and Geothermal Research , 72: 1 99-21 5 (1 996). S.J. Cron in : Principal investigator Carried out: sampling and laboratory preparation of tephras optical microscopy electron microprobe analysis statistical programming and analysis manuscript preparation and writing V.E. Neal l, R.B. Stewart, A.S. Palmer: Advisers aided the study by discussing results and methodology with SJC as well as editing and discussion of the manuscript. 44 3.3 SOURCING AND IDENTIFYING ANDESITIC TEPHRAS USING MAJOR OXIDE TITANOMAGNETITE AND HORNBLENDE CHEMISTRY, EGMONT VOLCANO AND TONGARIRO VOLCANIC CENTRE, NEW ZEALAND S. J Cronin, R C. Wallace, and V. E Neall Department of Soil Science, Massey University, Private Bag 1 1 222, Palmerston North, New Zealand 1 996, Bul letin of Volcanology, 58: 33-40. Abstract. Canonical discriminant function analysis was employed to d iscriminate between electron microprobe-determined titanomagnetite and hornblende analyses from Egmont volcano and Tongariro Volcanic Centre. Data sets of 436 titanomagnetite and 206 hornblende analyses from the two sources were used for the study. Titanomagnetite chemistry provided the best d iscrimination between these two sources with classification efficiencies of 99 % for sample averages and 95 % for individual analyses. The d ifference between sources for hornblende chemistry was less marked, but classification efficiencies of 1 00 % for sample averages and 87 % for individual analyses were achieved . Using the same methods, a prel iminary discrimination of individual Egmont volcano-sourced tephras was attempted . Titanomagnetite chemistry enabled the discrimination of several individual tephras or at least pairs of tephra units, but hornblende chemistry provided l ittle discrimination . This technique provides an improvement on previous methods for chemically distinguishing distal tephra from the two sources as well as potentially identifying individual tephras from a particular source. A major advantage over previous d iscrimination techniques is that individual analyses can be classified with a known probabil ity of group membership (with groups such as volcano source or an individual tephra unit). Tephras in a depositional environment where mixing is common such as within soi l , loess and marine sequences, can be sourced or identified more easily with classification of individual grains. Key words: Tephrostratigraphy-Egmont discriminant function analysis-OF A. 3.3.1 Introduction volcano-Tongariro Volcanic Centre- The stratigraphic importance of tephra layers is well recognised in Quaternary studies world-wide as well as in New Zealand (e.g. Thorarinsson, 1 949; Pullar, 1 967; Lowe, 1 990). Tephrochronology studies in New Zealand have mostly concentrated on the many, widespread and voluminous rhyolitic tephras erupted from calderas with in the Taupo Volcanic Zone (e.g. Vucetich and Pullar, 1 969 and 1 973; Froggatt, 1 983; Froggatt and Lowe, 1 990). Studies of andesitic tephrochronology have been fewer in New Zealand due to the more restricted distribution of andesitic tephras, the ease with which 45 they weather, apparent difficulties involved in their identification, and their perceived l imited use in petrographic studies. Andesitic tephrochronology has however proved to be important in studies on and around the two major andesitic volcanic areas in the North Island (Fig. 3 . 1 ); Egmont volcano and Tongariro Volcanic Centre (e.g. Kohn and Neal l , 1 973; Topping, 1 973; Donoghue et al. , 1 995), as well as in d istal regions (Lowe, 1 988a; Wallace, 1 987; Eden et al. , 1 993). In these areas andesitic tephras have been used to either complement the rhyolitic tephra record or provide greater stratigraphic resolution. 1 75" E 38? s 0 50 1 00 km Fig 3.1 . North Island of New Zealand with locations of Egmont volcano and Tongariro Volcanic Centre. Methods of rhyol itic tephra identification have become increasingly sophisticated as the need arises for accurate and reliable identification of tephras in d istal areas, where field criteria are sometimes ambiguous. Methods have involved mineralogical criteria, (e.g. Randle et al. , 1 971 ; Lowe, 1 988) as wel l as chemical criteria , (e.g . Smith and Westgate, 1 969; Kohn, 1 970; Borchardt et al. , 1 971 ; Froggatt, 1 983; Wal lace , 1 987; Stokes et al. , 1 992). Chemical techniques have mostly involved glass and titanomagnetite, and in New Zealand glass chemistry has achieved the most widespread use for chemical characterisation of tephra (e.g. Froggatt, 1 983; Stokes et al. 1 992). Andesitic tephra identification methods in New Zealand have followed those developed for rhyolitic tephras. However in d istal areas of tephra accumulation it remains difficult to d istinguish Tongariro Volcanic Centre- (TgVC) and Egmont volcano- (EV) sourced tephras because they have similar mineralogy, and mixing occurs . The greatest d ifficulty with the identification of andesitic tephras results from them being more easily 46 weathered in most depositional environments than rhyolitic tephras (Ki rkman and McHardy, 1 980; Lowe 1 986). There are major differences in g lass chemistry between the two centres, (Wallace et al. , 1 986) but rapid weathering, renders andesitic g lass unusable for tephra identification in most circumstances. Mineralogy is often but not always useful for distinguishing EV- and TgVC-sourced distal tephras. Lowe (1 988a) d istinguished EV tephras by a ferromagnesian assemblage of cl inopyroxene + hornblende ? orthopyroxene, compared with orthopyroxene + clinopyroxene ? olivine ? hornblende for TgVC tephras. However, Wal lace et al. ( 1 986) concluded that olivine and orthopyroxene are more abundant in EV-sourced tephras than previously thought, and several TgVC? sourced tephra layers a lso l ie outside of the general assemblage fields defined by Lowe (Donoghue et al. , 1 991 ; Cronin et al. , 1 996). Mineral assemblages may also be affected by winnowing (Juvigne and Shipley, 1 983), weathering (Hodder et al. , 1 991 ) , and pedogenic mixing (Wallace, 1 987). Titanomagnetite trace element chemistry has been shown to be useful in distinguishing individual EV tephras, (Kohn and Neall , 1 973; Wal lace et al. , 1 986) as wel l as d istinguishing between EV- and TgVC-sourced tephras (Kohn and Neal l , 1 973; Lowe, 1 988a). Kohn and Neall ( 1 973) used emission spectrographic analyses on bulk samples of titanomagnetites, but this technique is unsuitable in any environment where there is potential mixing of tephra layers, such as in loess and soi l . The elements which provided the greatest d iscrimination of sources were, chromium, vanadium, nickel , and manganese. Lowe (1 988a) used a bivariate plot of Cr203 vs. MnO wt % to show a provisional d ifference between tephras from the two sources. Hornblende chemistry has also been used to distinguish between EV- and TgVC? sourced tephras. Wallace ( 1 987) used MgO, FeO and K20 content of hornblende to d istinguish between EV- and Taupe Volcanic Zone-sourced tephras and Eden et al. (1 993), used calcium and sil icon to d iscriminate between TgVC and EV hornblendes. These approaches may be useful but they do not use the ful l range of chemistry data available. Other mineral phases which have been used to d iscriminate individual tephras or provide l imited d iscrimination between EV and TgVC sources are olivine, clinopyroxene, and plagioclase (Lowe, 1 988a; Donoghue et al. , 1 991 ). Compared to bivariate plots, a more statistical ly powerful technique which uses the total chemistry of a sample in comparing and contrasting compositional data is canonical d iscriminant function analysis (DFA). DFA was introduced to tephra studies by Borchardt et al. ( 1 971 ) using rhyolitic g lass analyses, and has since been appl ied to titanomagnetite major element analyses to discriminate tephras in Canada (King et al. , 1 982; Beaudion and King, 1 986). In New Zealand, DFA using major oxide g lass analyses has been used to discriminate volcanic source areas as wel l as some individual rhyolitic eruptives (Stokes and Lowe, 1 988; Stokes et al. , 1 992; Shane and Froggatt, 1 994). This study was firstly aimed at discriminating between TgVC- and EV-sourced andesitic tephras by using canonical DFA of al l titanomagnetite and hornblende major oxides. The second step was to apply this methodology on the same data set in a prel iminary investigation to discriminate individual tephra eruptives from one of the 47 sources. We also present here prel iminary results from our investigation of EV-sourced tephras. 3.3.2 Methods Tephra samples were taken from localities proximal to EV and TgVC. Phenocryst phases were extracted , mounted in epoxy resin, cut and polished . Phenocrysts of titanomagnetite and hornblende were analysed in this study. Orthopyroxene, clinopyroxene and plagioclase were not used because they d isplay strong oscil latory zoning in TgVC tephras and the chemical variation with in a single grain was as great as the variation between samples. Olivine was also not targeted because it was not present in many of the tephras. The chemistry of the titanomagnetites and hornblendes varied less with in each sample population and there was no observable osci l latory zoning. Further advantages of using titanomagnetite are that it is relatively stable during weathering (Ruxton, 1 968) and is easy to separate from a sample. The analyses were carried out with a JEOL JXA-733 electron microprobe using an accelerating voltage of 1 5 kV, a 1 2 nA beam current, and a 3 11m beam diameter. M ineral standards of the Victoria University of Well ington collection were analysed routinely to check for any machine drift. Between six and ten titanomagnetite and hornblende crystals were analysed where possible from each tephra sample. 3.3.3 Statistical Methods Canonical d iscriminant function analyses (DFA) were used to discriminate between the Egmont and Tongari ro mineral analyses. This is a technique related to principle component analysis that reduces the dimensional ity of data, such as compositional analyses, which consist of a large number of variables. Canonical DFA enables the derivation of a small number of linear combinations of the quantitative variables which best discriminate pre-defined groups of observations or analyses. This means that instead of working with ten oxide scores to discriminate groups of samples, one or two canonical variables contain the information. Before identification of an unknown tephra can be undertaken, a reference set of data with known associations must be establ ished . The canonical DFA from this known set is used to produce a discriminant model which then can be used to classify unknown data. The analyses obtained in this study from EV and TgVC enable the creation of a discriminant model . The theory of OFA has been outl ined by many authors (e.g. Srivastava and Carter, 1 983; Johnson and Wichern , 1 992) but is not d iscussed further here. As part of canonical DFA the Mahalanobis d istance statistic or 02 value is often calculated . lt ind icates the multivariate spacing between data groups in multiple d imensions (Srivastava and Carter, 1 983). The 02 statistic is therefore a measure of the separation of groups of samples (Stokes et al. , 1 992), in a similar manner to the coefficients of variation and simi larity coefficients of Borchardt et al. ( 1 971 ) . 48 Beaudion and King ( 1 986), and Stokes and Lowe ( 1 988) used a technique which selected variables that had the greatest discriminating power. This subset of h ighly discriminating variables was shown to improve classification within groups and discrimination between groups. This method is known as stepwise DFA and is further described by Srivastava and Carter ( 1 983), and Stokes and Lowe ( 1 988). In this study the SAS system programs STEPDISC and CANDISC were used (SAS Institute I nc. , 1 985). These programs perform stepwise DFA and canonical DFA respectively. Prior to statistical analysis the data used in this study were transformed in the manner described by Aitchison ( 1 983) and Stokes and Lowe (1 988). This is necessary due to the statistical problem of closure in compositional data. The pre-treatment used is termed a log ratio transformation, whereby one oxide score is used to d ivide into a l l of the other scores and the logarithm (base 1 0) is taken of each of these ratios. Use of the logarithm constra ins component scores to being greater than zero. 3.3.4 Discrimination between sources Titanomagnetite I n this study 300 titanomagnetite phenocrysts were analysed from 70 individual TgVC? sourced tephra units, and 1 36 from 1 1 ind ividual EV-sourced tephra un its . The tephra units sampled range in age from ea. 3-35 ka. The mean titanomagnetite compositions for each centre are presented in Table 3 . 1 . The analyses were normalised and then transformed with the log-ratio transformation using Si02 as the oxide divisor. The choice of oxide for the d ivisor was found to have no effect on the d iscriminating abi l ity of the DFA (Stokes and Lowe, 1 988). Table 3.1 . Titanomagnetite and hornblende average chemistry from the two tephra sources. Titanomagnetite Hornblende Oxide wt% Tongariro Egmont Tongariro Egmont Si02 0. 1 8 (0 . 1 6) 0 . 1 8 (0.06) 43 . 1 3 ( 1 .55) 42.62 ( 1 .33) Ti02 1 0 .66 (2.22) 9 .09 ( 1 .40 ) 2.22 (0.65) 3 .35 ( 1 .95) Al203 4.00 ( 1 . 1 0) 3 . 9 1 ( 1 .32) 1 2 .46 ( 1 .43) 1 1 .9 9 (2.30) FeO 80.81 (2.02) 82.65 ( 1 .79) 1 2 .77 ( 1 . 1 7) 1 1 .9 9 (0.83) M nO 0.42 (0 . 1 9) 0 .68 (0.20) 0 .33 (0. 1 5) 0.25 ( 0 . 1 3) M gO 3 . 1 3 (0.68) 3.35 (0 .65} 1 4 . 5 1 (0. 78) 1 4 .27 (0.66) CaO nd nd 1 1 .58 (0.62) 1 2 .06 (0.39) Na20 nd nd 2.34 (0.34) 2 . 50 (0. 1 2 ) Kp nd nd 0 . 58 (0.27) 0 . 96 (0 .09) Cr203 0 .42 (0.38) 0.07 (0.07) nd nd n 300 1 36 1 1 7 89 n = number of analyses to calculate the mean, standard deviations in brackets. nd = not determined 49 Two SAS data sets were created for OFA, one using the mean analyses for each tephra unit, and one using al l of the individual analyses. Shane and Froggatt ( 1 994) found that mean analyses produced better d iscrimination than individual glass shard analyses for New Zealand rhyolitic tephras. The total spread of the data is however better indicated by individual analyses. The variables used in both databases were transformed Ti02, Al203 , FeO, MnO, MgO and Cr203 . Canonical OFA of the means data set produced very good separation between the EV and TgVC sample groups. A plot of the fi rst two canonical variates is used to i l lustrate the separation (Fig. 3.2A). The 02 value of 1 8 . 1 between groups indicates a good separation of the two groups with very l ittle overlap occurring. The efficiency of group classification is presented in Table 3.2. The stepwise procedure STEPOISC selected the most discriminating variables in order of Cr203, MnO, Ti02, FeO and Al203. Using these variables it was possible to achieve a group separation a lmost as good as using all of the oxides. The Cr203 values in the EV-sourced tephras are very low, close to detection l imits of the microprobe. Removing Cr203 from the OFA reduces the degree of separation of the two tephra groups to a 02 value of 1 2.3 (Fig. 3 .28, Table 3.2). The most d iscriminating variables now become MnO, FeO, Ti02, and MgO. Canonical OFA using al l of the data including Cr203 also produced very good group separation (Fig. 3 .2C). There is very l ittle overlap between the two groups and the 02 value of 1 3 . 1 is still high ind icating good separation (Table 3.2) . The STEPOISC procedure selected the most discriminating variables in order of Cr203, MnO, Ti02, MgO, and FeO. Removing Cr203 from the OFA reduced the 0 2 value between the source groups to 7.2 but sti l l enabled a good classification of the groups (Table 3.2). The most discriminating variables became MnO, FeO, Ti02, and MgO. Hornblende 1 1 7 hornblende analyses were obtained from 23 individual TgVC-sourced tephras, and 89 analyses from 1 1 ind ividual EV-sourced tephras. A further 1 5 hornblende analyses from 5 EV-sourced tephras were also available (Lowe, 1 987). The mean hornblende compositions for each centre are presented in Table 3. 1 . The analyses were normalised and transformed with the log-ratio transformation using Na20 as the oxide d ivisor. As for titanomagnetite, two SAS data sets were created , one with the average analysis for each tephra , the other with all of the analyses. The same transformed oxides were used in both data sets: Si02, Ti02, Al203 , FeO, MnO, MgO, CaO, and K20. Canonical OFA of the average data produced a good separation of the TgVC and EV tephras (Fig. 3 .3A). The 02 value of 9.9 is not as high as for the titanomagnetite averages separation, but sti l l indicates the volcanic centre groups are wel l separated with no overlap (Table 3.2) . The STEPOISC procedure selected the most d iscriminating variables in order of K20, MnO, Si02, CaO, and MgO. 50 6 3 N ? 0 {) -3 A. + -6 +----r---1------.----.-----, 6 3 N ? 0 {) -3 6 3 N ? 0 {) -3 -4 -4 -2 -2 + - ? + + 0 2 Can 1 0 2 Can 1 -lt 4 4 6 B. 6 c. 0 -6 +----..--?--+--....----r-----, -6 -4 Figure 3.2 -2 0 2 Can 1 4 6 Plots of the first and second canonical variates (Can 1 and Can 2) for titanomagnetite data together with 02 values between source groups. Circles represent EV data and Crosses TgVC data. (A) Sample mean data with all oxide variables, (B) sample mean data excluding Cr,03, (C) al l individual analyses using al l oxides. 4 2 N ? 0 {) -2 0 0 0 8 0 - J) c9 Cfj o 0 A. + -4 +----.-----1,---.,----..., 6 4 2 N c:: Cll {) 0 -2 -4 -2 0 Can 1 + + 2 4 B. + -4 +----r----+---.-----, -4 -2 Figure 3.3 0 Can 1 2 4 Plots of the first and second canonical variates (Can 1 and Can2) for hornblende data together with D2 values between source groups. Circles represent EV and Crosses TgVC data. (A) Sample mean data, (B) al l individual analyses. 51 Canonical OFA using al l of the ind ividual analyses produced a reasonable separation of samples from the two sources (Fig. 3.38). There is a small degree of overlap between groups and the 02 value is correspondingly lower at 4.4 (Table 3.2) . The STEPOISC procedure selected al l of the variables as being highly d iscriminating but in the order of K20, MnO, Si02, MgO, FeO, Ti02 , Al203 , and CaO. Table 3.2. Classification efficiency of the between-source discriminant functions. Actual group Number of Classified group membership Overall observations classification TgVC EV efficiency (%) Titanomagnetite Mean data TgVC 70 69 1 EV 1 1 1 1 98.8 Mean data excluding Cr2 03 TgVC 70 65 5 EV 1 1 1 1 93.8 Individual data TgVC 300 285 1 5 EV 1 36 7 1 29 95.0 Individual data excluding Cr203 TgVC 300 277 23 EV 1 36 1 2 1 24 9 1 .9 Hornblende Mean data TgVC 23 23 EV 1 6 1 6 1 00.0 Individual data TgVC 1 1 7 93 24 EV 89 2 87 87.4 3.3.5 Discrimination of individual Egmont volcano-sourced tephras Titanomagnetite An EV-source subset of the individual titanomagnetite analyses database described in the previous section was used to attempt discrimination of individual tephras. The analyses from each tephra unit in Table 3.3 were grouped separately except for samples Tariki a , Tariki b ,c,d and , Tariki e , f which were combined as a single group representing Tariki tephra . The separation of these tephra units appeared very promising with the canonical OFA approach (Fig . 3.4A, Table 3.4). 02 distances between many of the tephras were very high and their degree of classification was also good (Table 3.4). Four tephra units were not as well separated from al l of the others; Konini Tephra and Kaponga Tephra analyses appear very closely related, also Mahoe Tephra and Poto Tephra (members f, g) were also very closely related . The most discriminating variables were chosen as MnO, MgO, FeO, Ti02 and Al203. 52 Table 3.3. Egmont-sourced tephras used in the d iscrimination study. Tephra unit Symbol Estimated age (AIIoway et al. , 1 995) (ea. ka B .P .) Manganui Tephra lnglewood Tephra Mangatoki Tephra Tariki Tephra, e, f Tariki Tephra, d, c, b Tariki Tephra, a Waipuku Tephra Kaponga Tephra Konini Tephra Mahoe Tephra Poto Tephra, f, g Hornblende l ? J Mg 11 Mt Tr Wp Kp Kn Mh Pt 2.9 - 3 .3 3.6 - 3 .7 4 . 1 - 4.6 4.6 -5.2 5.0 - 5.2 5.3 - 1 0.0 1 0 . 1 -1 0 .4 1 0 .4 - 1 2 .0 22 .5 An EV-source subset of the database of hornblende individual analyses was used for this d iscrimination. The analyses from each tephra unit in Table 3.3 were grouped in the same manner as for the titanomagnetite data. The DFA enabled very l ittle discrimination of the individual tephra units (Fig 3.48). The 02 distances were very low between many of the tephra sample groups, and with in many tephra groups there was a large spread of data. The classification efficiency was also very low with this data (Table 3.4). The only tephra unit which was effectively d iscriminated was the Manganui tephra . Table 3.4. Classification efficiencies of the d iscriminant function analyses for the individual Egmont-sourced tephras. Actual Number of Classified group membership group* observations Mg 1 1 Mt Tr Wp Kp Kn Mh Titanomagnetite Mg 1 1 1 1 4 Mt 1 0 Tr 38 Wp 1 1 Kp 6 Kn 1 3 Mh 1 2 Pt 9 Hornblende Mg 3 1 1 9 Mt 7 Tr 20 Wp 8 Kp 4 Kn 4 Mh 5 Pt 8 1 1 3 2 2 1 0 4 28 6 6 2 2 2 2 1 1 1 1 1 0 3 7 1 1 6 * Tephra abbreviations from Table 3.3. 53 6 4 3 9 2 3 1 1 1 3 Overall classification Pt efficiency (%) 1 8 1 4 5 83.3 55.9 6 A. . \. 3 B . 4 0 2 1 6 o l X+ ? 0 +? I ? X x:\;! 2 0? ' 6 ? ? 1 N ? L. N r tJ3 - : ? + ? \00 c: 0 - - - c: 0 - - - - - Qi6 ? ? ro ? ro () () X -2 0 : 04 - 1 D 6tf ? 1 T o T o o -4 -2 o. I s T ? I ? -6 I -3 I - 1 0 -5 0 5 1 0 1 5 -6 -4 -2 0 2 Can 1 Can 2 I ? = Mg 0 = 11 + = Mt 0= Tr += Wp D = Kp L.= Kn X= Mh T= Pt I A: titanomagnetite 02 1 1 Mt Tr Wp Kp Kn Mh Pt Mg 237 . 1 256 . 5 1 62 . 7 1 66 . 7 79.4 7 2 . 3 82.0 6 8 . 1 1 1 1 1 . 7 28.9 20.3 76 .8 78.6 1 22 . 5 1 40 . 0 Mt 1 4 .4 1 4 . 1 65.8 7 0 . 0 1 08 . 1 1 27 . 1 Tr 6.4 2 1 . 5 22.8 5 0 . 9 64 .6 Wp 36.4 3 1 . 9 76.8 89.9 Kp 4 . 0 1 0 . 0 1 3 . 6 Kn 1 6 .6 2 1 . 3 Mh 2 . 2 B: hornblende 02 1 1 Mt Tr Wp Kp Kn Mh Pt Mg 37.9 2 1 . 1 27.8 2 7 . 3 2 7 . 6 3 5 . 0 1 5 . 1 27.6 1 1 5 . 6 4 . 0 9 . 5 8 . 0 9 . 8 2 1 .6 4 . 4 Mt 1 .4 1 . 9 4 . 7 5 . 8 8 . 2 3 . 1 Tr 3 . 0 5 . 9 4 . 8 1 0 . 7 2 . 2 Wp 9 . 9 8 . 3 7 . 8 5 . 7 Kp 6.6 1 6 . 0 6.2 Kn 1 5 . 5 5 . 7 Mh 1 2 . 9 F i g u re 3 . 4 Plots of the first and second canonical variates (Can1 and Can 2) for Egmont-sourced tephras together with 02 values between tephra groups (tephra abbreviations from Table 3 . 3 ) . (A) Using titanomagnetite data, (B) using hornblende data. 54 0 4 3.3.6 Summary and Conclusions Both phenocryst phases examined in this study can be used with the Canonical DFA method to easily and accurately d iscriminate tephras from EV and TgVC. Titanomagnetite is preferable for this distinction because: ( 1 ) there are greater d ifferences in titanomagnetite chemistry between sources, (2) it occurs with in nearly al l samples, (3) it is relatively stable during weathering, (4) it is rapidly and easily separated from a bulk sample. Canonical OFA of the mean tephra analyses for both of the mineral phases enabled better classification efficiencies of the two volcanic sources and correspondingly larger 02 values, which is consistent with the findings of Shane and Froggatt ( 1 994 ). To apply this technique to d iscriminating tephras in soil and loess we prefer however, to use a discrimination model based on all of the individual analyses. The analysis of each ind ividual grain of an unknown sample can then be classified by the discriminant model and mixed tephra populations can easily be identified and accounted for. Using this canonical OFA method the probabil ity of any given sample belonging to either of the volcano source groups can be assessed . I n situations where unknown samples are close to or with in the region of overlap between source groups the probabil ity of group membership is important and can be reported with any correlation made. For the discrimination of individual analyses, titanomagnetite appears very promising. Using the l imited database available we can show good discrimination of several individual tephra units , or at least pairs of the stratigraphically closest units, with mostly high 02 values and classification efficiencies. Hornblende provided very l ittle discrimination between tephra groups due to the large spread of data for each tephra as well as small d ifferences in chemistry between tephra groups; only one tephra was clearly d iscriminated . The most easily distinguished tephra unit, the Manganui tephra was erupted from the parasitic cone of Fanthams Peak on the side of Egmont volcano, whereas the others were probably erupted from the main vent region (AI Ioway et al. , 1 995). This tephra unit is a lso easily discriminated by its characteristic field appearance and mineralogy. The d ifference in d iscriminating abi l ities of titanomagnetite and hornblende may be related to the petrology of the Egmont volcano system. Stewart et al. (in press) describe titanomagnetite as an early crystal l ising and stable phase in EV magmas, while hornblende was formed when the melts reached the base of the crust, and on subsequent rising the hornblende was partial ly resorbed . Stewart et al. (in press) also suggest that these hornblende phenocrysts are largely xenocrysts entra ined from lower crusta! and upper mantle sources. This may explain the large spread in the hornblende data for each tephra unit as well as the d ifficulty in separating the individual tephras. The results of this study demonstrate the potential of the methods described for future tephra discrimination studies of EV and TgVC units as well as provid ing a more rigorous method of d iscriminating tephras from the two sources in distal areas. As well as the advantages of OFA for tephra identification reported by others, (Stokes et al. , 55 1 992; Shane and Froggatt, 1 994) this method is ideal for tephra layers which may be mixed with in soi l , loess or marine sequences. Using ind ividual grain analyses and their probabi l ities of group membership, mixed tephra populations can be easily d iscriminated. 3.3. 7 Acknowledgements We wish to thank David Lowe for the use of his hornblende analyses, and Ken Palmer (Victoria University of Well ington) for his introduction to the electron microprobe. Thanks are a lso extended to R.B. Stewart and A.S. Palmer for helpful criticism of an earlier version of this manuscript, as well as P. Froggatt and an anonymous reviewer for their useful comments. 3.4 A MULTIPLE-PARAMETER APPROACH TO ANDESITIC TEPHRA CORRELATION, RUAPEHU VOLCANO, NEW ZEALAND S. J. Cronin, V. E. Neall , R. B. Stewart, A. S. Palmer Department of Soil Science, Massey University, Private Bag 1 1 222, Palmerston North, New Zealand 1 996, Journal of Volcanology and Geothermal Research , 72: 1 99-2 1 5. Abstract A multi-parameter approach was used to correlate andesitic tephras in a complex tephra sequence ranging in age from ea. 23 ka to ea. 75 ka on the eastern ring plain of Ruapehu volcano, North Island. Field properties, combined with ferromagnesian mineral assemblages and mineral compositions, were required to map and correlate this sequence. Three tephra units could be identified based on their un ique physical appearance, but other tephras could not be correlated on this basis alone. Hornblende and olivine proved to be valuable marker minerals enabling further d istinction of two of the marker units recognised by field properties, as wel l as defining two further marker tephras. Unweathered titanomagnetite crystals, present in al l of the tephras, were subjected to major element analysis by electron microprobe. Canonical d iscriminant function analysis (DFA) of these analyses enabled the grouping and d iscrimination of tephra units, further aiding the identification of defined marker units, as well as defining new marker units. The titanomagnetite chemistry showed a strong relationship to the ferromagnesian mineralogy, showing that the ferromagnesian phenocrysts formed from the same melt or under the same melt conditions prior to eruption of each tephra . Canonical DFA was also applied to hornblende and olivine mineral analyses to identify further marker beds and to confirm identifications of previously defined units . This statistical analysis was found to be invaluable in reducing the large amount of 56 compositional data from this study into a useable form for andesitic tephra correlation and mapping. 3.4.1 Introduction Andesitic tephrochronology plays an important role in the relative and numerical dating of sediments and geomorphic surfaces on the ring plains of composite volcanoes and surrounding areas. The techniques for andesitic tephra correlation in New Zealand are however less well developed than those for the rhyolitic tephra record of the central North Island. In previous studies of the ring plains of Ruapehu and Tongariro, tephrochronology has played an important role in assigning numerical and relative ages to ring plain surfaces and sediments (Topping, 1 973; Topping and Kohn , 1 973; Donoghue et a/. , 1 995). However studies have been restricted mostly to the younger parts of the ring plain record (< ea. 23 ka. ) in which distal rhyolitic tephras present can be correlated to the well establ ished record of the Taupo and Okataina volcanic centres (Froggatt and Lowe, 1 990; Wilson , 1 993). In this study, ring plain deposits ranging from ea. 23 ka. up to 75 ka are investigated. Radiocarbon dating is less useful in this time frame and fewer rhyolitic tephras are present, with ages less well constrained than those of the post 23 ka record. This constraint places more emphasis on the role of andesitic tephras as local marker horizons for relative dating of surfaces and sediments. In this study we have used multiple criteria to correlate stratigraphic successions and surfaces in different parts of the ring plain. I n particular to extend from physical tephra characteristics and mineralogy, canonical d iscriminant function analysis of titanomagnetite, olivine and hornblende phenocryst compositions were used to correlate andesitic tephras. 3.4.2 Setting Ruapehu volcano with in the Tongariro Volcanic Centre, is a large, active, andesitic stratovolcano, and the highest point in the North Island at 2797 m. Its latest eruption was in 1 995. The current massif comprises a 1 1 0 km3 cone surrounded by a volcaniclastic ring plain of simi lar volume (Hackett and Houghton, 1 989). The adjacent Tongariro volcano is a sl ightly smaller andesitic massif made up of several coalescing volcanic cones (Mathews, 1 967), the largest of which is the recently active cone of Ngauruhoe. The ring plains of Ruapehu and Tongariro volcanoes are confined to the east by the Kaimanawa Mountains, with the boundary marked by the Tongari ro River. The dominant wind direction is from the west, thus the andesitic tephras are generally thickest on the ring plain to the east of the volcanoes. The principal reference sections used in this study are exposed along Upper Waikato Stream (Fig. 3.5), on the north-eastern Ruapehu ring plain . 57 Mt. Tongariro ... Mt. Ngauruhoe ... 39? 1 0 I Mt. Ruapehu ... - State Highways 1 75? 45' SH 1 0 5 km Figure 3.5. Location map of the eastern ring plains of Tongariro and Ruapehu volcanoes. Numbered dots indicate locations of principal reference sections, numbers correspond to section descriptions contained with in Appendix 4. 58 This stream is immediately north of the catchment boundary where present drainage from the eastern flanks of Ruapehu is spl it between the Whangaehu River to the south and the Tongariro River system to the north . 3.4.3 Methods A composite stratigraphy of the principal reference sections was first established, provid ing the longest and most complete record of deposition in the area. The andesitic tephras in this master section were then characterised according to their physical appearance and mineralogy. The simplest and most valuable stratigraphic markers were those which possessed a unique physical appearance enabling their recognition in other areas. The next most valuable markers were those that possessed a unique minera logy enabl ing their discrimination from other tephras in the sequence. Those andesitic tephras that could be reliably identified in other sections based on these criteria were few and further fingerprinting was deemed necessary. The major element composition of various mineral phases and andesitic glass were then determined using an electron microprobe for as many of the andesitic tephras as possible. The largest pumice clasts of each tephra sample were cleaned in water with an ultrasonic probe, crushed and their ferromagnesian minerals separated using a Frantz lsodynamic Separator. The mineral grains were then mounted in an epoxy resin plug which was cut and polished (Froggatt and Gosson, 1 982). The phases targeted for analysis were titanomagnetite, olivine and hornblende; some analyses were also obtained from andesitic glass, orthopyroxene and clinopyroxene. Orthopyroxene, clinopyroxene, and plagioclase were not used because these minerals al l d isplayed strong oscil latory zoning and greater compositional variation than titanomagnetite, olivine and hornblende. Andesitic glass was poorly preserved in these samples, being present only in some of the younger tephras and in tephras preserved with in l ignite. Analyses were carried out on a JEOL JXA-733 electron microprobe, employing an accelerating voltage of 1 5 kV and a 1 2 nA beam current. A beam diameter of 3 11m was used for the mineral phases and 1 0 11m with a 8 nA beam current for the andesitic g lass (Froggatt, 1 983). Mineral standards of the Victoria University of Wellington collection were analysed routinely to correct any machine drift. Between six and ten analyses of ind ividual titanomagnetite crystals were obtained where possible from each tephra sample. Six to ten analyses of hornblende, olivine and andesitic g lass were obtained from the samples containing these phases. The resulting data were then examined using traditional oxide plot techniques and statistical analysis. 3.4.4 Statistical methods Canonical d iscriminant function analyses were used to establish groups of samples which could be used for correlation and stratigraphic purposes. Canonical discriminant function 59 analysis (OFA) is a technique related to principal component analysis, which reduces the d imensional ity of data such as compositional data that has scores on a large number of independent variables. Canonical OFA enables the derivation of a small number of l inear combinations of the quantitative variables which best discriminate pre-defined groups of observations or analyses. A reference set of observations or analyses with pre-defined groupings must first be set up and canonical OFA is used to produce a d iscriminant model which can be used to classify unknown observations or analyses. The theory of OFA is outl ined in many texts on multivariate analysis such as Srivastava and Carter ( 1 983) and Johnson and Wichern ( 1 992). The 02 or Mahalanobis distance statistic is produced within the results of canonical OFA, and ind icates the multivariate spacing between data groups in multi-d imensions (Srivastava and Carter, 1 983). The 02 statistic is then a useful statistic measure of the separation of groups of samples (Stokes et al. , 1 992), in a manner similar to the numerical coefficients of variation and similarity coefficients of Borchardt et al. ( 1 971 ) . OFA was first used to discriminate tephras by Borchardt et al. ( 1 971 ) , based on instrumental neutron activation analysis of g lasses. King et al. ( 1 982) and Beaudoin and King ( 1 986) used this type of OFA on titanomagnetite major element chemistry to identify Holocene-aged tephras in western Canada. In New Zealand, Stokes and Lowe ( 1 988) and Stokes et al. ( 1 992) demonstrated the use of canonical OFA to d iscriminate volcanic source areas and later some individual eruptive units, using major element glass analyses. A simi lar study but including trace and rare earth element analyses was reported by Shane and Froggatt ( 1 994 ). These OFA studies also introduced the use of methods which selected variables that had the greatest discriminating power. This method is known as stepwise DFA and is further described by Srivastava and Carter (1 983), Stokes and Lowe (1 988) and Stokes et al. ( 1 992). Cluster analysis, another form of multivariate analysis , involves the placement of observations into groups suggested by the data only, without any prior groups being established (Johnson and Wichern, 1 992). A form of cluster analysis was used by King et al. ( 1 982) and was shown to be ineffective in obtain ing a clear, objective d iscrimination of groups. l t was, however, useful as a prel iminary technique to examine any major groupings in the data prior to the use of canonical OF A. In this study the SAS system programs CLUSTER, STEPOISC and CANDISC were used (SAS Institute Inc. , 1 985). These programs perform cluster analysis , stepwise OFA and canonical OFA, respectively. Prior to statistical analysis the compositional data used in this study was pre? treated to avoid statistical closure, in the manner described by Aitchison ( 1 983, 1 986) and Stokes and Lowe (1 988). The pre-treatment used is termed a log ratio transformation, whereby one oxide score is used to divide into al l of the other scores and the logarithm (base 1 0) is taken of each of these ratios. The oxide chosen as the d ivisor for all of the analyses in this study was MnO, for its moderate abundance and relatively low pooled and with in sample variance (Stokes and Lowe, 1 988; Shane and Froggatt, 1 994). 60 3.4.5 Stratigraphy and distribution of 23-75 ka andesitic tephras The age of the andesitic tephras in this study is constrained at the top by the Kawakawa Tephra , dated at 22 590 ? 230 years B.P. (Wilson et al. , 1 988). The age of the base of the tephra sequence is less well defined and is marked by a large thickness of lahar and stream flow deposits correlated to marine 81 80 stage 4 (65-75 ka; Cronin et al., 1 996). Throughout the sequence, however, additional dated rhyolitic tephras occur which lend further time control . These rhyolitic tephras are found as glass shards and mineral grains scattered over several centimetres in a matrix of fine-grained andesitic ash. Their identification has been achieved using a combination of electron microprobe major element g lass shard chemistry, ferromagnesian mineral assemblages and stratigraphic position (Cronin et al. , in press). The microscopic tephras are identified as the Taupe Volcanic Centre-sourced Okaia Tephra and the Okataina Volcanic Centre-sourced Omataroa Tephra , Hauparu Tephra and Rotoehu Ash . The ages of these units are g iven in Table 3 .5 , and their relative stratigraphic positions in Fig. 3.6. Table 3.5 Rhyolitic tephras identified with in the eastern r ing plain sequence, Ruapehu. Tephra name Kawakawa Tephra Okaia Tephra Omataroa Tephra Hauparu Tephra Rotoehu Ash Sourcea TVC TVC ovc ovc ovc Age (Yrs BP) 22 590 ? 2301 ea. 23 0002 28 220 ? 6301 35 870 ? 1 2701 64 000 ? 40003 a TVC = Taupo Volcanic Centre; OVC = Okataina Volcanic Centre. 1 Denotes 14C ages on old half l ife basis. 2 Estimated stratigraphic age. 3 Whole rock K-Ar age of enclosing lavas. Reference for age Wilson et al . ( 1 988) Froggatt and Lowe ( 1 990) Froggatt and Lowe ( 1 990) Froggatt and Lowe ( 1 990) Wilson et al. ( 1 992) Andesitic tephras occur throughout the entire sequence at Upper Waikato Stream (Fig. 3.6) . The tephras occur as ind ividual pumice lapi l l i units or as accumulations of fine ash representing the products of several eruptions over time. The lapi l l i and coarse ash units were used for correlation and fingerprinting studies. Over 60 individual andesitic lapi l l i un its are interbedded with in fine ash as well as fluvial and lahar deposits. The distribution of these tephras is not well delimited because their exposure in other sectors of the ring plain is sporadic. They are generally distributed to the east of Ruapehu Volcano and thin rapidly away from their axes of dispersal . Distal equivalents of some of these andesitic lapi l l i units are mapped to the south in the Rangitikei River valley, lying stratigraphically above the Porewan loess as middle Tongari ro Subgroup tephras (Leamy et al. 1 973; Mi lne and Smalley, 1 979). Andesitic ash on top of a Porewan loess correlative further to the east in Hawkes Bay is also commonly found (A.P. Hammond, pers. comm. , 1 995). Partial isopachs of two of the marker horizons are shown in Fig. 3.7. The l imited distribution information of these tephras would suggest a Ruapehu volcano source for most of the lapi l l i units rather than Tongariro volcano. 6 1 en N (m) A Kawakawa Tephra 1 . . . . . . . . . . . . . . ? marker unit 1 8ft$iJ . . . . . . . . . . . . . . . WJWj 1 20--kl? . ????- :I ? Distinguishable from physical characteristics (m) B 20 -????J???- Okaia Tephra / mmM Omataroa Tephra * I 30- 11111111111 Rotoehu Ash -.?-'{,?:;? G:;'b ?tq::::: ? marker unit 3 35 I/ Lrker unit 4 (m) I c ? marker unit 5 marker unit 6 marker unit 7 Section Key 0 2 3 4 5 0 - A 0 0 - I B 0 - c D - - Lignite ? Sandy matrix debris ? flow deposits [?:? ,?;-?] Hyperconcentrated streamflow deposits ? Silty matrix debris flow deposits i Fine andesitic ash Andesitic lapil l i layers Strongest paleosol development 1: ? : ? : ? : ? :? : ?1 Bedded sands, silts and gravels Figure 3.6 Composite stratigraph ic sequence from principal reference sections observed in the Upper Waikato Stream area with positions of andesitic and rhyol itic marker tephras shown. 3.4.6 Physical properties and mineralogy of 23-75 ka andesitic tephras The coarse-grained andesitic tephra are dominantly fine-medium pumice lapi l l i which are highly vesicular with very fine vesicles; the proportion of l ithic components is usually < 1 0 % by volume. The pumice is soft, highly weathered, and ranges from yel low to reddish brown. The degree of weathering, colour, and hardness of the pumice lapil l i changes markedly from site to site, depending largely on ind ividual site hydrology. In a single outcrop an individual tephra may range from a pale yellow soft pumiceous lapill i to a reddish brown very firm pumiceous lapil l i unit. This makes these parameters virtually unusable for discriminating and correlating the tephra units from place to place even on a very large scale with sites as l ittle as 1 00 m apart. Shower bedding and graded bedding are a lso relatively common features and so can only be used in combination with other means to correlate units. Three units can be uniquely identified from the other tephras in the sequence by their physical properties alone (other marker units can additionally be identified using compositional and mineralogy data). The properties of the three units at the principal reference sections are given below, and their stratigraphic positions are shown in Fig. 3 .6 . Unit 1 is an approximately 400-500 mm thick grey and olive brown lithic coarse ash mixed with yel low and yellow-brown coarse pumice ash. lt is well shower-bedded with alternating 50 mm beds dominated either by grey l ithic ash or yellow pumice ash giving a distinctive striped appearance. The basal 20 mm is composed of yellow fine pumice lapi l l i . The Kawakawa and Okaia Tephras overlie and underlie this unit, respectively, giving a stratigraphic age of ea. 23 ka. The only other tephras found in this area that have a similar appearance to this are members of the Mangamate Tephra described by Topping (1 973). The Mangamate Tephra is easily d istinguished by stratigraphic position, having been erupted ca. 1 0 ka from Tongariro volcano. Unit 2 is a grey, fine ash tuff, which is very hard and breaks up into blocks. lt is showerbedded on a 1 0 mm scale from very fine to medium ash and contains abundant accretionary lapil l i ranging in diameter from 1 to 5 mm within three ea. 40 mm layers. The unit totals ea . 200 mm in thickness. The Omataroa Tephra overlies this unit within a paleosol and the Hauparu Tephra underlies it, g iving a stratigraphic age range of 28-36 ka. No other tephra found in the study area bears any resemblance to this unit. Unit 3 is a reddish brown and strong brown fine pumice lapil l i and coarse ash mixed with grey l ithic coarse ash. Two distinctive 1 0 mm thick bands of grey l ithic? dominated coarse ash 20 mm apart occur near the top of the unit. This unit is ea. 300 mm thick. The Rotoehu Ash occurs above the unit giving a minimum stratigraphic age of 64 ka. Apart from these three units , there are no other tephra units which can be positively correlated based on their physical features a lone. Marker Units 4 and 5 are d iscriminated on the basis of hornblende and olivine chemistry respectively, while Units 6 and 7 are d iscriminated using a combination of mineralogy and titanomagnetite chemistry. 63 3.4.7 Mineralogy The andesitic tephras commonly contain phenocrysts of plagioclase, orthopyroxene, clinopyroxene and titanomagnetite. Some units a lso contain hornblende and olivine phenocrysts with rare i l lmenite and chrome spine!. The dominant ferromagnesian assemblage is: 1 . orthopyroxene + clinopyroxene > titanomagnetite ? olivine ? hornblende. This assemblage accounts for 90 % of the tephras in this sequence. Hornblende and olivine occur only in small quantities (<2% by volume) in most of the lapil l i . Two other ferromagnesian mineral assemblages are also observed in the tephra sequence, and can be characterised as hornblende-dominant and olivine-dominant: 2. Olivine > orthopyroxene + clinopyroxene > titanomagnetite. 3 . Hornblende > orthopyroxene + clinopyroxene > titanomagnetite. These assemblages are restricted in their occurrence with in the sequence and hence can be used to correlate ind ividual un its or small sequences of units to provide further marker beds for stratigraphic study. The bulk of the tephras fit the "type 1 " petrological classification of Ruapehu lavas (Cole et al. , 1 986; Graham and Hackett, 1 987), a lthough much less hornblende occurs in the lavas. The olivine-dominant assemblages fit into the "type 5" lava classification . The lavas with "type 5" mineralogy are generally found in satell ite vents rather than on the main Ruapehu cone from where the ol ivine-dominant tephra appears to have been erupted (Marker unit 1 , Fig. 3. 7 A). No hornblende-dominant mineral assemblages are recognised in Ruapehu lavas but rare hornblende-bearing lavas are described from Tongariro volcano (Cole, 1 978). Only one tephra has a ferromagnesian mineral assemblage dominated by olivine, (55 % by volume) namely Unit 1 as described previously. This distinctive mineralogy adds to the versatil ity of this marker bed because it can be identified from its mineralogy in local ities where its distinctive physical features may not be evident, e .g . in distal areas or off the dispersal axis. The tephra directly above Unit 1 a lso contains appreciable olivine (ea. 20% by volume), but al l other tephras throughout the entire sequence contain mostly 0-2% by volume olivine. Abundant olivine has only been described previously in Tongariro volcano-sourced members of the Mangamate Tephra (Lowe, 1 988a; Donoghue et a/. , 1 991 ) . Hornblende is another valuable marker mineral because i t occurs in only 1 1 of the tephras in the sequence and mostly in very minor quantities (<1 % by volume). l t does, however, occur in greater quantities in two tephras at the very base of the sequence. I n these tephras the hornblende content is >5% and in one is up to 30% by volume. The units do not have diagnostic physical features, but they can be used as marker horizons because of their distinctive hornblende rich-mineralogy. The stratigraphic positions of these two tephras (Units 6 and 7) are shown in Fig. 3 .6 . Both tephras are medium-coarse grade ash and are interbedded with in the l ignite near the base of the principal reference section . 64 A. ? Mt. Tongariro ? 39? 10' Mt. Ngauruhoe Mt. Ruapehu ? B. ? Mt. Tongariro ? Mt. Ngauruhoe Mt. Ruapehu ? Figure 3.7. Partial andesitic tephra isopach maps, th ickness given in mi l l imetres. (A) Marker Unit 1 , (B) Marker Unit 3 . 30 + 20 ? + + 0 tt + ON :1: I= 1 0 + + + + 0 I I I I 30 35 40 45 50 FeO % (recalculated) Figure 3.8. Plot of Ti02 wt % vs. FeO(recalculated) wt % of Titanomagnetite sample data. 65 The Rotoehu Ash occurs stratigraphical ly higher in the sequence giving a minimum age of 64 ka for Units 6 and 7. Hornblende is a lso found in small quantities within the previously described marker Unit 3, further enabling its identification as a marker horizon. Hornblende has been previously described only in Tongariro-sourced members of the Mangamate Tephra (Donoghue et al. , 1 991 ). Although units 4 and 5 intervene stratigraphically they are distinguished on the basis of their hornblende and olivine chemistry rather than mineralogy and are discussed later in the text. 3.4.8 Mineral chemistry of 23-75 ka andesitic tephras Table 3.6 Mean electron microprobe analyses of final titanomagnetite , hornblende and olivine groupings. Titanomagnetite Si02 Ti02 Al203 FeO M nO M gO Cr203 n Hornblende Si02 Ti02 Al203 FeO M nO M gO CaO Na20 K20 Cl n Olivine Si02 Ti02 AIP3 FeO M nO M gO CaO Na20 K20 Cl n Group 1 0 . 1 1 (0.08) 2 1 .76 (3.95) 1 .09 (0.27) 74 .78 (5.04) 0.30 (0.07) 1 .68 (0.37) 0.07 (0.03) 1 2 Group hb1 4 1 .92 ( 1 .23) 2 .46 (0.53) 1 2 .93 ( 1 .26) 1 2 .64 ( 1 . 1 4) 0.30 (0. 1 3) 1 3 .94 (0.92) 1 2 .32 (0.6 1 ) 2 .53 (0.22) 0.85 (0. 1 5) 0 . 1 1 (0 . 1 1 ) 30 Group ol1 38.87 (0.88) 0 .04 (0.02) 0.03 (0.01 ) 1 4 .39 (3.94) 0.24 (0.08) 46.20 (3.48) 0 . 1 4 (0.02) 0 .03 (0.03) 0 .03 (0.02) 0 .02 (0.01 ) 53 Group 2 0.27 (0. 1 0) 8 .91 (2.32) 1 .87 (0.32) 81 .39 (2.27) 0.42 (0.0 1 ) 1 .69 (0.66) 0 .20 (0 . 1 3) 1 2 Group hb2 42.20 (0.88) 2 .57 (0.60) 1 3 .20 (0 .94) 1 2 .31 (0.6 1 ) 0 .32 (0. 1 1 ) 1 4 .63 (0.65) 1 1 .60 (0.59) 2 .49 (0 . 1 3) 0 .61 (0.27) 0 .08 (0.08) 31 Group ol2 36.91 (0. 1 4) 0 . 1 2 (0 .0 1 ) 0 .35 (0. 1 7) 3 1 .45 ( 1 .30) 0 .49 (0.05) 30. 1 3 ( 1 .57) 0 .34 (0 .04) 0 . 1 3 (0.03) 0 .04 (0.0 1 ) 0.03 (0.0 1 ) 1 2 Group 3 0 . 19 (0. 1 0) 1 0 . 1 9 (2.28) 3 .75 (0.80) 81 .85 (2.22) 0.41 (0.08) 2 .82 (0.65) 0 .42 (0.2 1 ) 48 Group hb3 43.81 (0.30) 1 .25 (0.03) 1 2 .58 (0.28) 1 4.55 (0.36) 0.35 (0. 1 4) 1 4 .05 (0.22) 1 1 .05 (0.21 ) 2 .03 (0.05) 0.28 (0.06) 0.05 (0.0 1 ) 7 Group ol3 38.51 ( 1 . 1 4) 0 .04 (0.03) 0 .06 (0.02) 1 8 . 1 1 (3.52) 0 .34 (0. 1 5) 42 .64 (2.78) 0 . 1 4 (0.03) 0.05 (0.03) 0.07 (0.07) 0.03 (0.02) 46 Analyses obtained using a 1 2 nA beam current at 1 5 kV, with a 3 1-1m beam. Standard deviation in brackets. 66 Group 4 0 . 1 5 (0.05) 1 0 .98 (2.2 1 ) 4 .49 ( 1 .0 1 ) 79.78 (2.25) 0.39 (0.08) 3 .40 (0.64) 0 .46 (0.2 1 ) 234 Group ol4 36. 1 2 (0.28) 0 .02 (0.01 ) 0.07 (0.04) 24 .44 (0.25) 0 .44 (0.01 ) 38.65 (0.60) 0.08 (0.02) 0 . 1 0 (0.05) 0.04 (0.0 1 ) 0.04 (0.02) 8 All olivine phenocrysts analysed from tephras studied are forsteritic, ranging in composition from fo74 to fo87 (Table 3.6). The olivine phenocrysts are not zoned and do not display skeletal morphologies as described by Donoghue et al. ( 1 991 ) . Hornblende compositions range from edenite to pargasite (Table 3.6). Cl inopyroxene compositions fa l l in the augite field and orthopyroxenes all l ie with in the enstatite field. Titanomagnetite occurs in a range of ulvospinel compositions (Table 3.6). The mineral chemistry was used to identify any further marker horizons that could be used for stratigraphic study. 3.4.9 Titanomagnetite (discrimination of marker Units 1 , 2 and 6) Titanomagnetite chemistry has been used in several stud ies to correlate tephra marker beds. In New Zealand, Kahn ( 1 970) demonstrated the use of titanomagnetite composition to distinguish rhyolitic tephras. Kahn and Neall ( 1 973) were able to group andesitic Egmont volcano (EV) tephras into chemically d istinct groups and correlate distal andesitic tephras. Dista l Tongariro Volcanic Centre-(TgVC) and EV-sourced tephras can also be separated on the basis of their chemistry (Kahn and Neal l , 1 973; Lowe, 1 988a). All of these methods relied on bivariate plots to display d ifferences in selected elements and thus only a small subset of the available composition information is used. King et al. ( 1 982) and Beaudoin and King ( 1 986) used DFA on titanomagnetite compositions to separate individual distal tephra marker beds in Canada . In this study 306 titanomagnetite analyses were made on 53 tephra samples. As a first approach for classification, a number of two oxide plots were examined. The only useful plot for grouping the analyses into coherent groups was the plot of Ti02 vs. FeO (recalcu lated) (Fig. 3.8) . FeO recalculation was from stoichiometry (Droop, 1 987). This plot indicates a tightly clustered group of low Ti02 and FeO (recalculated) content samples and a group with higher contents of both oxides; two samples are outl iers from these groups. The two outlying samples are those from the marker units 1 and 6. The titanomagnetite oxide analyses were averaged for each sample before being entered into a SAS datafi le. The transformed oxides used in the fol lowing statistical analyses were Si02, Ti02, Al203 , FeO (total as determined by microprobe), MgO, and Cr203 . The first approach was assess any 'natural ' grouping in the data by using the SAS program CLUSTER (SAS Institute Inc. , 1 985). The cluster analysis resulted in the recognition of four groups. The Mahalanobis statistics (02) between the groups are large, with the closest groups having a 02 value of 8 between them (Fig. 3 .9 , Table 3.7) . The membership of these groups was examined and a relationship between the ferromagnesian mineral assemblage and the clusters was found . Cluster Group 1 , contains only one sample, the hornblende-rich marker Unit 6 . This unit is well separated from the others in the cluster analysis. Cluster Group 3 contains six samples, five of which are hornblende-bearing. Cluster Group 2 contains ten samples, eight of which contain olivine. Cluster Group 4 contains the bulk of the samples which have mineral assemblages mostly without appreciable olivine or hornblende. There is, however, mixing of samples which have mineral assemblages that do not conform to the group in which 67 the clustering process has placed them. Clustering techniques are usually only an exploratory technique to examine multivariate data (SAS Institute I nc . , 1 985). The grouping of the samples on the basis of their ferromagnesian mineral assemblage as suggested by the clustering was then tested further. All of the samples were assigned a group according to their ferromagnesian mineral assemblage. These groups were tested using canonical DFA with al l the log ratio-transformed oxide scores. The SAS program CANDISC was used (SAS Institute I nc. , 1 985). The groups were compiled as fol lows: Group 1 Group 2 Group 3 Group 4 hornblende-rich samples (>5%) ol ivine-rich samples {>1 0%) hornblende-bearing samples {>0.5%) al l other samples. All of these groups were well discriminated by canonical DFA with high 02 values ranging from 1 58 to 1 0 between groups (Fig. 3.98, Table 3. 7). The marker units which are particu larly wel l separated by this analysis are Unit 2 and Unit 6 (Group 1 ) and Un it 1 (Group 2). Samples of the hornblende bearing tephras in the sequence can also be d istinguished from the rest, which may also help to narrow down tephra correlations. If an unknown sample is analysed , this statistical analysis should result in a more precise identification of its possible correlatives. The mean compositions of the titanomagnetites in these four groups are presented in Table 3.6. Stepwise DFA was used to select a subset of variables which enabled the greatest separation between groups. The SAS program STEPDISC was used (SAS Institute I nc. , 1 985). The variables Ti02, Cr203, MgO, FeO and Al203 were chosen in order as the most d iscriminating variables. Using these variables in the DFA produced a group separation almost identical to using all of the variables (Table 3.7) . Cr203 was chosen as a highly discriminating variable in the analysis but the contents of this oxide is close to the microprobe detection l imits in many of the tephras. With Cr203 removed from the analysis good group separation is sti l l produced (Fig. 3 .9C, Table 3.7) . The order of the remaining variables d iscriminating power becomes, Ti02 , Al203, FeO, and MgO. The well defined DFA groupings show that the differences in major element titanomagnetite composition correlates with differences in phenocryst assemblages of the tephras. Most notably, the hornblende bearing and olivine rich tephras have a different titanomagnetite composition to one another and to the rest of the tephras. Aside from the tephra correlation implications as previously mentioned , the statistical groupings therefore a lso provide petrological information. In these tephras it appears that the phenocryst phases are genetically related , if not crysta ll ising from the same melt at least the same melt composition for each tephra. This relationship and the fact that all of the tephras examined have a single population of titanomagnetite compositions indicates little magma mixing occurring in this suite of tephras contrasting with a younger Ruapehu-sourced , si l ica-rich tephra described by Donoghue et al. ( 1 995). The groupings of titanomagnetite samples are not just simply related to the ferromagnesian mineralogy. Other factors appear to affect the group membership. The 68 Ti02 vs. FeO(recalculated) plot described previously shows two main groupings of samples with two outlying samples. The groupings suggested by these two elements were tested using the CANOISC program: Group H High Ti02 and FeO(recalculated) content Group L Group 1 Low Ti02 and FeO(recalculated) content as defined previously (Hornblende rich samples) Group 2 as defined previously (Oiivine rich samples). This procedure clearly separated the groups defined on this basis (Fig. 3.90, Table 3.7). These groupings, which are characterised by different relative contents of Ti02 and FeO(recalculated), could be indicating different eruptive sources e .g . Tongari ro vs. Ruapehu, or d ifferent batches of magma over time. There appears to be no clear d ivision of Tongariro-sourced and Ruapehu-sourced tephras between Groups H and L. The major element titanomagnetite chemistry does not appear to d iffer consistently for the two volcanoes for this set of samples. Investigating the order of eruption of the tephras indicates that the mixing of groups over time is not random. There are two instances in the tephra record where the titanomagnetites are dominantly of group H, otherwise they are group L. Group H samples, characterised by higher Ti02 and FeO contents may ind icate the introduction of a more basic melt at these times. This corresponds with greater quantities of olivine present with in the group H tephras. I n some cases the greater proportions of ol ivine are replaced by higher relative quantities of orthopyroxene, hornblende or titanomagnetite in the ferromagnesian mineral assemblage. The outlying groups are again the samples from the marker Unit 1 and Units 2 and 6 as described previously. Table 3.7 02 values between titanomagnetite groupings. Group Defin ition Cluster Grouping (Fig. 3 .9A) Mineralogical Groupings (Fig. 3.98) Mineralogical Groupings with STEPDISC variables Mineralogical Groupings with reduced variables (Fig. 3.9C) Chemically defined Groupings (Fig. 3.90) 02 Group 1 (marker Unit 6) Group 2 Group 3 Group 1 (Marker Units 2, 6) Group 2 (Marker Unit 1 ) Group 3 Group 1 (Marker Units 2 , 6) Group 2 (Marker Unit 1 ) Group 3 Group 1 (Marker Units 2, 6) Group 2 (Marker Unit 1 ) Group 3 Group H Group L Grou 2 69 Group 2 1 77 1 58 1 58 72 Group L 9 Group 3 1 04 32 46 82 45 82 26 59 Group 2 1 1 9 95 Group 4 1 1 8 1 1 8 50 1 49 1 0 49 1 48 1 0 4 1 1 09 8 Group 1 95 1 22 1 74 8 A. Cluster Groupings 5 B. Mineralogical Groupings I I I 4 I r ?-?Dg + D I 0 ? DD - - - - N ~ N c:: 0 c:: ro r- - - - - - - ro I 0 0 I I -5 I -4 + ... ... I ... I I -8 I - 1 0 I -1 2 -8 -4 0 4 8 -5 0 5 1 0 1 5 Can 1 Can 1 C. Mineralogical Groupings with D. Chemical Groupings 1 0 reduced variables 5 I I ... ... I 0g 0 1 + l 0 I o-?? ? 5 0 r- - - - - -I N I N , . c:: c:: I ro ro ? 0 0? 0 I 0 f- - - - - -5 ...... D DCf!JD I fSJ I t I I I t I -5 - 1 0 I - 1 0 -5 6 5 - 1 0 -5 0 5 Can 1 Can 1 Symbol Key .A. Group 1 (Marker Un its 2 , 6) 0 Group 4 + Group 2 (Marker Unit 1 ) 0 Group H D Group 3 ? Group L Figure 3.9. Plots of the first two canonical variables (Can 1 and Can2) for titanomagnetite data. (A) Cluster defined groupings. (B) M ineralogical groupings. (C) Mineralogical groupings with reduced variables (Crp3 omitted). (D) Chemically defined groupings (derived from the Ti02 vs. FeO (recalculated) plot). 70 3.4. 10 Hornblende (discrimination of marker Unit 4) Hornblende chemistry has been used in New Zealand tephra studies as a tool to separate eruptives from EV, TgVC and Taupe Volcanic Zone (TVZ) rhyolitic centres (Lowe, 1 988b; Froggatt and Rogers, 1 990; Eden et al. , 1 993). Eden et al. ( 1 993) used a plot of the atomic proportions of Ca vs. Si to separate EV, TgVC, and TVZ-rhyolitic hornblendes. In this study the hornblende chemistry of ind ividual eruptive units with in the tephra sequence was examined to attempt to identify marker horizons in the same manner as for titanomagnetite. A plot of the atomic proportions of Ca and Si d id not show any separation or grouping of samples, and no other two oxide plots proved to be useful in d istinguishing any marker units. Clustering analysis was applied to the transformed hornblende data in the same manner as for titanomagnetite. As there are only 1 1 hornblende-bearing tephras analysed in this sequence, the mean analyses of each sample cannot be used in the multivariate statistical procedures due to the lack of sufficient degrees of freedom. As a result, individual analyses were used in the fol lowing procedures rather than means. The clustering procedure produced three groups of samples with good separation, Groups hb1 , hb2 and hb3 (Fig. 3 . 1 OA, Table 3 .8). Several tephra samples had al l of their analyses contained with in a single group, but some of the samples had one or two of their analyses in another cluster grouping. The hornblende cluster groups were then refined by keeping the analyses of each tephra sample with in a single group (i. e. assuming a single population for each tephra sample). Canonical DFA of the refined hornblende groups produced better discrimination with higher D2 values (Fig. 3 . 1 OB, Table 3 .8) , ind icating that there are no mixed populations of hornblendes in these samples. The STEPDISC program chose, in order, K20, FeO, Ti02, Al203 , MgO, CaO, and Si02 as the most d iscriminating variables. Using this subset of variables the group separation was almost as good as using al l of the variables (Table 3.8) . The hornblende groupings enable the discrimination of marker Unit 4 from the other hornblende bearing tephras. The refined Group hb3 is well separated from the other groups and consists of analyses of marker Unit 4 (Fig. 3.6) . This unit had not been uniquely identified with any of the methods described previously. Group hb2 contains the analyses of several tephra samples but they all lie with in the same part of the sequence, in the middle part of the record below the d istinctive, previously described marker Unit 3 (Fig 3.6). Group hb1 contains the tephra samples which are at the very base of the sequence, including marker Unit 6. Group hb1 also contains the distinctive marker Unit 2, but this is able to be identified on the basis of its field appearance. The hornblende major element chemistry can be used to potential ly place an unknown tephra sample in a specific part of the sequence, and in the case of one tephra (marker Unit 4) uniquely identify it. 71 N c: ro 0 N c: ro 0 4 2 0 f- -2 -4 -6 -4 4 2 0 - -2 A. Cluster Grouping tJ 0 D fj;O 1 D ? ? D? D - o+ 0 or -?J ' - - - - ?* I? + + ? t I + I I -2 0 2 4 6 Can 1 B. Refined Groupings I 1 0 0 o p o o o 0 0 0 ? D B - - - - o 40? o o ? ? 0 0 0 - - I 0 - - + + +0 + I ? +J.I -!+ ++ + I -4 +----r-----..----,-- +-+-1 -?-...., -8 -6 -4 -2 0 Can 1 0 Group hb1 + Group hb2 2 D Group hb3 (Marker Un it 4) 4 Figure 3.1 O.Piots of the first two canonical variables for hornblende data. (A) Cluster defined groupings. (B) Refined cluster-defined g roups. 72 5 A. Cluster Grouping "* 0 1- - - - -? - - - - N D D I c: CJ I ro 0 0 D I -5 I I 0 I -1 0 I ' -1 0 -5 0 5 1 0 Can 1 1 0 B. Mineralogical Groupings N c: ro 0 N c: ro 0 o l + Group ol1 D Group ol2 5 I 0 Group ol3 0 1 0 Group ol4 (Marker Un it 5) @0 0 - -+ ? CO - - - G- - - - ? l D +-++ I I -5 +---?-----.---?--?. -5 0 5 1 0 1 5 Can 1 5 C. Mineralogical Groupings with reduced variables I + I ?? 0 1- - - - - -o - -D 0 0.5%) of olivine phenocrysts . No skeletal forms of olivine analogous to those described by Oonoghue et al. ( 1 991 ) in the Mangamate Tephra Formation were seen. In this study 1 1 9 grains of olivine were analysed from 1 6 tephras. Bivariate oxide plots showed no consistent groupings of samples that were easily d iscern ible by eye because oxide values are very simi lar from one analysis to another. Clustering analysis was applied to the transformed olivine data in the same manner as for titanomagnetite. The oxide variables used were Si02, Al203, FeO, MgO, CaO, and Na20, the other oxides reported in Table 3.6 were too low and close to microprobe detection l imits. Four groupings resulted , which were separated by sign ificant 02 spacings (Fig. 3 . 1 1 A, Table 3.9). The group membership of tephra units was found to be dominantly (but not exactly) the same as the previously defined titanomagnetite groupings. With this in mind, groups were defined on a simi lar basis to the titanomagnetite groups for canonical OFA: Group ol 1 Olivine rich samples (>5%) Group ol2 Group ol3 Group ol4 Hornblende bearing samples All other samples Marker Unit 5 Group ol4 had to be defined to contain analyses of a tephra sample which did not fit into any of the other groups (marker Unit 5). These four groups were wel l separated using OFA (Fig. 3 . 1 1 B; Table 3 .9) . The STEPOISC procedure chose, in order: MgO, Si02 Al203 , CaO, and FeO as the most discriminating variables. Using this subset of variables, 73 group separation almost as good as using all of the variables was achieved (Table 3.9) . The DFA was also tried without the STEPDISC chosen oxides Al203 and CaO which are of low content in these olivines. The resultant d iscrimination is sti l l good for al l groups but was reduced between groups ol1 and ol3 (Fig . 3. 1 1 C, Table 3.9) . Using these statistical techniques with olivine analyses from the tephra sequence the group separation defined by the titanomagnetite chemistry is able to be corroborated . Thus the olivine chemistry appears to be as sensitive to the ferromagnesian assemblage as the titanomagnetite chemistry. One further tephra unit can be uniquely identified in the sequence on the basis of its olivine chemistry. This is the unit represented by Group ol4, corresponding to marker Unit 5 (Fig. 3.6). Table 3.9 02 values between olivine groupings. Group definition Cluster Groupings (Fig. 3 . 1 1 A) Mineralogical Groupings (Fig. 3 . 1 1 B) Mineralogical Groupings with STEPDISC variables Mineralogical Groupings with reduced variables (Fig. 3 . 1 1 C) 3.4.12 Other phases D2 Group ol2 Group ol 1 40 Group ol2 Group ol3 Group ol 1 Group ol2 Group ol3 Group ol1 Group ol2 Group ol3 Group ol 1 Group ol2 Group ol3 1 45 1 42 1 07 Group ol3 Group ol4 (Marker Unit 5) ? 1 1 89 35 1 1 3 66 9 46 1 06 1 69 22 7 34 1 06 1 66 1 8 1 .8 1 9 93 1 61 1 5 Lowe (1 988a) found some provisional separation between EV and TgVC pyroxenes using analyses from the phenocryst cores. The pyroxene grains of the present sequence, however, were too strongly compositionally zoned to attempt chemical correlation and discrimination between individual eruptives. Andesitic glass chemistry was shown to be effective in discriminating EV and TgVC tephras (Lowe, 1 988a; Stokes and Lowe, 1 988). The preservation of andesitic glass is, however, poor in most sedimentary environments, and very poor in the New Zealand soil environment (Neal l , 1 977; Kirkman and McHardy, 1 980). Very few glass analyses could be obtained from the andesitic tephras in this sequence, and those that were obtained were considered unreliable due to the degree of weathering and hydration of the g lass. 74 3.4. 13 Conclusions 1 ) I n this andesitic tephra sequence, ranging in age from ea. 23 ka to 75 ka, correlation of individual units over the eastern Ruapehu ring plain has been achieved through a variety of laboratory and field methods (Table 3. 1 0). Seven units can be distinguished as marker beds over the eastern Ruapehu ring plain. This enables relative dating of ring plain deposits and surfaces, where other dating methods are less useful or more expensive. Table 3.1 0 Summary of the criteria for identification of andesite marker tephras in this study. Tephra marker Unique field Characteristic Unique Unique Unique appearance mineralogy titanomagnetite hornblende olivine chemist!Y chemist!Y chemist!:l Unit 1 ./ olivine rich ./ Unit 2 ./ hornblende rich ./ Unit 3 ./ hornblende ./ bearing Unit 4 hornblende ./ bearing Unit 5 ./ Unit 6 hornblende rich ./ Unit 7 hornblende rich 2) Three tephra units within this sequence are able to be identified over the eastern Ruapehu ring plain based on their unique field appearances; no other units can be uniquely identified on this basis. The field-based marker units are termed Units 1 , 2 , and 3. 3) The ferromagnesian mineral assemblage is another valuable identification criterion. The presence of >50 % modal olivine and > 5% modal hornblende are useful in further characterising Units 1 and 2, respectively. The presence of large quantities of hornblende (>5 to 30% by volume) enables the identification of two further tephra units near the base of the sequence, marker Units 6 and 7. Further identification of marker beds rel ies on electron microprobe analyses of phenocryst minerals. 4) The use of statistical clustering methods on electron microprobe-determined mineral compositions was found to have l imited use in accurately grouping and d iscriminating mineral data , but was a valuable reconnaissance technique. Canonical DFA was used to d istinguish groupings of sample data which were refined from clustering analysis by using other factors such as ferromagnesian mineral assemblage. 5) The grouping and discrimination of tephras using their titanomagnetite major element analyses reflected the tephra ferromagnesian mineral assemblage. Four d istinct chemical groups were defined : 75 Group 1 Group 2 Group 3 Group 4 hornblende-rich samples (>5%) ol ivine-rich samples (> 1 0%) hornblende-bearing samples all other samples This impl ies that al l of the phenocrysts in these andesitic tephras were formed together in the same crystall ising event or under the same magmatic conditions, and that these conditions are also reflected by the titanomagnetite chemistry. Titanomagnetite mineral chemistry was used to further discriminate marker Units 1 , 2, and 6, as well as narrow down the identification of the other units. This is especially useful in situations such as distal areas where the ferromagnesian mineral assemblage is not well represented. The titanomagnetite chemistry also ind icates episodes of changing melt composition during the eruptive history of Ruapehu volcano. Two episodes, thought to represent a more basic melt composition were seen. 6) Marker Units 2 and 6 are able to be further identified on the basis of hornblende composition and one other unit is able to be uniquely identified : marker Unit 4. The remaining hornblende bearing units are specifically grouped according to their stratigraphic position, enabling correlation to a general part of the sequence if not a specific tephra unit. 7) Olivine chemistry corroborates the groupings of tephra samples based on their titanomagnetite analyses, giving further means of identifying Unit 2 and the groups defined by the titanomagnetites. One other tephra unit can also be uniquely identified by its olivine chemistry: marker Unit 5. 8) In this study the usefulness of a multi-parameter approach and the statistical analysis of data for andesitic tephra correlation has been shown . In an andesitic ring plain environment very few tephra units can be discriminated by physical features alone as the physical appearances of small-medium volume andesitic tephra units change over very small distances. Detailed field mapping needs to be combined with increasingly diverse techniques to be able to correlate such tephras. The described statistical methods have proven useful in conjunction with more traditional methods currently used for andesitic tephra fingerprinting and correlation. 3.4. 14 Acknowledgements SJC gratefu lly acknowledges funding from the New Zealand Vice-Chancel lor's Committee, Massey University Graduate Research Fund, and the Helen E. Akers Scholarship Fund. We thank K. Palmer for introduction to the use of the electron microprobe, and B. Roser and D. Lowe for their thoughtfu l reviews and comments. 76 3.5 Combined reference l ist Aitchison, J . , 1 983. Principal component analysis of compositional data. Biometrika, 70: 57-65. Aitch ison , J . , 1 986. The Statistical Analysis of Compositional Data. Monographs on Statistics and Applied Probabil ity. Chapman and Hal l , London. Alloway, B.V. , Neal l , V .E . , Vucetich, C.G . , 1 995. Late Quaternary (post 28 000 year B .P . ) tephrostratigraphy of northeast and central Taranaki, New Zealand. J . Roy. Soc. N .Z. , 25: 385-458. Beaudoin, A.B. and King, RH . , 1 986. Using discriminant function analysis to identify Holocene tephras based on magnetite composition: a case study from the Sunwapta Pass area, Jasper National Park. Can . J. Earth Sci . , 23: 804-81 2. Borchardt, G.A. . , Harward , M .E . and Schmitt, RA. , 1 971 . Correlation of ash deposits by activation analysis of glass separates. Quat. Res. , 1 : 247-260. Cole, J .W. , 1 978. Andesites of the Tongariro Volcanic Centre, North Island, New Zealand. J . Volcano!. Geotherm. Res . , 3: 1 2 1 - 1 53 . Cole, J .W. , Graham, I . J . , Hackett, W.R and Houghton , B .F . , 1 986. Volcanology and petrology of the Quaternary composite volcanoes of Tongariro Volcanic Centre, Taupe Volcanic Zone. In : Smith, I .E .M . Late Cenozoic volcanism in New Zealand. Roy. Soc. N .Z. Bul l . , 23: 225-250. Cronin , S .J . , Neal l , V.E. and Palmer, A.S . , 1 996. The geological history of the north? eastern ring plain of Ruapehu Volcano, New Zealand. Quat. I nter. , 34-36: 21 -28. Donoghue, S .L . , Neal l , V.E. and Palmer A.S. 1 995. Stratigraphy and chronology of late Quaternary andesitic tephra deposits, Tongariro Volcanic Centre, New Zealand. J . Roy. Soc. N .Z . , 25: 1 1 5-206 . Donoghue, S .L . , Stewart, RB. and Palmer, A.S. , 1 991 . Morphology and chemistry of olivine phenocrysts of Mangamate Tephra, Tongariro Volcanic Centre, New Zealand. J. Roy. Soc. N .Z . , 21 : 225-236. Droop, G.T.R , 1 987. A general equation for estimating Fe2+ concentrations in ferromagnesian sil icates and oxides from microprobe analyses, using stoichiometric criteria . Min. 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Distribution of the heavy minerals in the downwind tephra lobe of the May 1 8, 1 980 eruption of the Mount St. Helens (Washington, USA). Eiszeitalter U. Gegenwart 33: 1 -7 . King, R.H . , Kingston, M .S. and Barnett, R .L . , 1 982. A numerical approach to the classification of magnetites from tephra in southern Alberta. Can. J. Earth Sci . , 1 9 : 201 2-20 19. Kirkman, J .H . and McHardy, W.J . , 1 980. A comparative study of the morphology, chemical composition and weathering rhyolite and andesite g lass. Clay Minerals, 1 5 : 1 65-1 73. Kohn , B .P . , 1 970. Identification of New Zealand tephra layers by emission spectrographic analysis of their titanomagnetites. Lithos, 3: 361 -368. Kohn , B .P . and Neal l , V.E . , 1 973. Identification of late Quaternary tephras for dating Taranaki lahar dep9sits. N .Z. J. Geol. Geophys . , 1 6 : 781 -792. Leamy, M .L . , Milne, J .D .G . , Pullar, W.A. and Bruce, J .G . , 1 973. Paleopedology and soil stratigraphy in the New Zealand Quaternary succession . N.Z. J . Geol . Geophys. , 16 : 723-744. Lowe, D.J . , 1 986 . Controls on the rates of weathering and clay mineral genesis in airfall tephras: a review and New Zealand case study. In: Colman, S .M . , Deth ier, D .P. (eds). Rates of chemical weathering of rocks and minerals. Academic Press, Orlando: 265-330. Lowe, D.J . , 1 987. Studies on late Quaternary tephras in the Waikato and other regions in northern North Island, New Zealand, based on distal deposits in lake sediments and peats. Unpub. PhD thesis, University of Waikato, Hamilton , New Zealand. Lowe, D .J . , 1 988a. Stratigraphy, age, composition, and correlation of late Quaternary tephras interbedded with organic sed iments in Waikato lakes, North Island, New Zealand. N .Z. J. Geol. Geophys . , 31 : 1 25-1 65. 78 Lowe, D.J . , 1 988b. Late Quaternary volcanism in New Zealand: towards an integrated record using distal a irfa l l tephras in lakes and bogs. J. Quat. Sci . , 3: 1 1 1 -1 20. Lowe, D.J . , 1 990. Tephra studies in New Zealand : an historical review. J . Roy. Soc. N .Z. ,20: 1 1 9-1 50. Mathews, W.H . , 1 967. A contribution to the geology of the Mount Tongariro massif, North Island, New Zealand. N .Z. J. Geol. Geophys . , 1 0: 1 027-1 038. Mi lne , J .D.G. and Smalley, I .J . , 1 979. Loess deposits in the southern part of the North Island of New Zealand: an outl ine stratigraphy. Acta Geologica Academiae Scientarium Hungaricae, 22: 1 97-204. Neal l , V .E . , 1 977. Genesis and weathering of Andisols in Taranaki , New Zealand . Soil Sci . , 1 23 : 400-408. Pullar, W.A., 1 967. Uses of volcanic ash beds in geomorphology. Earth Sci. J . , 1 : 1 64- 1 77. Randle, K. , Gorton, G .G. , Kittleman, L .R. , 1 971 . Geochemical and petrological characterisation of ash samples from Cascade Range volcanoes. Quat. Res. , 1 : 261 -282 Ruxton, B .P . , 1 968. Rates of weathering of Quaternary volcanic ash in north-eastern Papua. 9th International Congress of Soil Science Transactions Vol. 4, Paper 38: 367-376 SAS Institute Inc. , 1 985. SAS Users guide: Statistics. Version 5 Edition , SAS Institute Inc. , Cary N .C . , 956 pp. Shane, P.A.R. and Froggatt, P.C. , 1 994. Discriminant function analysis of g lass chemistry of New Zealand and North American tephra deposits. Quat. Res . , 41 :70-81 . Smith , D.G.W., Westgate, J .A. , 1 969. Electron probe technique for characterising pyroclastic deposits . Earth Planet. Sci . Lett. , 5: 31 3-3 1 9. Srivastiva, M.S. and Carter, E. M . , 1 983. An Introduction to Applied Multivariate Statistics. Elsevier Science Publishing Co. I nc. , New York. Stewart, R .B . , Price, R.C. , Smith , I .E .M . , (in press). Evolution of high-K arc magma, Egmont volcano, Taranaki , New Zealand: evidence from mineral chemistry. J. Volcano!. Geotherm. Res. Stokes, S. and Lowe, D.J . , 1 988. Discriminant function analysis of late Quaternary tephras from five volcanoes in New Zealand using glass shard major element chemistry. Quat. Res. , 30: 270-283. Stokes, S . , Lowe, D.J. and Froggatt, P.C. , 1 992. Discriminant function analysis and correlation of Late Quaternary rhyol itic tephra deposits from Taupo and Okataina volcanoes, New Zealand, using glass shard major element composition. Quat. Inter. , 1 3/1 4: 1 03-1 1 7. Thorarinsson, S. , 1 949. Some tephrochronological contributions to the volcanology and g laciology of Iceland. Geografiska Annaler, 31 : 239-256. 79 Topping, W.W. , 1 973. Tephrostratigraphy and chronology of late Quaternary eruptives from the Tongariro Volcanic Centre, New Zealand. N .Z. J. Geol. Geophys . , 1 6 : 397-423. Topping, W.W. and Kohn, B .P . , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island , New Zealand . N.Z. J . Geol. Geophys . , 1 6 : 375-395. Vucetich, C .G . , Pul lar, W.A. , 1 969. Stratigraphy and chronology of late Pleistocene volcanic ash beds in central North Island, New Zealand. N.Z. J. Geol . Geophys . , 1 2: 784-837. Vucetich, C .G . , Pul lar, W.A. , 1 973. Holocene tephra formations erupted in the Taupo area and interbedded tephras from other volcanic sources. N .Z. J . Geol. Geophys. 1 6 : 745-780. Wallace, R.C. , Alloway, B.V. , Stewart, R.B. , Neall , V.E . , 1 986. Mineral chemistry as an ind icator of petrogenisis at Egmont volcano. Abstracts of the International Volcanological Congress, 1 986 New Zealand: 23. Wal lace, R .C . , 1 987. The mineralogy of the Tokomaru Silt Loam and the occurrence of cristobalite and tridymite in selected North Island soils. Unpub. Ph.D . thesis, Massey University, New Zealand. Wilson , C.J .N . , 1 993. Stratigraphy, chronology, styles and dynamics of late Quaternary eruptions from Taupo volcano, New Zealand. Phi l . Trans. Roy. Soc. London A, 343: 205-306. Wi lson , C.J .N . , Houghton, B .F . , Lanphere, M .A. and Weaver, S .D . , 1 992. A new rad iometric age estimate for the Rotoehu Ash from Mayor Island volcano, New Zealand. N .Z. J. Geol . Geophys. , 35: 371 -374. Wilson, C.J .N . , Switzur, R.V. and Ward , A.P . , 1 988. A new 14C age for the Oruanui(Wairakei) eruption, New Zealand. Geol . Mag . , 1 25: 297-300. 80 CHAPTER 4: PALEOSOL DEVELOPMENT AND PALEOCLIMATIC INVESTIGATIONS OF THE RING PLAIN SEQUENCE 4.1 Introduction In the previous two chapters a stratigraphic framework of rhyolitic and andesitic tephras has been establ ished for the older ring-plain sequences found on the NE Ruapehu and E Tongariro ring plains. The fi rst way in which the stratigraphic framework has been applied was the investigation through time of weathering and soil development within the ring plain sequence. In particular the stratigraphic framework a l lowed the sequence of weathering and soil development on the ring plains to be correlated to other investigations of the New Zealand late Quaternary paleoclimatic record . In the following published study, parameters of weathering and soil development in the ring plain sequences, particularly the clay mineralogy, were investigated . I n this way past climatic and soil development conditions on the ring plain areas were elucidated. The sequence of soil development was compared to other paleosol sequences in other areas of the North Island of New Zealand using the interbedded tephra layers as time planes. The following paper has multiple authors and the contributions of each author to the work were: S.J. Cronin : Principal investigator Carried out a l l : field description and sampling laboratory preparation of samples optical microscopy work chemical , XRD and DTA analyses grainsize and soil-physical analyses manuscript preparation and writing V.E. Neall and A.S. Palmer: Advisers Aided the study by: d iscussion of methodology and results editing and d iscussion of the manuscript 81 4.2 INVESTIGATION OF AN AGGRADING PALEOSOL DEVELOPED INTO ANDESITIC RING-PLAIN DEPOSITS, RUAPEHU VOLCANO, NEW ZEALAND. Shane J . Cronin, Vincent E . Neal l , and Alan S. Palmer Department of Soil Science, Massey University, Private Bag 1 1 222, Palmerston North, New Zealand. Geoderma , 69 ( 1 996) 1 1 9-1 35. Abstract Within a sequence of andesitic volcaniclastic deposits on the north-eastern ring plain of Ruapehu volcano is a ca. 1 0 m-thick sequence of weathered andesitic tephras. Weathering and paleosol development is most evident in 3 .6 m of fine ash in this sequence. The age of these tephras are constrained between ea. 23-70 ka by dated rhyolite tephras erupted from central North Island volcanoes. Mineralogy of the fine ash deposits reveals their origin, and the processes involved in their soil development. The fine ash deposits are almost totally locally derived either as primary volcanic ash or fines reworked from the ring plain itself by aeolian processes. Aerosolic quartz input associated with regional loess deposition during the cool climatic episodes of mid-8180 stage 3 and 81 80 stage 4 is very low, having been di luted by rapid accumulation of andesitic tephras in these episodes. The observed weathering features and secondary minerals within the ash sequence were derived from a complex combination of factors including climate change, accretion rate, and post-depositional modification. Relatively strong weathering development in two parts of the ash sequence is correlated with two widespread soil development episodes during the Last Glacial observed throughout the southern North Island. The accretion rate of the soil surface at these times also affected the expression of climate-related weathering. Formation of allophane (with an AI/Si ratio of 2 : 1 ) and ferrihydrite occurred near the soil surface as the ash was accreting. The amount of a l lophane and ferrihydrite through the sequence appears to be inversely related to the accretion rate of the soil surface. Upon burial of the ash materials by a thick (>20 m) sequence of lahar and tephra deposits, halloysite was later formed in the buried ash. The leaching of si l ica from the thick overburden of volcaniclastics into the ash material as well as perched water is thought to have decreased the AI/Si ratio in the soil solution and thus promoted the formation of halloysite from weathering andesitic g lass. 4.3 Introduction Preserved on the eastern ring plain of Ruapehu volcano is a >50 m thick sequence of volcaniclastic deposits which have accumulated over the last ea . 75 ka (Cronin, et al. , 1 996). Within this sequence the contrasting morphologies of the deposits indicate the intensity of surficial weathering has varied over time. During the cold climatic episodes of marine 8180 stages 2 and 4, near-continuous aggradation of diamictons occurred over the entire eastern Ruapehu ring plain (diamicton is a non genetic term for poorly sorted 82 sediments which contain a wide variety of particle sizes; Fl int, 1 960). The diamictons of this sequence generally contain pebble- to boulder-sized clasts which are supported by a sand-silt matrix. The aggradation of the diamictons is thought to be a reflection of unstable conditions on Ruapehu volcano, and the mechanism of deposition is thought to be dominantly by lahars (volcanic mud-flows). Within the periods of rapid aggradation on the ring plain there appears to have been l ittle opportunity for the preservation of any air fa l l tephra or volcanic loess. The only tephras preserved in the diamicton sequences are the very large lapi l l i units and these have been reworked and eroded in many places. There is no soil development evident within the "packages" of diamictons. During the mild climatic episodes of 8180 Stage 3, deposition on the ring plain was dominated by tephra and volcanic loess accession. Soil development is evident throughout these deposits but is most strongly exhibited in the fine ash material . Diamictons sti l l occur in the sequence but were separated by significant t ime intervals. The aim of this study was to characterise the origin of the fine ash deposits and to investigate the paleosol-forming environment throughout the sequence of tephra and volcanic loess deposits . This was achieved through field interpretation of the deposits coupled with mineralogical studies. 4.4 Setting Ruapehu volcano with in the Tongariro Volcanic Centre, is a large, active, andesitic, stratovolcano, and the highest point in the North Island at 2797 m. The current massif comprises a 1 1 0 km3 cone with an apron of volcaniclastic deposits surrounding it of simi lar volume (Hackett and Houghton, 1 989). The apron of volcaniclastic deposits is termed the ring plain . The area of this study is located along the Upper Waikato Stream of the north-eastern ring plain {Chapter 3: Fig. 3.5) . Exposed in continuous stream bank exposures in this and adjacent streams are the deposits described in this paper. The altitude of the area ranges from 900 to 1 1 00 m above sea level . The Ruapehu region has a cool-temperate climate with numerous frosts and snow-fal ls, and a mean annual temperature of 1 0 oc at 600 m (McGione and Topping, 1 977). The orographic influence of Ruapehu volcano on the predominantly westerly airflow increases the rainfal l on the higher slopes of the volcano compared to surrounding areas. The average annual rainfal l varies from 1 600 mm at 900 m to 2400 mm at 1 1 00 m altitude on the eastern side of the volcano (N.Z. Meteorological Service, 1 973). 4.5 Stratigraphy The tephra dominant portion of this section of the ring plain sequence occurs between two "packages" of diamictons (Fig. 4 . 1 ) . Time control is provided by the presence of five rhyolitic tephras erupted from central North Island volcanoes to the north (Table 4 . 1 ). The four oldest tephras occur as rhyolitic glass shards and minerals dispersed over several centimetres within a matrix of fine andesitic ash. The identification of these tephras was 83 made on the basis of characteristic mineralogy and electron-microprobe major element glass chemistry. Table 4.1 . Rhyolitic tephra identified with in the north-eastern ring plain sequence. Tephra Name Source Kawakawa Tephra TVC Okaia Tephra TVC Omataroa Tephra ovc Hauparu Tephra ovc Rotoehu Ash ovc TVC = Taupo Volcanic Centre OVC = Okataina Volcanic Centre Age 22 590 ? 2301 ea . 23 000 28 220 ? 6301 35 870 ? 1 2701 64 000 ? 40002 1 Denotes 1 4C ages based on old half life (years B .P . ) 2 Whole rock K-Ar age (years) 4.6 Physical description Reference for age Wilson et al . , ( 1 988) Froggatt and Lowe, ( 1 990) Froggatt and Lowe, ( 1 990) Froggatt and Lowe, ( 1 990) Wilson et al . , ( 1 992) The ash materials of this study are 20 to 30 m below the present soil surface. The diamictons interbedded with , and above and below the tephra and volcanic loess sequence have a sandy matrix supporting clasts of andesitic lava; the clasts can be over 1 m in d iameter. All of the diamictons contain 5-1 0% by volume andesitic pumice lapi l l i but in an extreme case up to 60%. Two of the diamicton units in this sequence are firmly cemented , while the others are unconsolidated. The andesitic tephra occur as individual pumice lapi l l i and coarse ash beds or as accumulations of fine ash representing the products of several eruptions over t ime. The coarser andesitic tephra are dominantly fine pumice lapi l l i which are highly and very finely vesicular; the proportion of l ithic components is usually <1 0% by volume. The pumice is soft, highly weathered , and ranges from yellow to reddish-brown . The pumice lapi l l i occur interbedded with fine ash throughout the sequence. A high frequency of pumice lapil l i units with in fine ash is here considered to represent more rapid accumulation of the surface compared to slower accretion where pumice lapil l i are fewer within the fine ash. The finer grained andesite ash ranges in texture from fine sandy loam to loam. A few zones with in the ash column contain the occasional pumice lapil l i clasts while most of these deposits are uniformly fine grained <2 mm. The ash is dominantly yel low-brown and brown and some sites have lower chroma colours but l ittle or no evidence of mottl ing. lt is firm when moist and dries into very strong blocks. Very little soi l structure is seen apart from coarse blockiness when the ash material is dry. Root rhizomorphs are abundant throughout all of the fine ash. Two zones of more strongly weathered ash with common to very common root rhizomorphs were noted (Fig . 4. 1 ) . The upper zone is dark brown , contains finely d isseminated charcoal fragments, and has the greatest abundance of root rhizomorphs. 84 Overal l Sequence 25 30 ?+++++++-Om ?+++++++- Re : ;.?? '6? ? "': o-:- ? . . ,_; ? ? ? ? . . ,: _ ., . ? ? . . Cemented Diamicton ? Diamictons ? Andesitic ? Lapi l l i D Fine Andesitic Ash [ill] Stronger paleosol development Figure 4.1 . Stratigraphic column of part of the northeastern Ruapehu ring-plain sequence with paleosol development and its position within the overal l ring plain sequence. Kk = Kawakawa Tephra , Ok = Okaia Tephra, Om = Omataroa Tephra , Hu = Hauparu Tephra, Re = Rotoehu Ash. 85 The lower zone is not as wel l expressed but contains a greater abundance of root rhizomorphs than the surrounding ash, as wel l as finely d isseminated charcoal fragments. The dry bulk density of the ash material ranges from 0.68 to 0 .86 Mg m?3 (Table 4.2) . The lowest bulk densities are in the upper part of the ash column within the upper zone of stronger weathering. The highest bulk densities are within the lower zone of stronger weathering. Table 4.2. Soil physical properties of selected ash samples. Sample depth Dry bulk density Field-moist Air-Dry gravimetric Gravimetric water (m) (Mg m?3) gravimetric water water content at content of air d ry content at -1 . 5 -1 .5 MPa (%) soi l <2mm (%) MPa % 0 .4-0 .5 0.68 78 50 1 3 0 .9-1 .0 0.68 96 52 23 1 .5-1 .6 0 .86 64 5 1 1 5 1 .8-1 .9 0 .80 81 50 1 0 3 .5-3.6 0.75 75 39 1 5 4. 7 Mineralogy of ash grade material Selected mineralogy of the ash grade material was investigated to identify the provenance of the material and to elucidate the soil forming processes occurring in the ash. The fine ash was channel sampled at 1 0 cm intervals through its 3.6 m th ickness. 4.8 Methods Quartz, cristobalite, and plant opal were concentrated from the whole soil (<2 mm) using the method of Henderson et al. ( 1 972). Each soil sample was subjected to repeated dissolution in 6 M hydrochloric acid at 80 cc followed by 0.5 M sod ium hydroxide at 1 00 cc. After this procedure the sample was dissolved in 30% hydroflurosil icic acid at 1 5- 16 cc. Henderson et al. ( 1 972), went on to further concentrate the sil ica minerals by heavy l iquid separation but this step was not necessary here as sufficient quartz and cristobalite were present for identification using X-Ray Diffraction (XRD). The quantities of quartz and cristobalite in the concentrated sample were estimated with XRD from the 33.4 nm and 40.6 nm reflections respectively. Standards were prepared for both cristobalite and quartz with a matrix of ash from the sampling s ite which had a negligible content of quartz or cristobalite. The results of the determinations calculated for the bulk soil (<2 mm) are shown in Fig. 4.3A and B. The reflection counts from the standard mixtures were reproducible with in 1 0% or better, g iving rise to precision of ? 1 0% in the sample determinations. The quantities of plant opal were not estimated but its presence was noted in al l samples under a polarising microscope. Hal loysite was identified in the bulk soil (<2 mm) using the XRD methods described by Churchman et al. ( 1 984). In itially a 1 01 nm reflection and occasionally a 86 poorly defined peak in the region of 7 4 nm were obtained for ground samples mixed into a slurry and dried on a ceramic ti le. After spraying the sample with formamide the 1 01 - 1 02 nm peak sharpened and enlarged considerably and any reflection around 7 4 nm was reduced to background levels. This test indicates that the intermittent 7 4 nm reflection was not due to kaolin ite but to a hydrated form of halloysite which upon addition of formamide expanded to give reflections around 1 02 nm. Following heating of the sample at 1 1 0 oc the 1 02 nm reflection disappeared , and a small peak at 74 nm was seen. The disappearance of the 1 02 nm peak ind icated that mica minerals are not present. To confirm the identification of halloysite the 1 -2 )!m fractions of selected ash samples were separated by settling after dispersion of the sample with 1 : 1 ammonium hydroxide. These samples were then examined under a transmission electron microscope, where the characteristic tubular and spherical morphologies of hal loysite particles enabled their identification, after Kirkman ( 1 981 ). The quantity of halloysite was assessed throughout the ash sequence (Fig. 4 .3C) using Differential Thermal Analysis (DTA) fol lowing the methods of Whitton and Churchman ( 1 987). The depth of the dehydroxylation endotherm at around 540-550 oc was used to estimate the hal loysite content. Standards were prepared using an andesite ash matrix with negligible hal loysite content. Standard results were reproducible within 1 0% , g iving rise to a precision of ? 1 0% in the sample estimates. Amorphous constituents of the fine ash material were estimated using two methods. The first is an indirect method for estimating the short range order and organic constituents (SROCO) in a soi l (AIIoway et al. , 1 992a). Air-dried soi l (<2 mm) is shaken in the dark for 24 hours in 0 .2 M acid-oxalate reagent (pH 3.0), at a ratio of 1 00 ml of reagent to 1 g of soil . SROCO content is the weight of material dissolved from the soil . Air dry analysis does not however take into account the weight of water present with in the structure of, or held tightly by the short range order minerals such as allophane. A moisture correction factor is then applied here to account for the water held by the a ir dry soil before and after extraction. The SROCO content of the ash materials (Fig . 4.30) ranges from around 3-9 % of the oven dry bulk soil . The other, more quantitative method used is that of Parfitt and Wilson ( 1 985) using oxalate and pyrophosphate extractable chemistry. Bulk soil samples (<2 mm) were extracted with acid-oxalate and pyrophosphate reagents fol lowing the procedures of Blakemore et al. ( 1 987). The Si, AI, and Fe content of the acid-oxalate extracts (Sio, Alo, and Feo), and the AI content of the pyrophosphate extract (Alp) were assessed using flame atomic absorption . The acid-oxalate d issolves the short-range order and organic constituents, while the Alp provides an estimate of the aluminium in Al-humus complexes. The established methodology is then to asses the AI/Si ratio for allophane from (Aio-Aip)/Sio multipl ied by 28/27 to give the atomic ratio. The Sio content is then multiplied by a factor corresponding to the atomic ratio to give the percentage of al lophane in the soil sample (Fig. 4.3E) . Ferrihydrite content of the ash materials was estimated (Fig. 4.3F) by multiplying Feo by 1 . 7 after Childs ( 1 985). 87 The grain size d istribution through the fine ash material (Fig. 4 .2) was estimated using the method of Alloway et al. ( 1 992a). Short range order and organic constituents (SROCO) are extracted from a sample with 0 .2 M acid-oxalate reagent, and crysta l l ine clay, si lt and sand fractions are then assessed using a combination of wet and dry sieving. The water content at a matric potential of -1 .5 MPa was determined gravimetrically after 24 hrs soaking and 7 days to equi l ibrate under the matric potential . 4.9 Results and discussion The grain size is variable throughout the thickness of ash but shows no trends with depth, apart from the relative abundance of SROCO + crystall ine clay near the top of the ash column (Fig. 4.2) . The grain size variabil ity reflects additions of air fal l ash of varying grades which makes up the sequence . The field moist and a i r d ry gravimetric water content measured at a matric potential of -1 .5 MPa is high to very high for the ash (Table 4.2) . The -1 .5 MPa water content is highest where the clay + SROCO content is highest. 4.9.1 Primary ash mineralogy All of the ash samples have been studied under a polarising microscope. Major phases present are plagioclase, orthopyroxene, and clinopyroxene, in order of abundance. The three major phases make up usually >90% by volume of the mineral phases observed . Hornblende and titanomagnetite occur in about half of the samples in quantities usual ly <5% by volume of the mineral component, but sometimes up to 1 0%. Highly vesicular and microlite-rich andesitic glass is seen with in al l samples and comprises over 50% of grains counted in most samples. The andesitic glass is always partially weathered and brown in colour, but not completely replaced by secondary minerals as observed by Kirkman and McHardy ( 1 980) in andesitic g lass of tephras from Egmont volcano in western North Island. 4.9.2 Si l iceous phases The quartz content of these ash units is very low throughout the entire range of samples (Fig. 4 .3A). The peak of 0.5% quartz at the top of the sampling sequence is due to the presence of the quartz-bearing Okaia Tephra (sourced from Taupo Volcano). No quartz was found in andesitic lapi l l i units and the small amount of quartz with in the ash deposits is here regarded to be a result of aerosolic addition. A small increase in the quartz content occurs near the top of the sequence in a more strongly weathered zone below the Okaia Tephra, with fewer pumice lapil l i interbeds present. This suggests a more slowly accumulating soil surface at this time, providing an opportunity for greater weathering and larger quantities of quartz to be deposited onto the soil surface. 88 20 % Sand 40 60 80 % Silt 20 40 % SROCO + Clay 0 20 40 F igure 4.2. Grain s ize d istribution within the fine ash materia ls assessed us ing the method of Alloway et al. ( 1 992a) . Coarse ash/lap i l l i beds and d iam ictons were not samp led . Ok = Oka ia Tephra , Om = Omataroa Tephra , Hu = Hauparu Tephra and Re = Rotoehu Ash . Lithology symbols g iven in Fig 4 . 1 . 89 A previous study of aerosolic quartz with in andic materials in Taranaki (AIIoway et al. , 1 992b ), showed two peaks of quartz accumulation corresponding with oxygen isotope stages 2 and 4, and very little quartz in deposits accumulating during o180 stage 3 (c. 25- 60 ka B.P . ) . Quartz accumulation was correlated with episodes of regional loess deposition throughout the southern North Island in o180 stages 2, and 4. A loess deposition episode during o180 stage 3 did not correspond to a quartz peak in the sequence studied by Alloway et al. ( 1 992b) in Taranaki. The ash deposits studied here on the Ruapehu ring plain accumulated mostly during o180 stage 3 and part of o180 stage 4. Regional loess deposition occurred during both o180 stages 3 and 4, throughout the southern North Island (Mi lne and Smalley, 1 979; Pal mer, 1 985; Alloway et al. , 1 988; Pi l lans, 1 994 ). Neither of these regional loess deposition episodes are indicated by a quartz peak in the Ruapehu ash sequence even though source areas in the Wanganui hi l l country to the south-west, or the Kaimanawa Mountains to the east potentially could have supplied quartz to the site. This indicates that the accumulation rate of the ash in this sequence was too high to preserve appreciable quartz and/or the climate was insufficiently severe to mobil ise the quartz source. The quartz content in the Ruapehu ring plain ash sequence appears to be a function of the accretion rate of the soil surface rather than of climate change and consequent loess deposition as ind icated by the study of Alloway et al. ( 1 992b ). The cristobalite content throughout the ash column (Fig. 4.38) is highly variable from <0.5 to 4%. The orig in of cristobalite in volcanic soils has been attributed to both pedogenesis (Lowe, 1 986), and as a primary phase from the volcanic parent material (M izota, et al. , 1 987). The amount of cristobalite with in selected andesite pumice lapil l i layers interbedded in the sequence has been estimated using the same methods used for the ash samples. The content of cristobalite in the pumice lapil l i was of a similar range to that in the ash material . The cristobalite in the ash material was also in a highly crysta l l ine form as indicated by its sharp X-ray reflections and its presence was noted as microlites with in weathered andesitic glass. The cristobal ite content of the samples is thus most l ikely a reflection of the primary composition of the ash, and indicates that the cristobalite content of the erupted ash changed rapidly over time. 4.9.3 Secondary minerals The secondary minerals which have been identified with in the ash sequence are hal loysite, al lophane and ferrihydrite. The hal loysite content within the ash sequence ranges from 1 0 to 25 % of whole soil (<2 mm). The highest contents are found in the lower zone of strong weathering. Hal loysite within the deposits occurs in two morphological forms, as hollow tubes and as spheres or el l ipsoids. The spherical form is dominant. Kirkman ( 1 981 ) proposed that the tubular particles formed from feldspar and the spheres from rhyolite g lass. Due to the 90 virtual absence of rhyolite glass in this sequence it is considered that the spherical hal loysite is here formed from andesitic glass. The al lophane content of the ash calculated using the method of Parfitt and Wilson (1 985), is very low throughout the sequence (Fig. 4.3E), ranging from 1 to 4%. The trend of a l lophane content in the sequence is very similar to the SROCO trend, with h igher values recorded near the top with in the upper zone of strong weathering. The range of estimated ferrihydrite contents is from 0.3 to 1 .6%, showing a simi lar trend to the al lophane content (Fig. 4.3F). The calculated al lophane and ferrihydrite contents are lower than the SROCO contents of the ash material . Alp content with in the ash sequence is barely detectable ranging from 0 to 0.02%, indicating that there is l ittle organic material present which could be making up the rest of the SROCO estimate. This difference was also noted by Al loway et al. ( 1 992b), a lthough they did not take into account the water held by al lophane, ferrihydrite and humus complexes in air dried samples. I n air dried al lophane? rich soils significant water is held with in the particles and within the structure of SROCO constituents (Table 4.2). This water is measured as a weight difference in the SROCO estimation as the SROCO minerals have been dissolved , but is not seen in the Si and AI content of the extracted solution , leading to overestimation in the SROCO method compared to the Parfitt and Wilson ( 1 985) method . Even after a moisture correction factor is applied to the Ruapehu ash SROCO estimates, they are sti l l h igher than the calculated al lophane + ferrihydrite. Either the Parfitt and Wilson ( 1 985) empirical method underestimates the allophane within these samples or the acid-oxalate reagent is partially d issolving other phases, contributing to the SROCO estimate. The SROCO extractions were carried out in the dark and past studies have shown that under these conditions very l ittle dissolution of crysta l l ine minerals is expected (e.g. Fey and Le Roux, 1 977; Wada, 1 977; Parfitt and Childs, 1 988). The differences between the two methods is probably due to a combination of, longer extraction times used in the SROCO method (2 successive 24 hour extractions compared to a single 2 or 4 hour extraction), inaccuracies in recovering and weighing the undissolved sample fraction in the SROCO method , and a possible lack of understanding of which phases are being attacked by the oxalate reagent in long extraction times in these tephric samples. The formation of a l lophane and halloysite from volcanic ash in New Zealand conditions has been addressed in many studies (e.g. Parfitt et al. , 1 983 and 1 984; Lowe, 1 986; Singleton et al. , 1 989; Parfitt and Kimble, 1 989). The overal l conclusion from these stud ies is that volcanic glass can weather directly to either al lophane or halloysite; which mineral is formed depends on the AI/Si ratio of the soil solution. When the AI/Si ratio is low in soil solution, halloysite is formed and when the ratio is high a l lophane is formed . This model does not require al lophane to be formed as an intermediary which later transforms to hal loysite, as in the model of Kirkman ( 1 975). 91 c.o N % Quartz 0 0 .3 0.6 0 % Cristobalite 2 .5 5 5 % Halloysite 1 0 1 5 20 25 0 % SROCO 5 % Allophane % Ferrihydrite 1 0 0 2 4 0 1 2 (m) A B c D E F 30 35 lilllf-??::???::??::::??????::::::????::??????::::::????' - Figure 4.3. Selected mineralogy of the fine ash sequence. SROCO values have moisture correction applied . Ok = Okaia Tephra, Om = Omataroa Tephra , Hu = Hauparu Tephra and Re = Rotoehu Ash . Lithology symbols given in Fig. 4 .2 . There are many factors which can decrease the AI/Si ratio in soil solution (Lowe, 1 986) and thus promote the formation of hal loysite from volcanic glass. These factors include low ra infa l l , poor or impeded drainage, and deep burial of ash deposits. Strong evidence for poor drainage is not seen in the form of common mottl ing and g leying features in the ash deposits but the dominant brown colouring of the ash deposits could mask al l but very strong gleying processes. Some of the diamictons within the sequence have a sandy matrix and may not provide a large impediment to drainage, however others have a clay-rich matrix or are cemented and may impede drainage. The deposits are presently buried by at least 20 m of tephra and diamictons which is l ikely to have played an important role in their weathering. Dissolved si l ica has probably leached down into the sequence of ash deposits from the sediments and tephras above. This supply of si l ica would have promoted the formation of hal loysite from the weathering andesitic glass by reducing the AI/Si ratio in soil solution, especially where drainage is impeded. I n this sequence it is l ikely that the effects of both deep and rapid burial of the ash deposits, and poor drainage conditions created by water perching on or below interbedded diamictons have had the greatest effect on formation of secondary minerals. The AI/Si atomic ratio of the al lophane present in the ash sequence is 2 : 1 or greater throughout the entire sequence. The 2 : 1 a l lophane is coexisting in the ash with halloysite. This is at odds with the findings of Parfitt et al. , ( 1 984) who found that when al lophane and hal loysite were coexisting in a rhyolitic ash bed in a moderate or low leaching environment (<200 mm of percolation/year), the al lophane had an AI/Si ratio of close to 1 : 1 . Allophane with an AI/Si ratio of 2 : 1 was formed under conditions of greater leaching (>250 mm a year), and no halloysite was formed under these conditions. The paleosol sequence is not near the current soil surface and modern plant roots do not affect it; thus the al lophane is not considered to be modified by modern processes. The al lophane may also have lost Si post-formation, thus increasing its AI/Si ratio, but past stud ies have shown that 2: 1 a l lophane can persist in soils for hundreds of thousands of years in buried soil environments similar to the Ruapehu ring plain sequence (e .g . Kirkman, 1 981 ; Stevens and Vucetich , 1 985; Lowe, 1 986; Lowe and Percival , 1 993), so this affect is not thought to be dominant in the sequence. The coexistence of allophane with a 2: 1 AI/ Si ratio and appreciable hal loysite in the Upper Waikato Stream ash deposits may indicate that the two minerals were formed at different times in the weathering history of the ash materials due to a change in the weathering environment. If halloysite is forming from the weathering ash while tephra and ring-plain sediments are being deposited above, the 2 : 1 allophane may be remnant from weathering of the ash material when it was original ly in an acid leaching environment, at or near the soil surface. If this is the case then the trends shown in the al lophane content may indicate the length of time the soil surface was stable, or a record of the accumulation rate. Where the soil surface is stable for a longer time more allophane is formed. This agrees with field observation of stronger weathering features and a low frequency of pumice lapi l l i additions where there is greatest allophane content in the top of the ash sequence. This also correlates with the preferential concentration of quartz in 93 the sequence at this point, due to slower accumulation rates and more intensive weathering . The trend of ferrihydrite contents of the ash paral lels that of al lophane, and indicates that the ferrihydrite is likely to have been formed when the ash was at or near the soil surface at the same time as allophane. The lower zone of observed relatively strong weathering with in the fine ash does not show a peak in allophane or ferrihydrite content. This could be due to the soil surface accumulating too quickly to produce favourable conditions for the formation of al lophane and ferrihydrite. Field observation at this point shows that there is a much greater frequency of pumice lapi l l i additions to the sequence at this time, indicating a relatively high rate of deposition . In this sequence of andesitic tephra with very l ittle rhyol itic glass present, the AI/Si ratio of the soil solution appears to be driving the formation of the secondary minerals as found by Singleton et al. (1 989), rather than the AI/Si ratio of the parent g lass as found by Kirkman and McHardy ( 1 980). The parent glass composition obviously has an effect on the soil solution composition. As it weathers, andesite glass wil l release more AI into solution than rhyolite glass reflecting their initial AI content differences. The result of this is observed in soils from Taranaki which contain large quantities of a l lophane (AIIoway et al., 1 992b ). In the ash materials on the Ruapehu ring-plain sequence the effect of the weathering andesitic glass composition on the soil solution is considered to be overshadowed by the other environmental factors of rapid burial and impeded drainage. This is reflected by the dominance of halloysite as a weathering product and only a l imited time for al lophane formation when the ash material was at or near the surface. 4.1 0 Relationship of Ruapehu ring-plain sequence to climate record for southern North Island The observed features of stronger weathering and more abundant root rhizomorphs with in parts of the ash sequence could be indicating the climate was warmer during these periods of deposition than at other periods with in the sequence. The effect of climate change during the period of deposition on these ash deposits would have been overprinted onto the effect of accumulation rate d iscussed previously. The timing and nature of climate osci l lations with in southern North Island , New Zealand has been well documented (Palmer, 1 985; Allow ay et al. , 1 992b and 1 992c; Pi l lans, 1 994), and landscape events can be shown to be related to the marine o180 record (Fig. 4.4). The presence of identified rhyol itic tephras provide time planes which enable correlation of features in the ash sequence to the establ ished climate record of the southern North Island. The range in age of the deposits with in this sequence is from c. 24 to 70 ka, mostly during o180 stage 3. Within the upper zone of strong weathering, the presence of the Omataroa Tephra (ea. 28.2 ka; Table 4. 1 ) correlates this weathering period with a widespread soil development episode in loess sequences of the southern North Island (Fig. 4.4; Mi lne and Smalley, 1 979 ; Leamy et al. , 1 973; Palmer, 1 985; Alloway et al. , 1 988; Pillans 1 988). 94 (0 CJ'1 Age M.O.I . stages (ka) 20 2 30 40 3 50 60 70 4 Rangitikei Whanahuia Paleosol Kimbolton Paleosol Taranaki Wanganui NE Ruapehu Sy1 L1 1 1 ; r;r? 1 1 I I I At ; l l L-----1-- Hu Sy2 L2 1 1 1 1 1 1 I l l I Sr3 S3 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 11 11 1111111 Ill 11 11 11 11 Re Sy3 L3 ffi:{J Diamictons D Andesitic tephra ? Aggradation ? gravels D Loess - Strongest paleosol development Figure 4.4. The relationship of the northeastern Ruapehu ring-plain sequence with deep sea 180 isotope record (M.O. I . Stages; Shackleton et a/. , 1 990), and southern North Island loess stratigraphy from the Rangitikei valley (leamy et al. , 1 973; Mi lne and Smal ley, 1 979), Wanganui (Pi llans, 1 988; 1 994), and Taranaki (AIIoway et al. , 1 988). Oh = Ohakea loess, Rt = Rata loess and Po = Porewa loess L 1 = loess 1 , S2 = buried soil 2 etc. Sy1 = loess 1 correlative, Sr2 = buried soil 2 correaltive etc. Kk = Kawakawa Tephra , Ok = Okaia Tephra , Om = Omataroa Tephra , Hu = Hauparu Tephra and Re = Rotoehu Ash. This soil development is represented by one of the weakest of the Last Glacial paleosols. In the ash sequence from eastern Ruapehu the weathering of this paleosol is further enhanced by relatively slow accretion of the soil surface as d iscussed previously. Within the lower zone of strong weathering, the presence of the Rotoehu Ash (ea. 64 ka; Table 4. 1 ) ind icates this weathering episode was contemporaneous with another period of widespread soil development on loess throughout the southern North Island (Fig. 4.4; Mi lne and Smal ley, 1 979; Leamy et al. , 1 973; Palmer, 1 985; Al loway et al. , 1 988; Pil lans, 1 988). This soil development is represented by very strong paleosols throughout the southern North Island. In the eastern Ruapehu sequence the intensity of soil development was probably hindered by rapid accretion of tephra at the soil surface. The cool climatic episode in late 8180 stage 3, represented by loess deposition in the southern North Island (F ig . 4 .4) , is not evidenced in the Ruapehu sequence. Quartz input is swamped by a high accretion rate of andesite ash and lapi l l i . The only manifestations of a cool climate are less observable weathering features, less root rhizomorphs, and lower amounts of al lophane and ferrihydrite in the ash deposited during this time. There were intervals of slow deposition within this time frame evidenced by low frequencies of pumice lapi l l i layers at various levels in the sequence. In these parts of the sequence the weathering development may have been slow under a cool and possibly dry climate. 4.1 1 Conclusions The provenance of ash material with in the sequence is almost entirely local , and represents continuous deposition of andesite ash and lapi l l i . If there is any redeposited material of ash grade within the sequence it is very local ly derived volcanic loess blown from other parts of the ring plain. The input of material from outside of the local area such as regional loess deposition recorded in other parts of the southern North Island is very low. Although source areas proximal to the study area exist {< 1 0 km away), aerosolic quartz input into this sequence appears to have been di luted by an overwhelming component of rapidly accumulating locally derived ash and lapi l l i . Weathering zones within the ash materials on the eastern Ruapehu ring plain are correlated to mild climate episodes during the Last Glacial , contemporaneous with periods of widespread soil development on loess throughout the southern North Island (Fig. 4.4; Leamy et a/, 1 973; Palmer, 1 985; Alloway, et al. , 1 988; Pi l lans, 1 988). However, weathering features with in the ash materials on the eastern Ruapehu ring plain are not only a function of the climate when the ash was accumulating, but are also strongly dependent on the accretion rate of the soil surface. Slow tephra accretion enhanced weathering features during the development of the soil on fine ash deposited during late 8180 stage 3. Rapid tephra accretion during the development of the soil in fine ash deposited during early 81 80 stage 3 may have reduced the expression of weathering features and secondary minerals in the ash at this time. 96 The weathering minerals with in this ash sequence appear to have been formed in two separate periods in the history of the ash sequence. This is deduced from the coexistence of hal loysite in appreciable quantities (1 0-25% of bulk soil <2 mm) with al lophane which has an AI/Si atomic ratio of >2: 1 . Allophane is present in small quantities according to estimates using the Parfitt and Wilson ( 1 985) method. The sequence can be regarded as an aggrad ing sequence of Entisols and Andisols in which the rapid accretion of the soil surface is hindering further development of the soil . The al lophane and ferrihydrite content of the ash material shows a distribution which has an inverse relationship with the accumulation rate ind icated by quartz content, field observations of pumice lapi l l i frequency and weathering features. The al lophane and ferrihydrite content is greatest where the accumulation rate of the ash appears lowest. This indicates that allophane and ferrihydrite in this sequence were formed from weathering andesitic glass when the ash material was at or near the surface. Subsequent, rapid burial of the ash and poor drainage conditions in the sequence probably hindered further formation of allophane as si l ica leached from the deposits above to decrease the AI/Si ratio in soil solution and thus prevent further al lophane formation (Parfitt et al. , 1 984; Singleton et al. , 1 989). Hal loysite probably formed after the burial of the ash materials. As si l ica was leached down from tephra and diamictons above, the AI/Si ratio in the soil solution was decreased , and the formation of hal loysite was promoted from weathering andesitic g lass (Parfitt et al. , 1 984; Singleton et al. , 1 989). The peaks in concentration of hal loysite with in the ash profi le may relate to where the drainage is impeded as water and si l ica move down the profi le. The drainage impediment could be a textural change within the ash or a diamicton interbedded within the sequence. The highest contents of hal loysite occur beneath a large cemented diamicton unit (Fig. 4 . 1 }, exempl ifying this interpretation. The now buried ash sequence represents a continuously accreting Entisoi/Andisol . The weathering features and secondary minerals with in the sequence are a function of a complex mix of accretion rate, late Quaternary climate change, and post-depositional weathering. 4.12 Acknowledgements This work forms part of the Ph.D. research of Shane Cronin and we grateful ly acknowledge funding from the New Zealand Vice Chancellors Committee, Massey University Graduate Research Fund, the Helen E. Akers Scholarship fund, and the Department of Soil Science of Massey University. J .S. Whitton is thanked for his help with mineral analyses, J .H . Kirkman and R.B. Stewart are thanked for their comments on an earl ier version of the manuscript. We also wish to thank B.V. Alloway and R.L. Parfitt for their comprehensive reviews of the manuscript. 97 4.1 3 References Alloway, B.V. , Neal l , V.E . and Vucetich, C .G . , 1 988. Localised loess deposits in north Taranaki , North Island , New Zealand. In : Loess - Its d istribution geology and soils, Eden, D .N . , and Furkert, R.J. 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Paleopedology and soil stratigraphy in the New Zealand Quaternary succession . N. Z. J. of Geol . and Geophys . , 1 6 , 723-744. Lowe, D.J . , 1 986. Controls on the rates of weathering and clay mineral genesis in airfal l tephras: a review and New Zealand case study. In : Colman, S.M . , and Dethier, D .P. (eds) Rates of chemical weathering of rocks and minerals. Academic Press, Orlando, pp. 265-330. Lowe, D.J . and Perciva l , H .J . , 1 993. Clay mineralogy of tephras and associated paleosols and soils, and hydrothermal deposits , North Island. Guide book for New Zealand pre-conference field trip F. 1 . 1 Oth International Clay Conference, Adelaide, Austral ia. McGione, M.S. and Topping, W.W. , 1 977. Aranuian (post-g lacial} pol len d iagrams from the Tongariro region, New Zealand . N . Z. J . of Botany, 1 5, 749-760. Mi lne, J .D .G . and Smal ley, I . J . , 1 979. Loess deposits in the southern part of the North Island of New Zealand: an outl ine stratigraphy. Acta Geologica Academiae Scientarium Hungaricae, 22, 1 97-204. Mizota, C . , Toh , N. and Matsuhisa, Y. , 1 987. Origin of cristobalite in soils derived from volcanic ash in temperate and Tropical regions. Geoderma, 39, 323-330. New Zealand Meteorological Service, 1 973. Rainfall normals for New Zealand, 1 94 1 - 1 970. Mise. Publ . , 1 45. Palmer, A.S., 1 985. The Last Interglacial record in Wairarapa Valley, New Zealand. In : Pi l lans, B .J . (ed). Proceedings of the second CLIMANZ conference 1 985. Publication No.31 of Geology Department, Victoria University of Well ington, N.Z. Parfitt, R.L. and Childs, C.W. , 1 988. Estimation of forms of Fe and AI: A review, and analysis of contrasting soils by dissolution and Moessbauer methods. Australian J . of Soil Res . , 26, 1 2 1 - 144. Parfitt, R.L . and Kimble, J .M . , 1 989. Conditions for formation of al lophane in soils. Soil Sci. Soc. of America J . , 53, 971 -977. Parfitt, R.L. , Russell , M. and Orbell , G .E . , 1 983. Weathering sequence of soils from volcanic ash involving allophane and hal loysite, New Zealand. Geoderma, 29, 4 1 - 57. Parfitt, R.L. , Saigusa, M. and Cowie, J .D . , 1 984. Allophane and hal loysite formation in a volcanic ash bed under different moisture conditions. Soil Sci . , 1 38, 360-364. Parfitt, R .L . , and Wilson, A .D . , 1 985. Estimation of a l lophane and hal loysite in three sequences of volcanic soils, New Zealand. Catena Suppl. 7, 1 -8 . Pi l lans, B.J . , 1 988. Loess chronology in Wanganui Basin, New Zealand. In : Loess - Its distribution geology and soils, Eden, D .N . , and Furkert, R.J. (eds). A.A. Balkema Publ ishers, Rotterdam. 99 Pil lans, B.J . , 1 994. Direct marine-terrestrial correlations, Wanganui Basin, New Zealand: the last 1 mil l ion years. Quat. Sci. Reviews, 1 3, 1 89-200. Shackleton, N .J . , Berger, A. and Peltier, W.R. , 1 990. An alternative astronomical calibration of the lower Pleistocene timescale based on ODP Site 677. Trans. Ray. Soc. of Edinburgh: Earth Sci . , 81 , 251 -261 . Singleton, P .L . , Mcleod , M . and Percival , H .J . , 1 989. Allophane and hal loysite content and soil solution si l icon in soils from rhyol itic volcanic material , New Zealand. Austral ian J . of Soil Res . , 27, 67-77. Stevens, K .F . , and Vucetich, G .C . , 1 985. Weathering of Upper Quaternary tephras in New Zealand. Part 1 1 Clay minerals. Chem. Geol . , 53, 237-247. Wada , K. , 1 977. Allophane and lmogolite. In : Minerals in Soil Environments, Dixon, J .B . , and Weed, S .B . (eds), 603-638. Soil Sci. Soc. of America, Madison, Wisconsin. Whitton, J.S. and Churchman, G.J. , 1 987. Standard methods for mineral analysis of soil survey samples for characterisation and classification in New Zealand Soil Bureau. N .Z. Soil Bureau Sci . Rep . , 79. Wilson , C.J .N . , Switzur, R.V. and Ward, A.P . , 1 988. A new 14C age for the Oruanui (Wairakei) eruption , New Zealand. Geol. Mag . , 1 25, 297-300. Wilson , C.J .N . , Houghton, B .F . , Lanphere, M .A. and Weaver, S.D . , 1 992. A new radiometric age estimate for the Rotoehu ash from Mayor Island volcano, New Zealand. N. Z. J. of Geol . and Geophys . , 35, 371 -374. 1 00 CHAPTER 5: THE LAHAR RECORD AND CONSTRUCTION OF THE NORTHEASTERN RUAPHEU AND EASTERN TONGARIRO RING PLAINS 5.1 I ntroduction The NE Ruapehu and E Tongariro ring plains are composed of laharic, fluvial and g lacial sediments as wel l as tephra and lava l ithologies. However, the ring plains are volumetrical ly dominated by volcaniclastic diamictons deposited by lahars. Thus by dating and mapping these lahars, the timing and landform construction of much of the ring plain areas can be established . In addition, the timing of lahars can be used to assess the lahar hazard , which is contained in the following chapter. The rhyolitic and andesitic tephra stratigraphy of Topping ( 1 973), Donoghue et al. , ( 1 995), and that established in Chapters 2 and 3 were used to date and map lahar deposits on the ring plain areas stud ied . Once the lahar deposits were dated and mapped , the distribution and t iming of lahars in conjunction with information from the paleosol record developed in Chapter 4 was used to elucidate the construction of the ring plain areas studied. In this way a history of the timing of construction of various ring plain areas was established . In addition , the influence of climatic and volcanic events on the ring plain construction is explained . This part of the study is in press within the New Zealand Journal of Geology and Geophysics, Vol . 40, No. 2 (1 997). The contributions of the two authors to the study were as fol lows: S.J. Cronin : Principal investigator Carried out a l l : field descriptions and sampling tephra and lahar correlation and mapping preparation and writing of the manuscript V.E. Neal l : Adviser Aided the study by: d iscussion of results and methodology editing and discussion of the manuscript 1 0 1 5.2 A LATE QUATERNARY STRATIGRAPHIC FRAMEWORK FOR THE NORTHEASTERN RUAPEHU AND EASTERN TONGARIRO RING PLAINS, NEW ZEALAND Shane J . Cronin and Vincent E. Neall Department of Soil Science, Massey University, Private Bag 1 1 222, Palmerston North, New Zealand New Zealand Journal of Geology and Geophysics 40, No. 2. Abstract The northeastern Ruapehu and eastern Tongariro ring plains record a complex sequence of episodic lahar sedimentation. Using andesitic and rhyolitic tephrostratigraphy, fifteen lahar episodes are recognised in the northeastern Ruapehu ring-plain record ranging in age from >65 to 5 ka, and five in the Tongariro ring-plain record ranging in age from >23 to 14 ka. The most voluminous and widespread lahar deposition occurred during cool and stormy climatic periods equivalent in age to marine 8180 stages 2 and 4. In these periods, accelerated physical weathering on the volcanoes suppl ied erosion debris, while large areas of snow and ice acted as sources of water to form lahars triggered by a variety of mechanisms. Lahar d istribution after c. 22.5 ka was affected by two landform changes in the area at about this time. First, a large lava flow was emplaced along the boundary between Ruapehu and Tongariro ring plains shortly before 22.5 ka, effectively separating the two ring plains since. Second, Last Glacial moraines along the Whangaehu and Mangatoetoenui Rivers have blocked d i rect drainage from the Ruapehu summit region to a large sector of the northeastern ring plain, including the Upper Waikato Stream, formerly an important lahar path . These moraines have directed subsequent lahars (after c. 1 5 ka) a long their current routes (active in 1 995) in the Whangaehu and Mangatoetoenui catchments. Lahar deposition in the study area during this time is l inked to large, explosive andesitic eruptions impacting on catchments where retreating glaciers provided water for lahar generation. 5.3 Keywords Ruapehu volcano, ring pla in , volcanic stratigraphy, lahars, Late Quaternary, paleoclimatic change. 5.4 Introduction Ring-plain sediments of composite volcanoes provide a valuable record of past eruptive and sedimentary events that may not be preserved closer to source. The sedimentary record of the ring plain can often be dated precisely using interbedded tephras and radiometric techniques to provide a stratigraphic record of such events missing on the volcano. In the central North Island of New Zealand , coalescing ring plains of the eastern flanks of Tongariro and Ruapehu volcanoes are incised by numerous stream channels 1 02 that expose a deta iled record of their ring-plain sediments and structure. A well? established rhyolitic tephra record from the North Island (Froggatt and Lowe, 1 990) and the developing andesitic tephrochronology in the Tongariro Volcanic Centre (TgVC - Topping, 1 973; Donoghue et al. , 1 995; Cronin et al. , 1 996(a)) provide a good chronological framework for the ring-pla in deposits. The aim of this study was to elucidate the stratigraphy and construction of the northeastern Ruapehu and eastern Tongariro ring plains, based on detai led investigations of sections in streams draining the eastern flanks of the volcanoes. 5.5 Setting Tongariro and Ruapehu are the two largest and most recently active volcanoes of TgVC (Gregg , 1 960). Ruapehu is presently active. lt is, the highest peak in the North Island at 2797 m, comprising a 1 1 0 km3 composite cone with a ring pla in of similar volume surrounding it (Hackett and Houghton, 1 989). Tongariro volcano is a slightly smaller massif constructed from several coalescing volcanic cones, the largest of which is the recently active cone of Ngauruhoe (Mathews, 1 967). Tongariro volcano is also surrounded by an extensive ring plain . The ring-plain deposits of these volcanoes are confined in the east by the Kaimanawa Mountains and extend down drainage channels to the north and south. Sections examined in this study are along streams indicated in Fig. 5 . 1 . 5.6 Time control Eighteen dated rhyolitic tephras erupted from Taupe Volcanic Zone calderas to the north are preserved with in the TgVC ring-plain sediments {Topping and Kohn , 1 973; Donoghue et al. , 1 995; Cronin et al. , 1 996(a)). The rhyolitic tephras are identified using combinations of their stratigraphic position , field appearance, mineralogy, and major element glass chemistry. In addition, dated andesitic tephras erupted from Tongari ro and Ruapehu volcanoes provide valuable stratigraphic markers {Topping, 1 973; Donoghue, et al. , 1 995). They are identified using their characteristic field appearances, stratigraphic position and occasionally their mineralogy. The names and ages of marker tephras used in this study are listed in Table 5. 1 . 5.7 Terminology and identification of ring plain deposits Ring-plain sed iments range greatly in their nature and mode of deposition . At one end of the depositional series are well-bedded si lts , sands, and gravels deposited by streamflow mechanisms. At the other end of the series are poorly sorted , matrix-supported units deposited by debris flow mechanisms. A whole range of deposits intermediate in character occur between these two extremes. 1 03 North Island Mt Tongariro .A. ) M! Ng?ho? 39? 1 0 I Mt Ruapehu .... 1 500 m Group 2 . ? I ,. ... - State Highways 1 75? 45' / / / Group 3 \ \ I I I \ I I I 0 I I I I \ I I 1 Group 1 I 5 km Figure 5.1 Location of Tongari ro Volcanic Centre including Mts. Tongariro, Ngauruhoe and Ruapehu, and the streams dissecting the eastern Ruapehu and Tongariro ring plains. The streams are d iscussed in the text in three groups; labelled Groups 1 , 2 and 3 on the map. 1 04 Table 5. 1 . Tephra coverbeds used in this study. Te?hra la:ters Abbreviation Source? Age {ka} Reference to age Ngauruhoe Tephra Ng TgV ea. 1 .8-01 Donoghue (1 991 ) Taupo Tephra (Unit Y) Tp TVC 1 .852 Froggatt and Lowe (1 990) Mangatawai Tephra Mgt TgV 2.5-1 .852 Donoghue (1 991 ) Waimahia Tephra (Unit S) Wm TVC 3.32 Froggatt and Lowe (1 990) Hinemaiaia Tephra (Units 1-R) Hm TVC 5.2-3.952 Wilson (1 993) Motutere Tephra (Units G-H) Mt TVC 5.8-5.32 Mangamate Tephra (Mm), Poutu Pt TgV ea. 9.J1 Topping (1 973) Lapil l i Mm, Wharepu Tephra Wp TgV ea. 9.71 Poronui Tephra (Unit C) Po TVC 9.81 2 Froggatt and Lowe (1 990) Mm, Ohinepango Tephra Oh TgV ea. 9.71 Topping (1 973) Mm, Waihohonu Lapi l l i Wa TgV ea. 9.71 Mm, Oturere Lapill i Ot TgV 9.782 Karapiti Tephra (Unit B) Kp TVC 1 0Y Wilson (1 993) Pahoka Tephra Pk TgV ea. 1 0-9.81 Topping (1 973) Bullot Formation (Bt), Pourahu Ph RV ea. 1 01 Donoghue (1 991 ) Member Waiohau Tephra Wh ovc 1 1 .852 Froggatt and Lowe (1 990) Rotorua Tephra Rr ovc 1 3.082 Rotoaira Tephra Ra TgV 1 3 .82 Topping (1 973) Rerewhakaaitu Tephra Rk ovc 1 4.72 Froggatt and Lowe (1 990) Kawakawa Tephra Kk TVC 22.592 Wilson et al., (1 988) Okaia Tephra Ok TVC ea. 231 Froggatt and Lowe (1 990) Omataroa Tephra Om ovc 28 .222 Hauparu Tephra Hu ovc 35.872 Rotoehu Ash Re ovc 643 Wilson et al., (1 992) a TgV = Tongariro volcano, RV = Ruapehu volcano, TVC = Taupo Volcanic Centre, OVC = Okataina Volcanic Centre. 1 Estimated ages . 2 Average or single 14C ages on old (Libby) half l ife basis. 3 Whole rock K-Ar age. We use the Smith and Fritz ( 1 989) definition of the term "lahar" in this study as: "a rapidly flowing mixture of rock debris and water (other than normal streamflow) from a volcano". This defin ition encompasses volcano-derived hyperconcentrated streamflows and debris flows. The definition is restricted to the process and does not include the deposit. The use of the terms "debris flow" and "hyperconcentrated" streamflow fol low that of Smith 1 05 ( 1 986), Pierson and Costa (1 987), and Scott (1 988). Table 5 .2 outl ines the characteristic features of the sediments within the ring-plain sequence, and relates their observed l ithologies and sedimentary features to their interpreted emplacement mechanisms. Table 5.2. Sedimentary features of ring plain deposits and their inferred mode of deposition. Sediment type Bedded sands, si lts and gravels Horizontally/planar bedded sands Sandy-matrix massive d iamictons Si lty-matrix massive diamictons Observed features -Variable grainsize, si lt, sand and gravels in layers and lenses -Ind ividual layers and lenses well sorted -Strong development of dominantly wavy and cross bedding -Ciast supported -Maximum clast d iameter 0.2 m -Grain size dominantly med-coarse sand, supporting common pebbles and rare cobbles -boulders -Poorly sorted -Ciast supported -Horizontal bedding d iscontinuous but overall planar or horizontal fabric -Larger clasts often in pebble or cobble "strings" -Maximum clast d iameter 1 m -Very poorly sorted -Matrix supported -Matrix dominantly med-coarse sand -unbedded, mostly ungraded and occasionally normally graded -Maximum clast d iameter 1 -3 m -Features as above except matrix dominated by silt and clay -can contain hydrothermally altered pumice and lithic clasts -ungraded, and normally graded 5.8 Present channel geography Inferred mode of deposition (after Smith, 1 986) Normal streamflow Hyperconcentrated streamflow Debris flow Debris flow A large number of sections were examined in several streams. Measured sections at different locations along the length of each stream (e.g. Mangatoetoenui Stream Fig. 5.2) were compared and correlated to obtain a composite stratigraphic column for each stream (Fig. 5 .3 , 5.5 and 5.6) . The streams can be split into three catchment groups. Group 1 comprises Upper Waikato, Tangatu, Wharepu, Te Piripiri, Mangatoetoeiti and Mangatoetoenui Streams (Fig . 5 . 1 ) which drain the northeastern flanks of Ruapehu volcano. Ohinepango and Waihohonu Streams form Group 2 which drain a sector of northeastern Ruapehu volcano as well as the southeastern sector of Tongariro volcano. Group 3 comprises Oturere, Makahikatoa, Mangatawai , Mangamate, Mangahouhounui , 1 06 and Tauhurangi Streams which drain the eastern and northeastern flanks of Tongari ro volcano. The three stream catchment groups receive lahars from different source areas and potentially provide different sets of information about the sources, timing, and d istribution of lahar events on the eastern flanks of the two volcanoes. 5.9 Group 1 - Northeastern Ruapehu streams (Fig. 5.3) A clear boundary exists between drainage from the northeastern and southeastern flanks of Ruapehu. To the southeast a large active fan of Holocene laharic and stream sediments has been formed by the Whangaehu River (Palmer et al. , 1 993). The fan sediments have been deposited by lahar events that are channelled down the upper part of Whangaehu River and avulse their courses on the relatively unconfined lower ring plain (Palmer et al. , 1 993). This route has been the major path for Ruapehu lahars in historic times (e.g . , 1 953, 1 969, and 1 975; Gregg, 1 960; Nairn et a/. , 1 979), including 1 995. All dra inage channels north of the Whangaehu River drain northeast into the Tongariro River. There is no historical evidence of lahars overflowing northward from the Whangaehu fan into the Tongariro. However, restricted lahar deposits younger than c. 2 ka are present in the upper portions of the Upper Waikato Stream, and are thought to originate from the Whangaehu catchment (Donoghue, 1 991 ) . This suggests that some lahars may have overflowed into the Upper Waikato Stream in the recent geologic past. Of the northeastern Ruapehu streams, the Mangatoetoenui is the only channel to have an historic record of lahars (Nairn et al. , 1 979), including at least one lahar in the 1 995 eruptive sequence. A correlation diagram for the sequences in the six main drainage channels from northeastern Ruapehu is presented in Fig. 5.3. Fifteen episodes of lahar deposition are recognised and numbered consecutively R01 -R1 5 from youngest to oldest. These episodes are recognised by debris flow and hyperconcentrated streamflow deposits, each episode containing a single lahar or series of lahars with in a short time interval . The stratigraphic ages of the diamicton packages are determined from their tephra interbeds (Fig. 5.4). Upper Waikato and Tangatu Streams contain the longest stratigraphic records, although Tangatu Stream sections show evidence of extensive coverbed stripping and erosional unconformities. The surfaces around Tangatu Stream do not appear to have stabi l ised until immediately before the eruption of the Hinemaiaia Tephra, c. 5 ka B .P . In Upper Waikato Stream, the oldest and also the thickest diamicton sequence recorded is R1 5, which comprises the deposits of several lahars. Rotoehu Ash (c. 64 ka) occurs as g lass shards scattered throughout fine andesitic ash overlying lahar deposits of episode R14 , thus providing a minimum age for R14 and R1 5. R1 3 comprises the deposit of a single lahar whi lst R1 2 contains deposits of two. Andesitic pumice lapi l l i are abundant with in both R1 2 and R1 3 and as a pinching shower-bedded tephra between them. R1 1 consists of a complicated collection of deposits of numerous lahars. 1 07 -->. 0 (X) 1 5 km from source T20/440143 Pt R06-09 I 2 m 1 6 km from source 1 7.5 km from source 1 8. 1 km from source 18.7 km from source 19.5 km from source 20.1 km from source Ng Tp T20/449148 T20/461 1 54 T20/4651 56 T20/4701 58 T20/4761 61 T20/480164 Mm Pk Ros - - r= = = ? ?;{j? I'" 1 Mt I I I I Pt Mm t=;:? .p?nr.......? u = Unconformity Key to lithology Andesitic lava lgnimbrite Pahoka and Pourahu Tephras Andesitic tephras Bedded sands, silts and gravels Sandy matrix debris flow deposits Hyperconcentrated streamflow deposits Silty matrix debris flow deposits Lignite Figure 5.2 A Sequence of selected measured sections in the d irection of stream flow in the Mangatoetoenui Stream. These sections and others were used to produce the composite section shown in Fig. 5.3. ? 0 CD Upper Waikato Stream ?k h l = ? ?? Rk Kk R10 cr"J . . . . . . . . ? . . ?1!33: R11 Ok Tangatu Stream ?r \ - u . Wharepu Stream '" l ? Wh - - - Bt Te Piripiri Stream South Tributary Figure 5.3 Composite stratigraphic sections for Group 1 streams draining the northeastern flanks of Ruapehu. Tephra abbreviations are l isted in Table 5.1 , lahar deposit nomenclature from text. Te Piripiri Stream Main Tributary Mangatoetoeiti Stream F4 - ,. Key to lithology Andesitic lava lgnimbrite Mangatoetoenui Stream I Mt I Pt Oh Wa 1x:z:. ?= .1 -} m Pahoka and Pourahu Tephras Andesitic tephras Bedded sands, silts and gravels Sandy matrix debris flow deposits Hyperconcentrated streamflow deposits Silty matrix debris flow deposits Lignite u = Unconformity Other than in the Upper Waikato and Tangatu Streams, lahar deposits of episodes older than R1 0 are only well preserved along the Desert Road Fault scarp beside the Whangaehu River. The youngest lahar deposit in the Upper Waikato Stream sequence is from the R1 0 episode. This is part of an overall aggradation package of sediments deposited during the Last Glacial Maximum. The R 10 deposit is a l ithological ly d istinctive unit. lt has a yellowish brown to brown silt and clay-rich matrix which supports pebbles to large boulders. These clasts are subangular to angular, multi-coloured and multi-lithologic, including abundant, red , yel low and white, hydrothermally altered soft clasts. In many places this deposit comprises two or three flow units separated by thin (5 mm) clay laminae. The uppermost flow unit exhibits crude normal grading with large boulders concentrated at the base. The lower one or two flow units are finer grained and ungraded . Unit R1 0 is generally the lowest unit exposed in the streams north of Tangatu Stream. The stream sections between Tangatu and Mangatoetoenui Streams col lectively record nine episodes of lahar deposition younger than R1 0. Wharepu Stream and small surrounding streams, including the southern tributary of the Te Piripiri , al l record essentially the same sequence, R1 0 and R09. The R09 sequence comprises the deposits of several lahars below the Rerewhakaaitu Tephra . The main Te Piripiri Stream channel records the southernmost occurrence of six lahar deposits younger than R09. These six units (ROB, R07, R06, R05, R04 and R02) are all deposits of single lahars and are well constrained in age by enclosing tephra layers (Fig. 5.4 ). Un its R04 and R05 are correlated to the fragmentary sequence within Managatoetoeiti Stream and R04-R09 can be traced into Mangatoetoenui Stream sections. In the latter sequence, two further lahar deposits are preserved; R03, together with the youngest recorded episode R01 (5.2-5.3 ka). 5.1 0 Group 2 - Streams draining both volcanoes (Fig. 5.5) The Ohinepango and Waihohonu Streams drain the area between the Tongariro and Ruapehu massifs and have the potential to receive sediment from both volcanoes. The records in these streams are complicated by the presence of a large lava flow and its associated autobreccia deposits. The composite stream section for Ohinepango Stream (Fig. 5 .5) shows a sequence of lahar deposits, which can be correlated to units in the neighbouring Mangatoetoenui Stream. Most notably, the d istinctive R1 0 debris flow deposit is present below the Kawakawa Formation and the lava flow. Sections showing the stratigraphic relationships between the lava flow and Kawakawa Formation occur in the adjacent Waihohonu Stream. The age of the lava flow is well constra ined between R1 0 (and the underlying Okaia Tephra) and the Kawakawa Formation , i .e . between c. 23 ka and 22.6 ka B .P. The Ohinepango Stream sections also record R1 1 , RO?, R06, and R04 lahar deposits (Fig. 5.4). The Waihohonu Stream has a much larger proportion of its headwaters on the slopes of Tongariro volcano. Here there are more fluvial deposits 1 1 0 throughout the sequence, as well as three lahar deposits which are equivalent in age to R09, RO? and R06 (Fig. 5.4). Figure 5.4 Stratigraphy of lahar deposition episodes on the north-eastern Ruapehu and eastern Tongariro ring plains. Marker tephra layers Tephra ages (ka) Group 1 Group 2 Group 3 Northeastern Streams draining Eastern Tongariro Rua?ehu streams both volcanoes streams Hinemaiaia Tephra 5.2-3.95 R1 Motutere Tephra 5.8-5.3 R2 Mm, Poutu Lapil l i c. 9.7 Mm, Wharepu Tephra c. 9.7 R3 Mm, Ohinepango Tephra c. 9.9 Mm, Waihohonu Lapil l i c. 9.9 R4 R4 Mm, Oturere Lapill i c. 9.9 Karapiti Tephra 1 0. 1 R5 Pahoka Tephra c. 1 0 R6 R6 Bt, Pourahu Member c. 1 0 R7 R7 Waiohau Tephra 1 1 .85 R8 R8 T1 Rotorua T ephra 1 3.08 Rotoaira Tephra 1 3.8 T2 Rerewhakaaitu Tephra 14 .7 R9 R9ff3 + Hinuera T3 + Hinuera Formation Formation Kawakawa Tephra 22.59 R10 R 10 T4 R1 1 R1 1ff4 T4 Okaia Tephra c. 23 Omataroa T ephra 28.2 R 12 ? ? Hauparu Tephra 35.87 R13 Rotoehu Ash 64 R14 R1 5 5.1 1 Group 3 ? Eastern and northeastern Tongariro streams (Fig. 5.6) Five lahar deposition episodes are recognised in the stream sequences from Oturere to Tahurangi Streams. These are mostly well constrained in age although more unconformities are present in the sequences (Fig. 5.4, 5.6). The oldest deposition episode {T5) consists of two lahar deposits interbedded with fluvial deposits . 1 1 1 Ohinepango Stream Waihohonu Stream Ng 1-r--r-r...,....,-1 Tp ????----------??? Key to l ithology Figure 5.5 Composite stratigraphic sections for Group 2 streams draining the northeastern flanks of Ruapehu and southeastern flanks of Tongariro. Tephra abbreviations are l isted in Table 5 . 1 , lahar deposit nomenclature from text. 1 1 2 T5 is preserved beneath a presently unidentified rhyolitic tephra , which is also below an unconformity in the Mangatawai Stream sequence; hence the ages of the T5 units are not wel l constrained . T4, which commonly consists of several lahar deposits, occurs d irectly below the Kawakawa Formation, roughly equivalent in age to R1 0 and R1 1 . Unit T3 comprises lahar deposits that are laterally equivalent to Hinuera Formation fluvial sediments, that are commonly found with in the Tongariro streams and are equivalent in age to R09. T2 consists of a d istinctive, bright yel low si lty matrix debris flow deposit which contains dominantly pebble-sized pumice supported with in the matrix and is only recognised in the Oturere, Makahikatoa and Mangatawai Streams. No evidence of lahars equivalent in age to the younger episodes in the Ruapehu streams is recognised in the Tongariro streams; the youngest deposit T1 is equivalent in age to R8 ( 1 1 .85- 13 .08 ka B.P. ) . 5.12 Lahar distribution on the eastern ring-plain sectors from 23 ka to the present The areal distribution of each episode of lahar deposition has been mapped from the stream sections and supplementary field data (Fig. 5.7-5.9) . The distribution of the oldest units (R1 2-R1 5, and T5) cannot be mapped because only a few deep sections expose these units. Lahar units of the two oldest mappable episodes have the largest d istribution. R 1 1 and T 4 lahar deposits are found over the entire northeastern Ruapehu and eastern Tongariro ring plains (Fig. 5. 7 A). This indicates that active lahar sedimentation was occurring over the entire eastern ring plains before the eruption of the Kawakawa Formation during the early part of the Last Glacial Maximum. Streamflow deposition was also occurring over large areas of the ring plains during this time. R1 0 lahar deposits, however, were derived solely from the northeastern flanks of Ruapehu (Fig. 5. ?B), and are l ithologically distinct from the contemporaneous R1 1 and T4 lahars. I n the period fol lowing the Kawakawa eruption and before the Rerewhakaaitu eruption ( i .e . the latter part of the Last Glacial Maximum) much of the area continued to be inundated by lahar and fluvial deposits. Contemporaneous lahar episodes occurred from northeastern Ruapehu sources (R09) and eastern Tongariro sources (T3), coupled with stream sedimentation and reworking of Kawakawa Formation to form Hinuera Formation deposits . In the same time interval , formation of two major landscape features had a major effect on subsequent lahar distribution. The first was a large lava flow which was emplaced between the present Waihohonu and Oturere Streams (Fig 5. ?C) immediately before the eruption of the Kawakawa Tephra . This extensive lava flow served as a d ivide, effectively isolating lahars with a source in the northeastern Ruapehu and eastern Tongariro catchments. The second landscape feature was deposition of a series of g lacial moraines along the Whangaehu and Mangatoetoenui Streams (Fig 5.7C). These moraines blocked the direct drainage from the eastern Ruapehu flanks to a sector of the northeastern Ruapehu ring plain between the present Upper Waikato Stream to the southern tributary of Te Piripiri Stream. 1 1 3 __.. __.. ? Oturere Stream Makahikatoa Stream Mangatawai Stream Mm ?? I ? Wh T1 Mangamate Stream Mangahouhounui Stream Tauhurangi Stream Key to lithology Lignite Andesitic lava Andesitic tephras lgnimbrite Pahoka and Pourahu Tephras Bedded sands, silts and gravels Sandy matrix debris-flow deposits Hyperconcentrated-streamflow deposits Silty matrix debris-flow deposits Po Wh I I Ra I2 m Figure 5.6 Composite stratigraphic sections for Group 3 streams draining the eastern flanks of Tongariro. Tephra abbreviations l isted in Table 5 . 1 , lahar deoosit nomenclature from text. A R11 and T4 B R1 0 0 5 km L.LJ 0 5 km L.LJ c D T2 0 5 km 0 5 km L...J.....J L.LJ Figure 5.7 Distribution of deposits from lahar episodes: (A) R1 1/T4, (B) R1 0, (C) R09/T3 and the Hinuera Formation, (D) T2. Ages of the deposition episodes are given in Fig . 5 .4. 1 1 5 A ROB and T1 B R07 and R06 0 5 km L.LJ 0 5 km L.LJ C R05 D R04 0 5 km 0 5 km L.J.......J L.LJ Figure 5.8 Distribution of deposits from lahar episodes: (A) R08/T1 , (B) RO? and R06, (C) R05, (D) R04. Ages of deposition episodes given in Fig . 5.4. 1 1 6 A R03 and R01 B R02 0 5 km L.LJ 0 5 km L.LJ Figure 5.9 Distribution of deposits from lahar episodes; (A) R03 and R01 and (B) R02; ages of episodes are given in Fig. 5.4. 1 1 7 With the exception of small overflows from the Whangaehu catchment, there have been no lahars in this ring plain sector since. Lahars generated on the eastern Ruapehu flanks since the formation of the moraine ridges have been directed to the southeast into the Whangaehu (Oonoghue 1 991 ) or to the northeast, dominantly into the Mangatoetoenui catchment. All of the lahars after the R09/T3 depositional episode were distributed over much narrower sectors of the ring plains. Their d istribution was partially controlled by the lava flow and moraines as previously d iscussed , together with deepening of drainage channels fol lowing the Last Glacial Maximum. T2 episode lahars were distributed only within the Oturere-Mangatawai Stream sector of the Tongariro ring plain (Fig. 5.70). The youngest lahar episode on the eastern Tongariro ring plain, T1 , occurred within the same time range as ROB on the northeastern Ruapehu ring plain. The deposits of these two episodes are confined to areas on either side of the large lava flow between Waihohonu and Oturere Streams (Fig. 5.BA). The distribution of ROB lahars is typical of many of the subsequent deposition episodes on the northeastern Ruapehu ring plain. R07, R06 and R04 lahars al l covered the same sector between Waihohonu Stream and the northern tributary of Te Piripiri Stream (Fig. 5.B8, 5.BO). R05 lahar deposits have a narrower d istribution within this zone, between the northern tributary of Te Piripiri Stream and Mangatoetoenui Stream (Fig. 5.BC). The three youngest lahar events occurred with in the same ring plain sector but were confined to single stream channels - R02 along the northern Te Piripiri Stream tributary, and R03 and R01 with in Mangatoetoenui Stream (Fig. 5.9A, 5.98). The youngest lahar to cross the northeastern Ruapehu ring plain was generated on 2B October 1 995, and flowed down Mangatoetoenui Stream channel to the Tongariro River ( i .e . simi lar to the path in Fig. 5 .9A). 5.13 Source and generation of lahars A framework for the eruptive activity of Tongariro and Ruapehu volcanoes in the period during which these lahars were generated is contained in Table 5.3. The oldest lahar deposition episode, R1 5, consists of a thick sequence of debris flow and hyperconcentrated streamflow deposits interbedded with gravel ly fluvial sediments derived from Ruapehu volcano. A moderate frequency of large-scale eruptions during this time is reflected by a few layers of andesitic pumice lapi l l i preserved between the fluvial beds of the sequence. However, very l ittle pumice is found within the lahar and fluvial sediments themselves. In addition, no paleosols are preserved and there is no evidence for major unconformities. These deposits thus appear to represent a period of intermittent volcanic activity with continuous syn- and post-eruptive aggradation on the eastern sector of the Ruapehu ring plain. A l ignite deposit within these sediments (Fig. 5.3) contains a grassland and shrubland palynoflora (M.S. McGione 1 995, pers. comm.). Above these deposits is a paleosol with the Rotoehu Ash preserved near its base. This enables correlation of the R 15 sequence to a widespread period of river aggradation and loess deposition in the lower North Island during the cool climate of marine 818 0 Stage 4 1 1 B (Mi lne and Smal ley, 1 979; Pi l lans, 1 988; Cronin et al. , 1 996(b)). During this period the climate in the region is interpreted from previous palynofloral studies (McGione and Topping, 1 983) as having been cool and stormy, with episodes of erosion and widespread cover-bed stripping. The harsher climate would have accelerated physical weathering processes on the volcanoes and thereby provided a ready source of loose sediment on the cone supplementing that produced by eruptions. Table 5.3 Summary of the eruptive activity of Ruapehu and Tongariro volcanoes for the last 75 ka based on the ring plain tephra record (Topping , 1 973; Donoghue et al. , 1 995; Cronin et al. , 1 996(a)). 0 - 1 .85 1 .8 - 2.5 2.5 - 9.7 9.7 - 1 0 c . 1 0 c . 1 0 Tongariro volcano frequent, low volume and low magnitude eruptions frequent, low volume and low magnitude eruptions frequent, low volume and low magnitude eruptions very frequent (1 per < 50 years), large volume and large magnitude eruptions c. 1 0 - 22.5 1 large volume and large magnitude eruption 22.5 - 35.8 35.8 - 64 64 - c. 75 Ruapehu volcano Mapping units frequent (1 per 1 00 years), low Tufa Trig and volume and low magnitude eruptions Ngauruhoe Formations infrequent, low volume and low Mangatawai Tephra magnitude eruptions infrequent, low volume and low Papakai Formation magnitude eruptions 1 large volume and large magnitude eruption 1 large volume and large magnitude eruption including a pyroclastic flow moderately frequent (1 per 500 years), large volume and large magnitude eruptions moderate-low frequency (1 per 800 years), large volume and large magnitude eruptions. very low frequency (1 per 7 ka), large volume and large magnitude eruptions and frequent low volume and low magnitude eruptions. moderately frequent (1 per 600 years), large volume and large magnitude eruptions and frequent low volume and low magnitude eru tions. Mangamate Tephra and Pahoka Tephra Okupata Tephra Pourahu Member of Bullot Formation Bullot Formation and Rotoaira Lapi l l i Unnamed Unnamed Unnamed Redeposition of this loose material then appears to have taken place by lahars or normal streamflow. These were probably triggered by a number of different mechanisms, such as storms, slope fai lures, avalanches, glacial collapse and eruptive events. A greater volume of ice and snow on the upper volcano during this cool period may have provided an additional water source for lahar formation . Scouring and melting of g lacier ice and snow has been an important mechanism in the formation of lahars in many historical eruptions (Major and Newhall , 1 989; Pierson et al. , 1 990; Waitt et al. , 1 994 ) . In addition, at the beginning of the 1 995 Ruapehu eruptive sequence, augmentation of lahar volumes by eroded snow from the summit glaciers was an important process (Cronin et al. , in press). Deposits of the next three lahar episodes R14, R1 3 and R1 2 are interbedded with in thick andesitic tephra deposits from infrequent but large-scale eruptions of 1 1 9 Ruapehu (Table 5.3) , and also contain pumice lapi l l i with in their matrices. R1 2 deposits in particu lar contain a 0.2 m-th ick andesitic pumice lapi l l i layer interbedded between debris flow units. R1 3 and R14 comprise the deposits of single lahar events. All three episodes appear to have accompanied, and were probably caused by sub-pl in ian tephra eruptions at Ruapehu. The age of these deposits ranges from c. 65-35 ka, during a period of relatively mild and settled climate in the Tongariro region (McGione and Topping, 1 983). R1 1 and its stratigraphic equivalent on the Tongariro ring plain, T4, were then deposited before the eruption of the Kawakawa Formation (before 22.6 ka B .P . , Wilson et al. , 1 988). These deposits are thick continuous sequences of debris flow, hyperconcentrated streamflow, and coarse fluvial deposits with occasional andesitic lapi l l i layers interbedded in the R1 1 deposits. They are widespread over a l l the examined sectors of both ring plains and ind icate that abundant sediment was available on the volcanoes at this time for redeposition. The mechanisms of deposition of these units were l ikely to be the same as for the R15 lahar deposition episode. The frequency of large-scale eruptions in the interval when R1 1 and T4 were deposited was moderate-low (Table 5.3) . However, th is interval was the beginning of the greatest period of environmental destabi l isation in the North Island of New Zealand (marine 818 0 stage 2 , or the Last Glacial Maximum - 23-1 3 ka) over the last c. 1 20 ka (Pil lans et al. , 1 993). R1 0 is the deposit of a single event or a closely spaced series of lahar pulses with in the same time period as R1 1 and T4. However, this unit is lithologically d istinct from them. lt has a clay-rich si lty matrix and hydrothermally altered clasts, ind icating that it has been derived from a collapse of a hydrothermally altered section of the former Ruapehu cone. The R09/T3 lahar deposition episode represents lahar aggradation during the Last Glacial Maximum (marine 8180 stage 2) after the Kawakawa eruption . l t is coeval with deposits of redeposited Kawakawa ignimbrite mixed with andesitic sand and gravels, which have been previously mapped as Hinuera Formation in the northern sector of Tongariro ring plain (Topping and Kahn , 1 973). R09/T3 deposits are a lso widespread over much of the ring plain examined . They appear to have ceased accumulating immediately before the eruption of the Rerewhakaaitu Tephra . This is coincident with climatic conditions beginning to amel iorate in the Tongari ro region (McGione and Topping, 1 977). The frequency of large scale eruptions during this period was moderate (Table 5.3) , although this activity continued after widespread lahar deposition had ceased . Deposits of the subsequent lahar episodes are d istributed over much narrower sectors of the two ring plains. This is a result of both landform changes, as d iscussed previously, as well as seemingly reduced availabil ity of loose sediment on the flanks of the two volcanoes with climatically induced landscape stabi l ity after the Last Glacial Maximum. Where lahars continued to be deposited they appear to have been more channell ised than previously. This is probably due to incision of stream channels fol lowing the Last Glacial Maximum when more water and less sediment became available. On the eastern Tongariro ring plain , the Oturere-Mangatawai Stream sector 1 20 was the only area active fol lowing the Last Glacial Maximum where the deposits of two lahar episodes, T1 and T2, are preserved. T2 deposits are rich in andesitic pumice (up to 30 % by volume) and appear to be associated with the eruption of Rotoaira Tephra from Tongariro volcano at 1 3.8 ka (Topping, 1 973). T1 , the youngest lahar deposit on the Tongariro ring plain, is with in the same time frame as the first of eight lahar episodes on the northeastern Ruapehu ring plain, restricted between the main tributary of the Te Piripiri and Waihohonu Streams. During the time of the lahar deposition episodes R08/T1 to R02 (c. 1 3-9 ka) both volcanoes were erupting thick sub-plinian tephra layers with a high frequency, including the Mangamate and Pahoka Tephras from Tongariro (Topping, 1 973) and the younger Bul lot Formation tephras from Ruapehu (Donoghue et al. , 1 995). Several of the lahar deposition episodes appear to be directly associated with these eruptives. The most notable are: R06 with the Pourahu Member of the Bullot Formation , R05 with Pahoka Tephra , R04 with Oturere Lapil l i member of the Mangamate Tephra , R03 with Ohinepango/Waihohonu Tephra members of the Mangamate Tephra , and R02 with the Poutu Lapi l l i member of the Mangamate Tephra . The association with explosive volcanism provides a triggering mechanism and a large volume of source material for these lahar episodes but it does not completely explain their consistently restricted area of deposition. The Waihohonu and Oturere Streams on the Tongariro ring plain and the Mangatoetoenui Stream on the Ruapehu ring plain all have evidence of glacial moraines in their headwaters (Mathews, 1 967; Hackett, 1 985; McArthur and Shephard , 1 990). None of the other streams examined in this study do. The Waiohau Tephra ( 1 1 . 85 ka B .P . ) occurs near the base of the coverbed sequence on the moraines beside Waihohonu Stream, the Rerewhakaaitu Tephra ( 14.7 ka B .P . ) on the Oturere Stream moraines, and the Pourahu Tephra (c. 1 0 ka) on Mangatoetoenui Stream moraines. This suggests the g lacier in the former Oturere valley retreated before the glaciers in the Waihohonu and Mangatoetoenui val leys. This retreat is also reflected by the cessation of frequent lahars in the Oturere Stream after T1 at c. 1 4 ka, in the upper Waihohonu Stream (upstream of the confluence with Ohinepango Stream) from c. 1 5 ka, and the Mangatoetoenui Stream (where a g lacier sti l l exists on the upper volcano slopes) at c. 9ka. The presence of three retreating g laciers at these times provides a potential source of snow and water for lahar formation when eruptive products landed on them. Also moraine deposits are a ready source of sediment. Thus, the lahar record suggests these catchments were predisposed to lahar formation compared to other catchments without glaciers. Furthermore, units such as the Pourahu Member of the Bul lot Formation had an associated pyroclastic flow (Donoghue et al. , 1 995), which could have melted a large amount of snow and ice to form the lahars of the R06 episode. The youngest lahar deposition episode occurred between 5.3 and 5.2 ka B .P. in the Mangatoetoenui Stream when the climate was wetter and milder than the present (McGione and Topping, 1 977). The activity of the two andesite volcanoes had reduced in magnitude at this time, with fine ash of the Papakai Formation accumulating slowly on the 1 21 ring plain. This single lahar event could have had many triggering mechanisms, the most l ikely being an eruption which was not large enough to be represented individually in the tephra record . The 1 995 lahar in the Mangatoetoenui Stream was a dominantly monolithologic unit derived from the sudden rainfal l-induced fai lure of large thicknesses of tephra (up to 80 cm thick) erupted onto the Mangatoetoenui Glacier. 5.1 4 Summary and Conclusions Using the coverbed stratigraphy of rhyolitic and andesitic tephra, 1 5 lahar episodes are recognised in the northeastern Ruapehu ring-plain record , ranging in age from >65 to 5 ka. Five episodes are recognised on the eastern Tongariro ring plain ranging in age from >23 to 14 ka. The two main periods of lahar and fluvial aggradation were from c. 75-65 ka and 23 to 14 ka, corresponding to the two coolest periods of the Last Glacial (marine 8180 Stages 4 and 2). The cool and stormy climate of these times coupled with an expanded area of g laciers appeared to result in greater sediment supply for lahar formation. Greater volumes of snow and ice also increased the availabil ity of water for lahar generation. The triggering mechanisms for these lahars could have been eruptive activity, storm events, slope fai lures, avalanches and glacier collapses. Two events during the period c. 23-14 .7 ka B.P. strongly influenced the distribution of subsequent lahars . Firstly, the eastern Tongariro and Ruapehu ring plains were separated by a large lava flow emplaced between the present Waihohonu and Oturere Streams immediately before 22.5 ka. Secondly, Last Glacial Maximum moraines a long the upper Whangaehu and Mangatoetoenui valleys blocked lahars from the upper eastern flanks of Ruapehu to the ring-plain sector between the Upper Waikato and Te Piripiri Streams. Subsequent lahars generated on the eastern Ruapehu flanks have thus been channelled to the southeast down the Whangaehu catchment and northeast into mostly the Mangatoetoenui catchment. Many of the late glacial and postglacial lahar episodes appear to be related to pl inian and sub-pl inian tephra eruptions of Tongariro and Ruapehu volcanoes. However, both tephra deposition and water supply were required to form lahars . lt appears major lahars at this time were formed only where tephra fel l onto catchments with valley glaciers . The cessation of lahars on the eastern flanks of Tongariro before 1 1 .6 ka B.P. coincided with vegetational stabil isation of the volcanic slopes and glacial moraines. On the northeastern Ruapehu ring plain, lahar deposition continued until 5.2 ka B .P . , possibly because the glaciers were slower to retreat, particularly in the Mangatoetoenui catchment. 5.1 5 Acknowledgements We gratefu l ly acknowledge funding from the New Zealand Vice-Chancellor's Committee, 1 22 Massey University Graduate Research Fund , the Helen E. Akers Scholarship Fund , and the Department of Soil Science of Massey University. We also thank A.S. Palmer, R.B. Stewart and J .A. Lecointre for their useful reviews of an earl ier version of the manuscript, and B. F. Houghton and A.W. Walton for their comprehensive and useful reviews. 5.16 References Cronin, S.J . , Neal l , V.E. and Palmer, A.S. , 1 996(b). Investigation of an aggrading paleosol developed into andesitic ring plain deposits, Ruapehu volcano, New Zealand. Geoderma, 69: 1 1 9-1 35. Cronin, S.J . , Neall , V.E . , Stewart, R .B . and Palmer, A.S . , 1 996(a). A multiple parameter approach to andesitic tephra correlation , Ruapehu volcano, New Zealand. J . Volcano!. and Geotherm. Res. 72, 1 99-21 5. Cronin , S.J . , Neall , V.E. , Lecointre, J .A. , Palmer, A.S. , in press. Unusual "snow slurry" lahars from Ruapehu volcano, New Zealand, September 1 995. Geology. Donoghue, S .L . , 1 991 . Late Quaternary volcanic stratigraphy of the south-eastern sector of Mount Ruapehu ring plain, New Zealand . Unpub. PhD thesis , Massey University, Palmerston North, New Zealand. Donoghue, S.L . , Neal l , V.E. and Palmer, A.S . , 1 995. Stratigraphy and chronology of late Quaternary andesitic tephra deposits, Tongariro Volcanic Centre, New Zealand. J . Roy. Soc. N. Z. , 25: 1 1 5-206 . Froggatt, P.C. and Lowe, D .J . , 1 990. A review of late Quaternary si l icic and some other tephra formations from New Zealand: their stratigraphy, nomenclature , distribution, volume, and age. N . Z. J . Geol . and Geophys . , 33 : 89-1 09. Gregg, D .R. , 1 960. The geology of Tongariro Subdivision. N. Z. Geol. Survey Bull . , 40. Hackett, W.R. , 1 985. The geology and petrology of Ruapehu volcano and related vents. Unpub. PhD Thesis, Victoria University of Well ington, New Zealand. Hackett, W.R. and Houghton, B .F . , 1 989. A facies model for a Quaternary andesitic composite volcano: Ruapehu, New Zealand. Bul l . Volcano! . , 51 : 51 -68. Major, J .J . and Newhal l , C .G . , 1 989. Snow and ice perturbation during historical volcanic eruptions and the formation of lahars and floods; a global review. Bul l . Volcano! . , 52: 1 -27. Mathews, W.H . , 1 967. A contribution to the geology of the Mount Tongariro massif, North Island, New Zealand. N. Z. J. Geol . and Geophys. , 1 0: 1 027-1 038. McArthur, J . L. and Shepherd , M.J . , 1 990. Late Quaternary glaciation of Mt. Ruapehu, North Island , New Zealand . J . Roy. Soc. N . Z . , 20: 287-296. McGione, M.S . and Topping, W.W. , 1 977. Aranuian (post-glacial ) pollen diagrams from the Tongariro region, New Zealand . N . Z. J . of Botany, 1 5 : 749-760. McGione, M.S . and Topping, W.W. , 1 983. Late Quaternary vegetation, Tongariro region, central North Island , New Zealand . N . Z. J . . Botany, 21 : 53-76. Mi lne , J .D.G. and Smal ley I . J . , 1 979. Loess deposits in the southern part of the North Island of New Zealand : an outl ine stratigraphy. Acta Geologica Academiae 1 23 Scientarium Hungaricae, 22: 1 97-204. Nairn , I .A. , Wood , C .P and Hewson C.A.Y., 1 979. Phreatic eruptions of Ruapehu: April 1 975. N . Z. J. Geol. and Geophys . , 22: 1 55-1 73. Palmer, B.A. , Purves, A.M . and Donoghue, S.L . , 1 993. Controls on the accumulation of a volcaniclastic fan , Ruapehu composite volcano, New Zealand. Bul l . Volcano! . , 55: 1 76- 1 89. Pierson, T.C. and Costa, J .E . , 1 987. , A rheologic classification of subaerial sediment? water flows. G.S.A. Reviews in Engineering Geology, V I I : 1 -1 2 . Pierson , T.C . , Janda, R.J . , Thouret, J .-C. and Borrero, C.A., 1 990. Perturbation and melting of snow and ice by the 1 3 November 1 985 eruption of Nevado del Ruiz, Colombia, and consequent mobil isation, flow and deposition of lahars . J . Volcano!. and Geotherm. Res. , 41 : 1 7-66. Pi l lans, B.J . , 1 988. Loess chronology in Wanganui Basin, New Zealand. In: Eden, D .N . and Furkert, R .J . (eds) Loess - Its Distribution Geology and Soils: 1 75-1 91 . A.A. Balkema, Rotterdam. Pi l lans, B . , McGione, M. , Palmer, A. , Mi ldenhall , D . , Alloway, B. , Berger, G. , 1 993. The Last Glacial Maximum in central and southern North Island: a paleoenvironmental reconstruction using the Kawakawa tephra formation as a chronostratigraphic marker. Pal . , Pal . , Pal . , 1 01 : 283-304. Scott, K .M. , 1 988. Origins, behaviour, and sedimentology of lahars and lahar-runout flows in the Toutle-Cowlitz River system. U .S.G.S. Prof. Pap. 1 447-A: 76pp. Smith , G.A. , 1 986. Coarse-grained nonmarine volcaniclastic sediment: Terminology and deposition process. G .S.A. Bul l . , 97: 1 - 1 0. Smith, G.A. Fritz, W.J . , 1 989. Volcanic influences on terrestrial sedimentation. Geology 1 7 : 375-376. Topping, W.W., 1 973. Tephrostratigraphy and chronology of late Quaternary eruptives from the Tongariro Volcanic Centre, New Zealand. N . Z. J. Geol . and Geophys . , 1 6 : 397-423. Topping, W.W. and Kohn B.P. , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island, New Zealand. N. Z. J. Geol. and Geophys. , 1 6 : 375-395. Waitt, R.B. , Gardner, C.A. , Pierson, T.C . , Major, J .J . , Neal, C.A. , 1 994. Unusual ice diamicts emplaced during the December 1 5 , 1 989 eruption of Redoubt Volcano, Alaska. J. of Volcano!. and Geotherm Res. 62: 409-428. Wilson, C.J .N . , Switzur, RV. and Ward , A .P . , 1 988. A new 14C age for the Oruanui (Wairakei) eruption , New Zealand. Geol . Mag . , 1 25: 297-300. Wi lson , C.J .N . , Houghton, B .F. , Lanphere , M.A. and Weaver, S .D . , 1 992. A new radiometric age estimate for the Rotoehu Ash from Mayor Island volcano, New Zealand. N. Z. J. Geol . and Geophys . , 35: 371 -374. Wilson, C.J .N . , 1 993. Stratigraphy, chronology, styles and dynamics of late Quaternary eruptions from Taupo Volcano, New Zealand. Phi l . Trans. Roy. Soc. of London A, 343: 205-306. 1 24 CHAPTER 6: LAHAR HISTORY AND LAHAR HAZARD OF THE TONGARIRO RIVER 6.1 Introduction The Tongariro River drains a large portion of the northeastern Tongariro Volcanic Centre and thus has the potential of being a conduit for devastating lahars as has happened in the geological past. Bui lt beside the river, Turangi, a town of more than 4 000 people is potentially at risk from these lahars. The aim of this chapter is also one of the main objectives of the overal l study outlined in Chapter 1 - to establish what is the hazard to Turangi and the surrounding area from lahars in the Tongariro River. This part of the study relies on many of the developments made in previous chapters. Using the rhyolitic and andesitic tephrochronology established for the study area in Chapters 2 and 3, the lahar stratigraphy along the Tongari ro River was investigated in the same manner as for Chapter 5. By combining the Tongariro River stratigraphy with that developed for the northeastern Ruapehu and eastern Tongariro ring plains (Chapter 5), the lahar hazards of the entire Tongariro River catchment have been assessed. This part of the study has been written as a manuscript which has been submitted to the New Zealand Journal of Geology and Geophysics . The manuscript has multiple authors and the contributions of the authors were as follows: S. J . Cronin : Principal investigator V. E. Neal l Carried out al l : Field descriptions and sampling Tephra and lahar correlation and mapping Drawing and designation of zones on the hazard map Preparation and writing of the manuscript A.S. Palmer: Advisers Aided the study by: Discussion of methodology and lahar hazard designation Editing and discussion of the manuscript and lahar hazard map 1 25 6.2 LAHAR HISTORY AND LAHAR HAZARD OF THE TONGARIRO RIVER, NORTHEASTERN TONGARIRO VOLCANIC CENTRE, NEW ZEALAND Shane J . Cronin , V.E . Neall and A.S . Palmer Department of Soil Science, Massey University, Private Bag 1 1 222, Palmerston North, New Zealand. Submitted to: New Zealand Journal of Geology and Geophysics Abstract Laharic surfaces beside the Tongariro River have been mapped and dated using andesitic and rhyolitic marker tephras. Coupling the stratigraphic record obtained with that of the Tongariro and Ruapehu ring plains, has enabled a history of lahars occurring in the Tongariro River to be compiled . This has formed the basis of a lahar hazard map for the entire catchment. Eight lahar hazard zones with assigned recurrence intervals ranging from 1 in 35 years to 1 in > 1 5 000 years have been mapped . Lahar surfaces between the ages of 1 4.7 and 9.8 ka B .P. cover the greatest areas, while younger lahar surfaces are confined to lower and restricted surfaces closer to the present river channel . Holocene lahar deposits along the Tongariro River are not as well preserved as older units, probably because the Holocene lahars were confined to a more deeply incised channel where their deposits were more readily eroded fol lowing emplacement. All recorded lahars in the Tongariro catchment post-1 1 .85 ka B.P . have been derived from Ruapehu volcano. The Mangatoetoenui Stream has been the conduit for the greatest number of Holocene lahars and for al l of the historic ones. Most of Turangi is built on a surface which has not been inundated by a lahar since c. 1 0 ka B .P . However, the area identified where h igh risk affects the greatest population is part of Turangi , having been inundated by a lahar since 1 850 years B .P. The infrastructure at greatest risk includes the State Highway 1 bridge across the Mangatoetoenui Stream and the Rangipo Dam and power station . 6.3 Keywords Volcanic hazards, volcanic risk, lahar hazard map, lahars, Ruapehu volcano, Tongariro volcano, Tongariro River, Late Quaternary lahars, Holocene Lahars. 6.4 Introduction The Tongariro catchment drains the northeastern portion of the Tongariro Volcanic Centre and includes the northeastern flanks of Ruapehu volcano and the eastern and northeastern flanks of Tongariro volcano. Lahars can enter the Tongariro River via a large number of tributary channels draining these two volcanoes. The most recent example was a small lahar from Ruapehu volcano in October 1 995. 1 26 At risk from lahars along the Tongariro River is the town of Turangi with a population of 4239 in 1 991 (Department of Statistics, 1 992). Two smaller settlements, Rangipo and Tokaanu and the Rangipo Prison l ie farther from the river, but are also located on laharic and fluvial surfaces. The Tongariro Power Development which util ises both the Tongariro river channel and water from its tributaries is a lso at risk from lahars. In 1 995 laharic and fluvial sediment fi l led a large portion of the Rangipo dam, sited within the Tongariro River channel. This and additional sediment over the fol lowing few months led to excessive wear of turbine blades in the Rangipo Power Station . Also at risk from lahars a long the Tongariro River is tourist revenue from trout fishing and other recreational activities. To assess the lahar hazards within the Tongariro River and its surrounds we have mapped the laharic surfaces and sediments along the River and dated them using rhyolitic and andesitic cover- and interbeds. Combining this with a knowledge of the lahar stratigraphy on the northeastern Ruapehu and eastern Tongariro ring plains (Cronin and Neall , in press) we have produced an integrated lahar hazard map for the entire Tongariro catchment. 6.5 Setting Tongariro and Ruapehu are the two largest and most recently active volcanoes of the Tongariro Volcanic Centre (Gregg , 1 960). Ruapehu was last active in 1 996. lt is the highest peak in the North Island at 2797 m and consists of a 1 1 0 km3 composite cone with a surrounding ring plain of similar volume, comprising mainly volcaniclastic deposits (Hackett and Houghton, 1 989). Tongariro volcano is a sl ightly smaller massif made up of several coalescing volcanic cones, the largest of which is the recently active cone of Ngauruhoe (Mathews, 1 967; Nairn and Self, 1 978). Tongariro volcano is also surrounded by an extensive ring plain. The ring plain deposits of these two volcanoes are confined in the east by the Kaimanawa Mountains and extend down drainage channels to the north and south . The Upper Waikato Stream is the southern boundary of the volcanic portion of the Tongariro catchment (Fig. 6 . 1 ) . South of this boundary (a low d ivide on the Whangaehu fan) , d rainage from the flanks of Ruapehu flows southwards into the Whangaehu River. From its origins at the junction of the Waipakihi River and Upper Waikato Stream, the Tongariro River flows for 47 km before entering Lake Taupo. Its gradient ranges from 1 m drop in 43 m to 1 m in 225 m, before it becomes meandering within a delta formed into Lake Taupo. Along its path , 9 major and several other smaller streams rising from the flanks of the Ruapehu and Tongariro volcanoes join the River. 6.6 Terminology The word lahar is here used to describe, "a rapidly flowing mixture of rock debris and water (other than normal streamflow) from a volcano" (Smith and Fritz, 1 989). 1 27 39? 1 0 I Taupo Volcanic Zone Mt Tongariro .A. ) MI N?uh? 1500 m Pihanga A Lake Taupo - State Highways 0 5 km Figure 6.1 Location of the Tongariro catchment, draining the northeastern Tongari ro Volcanic Centre in the central North Island of New Zealand. The n ine major tributary streams which drain from Ruapehu and Tongari ro volcanoes into the Tongariro River are label led . 1 28 Lahars are generally subdivided on the basis of d iffering sediment concentrations and resulting differences in rheology. A continuum of flow behaviour and rheology occurs between normal Newtonian streamflow and plastic plug-flows (Pierson and Costa, 1 987). Most lahars fall into two main rheologic categories which have been defined on the basis of field and laboratory experiment observations; debris flows and hyperconcentrated streamflows. Hyperconcentrated streamflows are defined as containing 20-60% sediment by volume (Beverage and Culbertson, 1 964 ). More importantly however, the onset of hyperconcentrated streamflow behaviour is when a sediment-water mixture begins to attain a measurable yield strength ( i .e. it becomes a non-Newtonian flu id) . Sediment is supported within these flows dominantly by clast-clast collisions/interactions and turbulence, and deposition is by a rapid grain by grain settl ing process at the base of the flow (Pierson and Scott, 1 985; Smith , 1 986). Deposits typical of hyperconcentrated flows are usually sand dominated, horizontally bedded , poorly sorted and clast supported. When the sediment concentration in the flow approaches 60% (the actual content varies according to the particle-size d istribution of the sediment), yield strengths of the flow increase markedly. At this stage the flow begins to behave l ike a laminar flowing, single-phase plug rather than sediment suspended in water (Pierson and Costa, 1 987). Clast support in these flows is by matrix support and buoyancy, and deposition is en masse, the deposits representing a frozen state of the flow. Debris flow deposits are dominantly matrix supported , massive and very poorly sorted (Smith, 1 986). 6. 7 Hazards of Lahars The hazards posed by lahars have been vividly portrayed by a number of disasters throughout the world in recent history. In 1 953, in a local example, 1 51 people were killed when their train plunged into the Whangaehu River as a lahar undermined the rai l bridge (Sti l lwel l et al. , 1 954). I n 1 985, the town of Armero in Colombia and 23 000 of its inhabitants were inundated by lahars from Nevada del Ruiz (Pierson et al. , 1 990; Voight, 1 990). In 1 991 and following years, lahars in rivers rad iating outward from Mt. Pinatubo in the Phi l ippines caused at least 1 43 fatalities. They destroyed bridges and inundated towns, roads and huge areas of arable land , forcing the evacuation of more than 70 000 people (Phi l ippine Institute of Volcanology and Seismology, 1 992; Pierson et al. , 1 992). Hazard to l ife from lahars results from their high speeds and sediment concentrations. People and animals are swept away or entombed in sediment. Bridges and other man-made structures are also easily destroyed by large, h ighly competent flows. Lahars can also deposit sediment across large areas of productive land, not only destroying crops but potentially resulting in a permanent loss of production . Other hazards can result from the acidity, toxicity and heat of some types of lahars . 1 29 6.8 Methods The surfaces and sediments in this study have been dated using andesitic and rhyolitic tephra cover- and interbeds. Lahar surfaces were mapped from field exposures and using aerial photographs. Eighteen dated rhyol itic tephras erupted from Taupo Volcanic Zone calderas are preserved within the Ruapehu and Tongariro ring plain and Tongariro River sequences (Topping and Kohn , 1 973; Donoghue et al. , 1 995; Cronin and Neal l , in press). These tephras were identified by their stratigraphic positions, physica l appearances, mineralogy and glass chemistry (Cronin e t al. in press(a)). In addition , 1 1 dated andesitic tephras erupted from Tongariro and Ruapehu volcanoes occur within the sequences (Topping, 1 973; Donoghue et al. , 1 995). These and further andesitic marker tephras were identified by a similar range of methods as those used for the rhyolitic tephras (Cronin et al. , 1 996). All the marker tephras d iscussed in this study are listed in Table 5 . 1 (Chapter 5). Laharic deposits with in the stratigraphic sequences were interbedded with fluvial sediments, tephras and lava flows. The laharic deposits were d istinguished from fluvial sediments by their laterally continuous and characteristic sedimentology outlined previously. In constructing the lahar hazard map, laharic surfaces of d iffering ages were delineated into zones and a lahar recurrence interval was assigned to each zone. For the three youngest zones this was a simple process of calculating the ratio of the number of lahars in a given time, e.g. within the h istoric record (1 00-1 50 years), or since the Taupo Tephra ( 1 850 years B .P . ; Froggatt and Lowe, 1 990). For older lahar surfaces this approach yields results which are not considered valid , e .g . a surface mapped in this study has not been inundated by a lahar since c. 1 0 ka B .P . This surface comprises the deposits of several lahars, and using tephra interbeds various recurrence intervals can be calcu lated . Since 1 3.8 ka B.P. the recurrence interval is 1 in 2 800 years, and since 22.6 ka B.P. it is 1 in 3 200 years. These intervals are not representative of a surface which has not been crossed by a lahar in the last 1 0 ka, nor are they representative of the actual frequency of the lahar deposition (from 22.5 to 1 3 .8 ka B.P.= 1 in 4 400 years, and from 1 3.8 to 1 0 ka B .P .=1 in 800 years). In situations such as this, the approach in this study was to assign a recurrence interval based on the last time a g iven surface was inundated by a lahar. 6.9 Lahar history of the Tongariro River 6.9.1 Stratigraphic record within the tributary streams The number and timing of lahars entering the Tongariro River may be obtained from the lahar record preserved with in its volcanic sourced tributaries (Cronin and Neall, in press). This indicates that prior to the eruption of the Rerewhakaaitu Tephra ( 14.7 Ka B .P. ) , multiple lahars occurred with in almost al l of its major tributaries (Table 6 .2). In contrast, 1 30 Holocene lahars are restricted to three streams on the northeastern Ruapehu ring plain . The Mangatoetoenui Stream has contributed the largest number of post-glacial lahars to the Tongariro River. During the 1 995/96 eruption episode of Ruapehu volcano, the only lahars to enter the Tongariro River travelled down the Mangatoetoenui Stream. 6.9.2 Stratigraphic record with in the Tongariro River val ley 6.9.2A Highest surface The oldest exposed sequences in the Tongari ro River valley form the h ighest surface, which is commonly 1 5-30 m above the present river level . This surface is extensive throughout the catchment between Upper Waikato Stream and the town of Turangi . Sections through it are described in exposures at various locations a long the Tongariro River (Fig. 6 .2) . Close to the Tongariro River the surface has been eroded and subsequently been infi l led by the Taupo lgnimbrite. As a result of this infi l l ing, lahar surfaces of d iffering ages have been buried to form a single younger surface. This complexity is exempl ified by the difference in age of the lahars comprising the highest surface described at Site 1 with those at Sites 2 and 3 which have been overlain by 4 to 6 m of pumiceous ignimbrite to form a laterally continuous surface. At Sites 2 and 3 beneath the pumice veneer are formerly lower and younger laharic surfaces than at Site 1 . Sites 2 to 7 from 1 .5 to 36 km down the river al l have coverbed sequences of simi lar ages. At Site 2, the lahar deposits above an unconformity are younger than any recorded in the Upper Waikato Stream and are probably derived from the Te Piripiri catchment. Sites 2 to 5 al l record the deposits of several lahars below either the Pourahu or the Pahoka Tephras (c. 9 .8-1 0 ka B .P.) . At Sites 6 and 7 the Pahoka and Pourahu tephras have thinned beyond recognition, but the lower members of Mangamate Tephra and the Poronui Tephra are present, providing a minimum age of c. 9 .7-9.8 ka B .P . for the underlying lahar deposits . None of the many lahars younger than 1 0 ka B .P . that are recorded by deposits in the Te Piripiri, Mangatoetoenui or Waihohonu Streams (Table 6.2) are represented in any of the sections described through this high surface. The Rotoaira Tephra preserved at Site 6 provides a lower age l imit for a package of several lahar deposits. This ind icates that this lahar package was probably derived from the Te Piripiri, Mangatoetoenui , Waihohonu, Oturere, and Makahikatoa catchments. Lahar deposits preserved below the Kawakawa Tephra at Sites 6 and 7 could have been derived from lahars in any of the tributary streams (Table 6 .2) . The post-Kawakawa lahars described in the Tongariro valley sequences cannot be individual ly correlated downstream on the basis of l ithology or stratigraphy. However, consistent changes in the sedimentology of the overal l package of post-22.6 ka B .P. lahar deposits are observed . In the upstream sites most of the deposits are: coarse grained - containing pebbles-large boulders, matrix-supported with a sandy or si lty matrix, poorly sorted and massive. 1 31 Table 6.2 Number and timing of lahars in tributary catchments of the Tongariro River, based on the exposed stratigraphic record in each catchment (Cronin & Neall in press). Marker horizons age (ka B.P.) Upper Waikato Te Piripiri MangatoetoenliL_ Waihohonu Oturere Makahikatoa Mangatawai Mangamate Puketarata Mangahouhounui Hinemaiaia Tephra Motutere Tephra Mm, Poutu Lapilli Mm, Wharepu Tephra 1 995 AD 5.2-3.95 5.8-5.3 c. 9.7 c. 9.7 Mm, Ohinepango Tephra c. 9.9 Mm, Waihohonu Lapilli c. 9.9 Mm, Oturere Lapilli Karapiti Tephra Pahoka Tephra Bt, Pourahu Member Waiohau Tephra Rotorua T ephra Rotoaira Tephra Rerewhakaaitu Tephra Kawakawa Tephra Okaia Tephra Omataroa Tephra Hauparu Tephra Rotoehu Ash c. 9.9 1 0. 1 c. 1 0 c. 1 0 1 1 .85 1 3.08 1 3.8 1 4.7 22.59 c. 23 28.2 35.87 64 I several I several I 2 I 1 I several I n 2 I I 1 I I 1 I I 1 I 1 1 1 I 1 1 I 1 1 1 1 1 1 r- -1-?---.,- I several several several I I 1 + I I several Unexposed 1 32 I 1 1 I I 2 1 1 I several 1 + 1 + I several several several 1 + 1 + I several I several Unexposed I ...... w w 5 m ?--:- 0-:-;. -..; o??. :..:. ?- . _. ,:_ ?- . . , . _ o . _-: ?o?. o ? .-: ?i o--- . ? o- - . ? ??: ???-;.?: ???-1 o .. -.: ?o? .o ?:-:- ?o? .-_ . o--- 0"':"";.?-: _o-:- ;. Key to lithology Andesitic lava lgnimbrite Pahoka and Pourahu Tephras Andesitic tephras Bedded sands, silts and gravels '..(', , , _ ' :?? ? . ; ?? ? :.?- ? .. ? , ? . - ' - ' ?. , ' '..t '. .?:,"..--\ :-; -? ??...: - ' "'i ??? - ? >;,? I ?: ?. , , _ ' . ... ? ? ? .. "?? -, ' ' ' : - ' - , ,_ 2 m ? , I ' ,, , . , , ... , - ' - ' . , '' "'..('. . , (' . , ? ' - , _ , , . ' , , _ -, "?";.., ... ? ,-'- \'' , , I . Silty matrix debris flow deposits I 2 m Ra I - - k ? Sandy matrix debris flow deposits Hyperconcentrated streamflow deposits Lignite u = Unconformity ':_/":-?,/? I ._ .. ??: ???.--?: ?- o-.o ?.-:- "o? .o ?.-:- . ?=-, ?_: ?=-? 2 m . ? ? ? . . ..; _ . . ?- -?_. -.: . ?. ?-_- ._ - 0 ? - 0 . ? Q ? -- ? o ? - -.?-: o-. _: c - ....: . . - - :..: _ . . Figure 6.2 Stratigraphy of sections preserved thro ugh the h ighest laharic surface beside the Tongariro R iver. S ites 1-7 are labelled on Figs. 4 and 5. S ites 2-7 are located at the labelled d istances downstream of the start of the Tongariro R iver (at the junction of the Waipakihi River and the Uooer Waikato Stream) . In contrast in downstream sites the deposits are: dominated by sands and large clast poor; clast-supported ; weakly planar or horizontally bedded with rare larger clasts in horizontal "strings". These changes in sedimentology indicate changes in the rheology of many of the lahars as they travelled downstream. I n upstream local ities, the deposits ind icate the lahars were l ikely to be debris flows, depositing sediment en masse. The downstream deposits imply finer-grained, more di lute hyperconcentrated streamflows, with incremental deposition of many th in layers to build up each deposit. These lahars appear to have transformed from debris flow to hyperconcentrated streamflow between c. 25 and 29 km along the Tongariro River. This was probably due to loss of sediment from the flows by deposition and their di lution by incorporating river water in their paths. Similar lahar transformations have been described by Pierson and Scott ( 1 985) at Mt. St. Helens, and Cronin et al. ( in press(b)) in 1 995 lahars in the Whangaehu River. 6.9.28 Lower surfaces Small areas of low surfaces are preserved close to the main channel in the upper reaches of the river. These are flood plains, composed of recent (post-1 850 years B .P . ) , coarse (bouldery and cobbly) a l luvial deposits, mostly with no stratigraphy exposed . In the lower reaches from the town of Turangi northwards, the lower surfaces are extensive. Where the surfaces are more extensive, only those preserving a stratigraphy were described. In a l l described exposures, lahar stratigraphy is very difficult to interpret because of extensive fluvial reworking of lahar deposits and poor preservation of tephra marker beds. However, a sequence of at least four lahar deposits is preserved in a small number of exposures (Fig. 6 .3) . At Site A (Fig. 6.3) two pre-Taupo Tephra lahar deposits are preserved , with a variable thickness of fluvial sands between them. Deposit 2 is unconsolidated and finer? grained than the large boulder-bearing, and firmly compacted deposit 3. Site A has been inundated by the River since the deposition of Taupo Pumice, but this deposit is not laharic. At Site B a similar stratigraphy is preserved, and the sed imentologies of lahar deposits 2 and 3 are a lso similar to Site A. Lahar deposit 2 was probably emplaced soon before the Taupo lgnimbrite, because little or no reworking or soil development is evident at the top of the lahar deposit. Site B also preserves the deposit of at least one lahar beneath lahar deposit 3 . Downstream, at Site C the lahar deposit preserved at the base of the sequence is correlated to deposit 3 from its grainsize characteristics, sed imentology and firmly compacted nature. The H inemaiaia Tephra (Hm on Fig. 6.3) provides a minimum age for this lahar. Lahar deposit 2 is not preserved at this site. At Sites D and E , which are on lower surfaces than the first three localities, the basal lahar deposits are correlated to lahar deposit 2, because of their unconsolidated nature and finer grainsize than deposit 3. Large parts of the upper portions of lahar deposit 2 at these sites and many others are reworked , the fine grained matrix having been elutriated leaving a cobbly-bouldery matrix-poor clast-supported deposit. 1 34 ....>. VJ (]1 Tp Site A Sand Pool Site B Stag pool Site C Hydro Pool m ??;s??s?;?:?::?:::e?: adn?????elly sands Site D Cableway Site E Judges Pool . . . . . . . . . . . Site F SH1 bridge Site G Swirl Pool ? +Tp ? Site H Upper Island Pool 8 m 7 6 5 4 3 2 1 ??--------------- ? +Tp --------- - -------? r.::>::: : ::::::::l ::??=? :?;ds E22Z2J Taupo lgnimbrite ? Hinemaia Tephra River Level + Tp Includes reworked Taupo Tephra clasts 1 1 1 1 1 1 Soil development I I Andesitic tephra Figure 6.3 Stratigraphy of sections through the lower laharic surfaces alongside the Tongariro River. Sites A to G are located on Figs. 4 and 5. "'t:. Sites F and H exempl ify many of the lowest surface exposures where only bedded sands and clast-supported cobbles and boulders are preserved. In these sites the lahar deposits appear to have been completely eroded or reworked . At site G the youngest (pre-1 995) lahar deposit in the Tongariro catchment is preserved (lahar deposit 1 ). This deposit contains reworked Taupo Tephra clasts, indicating a post-1 850 year B.P. age. Alluvial sands and silts with two episodes of weak soil development occur above the lahar deposit providing no definite minimum age. Lahar deposit 2 is also preserved at Site G, and in many places its upper portion is reworked . The deposit 4 lahar was probably derived from either Te Piripiri or Mangatoetoenui Streams, based on the presence of lahar deposits in a simi lar stratigraphic position (Table 6 .2 and Cronin and Neall , in press). The lahar that emplaced deposit 3 was probably derived from the Mangatoetoenui Stream, where a lahar deposit in the same stratigraphic position has been described. Lahar deposits 2 and 1 are not preserved in upstream areas, thus it is d ifficult to assess from which catchments they were derived. However, in the late Holocene many lahars were derived from Ruapehu volcano in the Whangaehu catchment (the Onetapu Formation, Donoghue, 1 991 ; Hodgson, 1 993; Palmer et al. , 1 993). So deposits 2 and 1 are l ikely to be from Ruapehu, and given the 1 995 example, the Mangatoetoenui Stream was their probable conduit. The fact that the youngest lahar deposits are not well preserved in the Tongariro catchment can be explained by comparison to the 1 995 lahars in the Whangaehu catchment (Cronin et al. , in press(b)). Of 35 lahars recorded in the Whangaehu River from September to December 1 995, one year later only a few localities preserve the deposits from only one of these - the largest. However, large amounts of reworked deposits occur. The reason for reworking of the 1 995 lahar deposits is that they were mostly confined to the river channel, so streamflow remobil ised them immediately following their deposition . The same circumstances probably appl ied to lahar deposits with in the Tongariro River in the late Holocene when the channel was incised almost as deeply as at present. In contrast, during the late glacial and early post-glacial period, the Tongariro River was probably not confined to a deeply incised channel . This resulted in emplacement of lahar deposits across a broad area, now represented by the highest lahar surface preserved extensively throughout the catchment. 6.1 0 Lahar hazards in the Tongariro River The lahar hazard map of the Tongariro catchment (Figs. 6.4 and 6 .5) is based on the lahar stratigraphy and mapped extent of laharic surfaces in the catchment as described above. Each lahar hazard zone was derived from a mapped laharic surface of known or inferred age. Each assignment is based on the age of the youngest lahar to cross the surface. 1 36 6.1 0.1 1 in >15 000 year zone This zone includes the most extensive surfaces in the Tongariro catchment. The laharic surfaces included with in this zone comprise lahar deposits older than the Rerewhakaaitu Tephra ( 14.7 ka B .P . ). Almost all of the eastern ring plain of Tongariro volcano and large parts of the northeastern Ruapehu ring plain comprise laharic surfaces of this age. In the southern part of the mapped area, near the Upper Waikato Stream, the zone includes lahar surfaces which are pre-Kawakawa Tephra age. A small patch of a pre-Kawakawa Tephra surface is also preserved immediately south of Turangi township (Fig. 6 .5). On the Ruapehu ring plain the lahar deposits with in this hazard zone belong to the Te Heuheu Formation (Donoghue, 1 991 ) . On Tongariro volcano these lahar deposits were previously mapped as the Rangipo Lahars (Grindley, 1 960). This extensive zone and the large number of lahars that comprise these surfaces (Table 6 .2 and Cronin and Neall , in press) indicate that lahars were a common occurrence across large areas of both ring plains during and following the Last Glacial Maximum. At risk with in this zone is the vil lage of Rangipo and part of the Rangipo Prison, State Highway 1 and other secondary roads. In addition, high voltage transmission l ines and the Poutu Canal cross this zone. 6.1 0.2 1 in 1 2 000 year zone This zone covers small areas a longside the Oturere and Makahikatoa Streams on the Tongariro ring plain and lower slopes. lt represents a lahar path following deposition of the Rotorua Tephra but prior to the eruption of Waiohau Tephra ( 1 1 .85 ka B .P. ) . The zone is crossed by State Highway 1 and high voltage transmission l ines, but mostly includes unpopulated land covered by native forest. 6.1 0.3 1 in 10 000 year zone This zone represents a lahar surface recognised by its oldest marker coverbed being either the Pourahu, Pahoka, or Poronui Tephra , al l of which are between the ages of 9.8- 1 0 ka B.P. This surface covers a sector of the northeastern Ruapehu ring plain, and comprises deposits of several post-glacial lahars which flowed down the Te Piripiri , Mangatoetoenui , and Waihohonu Streams (Table 6.2). The surface pinches out in the central reaches of the Tongariro River where lahars of this age were probably confined to an incised channel . Immediately upstream of the Rangipo prison the lahar surface again spreads out to cover a large area between Rangipo and Turangi . Much of Turangi township is bui lt on this surface as well as the Rangipo Prison and a few other outlying houses. Also at risk on the surface are numerous roads, telephone lines, high voltage transmission l ines, as well as large areas of pastoral land and l ivestock. 1 37 1 75? 40' Lahar hazard Zones Mangatoetoenui 1 . 35 a Stream In ye rs 1 in 1 00 years 1 000 years 2 000 years 39o 5 000 years 00' 1 0 000 years N A 1 2 000 years >1 5 000 years Figure 6.4 Lahar hazard map of the Tongariro River. Locations of sections in Figs. 6.2 and 6.3 are labelled. 45' t ill Pihanga ? I I I I I I I I 50' Lake Taupo --- Major roads --- Minor roads Power development tunnels 0 2 3 4 5 km 50' 39? 00' 05' 1 5' 6.1 0.4 1 in 5 000 year zone ?------------------ - - - - - Two small areas of this hazard zone are delineated , along Mangatoetoenui Stream (Fig. 6.4) and a small area south of Turangi township (Fig. 6.5) . These surfaces were last inundated by a lahar between the time of the eruptions of the H inemaiaia and Motutere Tephras (Table 6 .2 , c. 5 .2-5.3 ka B.P . ) . Both of these areas are unpopulated and are not used for agricu ltural production. 6.1 0.5 1 in 2 000 year zone Surfaces with in this zone are extensive only in the lower reaches of the Tongariro River (Fig. 6.5) . The last lahar to inundate this surface was immediately prior to the Taupo Tephra eruption. Upstream of Turangi these surfaces are confined close to the present river channel but fan outwards north of the town. Parts of Turangi , and Tokaanu and many outlying houses are built on this surface. An airstrip, the Turangi sewage treatment area, the Tongariro trout hatchery and many roads ( including State H ighway 1 ) are a lso within this zone. Large portions of the zone are also in pastoral production . 6.1 0.6 1 in 1 000 year zone This zone includes areas which are interpreted to have been crossed by a lahar since the eruption of the Taupo Tephra ( 1 . 85 ka B .P . ). Only a few local ities within this zone preserve deposits of a post-Taupo Tephra lahar because many of the deposits have been reworked by subsequent fluvial action. The area covered by this zone extends from Turangi to the delta in Lake Taupo (Fig. 6 .5). I n the Tongariro delta region, where exposure is poor, the extent of the zone has been del imited by consideration of the soil map of this region (Water and Soils Division, Ministry of Works and Development, 1 979). The mapped extent of the 1 in 1 000 year zone corresponds to "Recent soils from al luvium", whi lst "Organic soils" beyond the l imit of these lahars, occur in the surrounding swampy area. Parts of Turangi are included within the zone as wel l as a few outlying houses and the State H ighway 1 Bridge across the river. 6.1 0.7 1 in 1 00 year zone This zone comprises the channel of the Tongariro River into which at least one lahar flowed during the 1 995 eruption sequence of Ruapehu (Cronin et al. , in press(b)). Europeans did not settle in the Turangi region unti l the early 1 900's (Ciarke and Smith , 1 986), so that continuous records were not ava ilable unti l this time. Although the 1 995 lahar did not pass beyond the Rangipo Dam in the Tongariro River, a 1 in 1 00 year hazard zone is sti l l appl ied to the remainder of the river channel because this would probably be the case without human intervention. 1 39 Tokaanu Tokaanu Power Station Tongariro River 1 in 1 00 years channel 1 in 1 000 years 1 in 2 000 years 1 in 5 000 years 1 in 1 0 000 years 1 in > 1 5 000 years .. Pihanga 50' Lake Taupo N A --- Major roads --- Minor roads 39? 00' 03' 0 2 km Figure 6.5 Enlargement of lahar hazard map for Turangi and its surrounds. This area contains the greatest popu lation and most of the youngest laharic surfaces in the Tongariro catchment. Location of sections in Figs . 6 .2 and 6.3 are label led . 1 40 6.10.8 1 in 35 year zone This zone includes the channel of the Mangatoetoenui Stream which was affected by at least two lahars i n the 1 995 eruption sequence of Ruapehu (Cronin et al. , i n press(b )), and a lso by lahars in the 1 895 and 1 975 Ruapehu eruptions (Al ien, 1 902; Nairn et al. , 1 979). Observations of Ruapehu volcano have been made for ea. 1 40 years (Gregg, 1 960), and four lahars recorded during this time equates to a 1 i n 35 year recurrence interval . 6.1 1 Discussion The areas of greatest lahar hazard in the catchment are obviously the lowest lying areas closest to the Tongariro River and Mangatoetoenu i Stream. The area of greatest risk i n the catchment is where the highest lahar hazard and greatest vulnerabi lity of people and property are combined. Although the entire town of Turangi is bui lt on laharic surfaces, much of it is on a surface which has not been inundated by lahars since 1 0 ka B.P. However, parts of Turangi and many outlying houses are on surfaces which have been covered by much younger lahars. Thus, the area of greatest human risk in this catchment is where houses are bui lt within the 1 in 1 000 year hazard zone in part of Turangi . One of the greatest property risks i n the area has a lready been identified by lahar impacts during the 1 995 Ruapehu eruption sequence. The Rangipo Dam became substantially infi l led with sediment from lahars sourced within the Mangatoetoenui catchment. This dam retains water to be used for power generation i n the underg round Rangipo Power Station. Sandy and si lty sediment within water piped to the power station led to severe wear of the turbine blades, necessitating replacement of one of them (ECNZ pers. comm. , 1 995). The State Highway 1 bridge crossing the Mangatoetoenu i Stream on the Desert Road is probably the bridge at greatest risk from lahars in the Tongariro catchment. The source of most lahars in the period 1 4 .7-1 0 ka B .P . in the Tongariro catchment has been Ruapehu volcano, particularly via the Mangatoetoenu i and Te Piripiri Streams. All Holocene lahars have also come from Ruapehu and most of these were sourced within Mangatoetoenui Stream. Lahars in the Tongariro catchment have been attributed to a variety of generation mechanisms , including flank collapse , eruptions, g lacier collapse and storms . The most readily identifiable are those related to tephra eruptions of either Tongariro or Ruapehu (Cronin and Neall , in press). Almost al l of the Holocene lahars have been l inked to large? scale tephra eruptions from either volcano. The 1 995 lahars fol lowed this pattern , but were of a smal ler scale than most Holocene lahars. Un like the Whangaehu River, the Tongariro River tributaries do not d i rectly dra in Crater Lake, nor are they as close to the Lake as the Mangaturuturu, Whakapapaiti and Whakapapanui catchments. Thus, lahars generated by water expel led during smal l scale eruptions through the Lake have not occurred with the same frequency in the Tongariro 1 4 1 tributaries as they have in the other catchments. Two lahars derived from surges from Crater Lake were produced in the Mangatoetoenui Stream during eruptions in 1 895 and 1 975. I n contrast, 1 9 lahars derived from Crater Lake are recorded in the Whangaehu Catchment prior to 1 995 (Hodgson, 1 993), and a further 26 occurred during the 1 995 Ruapehu eruptive sequence (Cronin et al. , in press(b)). During 1 995, events in the Mangatoetoenui Stream ind icate another mechanism for creating lahars that enter the Tongariro River during eruptions of Ruapehu. These lahars were caused when large amounts of tephra fel l onto Mangatoetoenui Glacier, fol lowing several eruptions throughout September and early October 1 995. The largest of these eruptions on October 1 1 -1 2 contributed the greatest volume of tephra. Heavy rains in the following weeks caused col lapse, ri l l ing and remobi l isation of saturated tephra to form lahars (Cronin et al. , i n press(b)) . A further potential lahar generating mechanism in this catchment is the eruption of hot pyroclastic flows onto the Mangatoetoenui Glacier, which could rapidly entra in and melt snow and ice. Lahars caused by these mechanisms occurred on Nevado del Ruiz, where relatively small scale eruptions led to huge, devastating lahars (Pierson et al. , 1 990). Evidence of only one pyroclastic flow has been recorded on Ruapehu at c. 1 0 ka B.P. (Donoghue et a l . , 1 995) but most notably a lahar associated with this event is recorded in the Mangatoetoenui catchment (Cronin and Neal l , in press) . Another possible way for lahars to enter the Tongariro River is via overflow of a large lahar from the Whangaehu River into Upper Waikato Stream. Deposits recording such an event have not been described in this study, but are described by Donoghue ( 1 99 1 ) . During the 1 995 eruption sequence of Ruapehu this situation a lmost eventuated. Several lahars between September 1 8 and 25 gradual ly bui lt up the base level of the Whangaehu channel on the upper ring plain by several metres until on September 25 the largest lahars flooded into small tributaries which flow northwards before rejoin ing the Whangaehu River farther downstream. These northeastward-flooding lahars travel led to with in 300 m of tributaries of Upper Waikato Stream. If d iversion of the main Whangaehu River channel into this route were to occur, lahars would probably overflow into Upper Waikato Stream. I ncision of the Whangaehu River through the aggraded lahar deposits over the fol lowing few months has temporarily reduced this risk. If the northeastward flowing channels become further i ncised during heavy rainstorms, headward erosion could lead to capture of the main Whangaehu River channel . A northeastward course of the River would then lead to a new route within 300 m of Upper Waikato Stream. Hence the potential for riverbank erosion and overflow northwards could lead to future lahars being d i rected into the Tongariro River. 6.1 1 .1 Mitigation of hazards Three areas are identified where hazards of lahars in the Tongariro River can be mitigated. 1 42 ---------------- - --- - 1 ) Warning of lahars. Given adequate warning of a lahar, areas at risk can be evacuated and loss of l ife min im ised. Currently there is no lahar warning device i nstal led on the Tongariro River or any of its tributaries. Although monitoring of flow levels is carried out by ECNZ for managing the Tongariro Power Development, a purpose-bui lt lahar warning gauge would provide the best and most timely warning. 2 ) Containment of small lahars. Lahars of a certain volume could be potential ly retained behind the Rangipo Dam, particularly if the dam were emptied in preparation for such a lahar. The same strategy was advised and uti l ised in the Swift Reservoir to contai n a lahar from Mt. St. Helens in 1 980 (Crandell and Mul l ineaux, 1 978; Schuster, 1 98 1 ). Containment of a lahar in the Rangipo Dam would create problems for the power development but could potential ly reduce downstream impacts. However, if the lahar were larger than the dam capacity, the facility could be destroyed in attempting to contain it. 3) Planning of future expansion of Turangi . Parts of Turangi have expanded onto surfaces within the 1 in 2000 and 1 in 1 000 year lahar hazard zones across the River from the main area of town. In planning future housing expansion of the town, bui ld ing within the 1 in 1 0 000 year zone should be encouraged over areas of greater hazard . 6.12 Conclusions The greatest number and th ickness of lahar deposits in the exposed record of the Tongari ro catchment are from lahars occurring between 1 4.7 and 9.8 ka B .P. Consequently the preserved laharic surfaces of greatest area are also of this age. Deposits of Holocene lahars are confined to restricted surfaces, closer to the present river channel . These deposits are less wel l preserved than the older un its because they were probably confined to a more deeply incised channel than during late g lacial and early post-glacial times. The town of Turangi and many outlying houses are built on surfaces that are laharic in orig in . However, lahars have not inundated a large proportion of the town since c. 1 0 ka years B .P. Lower-lying parts of Turangi, closer to the Tongariro River and other outlying houses are bui lt on surfaces which have been inundated by much younger lahars . The area identified with the greatest human risk are the lowest-lying parts of Turangi , which were last inundated by a lahar less than 1 850 years B .P. M itigation of this risk cou ld be provided by a lahar warning system and careful planning of future u rban development in Turangi . The Mangatoetoenui Stream tributary is identified as the most important lahar conduit for the Tongariro catchment during the Holocene. l t has a lso been the only lahar condu it in this catchment in h istoric t imes. Consequently, infrastructure at greatest risk of damage from lahars includes the State Highway 1 bridge crossing Mangatoetoenu i Stream, the Rangipo Dam, the Rangipo Power Station that i t supplies, and the Poutu Canal intake structure. 1 43 6.1 3 Acknowledgements -- -- ? ----------?------?- - SJC grateful ly acknowledges funding from the New Zealand Vice-Chancel lor's Committee, Massey University Graduate Research Fund , the Helen E. Akers Scholarship Fund and the Tongariro Natural History Society. We thank J .A. Lecointre for his comments on an earl ier version of the manuscript. References Alien, G. F . , 1 902. Supplementary edition of Wil l is' guide book of new routes for tourists. Wil l is, Wanganui : 240 pp. Beverage, J .P . , Culbertson, J .K. , 1 964. Hyperconcentrations of suspended sediment. J . Hydraul . Div. , American Soc. of Civil Engineers, 90: 1 1 7-1 26. Clarke, C . , Smith , M . , 1 986. Turangi town centre, where to now? Taupo County Council Special Report, 1 5. Crandel l , D .R . , Mul l ineaux, D .R. , 1 978. Potential hazards from future eruptions of Mount St. Helens volcano, Washington. U.S.G.S. Bul l . , 1 383-C: 26 pp. Cronin , S.J . , Neal l , V .E . , in press. A late Quaternary stratigraphic framework for the northeastern Ruapehu and eastern Tongariro ring plains, New Zealand. N. Z. J. Geol. and Geophys . , 40. Cronin , S.J . , Neall , V.E . , Stewart, R .B . , Palmer, A.S. , 1 996. A multiple parameter approach to andesitic tephra correlation, Ruapehu volcano, New Zealand. J . Volcano!. and Geotherm. Res . , 72: 1 99-2 1 5. Cronin , S.J . , Neal l , V.E . , Lecointre, J.A. , Palmer, A.S. , in press(b). Changes in Whangaehu River lahar characteristics during the 1 995 eruption sequence, Ruapehu volcano, New Zealand. J. Volcano! . and Geotherm. Res. Cronin , S.J . , Neal l , V .E . , Palmer, A.S . , Stewart, R .B . , in press(a). Methods of identifying late Quaternary rhyolitic tephras on the ring plains of Ruapehu and Tongari ro volcanoes, New Zealand. N. Z. J . Geol. and Geophys, 40. Department of Statistics, 1 992. 1 991 Census of Population and Dwell ings, Waikato/Bay of Plenty Regional Report. Department of Statistics, Well ington, N .Z. Donoghue, S .L . , 1 991 . Late Quaternary volcanic stratigraphy of the south-eastern sector of Mount Ruapehu ring plain, New Zealand. Unpub. PhD thesis, Massey University, Palmerston North , New Zealand. Donoghue, S .L . , Neal l , V.E. , Palmer, A.S., 1 995. Stratigraphy and chronology of late Quaternary andesitic tephra deposits, Tongariro Volcanic Centre, New Zealand. J . Roy. Soc. of N. Z. , 25: 1 1 5-206. Froggatt, P .C . , Lowe, D.J . , 1 990. A review of late Quaternary si l icic and some other tephra formations from New Zealand: their stratigraphy, nomenclature, d istribution, volume, and age. N . Z. J. Geol . and Geophys, 33: 89-1 09. Gregg, D .R. , 1 960. The geology of Tongariro Subdivision. N .Z. Geol. Survey Bul l . , 40: 1 51 pp. 1 44 Grindley, G.W. , 1 960. Geological map of New Zealand, 1 st ed . , 1 : 250 000, Sheet 8, Taupo. Dept . of Scientific and I ndustrial Res . , Wel l ington. Hackett, W.R. , Houghton, B .F . , 1 989. A facies model for a Quaternary andesitic composite volcano: Ruapehu , New Zealand. Bul l . Volcano! . , 5 1 : 5 1 -68. Hodgson, K.A. , 1 993. Late Quaternary lahars from Mt. Ruapehu in the Whangaehu River val ley, North Island, New Zealand . Unpub. PhD thesis, Massey University, Palmerston North , New Zealand. Mathews, W.H . , 1 967. A contribution to the geology of the Mount Tongariro massif, North Island, New Zealand. N. Z. J. Geol. and Geophys. , 1 0: 1 027-1 038. Nairn , I . A. , Self, S., 1 978. Explosive eruptions and pyroclastic avalanches from Ngauruhoe in February 1 975. J . Volcano!. and Geotherm. Res . , 3: 39-60. Nairn , I .A . , Wood, C.P, Hewson C.A.Y. , 1 979. Phreatic eruptions of Ruapehu: April 1 975. N . Z. J. Geology and Geophys . , 22: 1 55-1 73. Palmer, B.A. , Purves, A.M . , Donoghue, S.L . , 1 993. Controls on the accumulation of a volcaniclastic fan , Ruapehu composite volcano, New Zealand. Bul l . Volcano! . , 55: 1 76-1 89. Phi l ippine I nstitute of Volcanology and Seismology, 1 992. Pinatubo: Lava dome growth; pyroclastic flow deposits spawn destructive lahars and secondary explosions. Bul l . Global Vole. Network 1 7(9): 8-1 0 . P ierson, T .C . , Costa, J .E . , 1 987. A rheologic classification of subaerial sediment-water flows. G .S.A. , Reviews in Engineering Geol . VI I : 1 -1 2. Pierson , T.C . , Janda, R.J . , Thouret, J .-C. , Borrero, C.A. , 1 990. Perturbation and melting of snow and ice by the 1 3 November 1 985 eruption of Nevado del Ruiz, Colombia, and consequent mobil isation, flow and deposition of lahars. J . Volcano!. and Geotherm. Res. , 4 1 : 1 7-66. P ierson , T.C . , Janda, R.J . , Umbal, J .V. , Daag, A.S . , 1 992. Immediate and long-term hazards from lahars and excess sedimentation in rivers draining Mt. Pinatubo, Phi l ippines. U .S.G.S . Water Resources Investigations Rep . , 92-4039: 1 82-203. Pierson, T.C . , Scott, K.M . , 1 985. Downstream di lution of a lahar: transition from debris flow to hyperconcentrated streamflow. Water Resources Res . , 2 1 : 1 51 1 - 1 524. Schuster, R.L . , 1 98 1 . Effects of the eruptions on civi l works and operations in the Pacific Northwest. In: Lipman, P.W. ; Mul l ineaux D.R. (Eds. ) The 1 980 eruptions of Mount St. Helens, Washington. U .S.G .S. Prof. Pap. 1 250: 701 -71 8. Smith , G .A. 1 986: Coarse-grained nonmarine volcaniclastic sediment: Terminology and deposition process. G.S.A. Bul l . , 97: 1 -1 0. Smith , G .A. , Fritz, W.J . , 1 989. Volcanic influences on terrestrial sed imentation. Geology 1 7: 375-376. Stilwel l , W.F . , Hopkins, H .J . , Appleton, W. , 1 954. Tangiwai rai lway disaster. Report of the Board of I nquiry. Government Printer, Well ington: 3 1 pp. Topping, W.W., 1 973. Tephrostratigraphy and chronology of late Quaternary eruptives from the Tongariro Volcanic Centre, New Zealand. N. Z. J. Geol. and Geophys . , 1 6 : 397-423. 1 45 Topping, W.W. , Kohn B .P . , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island, New Zealand. N. Z. J . Geol . and Geophys . , 1 6: 375-395. Voight, B. , 1 990. The 1 985 Nevado del Ruiz volcano catastrophe: anatomy and retrospection. J. Volcano!. and Geotherm. Res . , 44: 349-386. Water and Soils Division, M inistry of Works and Development, 1 979. N . Z. Land Resource I nventory Worksheets, N 1 02 Tokaanu and N 1 1 2 Ngauruhoe and Bay of Plenty - Volcanic Region Landuse Capability Extended Legend ( 1 2pp}. National Water and Soil Conservation Organisation, Ministry of Works and Development, Well ington, N .Z. Wilson, C.J .N . , Switzur, R.V. , Ward, A.P . , 1 988. A new 14C age for the Oruanui (Wairakei) eruption, New Zealand. Geol. Mag . , 1 25: 297-300. Wilson, C.J .N . , Houghton, B .F . , Lanphere, M .A. , Weaver, S .D . , 1 992. A new radiometric age estimate for the Rotoehu Ash from Mayor Island volcano, New Zealand. N. Z. J. Geol . and Geophys. , 35: 371 -374. Wilson, C.J .N . , 1 993. Stratigraphy, chronology, styles and dynamics of late Quaternary eruptions from Taupo Volcano, New Zealand. Phi l . Trans. Roy. Soc. of London A 343: 205-306. 1 46 CHAPTER 7: GEOLOGY AND LANDSCAPE DEVELOPMENT OF THE NORTHEASTERN TONGARIRO VOLCANIC CENTRE 7.1 I ntroduction In the three previous chapters, rhyolitic and andesitic tephrostratigraphy (developed in chapters 2 and 3) were used to establ ish a climate/soil development history and a h istory of lahars and landscape development by lahars in the study area. This chapter combines the results of the previous chapters and adds further information on other landscape and geological events on the ring plains to provide an overal l synthesis of their geology and development. This chapter comprises three parts: (7.2) a geological map of the northeastern Tongariro Volcanic Centre with accompanying notes, (7.3) a publ ished paper entitled "Geological history of the northeastern ring plain of Ruapehu volcano, New Zealand", and (7.4) a summary geological synthesis of the entire study area. The paper: Geological history of the northeastern ring plain of Ruapehu volcano, New Zealand by: Shane J . Cronin, V.E. Neall and A.S. Palmer, is published within Quaternary I nternational Vol . 34-36. The contributions of each author to the study were as fol lows. S. J . Cronin : Principal I nvestigator Carried out a l l : Field mapping, description and sampling Mineralogy analyses All other laboratory studies Preparation and writing of manuscript V. E. Neall and A. S. Palmer: Advisors Aided the study by: d iscussion of results and methodology editing and d iscussion of the manuscript 7.2 Surficial geologic map of the northeastern Tongariro Volcanic Centre The surficial geologic map of the northeastern Tongariro Volcanic Centre is presented in Fig . 7 . 1 . Figure 7.2 demonstrates the stratigraphy of the mapping units and their relationship to tephra marker beds and previously mapped formations in the surrounding area. 7.2.1 Methods The volcanic and volcaniclastic deposits and sediments with in the area were mapped using field sheets of 1 :25 000 scale. Field-section descriptions were supplemented with vertical aerial photographic interpretation to delineate surfaces. Stereo-pairs of 1 981 black and white vertical aerial photographs at 1 :25 000 scale were used . 1 47 MA P O F T H E S U RF I C I A L G EO LOGY O F A P O RT I O N O F T H E N O RT H EA S T E R N T O N G A R I RO VO LCA N I C C E N T R E Le g e n d Laharic surfaces < 1 . 85 ka. > 1 .85 ka > 5.3 ka > 9. 7 ka, Ruapehu > 1 2 ka, Tongari ro 1------'!....-i > 14 .7 ka, Ruapehu L...__ _.J > 14 .7 ka, Tongariro and Ruapehu Lavas 1-"--"-"---'--'--'i < 1 4.7 ka, Tongari ro > 1 4.7 ka, Ruapehu 1--::-:::----1 > 1 4.7 ka, Tongariro 1--='-----1 > 22.6 ka, Tongariro .____ _.J 39? 00' 600 m '-1 Tokaan Power Station Region not mapped Mangahouhounui Stream Moraines - > 1 0 ka moraines Composite surfaces > 1 4.7 ka Tongariro lahar surface, covered by < 1 .85 ka al luvium. > 14 .7 ka lahar surface veneering > 22.6 ka lava, Tongariro. > 1 4.7 ka Ruapehu lahar surface, reworked and partially covered by < 1 0 ka alluvium. Symbols 0 0 Covered by up to 30 m or Taupe i gnimbrite Major roads Minor roads Power development tunnels Topographic contours 1 00 m intervals State h ighways I Upper Waikato Stream I 900 m Rangipo Power Station Waipakihi River 0 1 2 3 4 5 km 39? 00' 1 5' Tephras Lahars La vas Moraines Ruapehu (Donoghue, 1 99 1 ) This study Tongariro This study This study (Fig. 7. 1 ) Age ka B.P. Onetapu Taupo Tephra Waimahia Tephra (Un' S) I 1 Hinemaiaia Tephra (Unit R) Hinemaiaia Tephra (Unit 1 1-=:::o Manutah? Motutere Tephra (Unit H) Motutere Tephra (Unit G) Poronui Tephra (Unit C Mangamate Tephra Karapiti Tephra (Unit Pahoka Tephra Pourahu Member Tangatu Formation Waiohau Tephra -----+-----+----- Rotorua Tephra I f Rotoaira Tephra ------+-----+-----1 Rerewhakaaitu Tephra Te Heuheu Formation Kawakawa Tephra I Fig. 7 . 1 (Grindley, 1 960) Fig. 7. 1 Ruapehu Tongariro I 0 Rangipo Lahars (Penultimate Glacial) Whakapapa Formation Mangawhero Formation l ? ? I =L 2 I 4 6 8 ?====?==?====??========? 1 0 Tongariro Andesite ?---=i- 1 2 1 4 1 6 1 8 20 22 24 Fig 7.2 Legend of geologic units mapped in Fig . 7 . 1 , showing their stratigraphic relationships to previously mapped formations and teph ra marker beds . The scale of the map presented in Fig. 7. 1 is 1 : 1 00 000. The base map was prepared by scanning and d igitising contours, rivers, roads and other features from NZMS 260 series topographic maps (1 :50 000 scale}, T1 9-Edition 2 (DOSLI , 1 994) and T20-Edition 1 (DOSLI , 1 982). The study area was mostly l imited to the ring plain and lower slopes of the Ruapehu and Tongari ro volcanoes but also included the lower Tongariro River val ley. Areas were del ineated and mapped according to their age (determined by cover-bed stratigraphy), their l ithology, and the volcano from which they were derived (Tongariro or Ruapehu}. 7.2.2 Laharic surfaces Seven laharic surfaces are mapped in the studied area. Each surface is del imited by the deposits of the youngest lahar preserved on it. The ages of these lahars are interpreted from tephra marker beds which under- and overlie them (Fig. 7.2). The stratigraphy of these surfaces was presented in Chapters 5 and 6. 7 .2.2A Ruapehu-derived lahar surfaces The youngest lahar surface (<1 .85 ka B.P . ) has been inundated by at least one lahar since the eruption of the Taupo Tephra . In Chapter 6 it was postulated that late Holocene lahars in the Tongariro catchment were derived from Ruapehu volcano. Thus lahar deposits forming this surface are correlated to the Onetapu Formation (after Donoghue, 1 991 ; Hodgson, 1 993). The > 1 .85 ka surface, if it were derived from the same source, is between Onetapu Formation and Manutahi Formation in age (Fig. 7.2) and comprises a newly recognised Ruapehu lahar surface. Ruapehu-sourced lahars mapped by Donoghue ( 1 991 ) as the Tangatu Formation, are here mapped as two separate surfaces. The youngest and smaller surface comprises a lahar deposit in the order of 5.2-5.3 ka (R1 , Chapter 5). This surface is preserved along the Mangatoetoenui Stream and a small remnant is preserved immediately south of Turangi . The other Tangatu Formation surface mapped here comprises multiple lahars which are > 9.7 ka in age. This surface occurs on the northeastern Ruapehu ring plain between the Te Piripiri and Ohinepango Streams and is also mapped over large areas from Turangi south to Rangipo. Large areas of Te Heuheu Formation occur on the northeastern Ruapehu ring plain between Te Piripiri and Upper Waikato Streams and are mapped as the > 1 4.7 ka (Ruapehu) surface. A portion of this surface has been eroded and reworked by the Holocene/recent activity of streams crossing the area and so is mapped as a composite surface. North of the Waihohonu Stream, throughout the area where the Tongariro River cuts through the Tongariro volcano ring plain, Te Heuheu Formation lahar deposits are also interbedded with contemporaneous lahar deposits derived from Tongari ro volcano. I n this area it is impossible to d ifferentiate the lahar deposits from the two volcanoes or a boundary between them. Consequently, this surface is mapped as containing lahars from both volcanoes, but is probably dominated by Tongariro-sourced lahars . 1 50 7.2.28 Tongariro-derived /ahar surfaces The lahars of the Tongariro ring plain were mapped by Grindley ( 1 960) as the Rangipo Lahars and were thought to be of Penultimate Glacial age. Here the eastern Tongariro ring plain is mapped mostly as Last Glacial-age lahar deposits with smaller areas of early post-g lacial lahars. The youngest lahar surfaces derived from Tongari ro volcano comprise lahar deposits which are > 1 2 ka in age (Fig. 7.2). These surfaces are mapped beside the upper portion of the Waihohonu Stream and along the Oturere and Makahikatoa Streams. These lahar deposits interdig itate with and are covered by Tangatu Formation lahar deposits (derived from Ruapehu volcano) in the lower Waihohonu Stream and along the Tongariro River. The remain ing eastern Tongariro ring plain mostly comprises surfaces composed of lahar deposits > 14.7 ka in age. This is mapped in two areas. The first area is mapped as a simple lahar surface comprising dominantly Tongariro volcano-derived lahar deposits > 14.7 ka in age. This surface is mapped on the Tongariro ring plain sector between the Mangamate Stream and Lake Rotoaira . This surface probably also includes subordinate lahar deposits derived from Ruapehu volcano, particularly in areas close to the Tongariro River. The second area (between the Waihohonu and Mangamate Streams) is mapped as a composite surface. This surface comprises lahar deposits > 14.7 ka in age which veneer Tongariro-sourced lava flows which are >22.6 ka B.P. in age. In the present stream valleys the lahar deposit cover can be up to tens of metres th ick, whi lst on some ridge tops and other isolated areas the lahar veneer is absent. The lahar deposits are mostly derived from Tongariro volcano, but probably a lso include lahar deposits derived from Ruapehu volcano, particularly at the southern part of the mapped area and near the Tongariro River. 7.2.3 Lavas Lava flows derived from both volcanoes were mapped on the ring plains and were dated by their tephra coverbeds. The petrology of some the lavas was also described in order to characterise them and to correlate exposures. 7 .2.3A Ruapehu-derived /a vas On the northeastern Ruapehu ring plain several lava flows are mapped . All of these flows have similar coverbed sequences and their oldest coverbed is the Rerewhakaaitu Tephra (Fig. 7.2) . These lava flows also have very similar lithologies. They all have a porphyritic? aphanitic texture and contain abundant g lomerocrysts . They are all two-pyroxene andesites, with a phenocryst assemblage dominated by large, lath-shaped plag ioclase crystals {Table 7. 1 ). Plagioclase phenocrysts d isplay strong osci l latory zoning. Orthopyroxene is the dominant ferromagnesian phenocryst with around twice the modal % of clinopyroxene. 1 5 1 Table 7.1 Minera logy and locations of lava sampled from the ring plains of northeastern Tongariro Volcanic Centre. Sample NZMS 260 Mapping Unit Phenoc!Yst modal % Location reference PL CPX OPX TM OL 93. 1 4 T20/4421 46 > 1 4.7 ka Ruapehu 60 1 7 1 8 5 - Flow north of Mangatoetoenui Stream 93. 1 65 T20/4481 59 " 46 1 9 35 <1 93.23 T20/4461 27 " 62 1 1 26 1 - Flow north of Te Piripiri Stream 93. 1 06 T20/4631 22 " 57 1 3 29 1 - Flow along Wharepu Stream 93. 1 07 T20/4351 30 " 53 1 5 32 <1 - Flow south of Te Piripiri Stream 95.5 T1 9/420243 < 1 4.7 ka Tongariro 32 24 30 1 0 3 Upper Oturere valley 95.8 T1 9/423339 " 40 1 7 37 6 - Flow Southwest of Lake Rotoaira 93. 1 9 T20/4641 74 > 22.6 ka Tongariro 53 1 8 26 3 - Flow in mid-Waihohonu Stream beside State Highway 1 93. 1 6 T20/4921 85 > 14.7 ka laharic surface veneering 62 1 9 1 9 <1 - Flow within lower Waihohonu Stream >22.6 ka lava, Tongariro 94.8 T20/5061 85 " 54 12 31 1 2 Within Tongariro River channel, downstream of Rangipo Dam 94.31 T20/4991 78 " 58 9 32 1 - At Rangipo Dam 94.33 T19/528227 " 50 13 35 2 - Tongariro River, downstream of Tree Trunk Gorge 94.36 T1 9/520221 " 34 16 49 1 - Tongariro River, upstream of Tree Trunk Gorge 94 .55 T1 9/506238 " 63 32 4 1 - Flow in lower Mangatawai Stream 94.75 T1 9/535246 " 41 10 44 1 4 Tongariro River, Pillars of Hercules 95. 1 6 T1 9/550331 " 44 19 33 1 3 Tongariro River, on Rangipo Prison Farm 95. 1 0 T1 9/448326 > 22.6 Tongariro 54 1 1 32 3 - South of Lake Rotoaira 95. 1 2 T19/466298 " 54 8 29 9 - North of Mangahouhounui Stream 94.80 T1 9/536376 Unmapped Pihanga flow <1 14 20 1 65 Tongariro River at Poutu Pool PI = Plagioclase, CPX = Clinopyroxene, OPX = Orthopyroxene, TM = Titanomagnetite, OL = Olivine. 1 52 Titanomagnetite occurs in association with pyroxene phenocrysts and with in glomerocrysts . Glomerocrysts are made up of 20 to 1 00+ crystals of al l four phenocryst phases. Two types of glomerocrysts were observed, those comprising few (20-30) large crysta ls, and others comprising larger numbers of smaller crystals which were dominantly plagioclase. The groundmass is dominated by (80-95% by volume) small laths of plagioclase with minor orthopyroxene and cl inopyroxene crystals. Based on their mineralogy, these lavas appear to belong to the Type 1 class (plagioclase-pyroxene phyric lavas) of Graham and Hackett ( 1 987) . The minimum age of these lavas (determined from their oldest coverbed, Fig. 7.2) indicate that these flows correlate to the Mangawhero Formation of Hackett ( 1 985). 7.2.38 Tongariro-derived lavas The Tongariro massif was previously mapped as a single unit, Tongariro Andesite, which spanned the Quaternary in age (Grind ley, 1 960). I n this study, three Tongariro-derived lava surfaces are mapped in addition to a composite surface comprising lavas and lahar deposits. The oldest lava surfaces are those overlain by the Kawakawa Tephra, indicating a minimum age of 22.6 ka B.P . The lava flow beside the Waihohonu Stream has the Okaia Tephra below it, providing an age bracket of 22.6 - c. 23 ka (Section 5 . 1 0). The other lava surface mapped with the same minimum age (northeastern Tongariro volcano) has K-Ar ages ranging between 1 05 and 1 30 ka for samples taken higher on the cone (Hobden et al. , 1 996). If one believes the radiometric ages, then this indicates that the northeastern Tongariro lava surface has an unconformable coverbed sequence. Samples from both areas have a very similar mineralogy to one another and to the Ruapehu lavas described in the last section (Table 7. 1 ) . However, these samples have a finer-grained, plagioclase-dominated groundmass, and glomerocrysts comprising fewer crystals ( 1 0-20) than the Ruapehu flows described above. These lavas also fit with in the Type 1 classification of Graham and Hackett ( 1 987). Lavas comprising the surface which is mapped as the composite of > 1 4.7 ka lahars veneering >22.6 ka lava, also derive their minimum age from being overlain by the Kawakawa Tephra. However, given that this sector of the Tongariro cone is K-Ar dated at between 65 and 1 30 ka (Hobden et al. , 1 996) these lavas are probably of similar or greater age. Samples from some of these flows have a pyroxene-dominant mineralogy rather than plagioclase-dominant. Three of the samples also contain a small percentage of large ol ivine phenocrysts . All samples have a very fine-grained groundmass comprised of laths of plagioclase and interstitial brown glass. These mineralogical features indicate that some of these lavas were more basic than those described above. These lavas include both Type 1 (plagioclase-pyroxene phyric lavas) and Type 3 (pyroxene-phyric lavas) classifications of Graham and Hackett ( 1 987) for Tongari ro Volcanic Centre lavas. The > 1 4.7 ka {Tongariro) lavas mapped are overlain by the Rerewhakaaitu Tephra, indicating their minimum age (Fig. 7.2) . However, samples from these flows 1 53 higher on the cone give K-Ar ages of 65- 130 ka (Hobden et al. , 1 996), indicating the coverbed sequences are potentially unconformable. No samples of these lavas were collected. The disparity between the K-Ar ages of Hobden et al. ( 1 996) and the coverbed sequences on the Tongariro lava surfaces, implies that these surfaces were exposed to intense physical weathering during the last stadia! of the Last Glacial . Two lava flows are mapped as < 14.7 ka. The flow southwest of Lake Rotoaira is immediately overlain by the Waiohau Tephra but the .Rerewhakaaitu Tephra (present on the adjacent lava surface) does not occur. This provides an age range for this lava flow of between 1 4.7-1 1 .9 ka B .P. The other flow mapped as < 1 4.7 ka occurs within the Oturere Valley. No coverbeds were found overlying this lava flow, which may indicate it is very young. Both of these two flows have a Type 3, pyroxene-dominant minera logy, and the Oturere flow also contains olivine (Table 7.1 ). 7.2.4 Moraines Parts of two sets of paired moraines were mapped in the study area based on their morphology. The moraines beside the Waihohonu Stream have been previously described by Mathews ( 1 967) and those flanking the Mangatoetoenui Stream by McArthur and Shepherd ( 1 990). Mathews (1 967) estimated that the Waihohonu moraines were around 1 5 ka in age by comparison to the youngest moraines in the South Island. McArthur and Shepherd ( 1 990) considered the Mangatoetoenui moraines to have been formed in multiple glacier advances and represented the last two stadials of the Last Glaciation. I n this study, tephra coverbeds on these two sets of moraines provide minimum ages for their stabil isation and the cessation of their construction (Fig. 7.2). The Waiohau Tephra occurs on the Waihohonu moraines provid ing a minimum age of stabil isation of 1 1 .9 ka B.P. The oldest tephra on the Mangatoetoenui moraines is the Pourahu Member of the Bullet Formation indicating a minimum age of ea. 1 0 ka. 7.3 GEOLOGICAL HISTORY OF THE NORTH-EASTERN RING PLAIN OF RUAPEHU VOLCANO, NEW ZEALAND Shane J . Cronin , Vincent E. Neall and Alan S. Palmer Department of Soil Science, Massey University, Private Bag 11 222, Palmerston North, New Zealand 1 996, Quaternary International 34-36: 21 -28. Abstract Continuous exposures along the Upper Waikato Stream provide new insights into the north-eastern ring plain of Ruapehu volcano, extending the known stratigraphy beyond 22.5 ka. Time control in the sequence is provided by five rhyolitic tephra units, erupted from central North Island volcanoes, comprising Kawakawa, Okaia, 1 54 Omataroa, Hauparu , and Rotoehu tephras. The sequence is dominated volumetrica l ly by diamictons and fluvial deposits resulting both from volcanic events and periods of instabi l ity on the flanks of Ruapehu . With in the sequence are >60 individual andesitic lapi l l i units , derived primarily from Ruapehu volcano via mostly sub-plinian eruption mechanisms. An average eruption rate of more than one lapi l l i eruption per 1 000 years is estimated for the c. 60 ka record . The style of deposition on the ring plain changes over time and appears to reflect climate change over the Last Glacial period. In periods of severe climatic conditions during marine &180 stage 4 (Porewan stadial) , and the Last Glacial Maximum of marine &180 stage 2 (Ohakean), the north-eastern ring plain aggraded rapidly with deposition of thick continuous diamicton sequences. The other recognised cool period in the southern North Island , the stadial of late &180 stage 3 (Ratan} , did not appear to induce major aggradation on the north-eastern ring plain . During periods of mi ld climate with in the Last Glacial , deposition on the north-eastern ring plain was dominated by fa l l accession of either tephra , or material reworked from other parts of the ring plain by aeol ian processes. 7 .3.1 Introduction Ruapehu volcano is an active andesitic composite volcano located at the southern end of the Taupe Volcanic Zone (TVZ) in the central North Island of New Zealand. Previous studies of the geological history of this volcano have mainly been confined to the present volcanic cone (e.g. Gregg, 1 960; Hackett and Houghton, 1 989), or to the younger (<22.5 ka) stratigraphy preserved on the ring plain, where a more complete record of events at the volcano are recorded , both spatially and temporally (e.g. Pal mer, 1 991 ; Donoghue et al. , 1 995). This paper presents a summary of the stratigraphy preserved in the north-eastern sector of the Ruapehu ring plain and describes events occurring on the volcano and this sector of the ring plain for the period 22.5 ka to c. 80 ka. 7.3.2 Geologic setting The Tongariro Volcanic Centre (TgVC) at the southern terminus of TVZ is composed of five composite andesitic volcanoes, as well as a number of outlying smaller vents. Ruapehu volcano is the largest in the TgVC and at 2797 m is the highest peak in the North Island. Tongariro volcano is also a large massif which lies to the north of Ruapehu. Both volcanoes have been historically active. The current Ruapehu massif comprises a volume of 1 1 0 km3 (Hackett and Houghton, 1 989) with a surrounding volcaniclastic ring plain of similar volume. Ruapehu is directly underlain by Tertiary marine sediments with Mesozoic metamorphosed greywacke (schist) occurring at greater depths. The Ruapehu ring plain deposits extend down drainage channels into Tertiary hi l l country to the south and west, interfinger with the Tongariro ring plain to the north, and are confined in the east by the Kaimanawa Mountains. 1 55 7 .3.3 Site of study The Upper Waikato Stream drains the north-eastern flanks of Ruapehu volcano and is immediately north of the watershed boundary where the present drainage from the eastern flanks of Ruapehu divides between the Whangaehu River to the south and the Tongariro River system to the north (Fig. 7.3) . Between State Highway 1 and the Tongariro River, Upper Waikato Stream has cut deeply through the ring plain deposits of Ruapehu volcano, exposing in near continuous sections a record of deposition spanning an estimated 80 000 years. 7.3.4 Stratigraphy The stratigraphy of the deposits in the age range of 22.5 ka to the present has been described by Topping ( 1 973) and Donoghue ( 1 995). Beyond 22.5 ka there is very little published information on the Ruapehu and Tongariro ring plains. Topping ( 1 973) describes these older deposits as the Rangipo lahars on the Tongariro ring plain, and the Waimarino lahars on the Ruapehu ring plain. This study focuses on the deposits older than the regional marker horizon of the Kawakawa Tephra , dated at 22 590 ? 230 years BP (Wilson et al., 1 988). The composite stratigraphic sequence preserved in Upper Waikato Stream cuttings beneath the Kawakawa Tephra is shown in Fig. 7.4. 7.3.4A Age Time control is provided by the presence of five d istal rhyolitic tephra layers interbedded with sediments in the depositional sequence. These are identified here as the Taupo sourced Kawakawa and Okaia Tephras, and the Okataina Volcano-sourced Omataroa Tephra, Hauparu Tephra, and Rotoehu Ash (Howorth , 1 975; Froggatt and Lowe, 1 990). The ages of these units are given in Table 7.2, and their stratigraphic position in Fig. 7.4. Table 7.2 Rhyolitic tephra identified with in the northeastern ring Ruapehu. Tephra name Source * Age (B.P.) Reference for age Kawakawa Tephra TVC 22 590 ? 230t Wilson et al. (1 988) Okaia Tephra TVC ea. 23 000* Froggatt and Lowe (1 990) Omataroa Tephra ovc 28 220 ? 630t Hauparu Tephra ovc 35 870 ? 1 270t Rotoehu Ash ovc 64 000 ? 4000? Wilson et al. ( 1 992) ? TVC - Taupo Volcanic Centre; OVC = Okataina Volcanic Centre. t Denotes 14C ages on old half l ife basis. * Estimated stratigraphic age. s Whole rock K-Ar age. plain sequence, The Kawakawa Tephra occurs in this area as a 0.2 to 0.5 m deposit. Abundant accretionary lapil l i are contained within the fall layers of the deposit, characteristic of this 1 56 tephra (Self and Healy, 1 987). The older four tephras do not occur as visible layers in the sequence. They were identified as thin zones of rhyolitic glass enrichment with in fine? grained andesitic ash. The identification of these microscopic tephra layers was elucidated using a combination of major element glass chemistry, ferromagnesian mineralogy, and stratigraphy. The major element chemistry was determined for polished individual grains on a JEOL-733 electron microprobe following the procedures and analytical conditions of Froggatt and Gosson ( 1 982), and Froggatt ( 1 983). A 20 f.lm beam diameter was used when possible, otherwise a 1 0 f.lm beam was used with a beam current of 8 nA at an accelerating voltage of 1 5 kV. Between 1 0 and 20 individual glass shards were analysed for each tephra layer. The glass chemistry was compared with published g lass analyses carried out under the same analytical conditions (Froggatt, 1 983; Froggatt and Rogers, 1 990; Pi l lans and Wright, 1 992; Stokes et al. , 1 992; and Pil lans et al. , 1 993). Similarity coefficients, and coefficients of variation (Borchardt et al. , 1 971 ) were calculated to compare the unknown samples with large volume tephra units in the general time frame. The glass chemistry provided good matches with stratigraphical ly consistent correlations. The presence of cummingtonite with in the layer identified as Rotoehu Ash gave further evidence of its identification based on glass chemistry (Froggatt and Lowe, 1 990). The time planes provided by the rhyolitic tephra horizons enable a reconstruction of the events bui lding up the north-eastern sector of Ruapehu ring plain. Near the base of the sequence a lign ite deposit is exposed. Given the time control provided by the rhyolitic tephras above, this l ignite may be equivalent in age to one of two other l ign ite deposits found adjacent to this area. McGione and Topping (1 983) describe two l ignite deposits each representing warm periods during marine 8180 stage 5a and 5c. Further palynology work wil l confirm whether the l ign ite deposit can be correlated to one of these warm periods at approximately 80 ka and 1 OOka respectively (See Section 7 .3 .9). 7.3.48 Sequence The stratigraphic column is d ivided into three parts (Fig . 7.4), each representing periods of d ifferent types of deposition on the north-eastern sector of the ring plain. The oldest part of the sequence (column C in Fig . 7.4) contains a cemented diamicton unit at the base. This unit forms the val ley floor and its base is not seen. Overlying this basal d iamicton is a deposit of dark brown and black, fibrous, firm, and centimetre to decimetre? scale laminar-bedded lignite. Interbedded with in this l ignite, as wel l as immediately above and below, are hornblende-rich andesitic, lapi l l i and ash layers. These tephra layers vary in th ickness from centimetres to tens of centimetres and are not exposed in many other localities; hence their d istribution is poorly known . I nterbedded within the l ignite, as wel l as above i t , are centimetre-scale finely-bedded fluvial sands. Above the l ignite deposit the remainder of column C is composed of stacked grey metre-th ick diamictons as well as bedded sands, si lts, and gravels. 1 57 1 75? 45' Mt Tongariro .A ) Mt Ng?ho? 1 500 m 39? 1 0 I ? = Section locations 0 5 km - State Highways Figure 7.3 Location of Tongariro Volcanic Centre including Mts. Tongari ro, Ngauruhoe and Ruapehu, and the streams dissecting the eastern Ruapehu and Tongariro ring plains. Upper Waikato Stream section locations marked by dots. 1 58 ....... 01 CD A B C (m ) (m ) (m ) Okaia Tephra Kawakawa Tephra / - Omataroa Tephra ?{Jl 1 ? grey andes itic tuft 1 0? . . . . . . . . . . . . . . . . 1 5 . . . . ? ? ? ? ? ? ? ? I I I -- ?., ? ?i:?????d P:.? ) ... . I 30 1 .Roto7 Ash 20-n '? ;>,.t' ? ?r....1 Cemented d iamicton 3 Lign ite 0 1 2 3 4 5 Section Key D - A D 0 - B 0 - c 0 ,____ - Lignite ? Sandy matrix debris flow deposits N,....,.,.,"<;,...,..?,??? ??"""{l Hyperconcentrated streamflow deposits ? Silty matrix debris flow deposits i Fine andesitic ash Andesitic lapill i layers Strongest paleosol development ?'""? ?'""'> :...,.- : ?"'""':- :'""- "1 Bedded sands, silts and gravels Figure 7.4 Composite stratigraph ic columns of the northeastern Ruapehu r ing p la in sequence below the regional marker horizon of the Kawakawa Tephra. These deposits are unconsolidated and there is no evidence for significant pause between the emplacement of each unit. The mechanisms of emplacement range from stream flow through hyperconcentrated flow and debris flow. There are a few andesitic lapi l l i layers interbedded near the top of this part of the sequence. Above the stacked diamictons in column C the nature of the deposits, and hence the style of deposition changes markedly. Column B shows that deposits on this sector of the ring plain now consist dominantly of andesitic pumice lapi l l i and fine ash. The occasional diamicton unit sti l l occurs but these appear to be separated by sign ificant th icknesses of lapi l l i and fine ash . The cemented diamicton in the central part of column B contains up to 50% by volume pumice clasts and a pumice lapi l l i layer occurs between two of the flow units of this deposit. At the base of column B the sequence consists of many andesitic pumice lapil l i layers stacked on top of one another with very l ittle fine ash between each layer. Further up the column there are greater thicknesses of fine ash material between each pumice lapil l i unit. The ash is brown to yellowish brown in colour, loam to clay loam in texture, very firm in consistence, and has a coarse blocky soil structure when dry. Root rhizomorphs are present throughout the ash and these occur in the greatest concentration where the ash is darker in colour and has more evidence of soil structure and soil development (indicated on column B as the zones of strong weathering) . The grey andesitic tuff unit (F ig . 7 .4) is firmly cemented, shower-bedded and contains accretionary lapi l l i . This unit is a locally important marker horizon. Column A shows the upper portion of the sequence, the nature of deposition inferred to have again changed . At this time deposition on this part of the ring plain consisted of stacked diamictons of debris, hyperconcentrated, and stream flow origin. There appears to have been l ittle or no time between depositional events. Thick (0.5 m) andesitic lapi l l i un its are interbedded between and within the diamictons and fluvial deposits (column A, Fig. 7.4). Above the Kawakawa Tephra, fluvial aggradation deposits of the Hinuera Formation are described by Topping and Kohn ( 1 973) in the Ruapehu and Tongariro area. 7.3.5 Lithology 7 .3.5A Diamictons Volumetrical ly this sequence is dominated by diamicton deposits. These vary considerably in their nature and inferred style of deposition. At one end of the depositional series are bedded si lts , sands, and gravels. These are well sorted within individual layers but are poorly sorted as a whole, with layers of d iffering grain size bedded on top of one another. These deposits reflect a stream flow orig in where turbulent, d i lute (Newtonian) flow mechanisms transport the sediment (Smith , 1 986; Pierson and Costa, 1 987). At the other end of the scale are debris flow deposits which are poorly sorted and display no bedding. Often these deposits contain very large clasts with in a fine sand matrix. These deposits have been transported and deposited by a much more concentrated (plastic or non-Newtonian) flow mechanism. Laminar flow 1 60 occurs under these conditions and sediment is supported and transported by a strong matrix (Smith , 1 986; Pierson and Costa, 1 987). Between these two extremes of deposit are a wide range of deposits intermediate in character. These deposits show varying amounts of planar bedding and varying degrees of sorting, with generally a finer grain size than debris flows. These units are termed hyperconcentrated flow deposits and are considered to have been deposited via an intermediate concentration (but stil l plastic and non-Newtonian) flow mechanism. Turbulence and matrix strength both play a role in transporting and depositing sediment in these flows (Smith, 1 986; Pierson and Costa, 1 987). There exists a wide range of deposits transitional in character between these three types. Table 7 .3 outlines the characteristic features of the surface flow sediments within the northeastern ring plain sequence, and relates the observed (purely descriptive) types of deposits with their features and inferred flow mechanisms. Table 7.3 Surface-flow sediment lithotypes within the northeastern Ruapehu ring plain area, with their characteristic properties and inferred mode of deposition. Sediment type Cemented d iamictons Sandy matrix diamictons Silty matrix diamictons Bedded silts and sands, and gravels Observed features - firmly cemented - sand matrix - matrix- and clast-supported - pumice lapil l i rich (up to 50% by vol .) - maximum clast diameter 1 -3 m - composed of several flow units - massive and planar fabric preserved - unconsolidated - fine-coarse sand matrix - matrix- and clast-supported - pumice lapil l i poor, dominated by lithic clasts - maximum clast diameter 1 m - massive and planar fabric preserved - unconsolidated - greasy, allophane rich, silt loam matrix - matrix-supported - maximum clast diameter 2 m - can contain hydrothermally altered clasts - unconsolidated, dominantly clast-supported - planar laminated and low angle cross-bedded - pumice and lithic rich zones - highly variable grainsize, silt, sand, and pebbles in well sorted layers and lenses - maximum clast diameter 0.2m 7.3.58 Andesitic Tephra Inferred flow type (Smith, 1 986) Debris flow and hyperconcentrated flow Debris flow, hyperconcentrated flow, and transitional to stream flow Debris flow Stream flow and transitional to hyperconcentrated flow Andesitic tephra deposits are common throughout the entire sequence. More than 60 ind ividual lapi l l i-grade units are described in the sequence, and thick deposits of fine ash occur in parts of it. The andesitic lapil l i un its are dominantly pumice that is highly vesicular with very fine vesicles, intermixed with <1 0% wall-rock lithic lapi l l i . The lapil l i layers are generally thickest immediately to the east of Ruapehu volcano, which is consistent with the prevai l ing westerly wind direction. Close to source there is no 1 61 evidence of these tephra layers and their preservation on the ring plain is patchy, thus the best way to describe their original distribution and volume is by comparison to better studied younger tephra layers of the Bullot Formation (Donoghue et a/. , 1 995). Several analogous layers can be found which give an idea of the approximate d imensions of these eruptives. The lapil l i layers would appear to be mostly of a sub-pl inian orig in , although pl in ian eruptives cannot be ruled out as the dispersion of the deposits is not well known . The tephra contain phenocrysts of plagioclase + orthopyroxene + clinopyroxene > titanomagnetite ? olivine ? hornblende. This assemblage accounts for 90% of the andesitic un its in the sequence. Hornblende and olivine occur only in small quantities (<2% by volume) in most of the units. Two other ferromagnesian mineral assemblages are observed in the andesitic tephra which can be characterised as, hornblende-dominant or ol ivine-dominant assemblages: Ol ivine > Orthopyroxene + Clinopyroxene > Titanomagnetite Hornblende > Orthopyroxene + Clinopyroxene > Titanomagnetite These assemblages are restricted in their occurrence with in the sequence. Two tephra layers at 1 2 m depth in the sequence (Column A, Fig. 7.4) have an ol ivine-dominated ferromagnesian assemblage, whi le two tephra layers at the very base of the sequence with in l ign ite (Column C, Fig 7.4) contain a hornblende dominated assemblage. Andesitic lapil l i falls occur throughout the sequence, and the rate of eruption is > one sub-pl inian lapi l l i eruption per 1 000 years for a period of approximately 60 000 years. Thick deposits of fine andesitic ash also occur in parts of the sequence and these are thought to represent the slow accumulation of fine ash directly from many eruptions as well as wind-blown fine ash reworked from other parts of the ring plain . 7.3.6 Interpretation of geological history The relationship between the interpreted geological h istory of the north-eastern ring plain , the 8180 record of deep sea cores, and the record of loess deposition and paleosol development of the southern North Island is summarised in Fig. 7.5. The l ignite in the lower part of the sequence is thought to represent deposition during marine 8180 stage 5a, the Otamangakau interstadial period of McGione and Topping ( 1 983) around 80 ka (See Section 7.3 .9). The organic materials accumulated slowly in a bog with occasional deposition of fluvial fine sands, and hornblende-rich tephra fal ls. The source of these hornblende-rich tephras could be either Tongariro or Ruapehu volcano, both of which were potentia l ly active at the time. No hornblende-rich tephras have yet been described from Ruapehu whereas younger Tongariro-sourced tephras occasionally contain appreciable hornblende (Lowe, 1 988; Donoghue et al. , 1 991 ; Donoghue et a/. , 1 995). This suggests that Tongariro Volcano is the most l ikely source for these tephras. The stacked diamictons and bedded si lts , sands and gravels above the l ignite represent a period of rapid aggradation on the north-eastern sector of the ring plain. 1 62 Aggradation without significant pause would imply that the slopes of Ruapehu were unstable, with much loose rock material available for transport and deposition to the north-east by lahars and stream flow. There are few interbedded lapil l i units within these sediments and also little primary pumice within the sediments themselves. This indicates that these aggradation deposits are not l ikely to be the result of large scale eruptive events on Ruapehu volcano. This does not rule out the role of small scale eruptive events which are not recorded in the stratigraphic record as tephra deposits, but which have the potential to produce lahar and flood depositional events. A good example of this were the lahars produced during the eruptions of Ruapehu in 1 975 (Nairn et al., 1 979), an eruption which was not accompanied by a tephra unit preserved on the ring plain. Small scale eruptives could potentially have produced the stack of diamictons and bedded deposits described here, but it is here considered that other environmental factors a lso played a major part. Aggradation was taking place prior to the eruption of the Rotoehu Ash at ca.64 ka (Wilson et al. , 1 992) and occurred during marine 8180 stage 4 (Porewan stadial) . The cooler climate of this period possibly accelerated physical weathering processes on Ruapehu, thus providing abundant material for redeposition on the north-eastern ring plain. The mechanism of this redeposition may have been small scale eruptives or simply slope fai lures and floods during storm events. The presence of a greater area of snow and ice on the higher slopes of the volcano in the cooler climate of 818 isotope stage 4 may have also provided a ready water supply for producing lahars and floods in small scale eruptions, such as was observed in the 1 985 eruption of Nevado del Ruiz (Pierson et al. , 1 990). Above the stacked diamictons, the deposits on this sector of the ring plain consist dominantly of andesitic pumice lapi l l i and fine ash beds. Occasional diamicton units occur but appear to be separated by sign ificant periods of time and hence do not suggest major instabil ity on the volcano. Deposition of the pumice-rich cemented diamicton unit (in the central part of column 8, Fig. 7.4), which contains an andesitic pumice lapi l l i layer between flow units, probably was initiated by a large tephra-producing eruption on Ruapehu volcano. At the base of the sequence represented by column B, the eruption rate of pumice lapi l l i falls on this sector of the ring plain appear to have been very high because there is l ittle, or no fine ash between each lapil l i layer and the lapil l i units are often very thick and stacked on top of one another. Such a high eruption rate occurred in late marine 8180 stage 4, corresponding to the period encompassed by the previously-named middle Tongariro Subgroup tephras (Leamy et al. , 1 973; Milne and Smalley, 1 979) which are mapped as occurring on top of the Porewa loess in the Rangitikei region to the south of Mt Ruapehu . Distal andesitic ash is also mapped on top of a correlative of the Porewa loess in the Hawkes Bay region to the east of Mt. Ruapehu (A.P. Hammond, pers. comm., 1 994 ). Thus the lapi l l i layers found on the north-eastern ring plain are probably proximal correlatives of the middle Tongariro Subgroup tephras. 1 63 ...... 0> ? Age 0 Isotope (ka) stages 20 2 30 40 3 50 60 70 4 80 5a Rhyolitic tephras Hauparu NE Ruapehu ring plain - - - - - -+--? Soil development and tephra accession Tephra accession Soil development and tephra accession Rangitikei Wanganui Oh 11 1 1 1 1 1 1 1 1 Rt L1 I - - - - - - - - - - - - - 1 1 l l l ?i ; l l Whanahuia Paleosol Kimbolton Paleosol L2 Taranaki Sy1 l l ' s'r2 1 1 1 1 1 1 1 Sy2 Rotoehu - - - - - - - - 1 ' ' ' ' ' ' ' '? _ _ _ _ _ _ _ Middle Tongariro _ _ _ _ _ _ I''''''''' I 1 1 1 1 r1 1 1 1 1 1 1 1 1 fr? ? 1 1 --- - - - - - - - - - - - Wttttm Subgroup Fluvial and lahar aggradation Peat accumulation Po Tapuae Paleosol L3 1 1 1 1 1 lillt Sy3 1 1 1 1 1 Sr4 lLwl Figure 7.5 Comparison of the northeastern Ruapehu ring-plain landscape events with deep sea 0 isotope record (Shakleton et al. , 1 990), rhyolitic tephra marker beds (Froggatt and Lowe, 1990), and southern North Island loess stratigraphy from the Rangitikei valley (Leamy et al. , 1 973; Milne and Smalley, 1 979), Wanganui (Pi l lans, 1 988; 1 994), and Taranaki (AIIoway et al. , 1 988). Oh = Ohakea loess, Rt = Rata loess and Po = Porewa loess, L 1 = loess 1 , S2 = buried soil 2 etc. Sy1 = loess 1 correlative, Sr2 = buried soil 2 correaltive etc. Above these stacked pumice lapi l l i beds, the eruption rate of lapi l l i grade units appears to have slowed , indicated by greater thicknesses of fine ash between each lapi l l i unit. This may indicate that the dispersal axes of eruptives changed at this time or there was a reduction in magnitude or frequency of eruptive events. Given that the sites studied are d irectly down wind of the volcano under the prevail ing westerly winds, it is unl ikely that eruptives were deposited in different directions for the extended periods of time represented by this sequence. Therefore it is more l ikely that there was a reduction in the magnitude and/or the ? frequency of eruptive events at this time. Coupled with this apparent slowing of eruption rate or reduction in magnitude of the eruptive events, the degree of weathering and paleosol development within the fine ash increases, as the soil surface was accreting more slowly. The strongly weathered zone extends to just above the level of the Rotoehu Ash . This paleosol appears to have formed at the same time as the paleosol developed in the Porewa loess throughout the southern North Island (Leamy et al. , 1 973; Milne and Smalley, 1 979; Palmer, 1 985; Pillans, 1 988) during early marine 8160 stage 3. During the subsequent stadial period in mid-marine 8160 stage 3 (Ratan) there is no expression of major aggradation on the north-eastern ring plain . The diamicton bracketed by the Hauparu and Omataroa tephras contains andesitic lapil l i and appears to have been generated by eruptive rather than climatic processes, in contrast to the earlier diamictons. Deposition continued with accretion of fine ash and pumice lapil l i beds. The weathering and soil development with in fine ash deposited in this period is, however, very weak. This ind icates that, either the eruption or accumulation rate was too high to allow soil development, or soil development was affected by cooler climate conditions during this period . The fine ash nature of the deposits and the thickness of ash between dated rhyolitic tephra layers would suggest a relatively slow deposition rate, indicating soil development was probably slowed by cool climate conditions. The absence of appreciable aggradation deposits on the north-eastern sector of the ring plain at this time may indicate that the climate during the mid-marine 8160 stage 3 stad ial was not as severe as during the marine 8160 stage 4 stadial . This is supported by pollen evidence from the area. McGione and Topping (1 983) and McGione ( 1 985) proposed a "cool interstadial" climate in the Ruapehu area during the time of the deposition of the Rata loess rather than a ful l stadia! period. I n Taranaki, andic deposits record peaks of aerosolic quartz accumulation indicative of cool climate in marine 8160 stages 2 and 4, but negligible amounts in stage 3 {AIIoway et al., 1 992). This also indicates the climate was not as severe in marine 8160 stage 3 in comparison with that of stages 2 and 4. Above the grey tuff unit in column B, the fine ash exhibits much stronger weathering. Root rhizomorphs become abundant and finely-d isseminated charcoal layers are present. Near the top of this strongly weathered zone is the Omataroa Tephra , dated at 28 220 ? 630 BP (Froggatt and Lowe, 1 990). This paleosol development correlates with the paleosol in the Rata loess in the southern North Island (Leamy et al. , 1 973; Milne and Smalley, 1 979; Palmer, 1 985; Pi l lans, 1 988), developed during late marine 8160 stage 1 65 3. The fine ash in this part of the sequence is not interbedded with any lapil l i layers and appears to have accumulated slowly, thus enhancing the paleosol and weathering features. Weathering features become less pronounced above the Omataroa Tephra , potentially ind icating deteriorating climate with the onset of 8180 stage 2 (Last Glacial Maximum; Pil lans et al., 1 993). Above the Okaia Tephra, rapid aggradation of diamictons began on the north? eastern ring plain, again indicating instability on the slopes of Ruapehu volcano. These deposits accumulated during marine 8180 stage 2. Throughout the aggradation sequence, represented by column A, andesitic lapi l l i continued to be erupted , indicating Ruapehu was active throughout the early part of the Last Glacial Maximum. 7.3.7 Discussion and Conclusions The north-eastern Ruapehu ring plain sequence not only reflects the volcanic history of Ruapehu volcano but also indicates the response of the volcano-ring plain system to g lobal climate oscil lations. Periods of severe-cold climate during the Last Glacial have caused large scale aggradation on the ring plain, with more frequent occurrences of lahars and deposition dominated by surface flow mechanisms. These processes appear to attain their maximum volume and frequency during marine 8180 stages 2 and 4 (Fig. 7.5) . The climate during mid-marine 8180 stage 3 may not have been so severe, because no widespread aggradation is noted in the deposits of this age on the north-eastern ring plain . The climate-related aggradation may be driven by i ncreased physical weathering on the higher slopes of Ruapehu volcano. The aggradation deposits to some degree mask the purely eruptive or volcanic? triggered events recorded on the ring plain. Only deposits from the very large tephra eruptions are preserved in this environment; the smaller tephra units and fine ash deposits are mostly reworked by the wind or entrained in successive lahars and stream flow deposits. In the milder periods on the north-eastern ring plain, deposition reflects the eruptive and volcanic-triggered events occurring on Ruapehu volcano. Deposition is dominated by fall processes, primary fall ash and lapi l l i deposition and aeolian redistribution of fine ash on the ring plain. Diamicton deposits are sti l l present in this sector but the time between each lahar event is much greater than during 8180 stages 2 and 4 . 7 .3.8 Acknowledgements This work forms part of the Ph .D . research of one of the authors (SJC). The authors grateful ly acknowledge funding from the New Zealand Vice-Chancellors' Committee, Massey University Graduate Research Fund , the Helen E. Akers Scholarship Fund, and 1 66 the Department of Soil Science of Massey University. Thanks are a lso due to B.V. Alloway, W.R. Hackett, and B .F . Houghton for their thoughtful and insightful reviews, which greatly improved the manuscript. 7.3.9 Subsequent comments on the paper A recent analysis of the palynoflora within the l ignite deposit at the base of the Upper Waikato Stream sequence has led to a slight modification of its estimated age. The l ignite contains a palynoflora composed of shrub and grassland species, indicative of a cool and stormy climate (McGione, pers. comm. , 1 995). Thus its correlation to &180 stage 5a in the paper (a relatively warm period) is not supported . I nstead it is now considered (see Chapter 5) that the l ignite was deposited immediately after &180 stage 5a, with in &180 stage 4 (or the Porewan stadial of the Last Glacial) . Consequently the record preserved on the northeastern ring plain extends back only to the Porewan stadial (represented by the Porewan loess, Loess 3 and Sr3 on Fig . 7.5). In addition, the identification methods of the interbedded rhyolitic tephras have been improved over those described in the paper (see Chapter 2). 7.4 SUMMARY GEOLOGICAL SYNTHESIS OF THE NORTHEASTERN TONGARIRO VOLCANIC CENTRE This synthesis concentrates on the events which occurred on the ring plains rather than on the Tongariro and Ruapehu volcano slopes. 7.4.1 c. 75 000 - 64 000 years ago The record from this period is preserved only in the Upper Waikato Stream sequences described in Section 7.3 and 5. 1 3 (Chapter 5). This interval encompassed the antepenultimate stadial of the Last Glacial (the Porewan stadial) , thus the periglacial climate of this time had a large influence on ring plain sedimentation. Palynoflora within a l ignite deposit from this sequence indicates that the climate was cool and stormy during this time (Section 5. 1 3 , and 7.3.9) . The northeastern Ruapehu r ing plain during this interval was aggrading rapidly with deposits from many lahars across it. These lahars were mostly non-cohesive, sandy matrix flows exhibiting both hyperconcentrated streamflow and debris flow sedimentation styles. Reworking of these lahar deposits probably occurred soon after their emplacement and large thicknesses of al luvial gravelly sands are associated with many of the lahar deposits . The lahars during this time were l ikely to be in response to greater physical weathering on the volcano slopes and consequently larger loads of sediment with in the upper stream catchments. Glaciers were probably present on the cone and suppl ied sediment (from ti l l and outwash) and water (from ice melt and kettle lakes) to lahars. Lahar-triggering mechanisms probably included ; eruptions from either Ruapehu 1 67 or Tongariro, storms, glacial lake breakouts, avalanches and possibly small flank col lapses. During the main period of ring-plain aggradation by lahars, the frequency of large tephra eruptions from either Ruapehu or Tongariro appears to have been low. However, hornblende-rich tephras below the lahar deposit sequence may ind icate that in the early part of this interval Tongariro volcano was actively erupting (Section 3.4.7 and 7 .3 .6). I n addition , fol lowing the main period of lahar aggradation, but prior to 64 ka, i t appears that there was a major period of eruptive activity from Ruapehu volcano (Fig. 7.6). Large numbers of thick lapi l l i layers interbedded within fine andesitic ash , ind icate that large and frequent eruptions were occurring at Ruapehu {Table 5.3, Sections 4. 1 0 and 7 .3 .6) . Fewer lahar deposits preserved in this part of the sequence imply that the climate had begun to amel iorate and the volcano slopes were more stable, despite these frequent and large tephra eruptions. 20 al 5 ro E :;:::. 1/) UJ 0 +---???----??----?-L? 80 60 40 20 Time range (ka) 0 Figure 7.6. Summary diagram of the estimated rate (per ka) of lapil l i-producing sub? plinian eruptions of Ruapehu and Tongariro volcanoes for the last 75 ka. Based on the ring plain record of Topping ( 1 973), Donoghue et al. , (1 995) and Cronin et al. , ( 1 996). 7 .4.2 64 000 - 36 000 years ago The most complete record of this interval is also preserved in the Upper Waikato Stream sequences. During this period, very little lahar deposition occurred on the northeastern Ruapehu ring plain . The deposits of only a single lahar are preserved at only a few local ities (R1 3, Section 5.9) . This was probably related to stabil ised landscapes in the 1 68 mild and settled climatic conditions prevail ing during this interval in the area (McGione and Topping, 1 983). A very low frequency ( 1 per 7 000 years) of large tephra eruptions from Ruapehu was recorded in this period (Fig. 7.6, Table 5.3, Sections 4. 1 0 and 7 .3 .6) . However, accretion of fine ash appears to have occurred throughout the interval, indicating frequent low-magnitude eruptions, from either Ruapehu or Tongariro. Soil development indicates that during this interval , the northeastern Ruapehu ring plain was a stable landscape surface, with low rates of accretion (Section 4. 1 0). Stronger soil development in the earl ier part of this interval corresponded in age to soil development in loess sequences throughout the lower North Island (Sections 4 . 1 0 and 7.3 .6) , during a period of warmer and more settled climate. 7 .4.3 36 000 - 23 000 years ago The ful l record of this period is a lso preserved only in the Upper Waikato Stream sequences. As in the preceding interval, deposition on the northeastern Ruapehu ring plain was dominated by accession of tephras. However, two lahars, closely spaced in time, inundated the area. These lahars were contemporaneous with and probably related to large scale tephra eruptions of Ruapehu (R1 2, Sections 5.9 and 5 . 1 3). Large-scale tephra eruptions of Ruapehu were much more frequent in this period compared to the last, with an average of 1 per 800 years (Fig. 7 .6 , Table 5.3 , Sections 4. 1 0 and 7 .3 .6) . However, the overall frequency of large scale eruptions was not uniform throughout the entire interval . The rate was high early in the period , but very low in the latter stages. Smaller scale eruptions (probably from both Ruapehu and Tongariro) occurred throughout the entire interval and resulted in continuous and slow accretion of the ring-plain surface. Soil development was strongest in the latter stages of the 36 - 23 ka interval due to the rate of large scale tephra eruptions being at their lowest, thus the soi l surface was accreting slowly. This period of strong soil development corresponds to a period of widespread soil development in loess sequences throughout the lower North Island (Section 4 . 1 0). 7 .4.4 23 000 - 15 000 years ago This was a period of major construction of both the Tongariro and Ruapehu ring plains due to both volcanic activity and climatic instabi l ity. On both ring plains deposits of this interval probably comprise a larger volume than those of any other interval described . This interval corresponds with the period of greatest climatic and landscape instabil ity in the North Island over the last 1 20 ka (Pil lans, e t al. 1 993). Response to this cooler and stormier climate on the ring plains was deposition of large amounts of sediment by lahars and streams (Section 5 . 1 3). Thick deposits of many lahars were deposited over the entire ring plain study area (R1 1 , R1 0 and R09 on the Ruapehu ring plain , T3 and T4 on 1 69 the Tongariro ring plain; Section 5. 1 2, Fig 5.7). I n addition to lahar sedimentation, al l of the streams in the area were transporting and depositing large quantities of sediment as well as reworking lahar deposits. On the Tongariro ring plain, particularly in its northern portion, emplacement of the Oruanui lgnimbrite contributed large volumes of material which was reworked and preserved extensively as Hinuera Formation alluvium (Sections 5. 1 1 and 5. 1 3) and remobil ised by wind as Mokai Sand . Eruptive activity of Ruapehu volcano in this interval was also very high, contributing to construction of the ring plains by large additions of tephra as wel l as generation of lahars. The voluminous middle and lower Bul lot Formation tephras from Ruapehu volcano were erupted between 22.6 and 1 4.7 ka B .P . (Donoghue et al. , 1 995). In addition, between the eruptions of Okaia and Kawakawa Tephras (22.6 ka B .P . to ea. 23 ka) several more thick pumice lapi l l i layers were erupted and preserved between lahar and fluvial deposits (Fig. 7.6, Section 3.4, Fig . 3.6). Soil development in this interval was minimal due to climatic instabil ity ( i .e . scant vegetation cover) and rapid aggradation of ring plain surfaces with lahar, fluvial and pumice tephra deposits. A large lava flow from Tongariro volcano occurred in the early part of this interval. This flow was emplaced between the ring plains of Ruapehu and Tongariro creating a boundary between them (Section 5 . 1 2) . Other lava flows on the northeastern Ruapehu ring plain may have also been emplaced during this interval (Section 7 .2 .3A). 7 .4.5 1 5 000 - 9 700 years ago In this interval the high rate of large tephra eruptions from Ruapehu volcano continued with large thicknesses of upper Bullot Formation tephras deposited on the northeastern Ruapehu and southeastern Tongariro ring plains (Donoghue et al. , 1 995). Tongariro volcano was also extremely active in this period , with the eruptions of the Rotoaira , Pahoka and Mangamate Tephras (Topping, 1 973). The maximum rate of large lapi l l i? producing eruptions was between 1 0 and 9.7 ka B.P. (Fig. 7.6), when at least six sub? plinian tephras were erupted from Tongariro (Mangamate Tephra). Many lahars continued to occur throughout this interval , although they were confined to narrow sectors of the ring plains. On the Ruapehu ring plain, lahar deposition was centred around the Mangatoetoenui - Te Piripiri Streams area and on the Tongariro ring plain , around the Oturere - Makahikatoa Streams (ROB - R02 and T1 , Section 5 . 1 2). These lahars were related to the frequent tephra eruptions of both volcanoes in this interval (Section 5 . 1 3). The major portion of the ring plains in between were unaffected by lahar and fluvial deposition and had relatively stable surfaces showing periods of soil development punctuated by deposition of thick tephra layers. The absence of widespread fluvial and lahar aggradation of the ring plains in this interval compared to the last, corresponds with post Otiran climatic amel ioration (McGione and Topping, 1 977). During this interval , lahars caused major aggradation in the lower Tongariro River, resulting in extensive laharic surfaces. These deposits ceased accumulating at around 9 700 years ago (Section 6.9.2A). 1 70 Another event that occurred during this interval was between 1 4.7 and 1 1 .9 ka B .P . , when a lava flow was emplaced on the northern flanks of Tongariro, reaching the ring plain (Section 7.2.38). 7 .4 .6 9 700 - 2 500 years ago During this interval most of the surfaces of both ring plains were stable with slow accretion of tephra from small eruptions of Ruapehu and Tongariro forming the Papakai Formation (Topping, 1 973; Donoghue et al. , 1 995). Soil development was strong throughout this interval with the combination of a mild climate (McGione and Topping , 1 977) and slow soil surface accretion. A single lahar occurred during this period but deposition was confined close to the Mangatoetoenui Stream (R01 , Section 5. 1 2). This lahar was probably related to a small eruption of Ruapehu (Section 5 . 1 3). In the Tongariro River the extensive laharic surface constructed in the preceding interval was incised and in places a small laharic surface was constructed at ea. 5.2 ka (Section 6.9 .28 and 6 . 1 0.4 ). 7 .4. 7 2 500 years ago - present Tephra accretion and soil development continued throughout this interval with deposition of the Mangatawai Tephra, Tufa Trig Formation and Ngauruhoe Formation (Topping , 1 973; Donoghue et al. , 1 995). However, this was interrupted by the emplacement of large volumes of Taupo lgnimbrite. The lgnimbrite was up to 30 m thick in the Tongariro River val ley and in many places on the ring plain, level l ing surfaces of formerly d iffering ages (Section 6.9 .2A). In the Tongariro River incision continued , particularly following infi l l ing of the river val ley with Taupo lgnimbrite. At least seven small lahars occurred in this interval , some producing depositional surfaces in the lower Tongariro River, others documented only in historic records and two in 1 995 which left deposits along the Mangatoetoenui Stream (6.9.28). All of the pre-1 995 lahars in this interval appear to have flowed down the Mangatoetoenui Stream. These lahars were all probably related to eruptions of Ruapehu. 7.5 Combined References Al loway, 8.V. , Stewart, R .8 . , Neal l , V.E. and Vucetich , C .G . , 1 992. Climate of the Last Glaciation in New Zealand , based on aerosolic quartz influx in an andesitic terra in . Quat. Res. , 38: 1 70-1 79. 8orchardt, G .A. , Harward , M.E . and Schmitt, R.A., 1 971 . Correlation of ash deposits by activation analysis of glass separates. Quat. Res . , 1 : 247-260. Cronin, S .J . , Neal l , V .E . , Stewart, R .8 . , Palmer, A.S. , 1 996. A multiple-parameter approach to andesitic tephra correlation, Ruapehu volcano, New Zealand. J . 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Holocene lahar deposits in the Whakapapa catchment, northwestern ring plain , Ruapehu Volcano (North Island, New Zealand). N . Z. J. Geol . and Geophys. , 34: 1 77-1 90. Pierson, T. C. and Costa, J. E . , 1 987. A rheologic classification of subaerial sediment? water flows. Geol. Soc. of America, Reviews in Engineering Geology, V I I : 1 - 1 2. Pierson , T.C . , Janda, R.J . , Thouret, J-C. and Borrero, C.A. , 1 990. Perturbation and melting of snow and ice by the 13 November 1 985 eruption of Nevado del Ruiz, Colombia, and consequent mobilisation , flow and deposition of lahars. J. Volcano!. and Geotherm. Res . , 41 : 1 7-66. Pi l lans, B.J . , 1 988. Loess chronology in Wanganui Basin, New Zealand. In: Eden, D .N . and Furkert, R .J . (eds) Loess - Its Distribution Geology and Soi ls: 1 75-1 91 . A.A. Balkema, Rotterdam. Pi l lans, B.J . , 1 994. Direct marine-terrestrial correlations, Wanganui Basin , New Zealand: The last 1 mi l l ion years. Quat. Sci . Reviews, 1 3 : 1 89-200. 1 73 Pil lans, B.J . and Wright, 1 . , 1 992. Late Quaternary tephrostratigraphy from the southern Harve Trough - Bay of Plenty, northeast New Zealand. N. Z. J. Geol. and Geophys . , 35: 1 29-1 43 . Pi l lans, B. , McGione, M . , Palmer, A. , Mildenhall , D . , Alloway, B. and Berger, G . , 1 993. The Last Glacial Maximum in central and southern North Island: a paleoenvironmental reconstruction using the Kawakawa tephra formation as a chronostratigraphic marker. Palaeo. , Palaeo. , Palaeo. , 1 01 : 283-304. Self, S. and Healy, J . , 1 987. Wairakei Formation , New Zealand: stratigraphy and correlation. N. Z. J . of Geol. and Geophys . , 30: 73-86. Shackleton, N .J . , Berger, A. and Peltier, W.R. , 1 990. An alternative astronomical cal ibration of the lower Pleistocene timescale based on ODP Site 677. Trans. Roy. Soc. of Edinburgh: Earth Sciences, 81 : 251 -261 . Smith , G.A. , 1 986. Coarse-grained nonmarine volcaniclastic sediment: Terminology and deposition process . G . S. A. Bul l . , 97: 1 - 1 0. Stokes, S . , Lowe, D.J . and Froggatt, P.C. , 1 992. Discriminant function analysis and correlation of Late Quaternary rhyolitic tephra deposits from Taupo and Okataina volcanoes, New Zealand , using glass shard major element composition. Quat. I nter. , 1 3/14: 1 03-1 1 7. Topping, W.W. , 1 973. Tephrostratigraphy and chronology of late Quaternary eruptives from the Tongariro Volcanic Centre, New Zealand. N . Z. J. Geol. and Geophys. , 1 6 : 397-423. Topping, W.W. and Kohn , B.P. , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island, New Zealand. N. Z. J. Geol. and Geophys. , 1 6 : 375-395. Wilson, C.J .N . , Switzur, R.V. and Ward , A.P . , 1 988. A new 14C age for the Oruanui (Wairakei) eruption , New Zealand. Geol. Mag. , 1 25: 297-300. Wilson, C.J .N . , Houghton, B .F . , Lanphere, M .A. and Weaver, S .D. ( 1 992). A new radiometric age estimate for the Rotoehu Ash from Mayor Island volcano, New Zealand. N. Z. J. of Geol. and Geophys . , 35: 371 -374. 1 74 CHAPTER 8: CONCLUSIONS 8.1 Fu lfilment of study objectives - Tephrochronology groundwork Chapter 1 outl ined the original objectives of this study as well as identifying areas in which the study could contribute to knowledge gained from past studies in and around the study area. Underpinning all of these objectives was the need to establish a chronostratigraphic framework for the ring-plain sequences. This was eventually provided by a stratigraphy of interbedded andesitic and rhyolitic tephras. For sequences < 22.6 ka B.P. a tephrochronologic framework had been establ ished in past stud ies (Topping, 1 973; Topping and Kohn, 1 973; Donoghue et al., 1 995). Consequently, in this interval the object of field and laboratory study was to correlate tephras from new sequences to tephras that were already known to occur in the area. For andesitic tephras this was readily achieved using field appearance and stratigraphic criteria . However, rhyolitic tephras were not as easily identified , instead laboratory-based geochemical methods were required . When existing methods were found to be inadequate for precise identification of these rhyolitic tephras, an existing but practically untested statistical method was attempted . This formed the basis of Chapter 2 and resulted in much more precise and quantitative rhyolitic tephra identification. Sequences > 22.6 ka B.P. had not been studied in the area prior to this study and consequently their tephrochronologic framework was unknown. To establish a chronology, rhyolitic tephras were in itially sought in the sequences. These were only found after channel sampling and microscopic analysis to identify rhyol itic g lass concentration layers with in fine-grained andesitic ash sequences. These glass concentrations were correlated with tephras known from the central North Island using the methods described in Chapter 2 . Once a rhyolitic tephrochronology was established for this time range in this area it was supplemented by establishment of a new andesitic tephrochronology. Chapter 3 describes the development of the andesitic tephrochronology. The first part of the approach was to test whether the d iscriminant function analysis (DFA) method used for the rhyolitic tephras in Chapter 2 could be used to discriminate andesitic tephras, and which mineral phases were best for the purpose. This was tested by examining different methods and geochemistry of different mineral phases to d istinguish andesitic tephras from two different sources (Egmont volcano and Ruapehu volcano). Once these methods were proven, they were appl ied , along with several other parameters , to establish andesitic marker tephras in the > 22.6 ka B.P. sequence on the northeastern Ruapehu ring plain. These marker tephras were then used to correlate the > 22.6 ka B.P. sequence. 1 75 8.2 Fu lfi lment of study objectives - Specific objectives The realisation of the orig inal objectives and planned contributions of this study form Chapters 4 - 7 of this thesis. I nd ividual planned objectives and contributions are as fol lows: 8.2.1 An improved assessment of the lahar hazards from Ruapehu volcano Lahar deposits on the northeastern Ruapehu ring plain and a long the Tongariro River were mapped and dated using interbedded tephra layers. This enabled the age, number, frequency, and distribution of Ruapehu-sourced lahars to be assessed on the northeastern Ruapehu ring plain (Chapter 5) and along the Tongariro River (Chapter 6). Dating and mapping lahar surfaces led to the development of a lahar hazard map for the enti re Tongariro catchment which includes the northeastern Ruapehu ring plain (Chapter 6) . Ruapehu volcano was the source of most lahars in the Tongariro catchment post- 1 4. 7 ka, and the source of al l Holocene lahars. Eight lahar hazard zones were delineated in the Tongariro catchment ranging from 1 in > 1 5 000 to 1 in 35 years. Ruapehu? sourced lahars occur in every hazard zone and Ruapehu is the sole source of lahars in the youngest s ix zones, ranging between 1 in 10 000 to 1 in 35 years. The Mangatoetoenui catchment has the greatest lahar hazard on the northeastern Ruapehu ring plain . The Upper Waikato Stream also has a high potential lahar hazard if capture of the Whangaehu River were to occur. 8.2.2 An assessment of the lahar hazards on the eastern Tongariro ring plain and the Tongariro River The number, age, frequency and distribution of the lahars on the Tongariro ring plain were assessed using the same mapping methods as on the Ruapehu ring plain and a long the Tongariro River (Chapter 5). A lahar hazard map for the Tongariro ring plain is included in the map produced for the entire catchment (Chapter 6). The eastern Tongariro ring plain is almost entirely with in a 1 in > 1 5 000 year lahar hazard zone. Small areas of the ring plain, surrounding the Waihohonu, Oturere and Makahikatoa Streams have a greater hazard of 1 in 1 2 000 years. Consequently, Tongariro-sourced lahars contribute only to the two hazard zones with the longest return periods of the eight zones mapped along the Tongariro River. 8.2.3 A better understanding of the eruptive history (particularly that of tephra eruptives) of the two volcanoes This study was the first to examine sequences older than the 22.6 ka B .P. Kawakawa Tephra in the area. A tephra eruptive history of both volcanoes (but mostly Ruapehu) 1 76 further back in time has therefore been obtained (Chapter 3; Section 5. 1 3; Table 5.3; Section 7.4, Fig. 7.6). From c. 75 - 64 ka, there was 1 large-scale (thick pumice lapil l i-producing) eruption per 600 years on average from Ruapehu, but in the period immediately prior to 64 ka the rate was much higher. Probable Tongariro-sourced tephras were l imited to the earliest part of this time interval . In the interval 64 - 36 ka there was a very low frequency of large tephra eruptions from Ruapehu, averaging 1 per 7 000 years. Between 36 and c. 23 ka the average rate of large Ruapehu eruptions was again higher, at 1 per 800 years. The rate was much h igher early in the interval and very low in the latter stages. From c. 23 to 22.6 ka the rate of large Ruapehu eruptions was extremely high at 1 per 1 00 years . This eruption rate was equivalent or higher than that of the Bul lot Formation (described by Donoghue et al. , 1 995), and probably ind icates the start of that eruptive period . Throughout the entire 75-22.6 ka period small scale eruptions were occurring frequently, probably from both volcanoes. These are recorded by accumulations of fine ash with soil development reflecting the slow rate of surface accretion. 8.2.4 An overall synthesis of the landscape development of the northeastern Ruapehu and eastern Tongariro ring plains Using the ring plain stratigraphy developed to meet the previous objectives, ring plain construction was examined over time and in the context of the late Quaternary geologic history of the lower North Island . This resulted in the development of a construction history of the northeastern Ruapehu ring plain from c. 75 - 22.6 ka (Section 7.3) , and for both ring plains from 22.6 ka B.P. to the present. (Chapter 5). Landscape stabil ity and paleosol development in the c.75 - 22.6 ka sequence was also elucidated (Chapter 4). A summary geologic synthesis (Section 7.4) combines al l of the above information as wel l as add itional data from geological mapping (Section 7.2). 8.3 Additional contributions made by this study During the process of meeting the prime objectives of this study, other significant developments were made in the following areas: 8.3.1 Rhyolitic tephra identification I n previous studies, rhyolitic tephras have been identified using mineralogy (e.g . Lowe, 1 988), titanomagnetite chemistry (e.g . Kahn , 1 970) and glass chemistry (e .g . Froggatt, 1 983). Electron microprobe-determined glass chemistry has proved to be the most successful tool, particularly when mineralogy and stratigraphic data are lacking. 1 77 Comparison and discrimination of glass chemistry was initially by graphical and numeric means (e.g. Borchardt et al. , 1 971 ; Froggatt, 1 983). Later studies demonstrated the potential for using canonical discriminant function analysis (DFA) to d iscriminate g lass chemistry from d ifferent sources and d ifferent tephras (e.g . Stokes and Lowe, 1 988; Stokes et al. , 1 992; Shane and Froggatt, 1 994 ). However, a lthough these methods were used to discriminate tephras, they were not proved nor developed in a practical study in which the aim was to identify tephras. In Chapter 2 a DFA model was developed for potential tephra correlatives in the area (the point where previous studies had reached). Following on from this, unknown tephras were identified using probabil ities of their classification to tephras in the model . This was the first practical demonstration of these techniques on New Zealand tephras. In add ition, methods of improving the identification of the tephras were tried , including add ition of correctly classified previously unknown tephras to the original model , and treatment of some unknowns as mixed tephras. 8.3.2 Andesitic tephra discrimination The DFA methods used for rhyolitic tephra discrimination had never been used for andesitic tephras in New Zealand . I n the first part of Chapter 3 (Section 3.3) the DFA methods were tested on electron microprobe-determined chemistry of various phenocryst phases to discriminate between two volcanic sources (Ruapehu and Egmont volcanoes) and then between individual tephras of one of the sources (Egmont). This study establ ished that these discriminations were possible and that titanomagnetite was the best mineral phase for this purpose. In the second part of Chapter 3 (Section 3.4) the use of DFA and clustering techniques were demonstrated for development of an andesitic tephrostratigraphy in a previously unknown sequence. These techniques were shown to be able to d istinguish marker tephras which could be used in correlation. 8.3.3 Hal/oysite/allophane formation in andesitic tephras I n Chapter 4 (Section 4 .9), a two stage weathering process was shown to account for an apparently unusual combination of 2: 1 allophane and halloysite present in a paleosol sequence developed into andesitic tephras. Most studies of weathering tephras had not taken such a process into serious consideration . lt is commonly considered (e .g . Parfitt et al. , 1 984; Singleton et a/. , 1 989) that soil solution Si/ AI ratios determine whether 2: 1 allophane, 1 : 1 al lophane or hal loysite is formed from weathering tephras. Soil solutions high in Si promote formation of 1 : 1 al lophane and halloysite, low Si :AI ratios promote 2 : 1 allophane. I n andesitic tephras, lower Si:AI ratios normally promote the formation of 2:1 al lophane (e.g. Kirkman 1 981 ; Lowe, 1 986). This occurred in the Ruapehu tephra sequence studied when the tephra/soi l surface was originally accreting. Later rapid burial of this weathered material 1 78 by 20 m of lahar deposits and tephras created poor drainage conditions within it. In addition , weathering of the overburden resulted in large amounts of d issolved si l ica leaching downward into the buried tephra . This resulted in ongoing weathering of remaining andesitic glass into halloysite rather than the 2: 1 a l lophane previously formed at the soil surface. 8.3.4 Relationship of ring-plain construction to late Quaternary climate change A wel l constrained rhyolitic tephrochronology was developed for the Ruapehu and Tongariro ring-plain sequences in Chapter 2. This enabled examination of the ring plains' depositional h istory in relation to other records of late Quaternary climate change in the lower North Island. In Section 4.1 0 , periods of paleosol development in the Ruapehu ring-plain sequence were correlated to periods of relatively warm climate and widespread soil development in the lower North Island . In Section 7.3 and 5. 1 3 , periods of large scale and widespread lahar and streamflow deposition on the ring plains were correlated to the last and antepenultimate stadials of the Last Glacial (Ohakean and Porewan stadials). The Ruapehu and Tongariro ring plains therefore record a composite history of both volcanic events and late Quaternary climate change. 8.4 Potential future work A) An examination of the so-cal led middle Tongariro Subgroup tephras (Milne and Smal ley, 1 979) preserved in loess sections to the south , east and west of the study area. Correlation of these to their near source equivalents would prove valuable in providing further chronology for the loess sequences. In addition, the provenance and correlation of tephras in loess sequences to the west of Ruapehu (which could contain tephras from both Egmont and the Tongariro Volcanic Centre) could be established. B) A pedological and mineralogical investigation of the Papakai Formation around the entire Tongariro Volcanic Centre. This study would provide valuable information on soi l-forming and weathering processes with in andesitic tephra of the same age in areas of d ifferent drainage and climate. lt may also provide additional information about the climate in this area during the Holocene. C) A detai led investigation of the upper ring-plain portions of the Upper Waikato Stream and the Whangaehu River. The purpose of this study would be to ( 1 ) identify definitely if lahars from the Whangaehu River have entered the Upper Waikato Stream, and (2) examine the potential for this to happen in the future, fol lowing the events of 1 995. D) Investigate the physical volcanology of the Mangamate Tephra , Bul let Formation and older tephras. This would provide information on column height, eruption rates and 1 79 potential distributions of these larger events from Ruapehu and Tongariro. I nformation such as this could be used to predict and prepare for the effects of larger eruptions of either of the two volcanoes in future. E) I nvestigation of the large lava flow(s) along the Tongariro River. This unit has not been adequately dated , nor has its origin been completely determined . Is it a series of large flows derived from Tongariro volcano or are the flows from satellite vents or a fissure a long the eastern TVZ boundary fault close to the present course of the Tongariro River? 8.5 References Borchardt, G.A. . ; Harward, M .E . ; Schmitt, R.A. , 1 971 . Correlation of ash deposits by activation analysis of glass separates. Quat. Res. 1 : 247-260. Donoghue, S .L . ; Neall , V.E . ; Palmer, A.S. , 1 995. Stratigraphy and chronology of late Quaternary andesitic tephra deposits, Tongariro Volcanic Centre, New Zealand. J . Roy. Soc. N. Z. 25: 1 1 5-206. Froggatt, P .C. , 1 983. Towards a comprehensive Upper Quaternary tephra and ignimbrite stratigraphy in New Zealand using electron microprobe analysis of glass shards. Quat. Res. 1 9: 1 88-200. Kirkman, J .H . , 1 981 . Morphology and structure of halloysite in New Zealand tephras. Clays and Clay Min . , 29, 1 -9. Kohn, B .P. , 1 970. Identification of New Zealand tephra layers by emission spectrographic analysis of their titanomagnetites. Lithos 3: 361 -368. Lowe, D .J . , 1 986. Controls on the rates of weathering and clay mineral genesis in airfall tephras: a review and New Zealand case study. In: Colman, S .M. , and Dethier, D .P. (eds) Rates of chemical weathering of rocks and minerals. Academic Press, Orlando, pp. 265-330. Lowe, D.J . , 1 988. Stratigraphy, age, composition, and correlation of late Quaternary tephras interbedded with organic sediments in Waikato lakes, North Island , New Zealand. N. Z. J. of Geol. and Geophys. 31 : 1 25-1 65. Mi lne , J .D .G . and Smalley, I .J . , 1 979. Loess deposits in the southern part of the North Island of New Zealand : an outline stratigraphy. Acta Geologica Academiae Scientarium Hungaricae, 22: 1 97-204. Parfitt, R .L . , Saigusa , M. and Cowie , J .D . , 1 984. Allophane and hal loysite formation in a volcanic ash bed under d ifferent moisture conditions. Soil Sci . , 1 38 , 360-364. Shane, P.A.R. , Froggatt, P .C. , 1 994. Discriminant function analysis of g lass chemistry of New Zealand and North American tephra deposits. Quat. Res. 41 : 70-81 . Singleton , P .L . , Mcleod , M . and Percival , H .J . , 1 989. Allophane and halloysite content and soil solution si l icon in soils from rhyolitic volcanic material , New Zealand. Austral ian J . of Soil Res . , 27, 67-77. 1 80 Stokes, S . : Lowe, D.J . , 1 988. Discriminant function analysis of late Quaternary tephras from five volcanoes in New Zealand using g lass shard major element chemistry. Quat. Res. 30: 270-283. Stokes, S. ; Lowe, D.J . ; Froggatt, P .C. , 1 992. Discriminant function analysis and correlation of Late Quaternary rhyolitic tephra deposits from Taupo and Okataina volcanoes, New Zealand , using glass shard major element composition. Quat. lnter. 1 3/1 4: 1 03-1 1 7. Topping, W.W. , 1 973. Tephrostratigraphy and chronology of late Quaternary eruptives from the Tongariro Volcanic Centre, New Zealand. N . Z. J . Geol. and Geophys. , 1 6 : 397-423. Topping, W.W. , Kohn , B .P . , 1 973. Rhyolitic tephra marker beds in the Tongariro area, North Island, New Zealand . N .Z. J . Geol. and Geophys . , 1 6 : 375-395. 1 81 APPENDIX 1 : SAS PROGRAMS USED IN THIS STUDY A 1 .1 Programs The analyses with in Chapter 2 were all carried out using SAS Release 6 . 1 1 for Windows 95. Chapter 3 analyses were carried out using SAS Release 5.0 on a UN IX system. A) Glass data were entered from tab-delimited text fi les, constructed in the fol lowing format: Sample 11 Group // Si02 // Ti02 I/ Al203 // FeO // CaO I/ Na20 I/ K20 . Consequently, the Data Step required for all of the programs was: data l ibname.sas-dataset-name; infile "absolute address of text file"; input sample group sio2 tio2 al2o3 feo cao na2o k2o; run; The sample field was a number individually identifying each analysis of each sample. The group field was an integer code, each number represented a different tephra . The other fields contained the log-transformed oxide values. B) To construct d iscriminant models the following program step was used : proc d iscrim data=libname.sas-dataset-name outstat=l ibname.outstat-dataset-name ncan=5 run; listerr d istance simple; class group ; var sio2 tio2 al2o3 feo cao na2o k2o; id sample; The "outstat" option was used to store the d iscriminant model parameters which were required to test the unknown samples against. The number of canonical variables was the lesser number of 1 -(number of tephra groups) and 1 -(number of oxide predictors). The "listerr'' option prints the observations that were classified incorrectly and lists their probabilities of classification to each of the tephra groups in the discriminant model . The "d istance" option prints the Mahalanobis (02) distances between tephra groups in the model . The "simple" option prints means and standard deviations of each of the tephra groups . A 1 C) To produce the plots of canonical variates for the d iscriminant models the following program steps were used : proc candisc data=libname.sas-dataset-name out=libname.outcan-dataset-name; class group; var sio2 tio2 al2o3 feo cao na2o k2o; run ; proc plot data=libname.outcan-dataset-name; plot can2*can1 =group I href=O vref=O; run; All canonical variables are stored in the "out" dataset by the first part of the procedure. The second part of the procedure plots the first two canonical variables from the "out" dataset. D) To test unknown analyses against the d iscriminant models the following program step was used : proc discrim data=libname.outstat-dataset-name testdata=libname.test-dataset-name run; testout=libname.testout-dataset-name testlist; class group; var sio2 tio2 al2o3 feo cao na2o k2o; testclass group; testid sample; This program uses the "outstat" dataset created when the discriminant model was initial ly constructed and tests the unknown analyses (test-dataset) against it. The "testlist" option prints probabil ities of classification of all of the unknown samples with each of the tephra groups in the d iscriminant model. E) To establish the variables which d iscriminate between tephra groups the most by stepwise DFA, the fol lowing program step was used : proc stepdisc data=libname.sas-dataset-name stepwise; class group; var sio2 tio2 al2o3 feo cao na2o k2o; run; A 2 F) To carry out clustering analysis of the tephra samples the following program steps were used : proc cluster data=libname.sas-dataset-name method=wards ccc pseudo; var sio2 tio2 al2o3 feo cao na2o k2o; copy group; proc tree ncl=(number of clusters you suspect) out=l ibname.outclus-dataset; copy sio2 tio2 al2o3 feo cao na2o k2o group; proc freq; tables cluster*group; The first program step carries out the clustering process using a minimum variance method. The second step plots a tree diagram to help interpret the number of clusters present. The third step produces a table comparing the cluster groupings with those which you have pre-defined. Usually a "candisc" step was added to this procedure to evaluate the efficiency of the clustering, with the class=cluster. Note: For each program or data step the list of variables was customised for the particular mineral or glass phase being considered . A 1 .2 Reference SAS Institute Inc. , 1 989. SAS users guide: statistics. Version 6 Edition. Cary N .C. , SAS Institute I nc. , 1 028 pp. A 3 Appendix 2 : Rhyolitic glass Appendix 2: Rhyolitic glass analyses All of the glass analyses carried out in this study follow. Samples are listed in the same order as Table 2 .2 (Chapter 2). The analyses are in a raw form (not normalised). Sample Location Sample 93.5 T20/465127 Sample 93.6 T20/453129 Sample 93.7 T20/430127 Sample 93.8 T20/435129 Sample 93.9 T20/4981 57 Analysis Si02 76.050 2 75.563 3 76.593 4 76.788 5 76. 1 75 6 78.617 7 75.637 8 76.51 1 Mean 76.492 1 77.442 2 73.210 3 75.842 4 74.592 5 75.656 6 79.033 7 78.614 8 77.977 9 76.916 10 79.594 Mean 76.888 77.655 2 74.621 3 76.167 4 75.672 5 75.572 6 75.186 7 74.603 8 74. 134 9 75.609 Mean 75.469 1 76.975 2 77.440 3 71 .81 2 4 77.496 5 74.878 6 77.166 7 77.280 8 74.892 9 78.737 1 0 73.917 1 1 77.022 12 78.007 13 77.894 14 75.064 Mixed 74.197 2 75.680 3 73.492 4 74.504 5 74.445 6 73.919 7 73.278 8 76. 138 9 75.713 1 0 73.635 1 1 73. 1 99 Mean 74.382 Ti02 A1203 0.529 0.278 0.509 0.345 0.522 0.748 0.316 0.340 0.448 0 . 187 0 . 175 0 . 163 0 . 164 0 . 168 0. 1 70 0.088 0.205 0.229 0.222 0 . 177 0.694 0.232 0.599 0.319 0.269 0.414 0.209 0.217 0.208 0.351 0.557 0.624 0.861 0.243 1 .094 0.000 0.074 0.491 0.866 1 .471 1 .320 0.926 0.301 0.936 0 . 106 0.1 1 0 0 . 167 0.075 0 . 130 0 .1 13 0 . 125 0 . 106 0 . 179 0 . 120 0.266 0 . 136 A 4 1 1 .899 12.225 12.004 1 1 .923 12 . 126 12.012 12.064 1 2.005 12.032 12.734 1 1 .845 12.403 12.058 12.384 12.604 12.381 12.357 12 .157 1 1 .887 1 2.281 12.323 1 1 .480 1 1 .639 12.235 1 1 .826 1 1 .945 1 2.058 1 2.338 1 2.01 7 1 1 .985 12. 1 97 1 1 .961 1 1 .792 12.469 12.002 12.542 12.337 1 1 .523 1 1 .978 1 1 .972 1 1 .678 12.231 1 1 .901 1 1 .304 12.017 12.022 12.266 1 1 .851 1 1 .949 1 1 .804 1 1 .950 12.164 1 1 .949 12.255 1 1 .818 12.004 FeO 0.792 1 .059 1 . 1 09 1 .049 0.897 0.909 1 .032 0.992 0.980 1 .029 1 .074 1 .093 1 .031 0.973 0.906 0.902 1 .010 1 . 1 24 0.926 1 .007 0.830 0.982 0.718 0.918 0.763 0.889 0.783 0.855 1 . 155 0.877 0.832 1 .093 0.935 1 .260 1 .217 0.989 0.976 1 . 1 77 1 .082 0.980 1 . 1 1 1 0.933 1 .021 1 .001 0.987 0.964 1 .058 0.945 1 . 1 68 1 . 1 92 1 .066 0.913 1 .080 1 .337 1 . 131 1 .076 M gO 0 . 190 0 . 161 0 . 120 0.108 0.065 0 .191 0 .121 0. 1 22 0 . 135 0.232 0.226 0.221 0 . 128 0 . 134 0.234 0.215 0.161 0. 141 0 . 197 0 . 189 0 . 174 0 . 191 0.187 0.124 0.212 0.072 0.231 0.144 0 . 154 0 . 165 0 . 186 0.136 0. 1 22 0. 1 56 0. 152 0. 1 80 0.235 0. 1 72 0.163 0 . 177 0 .101 0. 1 83 0. 1 1 4 0.145 0.074 0.065 0.202 0.084 0.1 1 8 0 . 166 0 . 132 0.074 0 . 128 0 . 186 0 .147 0 . 125 CaO 0.732 0.995 1 .069 1 .038 1 . 1 53 1 .084 1 .048 1 .323 1 .055 0.910 0.925 0.984 0.965 0.900 0.998 0.834 0.962 0.925 0.887 0.929 0.957 1 .045 0.931 0.909 0.728 0.815 0.991 0.708 0.894 0.886 1 .350 1 .613 1 .947 0.828 1 .071 1 .678 1 .331 1 . 1 27 0.814 0.384 1 .026 0.952 1 .935 1 .242 0.755 0.535 0.877 0.536 0.725 0.601 0.577 0.561 0.655 0.856 0.764 0.677 Na20 4.027 4.156 4.128 4 .183 4.237 4.236 3.896 4.146 4.126 4.301 4.158 4.302 4.352 4.314 4.152 3.876 4.225 4.147 4.346 4.21 7 3.956 4.190 3.995 4.149 4. 1 75 4.035 3.942 3.713 4.056 4.023 4.403 4.079 3.962 4.240 3.925 4 .123 4. 1 05 4.072 4.144 3.956 4.171 4. 1 02 4.069 3.902 4.220 4. 1 35 4.420 4. 1 64 4.451 4.323 4.023 4.200 4.278 4. 1 87 4.288 4.244 1<20 3.524 3. 1 07 3.825 3.687 3.826 3.443 3.783 3.320 3.564 3.333 3.156 3.429 3.478 3.357 3.303 3.386 3.359 3. 1 35 3.428 3.336 3.977 3.417 3.087 3.037 3.226 2.949 3.066 3. 1 38 3.393 3.254 3.687 3.379 3.359 3.684 3.684 3.316 3.682 3.210 3.625 3.578 3.958 3.778 3.235 3.329 3.457 3.721 3.499 3.776 3.305 3.296 3.31 1 3.745 3.458 3.250 3.831 3.514 Appendix 2 : Rhyolitic glass Sample 93.32 T20/469100 1 74.862 2 74.338 3 74.872 4 75.023 5 74.542 6 71 .756 Mean 74.232 Sample 93.59 T19/505248 78.01 1 Sample 94.7 T20/465127 Sample 94.9 T20/468162 Sample 94.21 T19/48121 1 Sample 94.24 T19/48621 1 Sample 94.27 T19/485221 2 74.733 3 74.021 4 78.826 5 75.769 6 75.989 7 76.539 8 76.667 9 75.320 1 0 78.489 Mixed 1 75.627 2 76. 161 3 72.616 4 75.023 5 76.403 6 72.965 7 76.166 8 76.104 9 74.466 Mean 75.059 76.328 2 74.926 3 72.836 4 75.351 5 75.859 6 75.876 7 74.500 8 72.239 9 76.376 1 0 72.517 Mean 74.681 1 73.883 2 73.903 3 75.398 4 75.472 5 76.873 6 75.862 7 72.994 8 74.943 9 74.222 Mean 74.839 1 75.850 2 75.608 3 75.050 4 72.989 5 74.509 6 74.391 7 75.569 8 75.009 9 71 .286 1 0 72.349 Mean 74.261 79.743 2 74.259 3 75.002 4 75.289 5 77.128 6 77.463 7 75.757 0 . 147 0.131 O.D78 0 . 131 0.090 0 . 122 0. 1 1 7 0.229 0. 1 96 0. 125 0.272 0.246 0. 136 0. 129 0. 128 0.273 0 . 159 0.1 14 0 . 104 0 .101 0.260 0. 1 86 0. 147 0. 1 63 0. 1 76 0. 155 0. 156 0.214 0 . 184 0 . 148 0.237 0 . 190 0.181 0 . 189 0.244 0 . 179 0.308 0.207 0.206 0.207 0 . 198 0 . 175 0 . 157 0.216 0.093 0 . 198 0.095 0 . 172 0 . 179 0.256 0 . 187 0.269 0.215 0.242 0.214 0.243 0.171 0.258 0.223 0.057 0 . 155 0.214 0 . 158 0 . 109 0 . 149 0.222 A 5 1 1 .925 12 . 169 12.390 1 2.363 12. 069 12.010 12 . 154 13 . 106 12.353 12 . 101 13.324 1 2.403 12.285 12.338 1 1 .801 12.318 12.307 12.012 12 . 152 1 1 .572 1 1 .801 12.429 1 1 .638 12 . 166 12.235 1 1 .854 1 1 .984 12.883 1 2.729 1 1 .768 12.771 12.776 12.891 12.802 1 1 .820 1 2.921 1 2.559 12.592 1 1 .760 1 2.042 1 2.014 12.628 1 1 .933 1 1 .066 1 1 .640 12.201 12.026 1 1 .923 12.800 1 2.941 12 .873 1 2.590 1 2.765 1 2.786 1 2.877 1 2.686 16 .033 12.495 13.085 12.912 1 1 .758 1 1 .848 1 1 .792 12.314 12.317 1 1 .997 0.868 0.844 0.954 0.882 0.870 0.838 0.876 1 .280 0.773 1 . 1 1 1 1 .336 0.752 0.780 0.928 0.996 0.981 1 .075 1 .0 17 0.988 2.004 0.883 0.834 0.737 1 .052 0.972 0.972 1 .051 1 .740 1 .530 1 .315 1 .528 1 .506 1 .616 1 .548 1 .492 1 .577 1 .321 1 .517 1 .015 0.998 0.922 0.972 0.879 1 . 147 0.871 1 . 1 71 0.964 0.993 1 .456 1 .766 1 .570 1 .448 1 .543 1 .501 1 .762 1 .786 1 .339 1 .604 1 .578 1 . 1 25 1 .002 0.959 1 .097 0.882 1 . 139 1 .067 0.052 0.067 0 . 109 0.048 0.064 0.072 0.069 0.257 0. 1 29 0.197 0.278 0.063 0.045 0.082 0.070 0 . 109 0 . 156 0 . 162 0 . 143 0 . 192 0. 1 68 0 . 150 0.083 0. 1 75 0.141 0.1 1 5 0. 148 0 . 198 0 . 174 0 . 134 0 . 147 0.200 0 . 179 0 . 165 0 . 189 0 . 194 0.255 0 . 184 0 . 185 0.237 0 . 161 0 . 187 0 . 197 0 . 121 0.209 0 . 195 0 . 145 0 . 182 0. 1 67 0 . 172 0 . 162 0.240 0.246 0.209 0. 1 56 0 .161 0. 144 0. 1 68 0 . 183 0.078 0.050 0 . 134 0 . 125 0.096 0.202 0 . 158 0.658 0.764 0.698 0.717 0.554 0.634 0.671 1 .559 0.717 0.869 1 .370 0.638 0.738 0.523 0.649 0.991 0.933 0.898 0.834 0.829 0.871 0.928 0.839 0.91 3 1 . 1 21 0.965 0.91 1 1 .380 1 .418 1 .043 1 .220 1 .454 1 .396 1 .410 1 .272 1 .519 1 .365 1 .348 1 .013 0.854 0.863 1 .274 0.888 0.663 0.927 0.888 0.787 0.906 1 .531 1 .433 1 .546 1 .498 1 .651 1 .484 1 .402 1 .262 2.982 1 .332 1 .6 12 0.702 0.724 0.851 1 .053 0.795 0.838 0.834 3.791 3.950 3.979 4.059 3.792 3.766 3.890 4. 1 50 3.707 4.291 4.091 3.744 3.9 1 1 3.993 4.041 4.1 1 7 4.124 3.874 3.749 3.756 3.946 3.858 3.632 3.848 3.571 4.003 3.804 3.912 3.942 3.604 3.933 3.938 3.885 4.026 3.931 4.207 4.236 3.961 3.752 3.944 3.781 4.144 3.939 3.531 3.791 3.938 3.797 3.846 4.065 4.022 3.984 3.960 3.884 4 039 3.936 4.220 4.779 4.058 4.095 3.679 3.602 3.901 3.883 3.775 4.013 4.002 4.428 4.266 4.347 4.191 4.408 4.161 4.300 2.814 4.056 3.421 3.528 4.620 4. 1 86 4.375 4.031 3.685 3.455 3.310 3.200 3. 1 54 3.087 3.263 2.901 3. 1 32 3.398 3. 1 18 3. 1 74 3.028 2.925 2.904 2.854 2.893 3. 138 2.895 2.981 3. 1 72 2.7 17 2.951 3.270 3.029 3.482 3. 1 1 9 3.282 3.364 2.907 3. 1 67 3.583 3.245 2.920 2.909 3. 1 88 3.022 3. 1 23 3.075 2.867 2.986 2.329 2.945 2.936 3.991 4.070 3. 1 09 3 .144 3.958 3.056 3. 1 93 Appendix 2: Rhyolitic glass 8 75.999 9 76.081 Mean 76.302 Sample 94.28 T1 9/495220 73.280 Sample 94.29 T1 9/495220 Sample 94.37 T1 9/485238 Sample 94.47 T1 9/496238 Sample 94.51 T1 9/504237 Sample 94.58 T1 9/505248 Sample 94.71 T1 9/488242 2 74.430 3 71 .086 4 73.820 5 74.483 6 70.450 7 73.91 7 8 72.529 9 71 .928 1 0 70.504 Mixed 1 73.167 2 72.856 3 72.770 4 73.401 5 73.704 Mixed 76.275 2 73.883 3 73.701 4 78.023 5 76.21 7 6 76.923 7 76.462 8 74.827 9 77.566 1 0 74.951 Mean 75.883 1 76.533 2 76.0 1 9 3 75.026 4 75.729 5 75.787 6 76. 1 66 7 75.920 8 74.862 9 75.598 1 0 75.021 Mean 75.666 1 76.588 2 73.653 3 75.575 4 76.264 5 75.477 6 73.925 7 72.491 8 72.490 9 70.81 1 Mean 74.142 1 75.099 2 75.708 3 73.637 4 75.082 5 73.992 6 72.901 7 76.702 8 72.265 9 72. 1 1 3 Mean 74.167 1 75.523 2 73.692 3 76.017 4 76.783 5 74.283 0. 1 03 0. 1 58 0. 1 47 0.052 0.061 0. 1 06 0. 1 03 0. 1 1 5 0. 1 02 0. 1 28 0.070 0. 1 28 0. 1 64 0.073 0. 1 57 0 . 1 05 0.219 0. 1 74 0 . 1 47 0.090 0 . 1 8 1 0 . 1 07 0 . 1 57 0 . 1 58 0 . 1 05 0. 1 44 0.1 1 3 0 . 1 58 0. 1 36 0. 1 20 0. 1 05 0. 1 69 0 . 1 5 1 0. 1 45 0. 1 75 0 . 1 75 0 . 1 37 0.251 0 . 1 22 0 . 1 55 0 . 1 78 0.203 0 . 1 79 0 . 1 76 0 . 1 22 0. 1 86 0 . 1 80 0. 1 77 0. 1 24 0. 1 69 0.054 0 . 1 28 0.1 1 9 0 . 1 26 0 . 1 48 0.096 0. 1 92 0.077 0.077 0.1 1 3 0.036 0 . 1 73 0 . 1 89 0 . 1 1 5 0 . 1 05 A 6 1 2 . 1 90 1 2 . 1 70 1 2. 144 1 1 .670 1 1 .824 1 1 .596 1 1 .752 1 1 .754 1 1 .309 1 1 .680 1 1 .663 1 1 .423 1 1 .583 1 1 .836 1 1 .542 1 1 .552 1 2.000 1 2.088 1 2.248 1 1 .687 1 1 .499 1 2.327 1 2.014 1 2.41 1 1 2 . 1 76 1 2.423 1 2.040 1 1 .833 1 2.066 1 1 .293 1 1 .427 1 1 .337 1 1 .268 1 1 .389 1 1 .368 1 1 .418 1 1 . 1 23 1 1 .4 1 2 1 1 .232 1 1 .327 1 2. 1 34 1 1 .639 1 1 .992 1 2 . 1 49 1 2.090 1 1 .759 1 1 .540 1 1 .5 1 8 1 1 .312 1 1 .793 1 2. 0 1 4 1 1 .926 1 1 .646 1 1 .821 1 1 .869 1 1 .766 1 2.349 1 1 .496 1 2.394 1 1 .920 1 2.082 1 2.096 1 2.372 1 2.066 1 1 .962 0.868 1 .039 1 .020 1 . 1 74 0.941 1 .357 0.904 1 . 1 97 1 . 1 1 1 1 .067 0.906 1 . 1 99 1 .257 1 .089 1 . 1 90 1 .003 1 .31 1 1 .374 1 .058 1 .055 1 . 1 1 3 1 . 1 27 0.928 1 . 1 37 1 . 1 55 1 .040 0.904 0.961 1 .048 1 .270 0.922 0.964 0.975 1 .058 1 .043 0.863 1 .006 0.961 0.988 1 .005 0.799 1 .008 0.753 0.892 0.860 0.835 1 .058 1 . 1 04 1 .060 0.930 0.759 0.887 0.637 0.733 0.570 1 .098 0.792 0.783 0.537 0.755 0.799 0.819 0.906 1 .063 0.981 0.071 0.101 0. 1 1 3 0.080 0.131 0.072 0. 1 26 0 . 1 2 1 0 . 1 05 0. 1 06 0.1 1 4 0 . 1 67 0 . 1 45 0 . 1 23 0.045 0.043 0 . 1 06 0 . 1 64 0.1 1 6 0. 1 78 0 . 1 7 1 0 . 1 40 0 . 1 74 0 . 1 84 0.242 0. 1 70 0 . 1 46 0 . 1 83 0 . 1 70 0.055 0.003 0.043 0.044 0.078 0.094 0.034 0.074 0.098 0 . 1 37 0.066 0 . 1 48 0. 1 98 0 . 1 40 0 . 1 68 0. 1 38 0. 1 1 2 0. 1 72 0.1 1 2 0 . 1 03 0 . 1 43 0.098 0 . 1 89 0. 1 1 9 0. 1 26 0 . 1 2 1 0.274 0.1 1 1 0. 1 93 0.093 0 . 1 47 0 . 1 42 0 . 1 34 0 . 1 7 1 0 . 1 48 0 . 1 70 0.833 0.982 0.846 0.755 0.755 0.828 0.702 0.778 0.972 0.664 0.791 0.573 0.982 0.709 0.759 0.732 0.944 0.871 0.929 0.856 0.880 0.897 0.958 0.867 0.965 1 .092 0.795 0.931 0 . 9 1 7 0.636 0.607 0.563 0.510 0.489 0.390 0.360 0.377 0.396 0.393 0.472 0.871 0.842 0.916 0.795 0.919 0.820 0.950 0.888 0.716 0.857 0.856 0.961 0.832 0.768 1 .094 1 . 062 0.941 0.886 0.871 0.919 0.854 0.791 0.979 0.892 0.944 3.865 4.017 3.860 3.381 3.660 3.796 3. 1 28 3.737 3.551 3.761 3.715 3.652 3.637 2.672 3 . 1 07 3.282 3.488 3.51 7 4.022 3.969 3.777 4.095 4.208 3.890 3.767 3.874 3.859 3.941 3.940 3.491 3.777 3.665 3.647 3.649 3.713 3.664 3.461 3.845 3.528 3.644 3.414 3.662 3.791 3.578 3.909 3.8 1 1 3.669 3.788 3.572 3.688 3.962 4.084 3.734 3.640 4. 1 08 3.623 3.932 3.476 4.323 3.876 3.51 1 3.620 4.054 4. 1 49 3.854 3.387 3.299 3.467 3 . 1 66 3.792 3.041 4.248 3.956 3.0 1 6 3.525 3.602 3.443 3. 1 08 3.505 3.575 3.774 3.316 3.424 3.31 9 2.951 2.834 3.347 3. 1 45 3.252 3. 1 04 3.038 3.280 3. 1 07 3. 1 38 3.81 3 3.707 3.7 1 8 3.972 3.496 3.775 3.678 3.753 3.538 3.727 3.718 2.963 3.246 3. 1 68 3.4 1 7 3.019 3.016 2.868 3.002 2.803 3.056 3. 1 52 3.215 3.099 3.747 2.943 3 . 1 82 3.330 3.002 2.590 3 . 1 40 4.088 4. 1 52 3.284 3.048 3.327 Appendix 2: Rhyolitic glass Sample 94.74 T1 9/499247 Sample 94.79 T1 9/364544 Sample 95.2 T1 9/430238 Sample 95.3 T1 9/430238 Sample 95.6 T1 9423339 Sample 95.9 T1 9/448326 6 76.948 7 74.888 8 75.921 9 74. 1 9 1 1 0 73.835 Mixed 1 77.275 2 76.234 3 74.633 4 75.454 5 76.484 6 74.2 1 2 7 75.794 8 75.541 9 74.963 1 0 75.025 Mean 75.562 1 75.220 2 74.605 3 74.716 4 75.099 5 75.133 6 74.998 Mean 74.962 1 75.323 2 76.403 3 74. 6 1 7 4 74.023 5 76.586 6 71 .486 7 75. 1 39 8 76.564 9 76.362 Mean 75. 1 67 1 74.844 2 73.657 3 74.676 4 73.806 5 75.048 6 72.598 7 74.831 8 75.977 Mean 74.430 75.755 2 75.375 3 73.722 4 75.129 5 73.909 6 76.427 7 74.366 8 74.891 9 73.660 1 0 75.950 Mean 74.918 1 74.315 2 73.074 3 74.463 4 75. 748 5 73.373 6 76.560 7 76.747 8 76.238 9 74.495 1 0 72.904 Mean 74.792 Sample 95. 1 3 T1 9/549328 79.480 2 74.747 0 . 1 30 0 . 1 36 0 . 1 73 0.060 0.093 0. 1 34 0. 1 04 0. 1 08 0. 1 60 0.307 0.225 0.336 0 . 1 1 5 0. 1 07 0 . 1 30 0 . 1 73 0.338 0.405 0.285 0.384 0.254 0.345 0.335 0.201 0.221 0 . 1 45 0 . 1 73 0 . 1 30 0 . 1 83 0. 1 84 0. 1 31 0. 1 82 0. 1 72 0. 1 1 2 0.063 0.080 0. 1 65 0.094 0. 1 09 0. 1 69 0.296 0. 1 36 0. 1 1 4 0 . 1 33 0.201 0 . 1 65 0 . 1 23 0. 1 90 0.206 0 . 1 6 1 0 . 1 42 0. 1 1 0 0. 1 55 0.261 0.205 0.240 0. 1 79 0.094 0.212 0.146 0. 1 79 0.246 0.167 0 . 1 93 0. 1 1 9 0 . 1 64 A ? 1 1 .994 1 2.089 1 2.439 1 2. 1 72 1 2 . 1 98 1 2. 1 84 1 1 .997 1 1 .938 1 2.015 1 2.061 1 1 .823 1 2. 1 31 1 2. 1 37 1 2.323 1 2.053 1 2.066 1 3. 638 1 3.438 1 3.377 1 3.207 1 3.345 1 3.002 1 3.335 1 1 .770 1 2.033 1 1 .975 1 1 .920 1 2. 206 1 1 .352 1 1 .883 1 2. 1 39 1 2.329 1 1 .956 1 2. 1 87 1 1 .775 1 1 .900 1 1 .796 1 2.345 1 1 .932 1 2.290 1 2.212 1 2.055 1 2. 1 05 1 1 . 969 1 1 .846 1 1 .752 1 1 .647 1 2. 1 41 1 2. 1 56 1 1 .854 1 1 .989 1 1 .935 1 1 .939 1 1 .550 1 1 .6 1 6 1 1 .602 1 2.264 1 1 .978 1 2.346 1 2. 1 78 1 2.245 1 2.009 1 1 .770 1 1 .956 1 2.638 1 1 .955 1 .039 0.748 1 . 1 02 0.971 0.923 1 . 1 1 0 1 .248 0.975 0.996 0.912 1 .076 0.935 0.884 1 .045 1 .084 1 .027 1 .889 2 . 1 40 1 .992 1 .976 1 .897 1 .995 1 .982 0.844 0.939 0.886 1 .002 1 . 1 77 0.891 1 . 1 25 1 .013 0.997 0.986 1 .084 0.867 0.873 0.907 1 .006 1 .004 0.861 1 . 1 92 0.974 1 . 1 84 1 .038 0.987 1 .056 1 .096 1 .062 1 .020 1 .098 1 .069 1 . 1 1 8 1 .073 0.857 0.844 1 .025 0.928 1 .068 1 .070 0.924 0.964 1 . 1 20 1 .080 0.988 1 .026 0.979 0. 1 62 0. 1 64 0.086 0 . 1 23 0.090 0. 1 74 0. 1 29 0 . 1 6 1 0.146 0.210 0. 1 86 0. 1 77 0. 1 1 0 0 . 1 3 1 0. 1 62 0 . 1 59 0.255 0.335 0.303 0.359 0.320 0.338 0.318 0. 1 55 0 . 1 9 1 0. 1 34 0. 1 1 6 0. 1 86 0 . 1 23 0.204 0. 1 51 0 . 1 2 1 0. 1 53 0.059 0.033 0.078 0.058 0.060 0.084 0. 1 35 0.241 0.094 0.220 0.233 0 . 1 24 0.206 0. 1 24 0.236 0. 1 90 0 . 1 44 0.205 0. 1 51 0. 1 83 0. 1 54 0.1 1 7 0.252 0 . 1 58 0.140 0.165 0 . 1 95 0 . 1 77 0.204 0 . 1 76 0. 1 74 0 . 1 06 0 . 1 31 0.970 0.909 0.935 0.688 1 .000 0.880 0.921 0.764 0.818 0.877 0.831 0.823 0.867 0.81 1 0.829 0.842 1 .441 1 .461 1 .388 1 .402 1 .4 1 2 1 .442 1 .424 0.896 0.894 0.871 0.898 0.914 0.827 0.883 0.869 0.898 0.883 0.641 0.581 0.671 0.603 0.779 0.682 1 .0 1 4 1 . 1 96 0.771 0.956 0.905 0.862 0.980 0.921 1 .042 0.985 0.834 0.938 0.941 0.936 0.852 0.910 0.874 0.782 0.851 0.867 0.904 0.925 0.958 0.958 0.888 1 .032 0.928 3.853 3.873 3.919 3.844 3.957 3.980 3.804 4.425 3.891 3.777 3.902 3.897 3.990 4 . 1 73 4.022 3.986 3.849 4.057 4. 1 50 4. 1 36 4.036 4.1 1 2 4.057 3.878 3.848 4 . 1 93 3.91 6 3.668 3.670 3.958 2.956 3.991 3.786 3.538 3.473 3.549 3.621 3.718 3.542 3.971 3.854 3.658 3.889 3.940 3.869 4.070 3.783 4.044 3.828 3.902 3.837 3.861 3.902 4.003 3.848 3.784 3.908 3.677 3.969 3.825 4.300 4.053 3.848 3.922 3.710 3.834 3.447 3.337 3.888 3.860 4.090 3. 1 33 3. 1 37 3.099 3. 1 74 3. 1 78 2.904 3.062 3 . 1 6 1 3.239 3.324 3 . 1 4 1 2.987 3.0 1 3 2.891 2.938 2.998 2.901 2.955 2.920 3.221 2.934 3.008 3.772 2.825 3.231 3.488 3.073 3 . 1 64 4. 1 44 4.1 1 6 3.898 4.039 3.860 3.793 2.883 3. 1 60 3.737 3. 1 63 3.285 3.099 3. 1 62 3.253 3. 1 74 3.218 3. 1 60 3.051 3.255 3. 1 82 3.049 2.841 3.035 3.577 2.909 3.348 3.236 3. 1 1 4 3 . 1 74 2.963 3. 1 25 3.034 2.860 Appendix 2: Rhyolitic glass Sample 93. 1 T20/455088 Sample 93.3 T20/465095 Sample 93. 1 7 T20/46 1 1 70 3 75.815 4 7 1 . 1 40 5 71 .762 6 74.703 7 73.479 8 75.169 9 71 .442 Mean 74. 1 93 1 74.231 2 73. 1 36 3 72.679 4 73.000 5 73.659 6 75.709 7 75.540 8 76. 1 39 9 73.218 1 0 75.809 Mean 74.31 2 1 70.768 2 70.197 3 73.239 4 73.307 5 74.545 6 72.958 7 72.515 8 73.907 9 75.796 1 0 75.877 Mean 73.31 1 72.683 2 75.642 3 75.094 4 74.458 5 73.607 6 73.175 7 73.396 8 74.0 1 9 9 72.013 10 73.893 1 1 74.964 Mean 73.904 Sample 93.33 T20/469100 72.696 Sample 7.37 T20/469100 Sample 7.36 T20/469100 2 72.563 4 75. 141 5 71 .388 6 77.992 7 77.409 8 75.353 9 70. 1 70 1 0 73.820 1 1 76.510 Mean 74.304 2 3 4 5 6 7 8 Mean 73.665 73.105 74. 1 23 73. 1 25 73.235 73.200 72.995 74.023 73.434 75.829 2 74.655 3 74.569 4 74.587 5 74.897 6 75. 1 1 2 0 . 1 1 4 0. 1 23 0.242 0 . 1 82 0 . 1 30 0. 1 78 0.213 0. 1 63 0.670 0.384 0.563 0.224 0.354 0.329 0.261 0.833 0.297 0.653 0.459 0. 1 73 0.191 0. 1 32 0.055 0.148 0.144 0.325 0.200 0. 1 25 0.098 0.159 0.205 0. 1 20 0.146 0.136 0. 1 81 0.236 0. 1 1 5 0.225 0.141 0 . 1 37 0.263 0 . 1 73 0.276 0.221 0 . 1 54 0.321 0.200 0 . 1 43 0.236 0.274 0.083 0.142 0.205 0. 1 58 0.268 0 . 1 56 0.251 0. 1 36 0.200 0.430 0.235 0.229 0.202 0.289 0.216 0.247 0.302 0.256 A 8 1 2.027 1 1 .304 1 1 .439 1 1 .8 1 2 1 1 .549 1 1 .705 1 1 .494 1 1 .769 1 1 .539 1 1 .953 1 1 .949 1 1 .425 1 1 .741 1 1 .653 1 1 .655 1 1 .453 1 1 .828 1 1 .650 1 1 .685 1 1 .753 1 1 .648 1 2. 1 68 1 1 .634 1 1 .684 1 1 .979 1 2. 1 45 1 2 . 1 97 1 1 .757 1 1 .365 1 1 .833 1 2.208 1 2.252 1 2.090 1 1 .842 1 2.368 1 1 .785 1 2.002 1 2.098 1 1 .904 1 2.258 1 2 . 1 49 1 2.087 1 1 .862 1 1 . 229 1 2 0 1 6 1 1 .598 1 1 .974 1 1 .733 1 1 .997 1 1 .658 1 2.594 1 2.510 1 1 .9 1 7 1 2.710 1 2.042 1 2.265 1 2.740 1 2.059 1 2. 1 1 1 1 1 .998 1 2.457 , 1 2.298 1 3.487 1 3. 383 1 2.998 1 3.258 1 3.498 1 3.003 0.898 0.881 1 .0 1 8 0.983 1 .0 1 6 1 .091 1 .041 0.993 1 .2 1 0 1 .233 1 .249 1 .029 1 .278 1 . 1 62 1 . 234 1 . 224 1 .290 1 .099 1 . 201 1 . 1 75 1 . 286 1 .258 1 .249 1 .374 1 .328 1 . 1 33 1 . 226 1 .240 1 .050 1 .232 1 .259 1 .071 1 . 1 56 0.950 0.998 1 .424 1 . 1 42 1 .435 1 .465 1 .455 1 .400 1 .250 1 .374 1 . 1 64 1 . 164 1 .320 1 .299 1 .2 1 8 1 .078 1 . 1 56 1 .434 1 .322 1 .253 1 .206 1 .824 1 .645 1 .468 1 .338 1 .665 1 .540 1 .568 1 .532 1 .672 1 .866 1 .532 1 .665 1 . 567 1 .587 0. 1 54 0. 1 22 0. 1 98 0.239 0 . 1 45 0 . 1 9 1 0. 1 96 0. 1 65 0.142 0 . 1 2 1 0 . 1 2 1 0.248 0.068 0. 1 30 0 . 1 09 0. 1 06 0. 1 53 0.083 0. 1 28 0.185 0. 1 1 6 0. 1 58 0. 1 54 0. 1 09 0. 1 57 0. 1 1 4 0.164 0.143 0.076 0 . 1 38 0. 1 56 0. 1 39 0.142 0.095 0. 1 95 0 . 1 8 1 0. 1 51 0.225 0 . 1 47 0 . 1 90 0 . 1 5 1 0 . 1 6 1 0.244 0 . 1 50 0.088 0 . 1 42 0. 1 54 0. 1 22 0. 1 1 6 0. 1 56 0.175 0.144 0.149 0.099 0 . 1 20 0 . 1 42 0. 1 25 0.145 0.163 0.251 0.099 0.143 0.247 0.274 0.257 0.243 0.236 0.213 0.893 0.862 0.918 0.789 0.905 0.878 0.904 0.901 0.926 1 .285 1 .287 1 . 1 41 1 .229 1 .595 1 . 455 1 . 264 1 .603 1 . 283 1 .307 0.949 1 . 1 60 1 .052 0.970 0.983 1 . 1 27 0.987 1 .064 1 .068 1 .021 1 .038 1 . 1 48 0.936 1 . 1 34 0.693 1 .070 1 .057 0.975 1 .034 1 .060 1 .038 1 . 1 30 1 .025 1 . 514 1 .032 1 . 1 07 1 . 1 86 1 . 5 1 9 1 .093 0.91 1 1 .076 1 . 237 1 .357 1 . 203 1 .507 1 .317 1 .332 1 .471 1 .358 1 .451 1 . 265 1 .3 1 5 1 .377 1 .659 1 .678 1 .699 1 .637 1 .521 1 .563 3.825 3.660 3.558 3.798 3.8 1 3 3.936 3.656 3.754 3.954 3.949 3.945 3.800 3.941 3.968 4.051 3.577 4 . 1 08 3.969 3.926 4.003 4.030 4.071 4 . 1 38 3.979 4.247 4. 263 4.250 4.016 3.841 4.084 3.938 4. 1 84 4.304 3.746 4.357 4.026 4 . 1 03 4.236 3.877 4.281 4 . 1 40 4 . 1 08 3.577 3.9 1 2 4.0 1 8 4. 1 25 4 . 1 32 4. 1 26 3.750 3.741 4.206 4. 1 82 3.977 3.385 2.832 3.698 3.889 3.678 3.587 3.900 3.547 3.565 3.692 4.101 3.889 3.952 3.265 3.777 3.050 2.757 2.836 3 . 1 6 1 2.935 3.21 1 2.723 2.952 3.422 3.332 3.247 3. 1 69 3.356 3. 1 89 3.243 3.332 2.996 3.403 3.269 3. 1 59 2.882 3.202 3.249 3.141 3. 1 96 3.302 3. 1 53 3.228 3.230 3. 1 74 2.798 3.268 2.963 3.993 3.007 2.791 2.999 3.003 2.820 3. 1 54 2.955 3.068 3.285 3. 340 2.986 2.990 3.597 3.4 1 2 4.313 2.983 3.067 3.466 3.344 3.547 3.509 3.269 3.358 3.332 3.457 3.698 2.998 3.396 2.982 2.782 3.204 2.936 2.568 2.886 Appendix 2: Rhyolitic glass Sample 9.37 T20/4681 02 Sample 9.36 T20/468 1 02 Sample 9.35 T20/4681 02 Sample 9.33 T20/468102 Sample 9.25 T20/468102 Sample 9.22 T20/4681 02 Sample 9.21 T20/468102 Mean 74.942 72. 1 00 2 71 .256 3 7 1 . 590 4 71 .845 5 73.379 6 72.169 7 73.057 8 72.475 9 7 1 . 924 1 0 7 1 . 750 Mean 72. 1 55 1 72.618 2 72.802 3 73.310 4 72.724 5 73.265 6 74.777 Mean 73.249 73.673 2 73.254 3 74.216 4 74.365 5 73.998 6 73.257 7 74. 1 1 1 8 74.369 9 75.002 1 0 73. 334 Mean 73.958 1 74.508 2 72.846 3 72.836 4 72.440 5 73.491 6 73.162 7 73.190 8 74. 1 78 9 74.396 Mean 73.450 70.521 2 73.076 3 73. 1 44 4 76.662 5 75.783 6 77.303 7 76. 1 58 8 75.974 Mean 74.828 75.663 2 72.623 3 75.509 4 74.301 5 74.605 6 74.7 1 6 Mean 74.570 1 76.538 2 76.252 3 78. 1 79 4 75.750 5 76.087 6 76.019 7 75.026 8 75.729 Mean 76.198 Sample 1 4.23 T20/4 771 1 2 76.213 0.252 0.242 0. 1 09 0 . 1 72 0. 1 1 7 0. 1 92 0.395 0. 1 50 0.000 0.000 0.000 0. 1 38 0.208 0.217 0 . 1 90 0 . 1 63 0.278 0. 1 89 0.208 0. 1 92 0. 1 62 0. 1 87 0.236 0.205 0 . 1 66 0. 1 1 4 0. 1 78 0 . 1 54 0. 1 25 0. 1 72 0. 1 64 0. 1 83 0. 1 73 0. 1 83 0 . 1 09 0. 1 52 0.097 0 . 1 0 1 0.060 0. 1 36 0.379 0.393 0.449 0.309 0.372 0.275 0.248 0.253 0.335 0.293 0.241 0.093 0.078 0.405 0.285 0.233 0.210 0. 1 67 0. 1 62 0 . 1 37 0.062 0 . 1 05 0 . 1 69 0 . 1 51 0 . 1 45 0.328 A 9 1 3.271 1 2.624 1 2 . 1 88 1 2.293 1 2.073 1 2 . 1 39 1 2. 1 1 8 1 2.329 1 2 . 1 20 1 2. 0 1 9 1 2.321 1 2.222 1 2.510 1 2.418 1 2.376 1 2.414 1 2.567 1 3.035 1 2.553 1 3.234 1 2.280 1 3.005 1 3.458 1 3.612 1 2.998 1 2.359 1 3.547 1 3.200 1 2.690 1 3.038 1 1 .854 1 1 .597 1 1 .451 1 1 .280 1 2 . 1 30 1 2.085 1 2.061 1 2.093 1 1 .659 1 1 .801 1 2.285 1 2.531 1 2.401 1 3.279 1 3.299 1 3. 089 1 3.041 1 3 . 1 25 1 2.881 1 3.352 1 2.922 1 2.773 1 2.382 1 3.438 1 3.377 1 3.041 1 2. 1 4 1 1 1 .865 1 2.245 1 1 .849 1 1 .854 1 1 .427 1 1 .337 1 1 .268 1 1 .748 1 3.295 1 .648 1 .561 1 .3 1 7 1 . 737 1 .605 2.0 1 9 1 .520 1 .954 2.032 2.082 1 .549 1 .738 1 .625 1 .965 1 .675 1 .226 1 .368 1 .333 1 .532 1 .822 1 .824 1 .668 1 .664 1 .624 1 .512 1 .699 1 .521 1 .478 1 .588 1 .640 1 .21 3 1 .064 1 .283 1 .205 1 . 1 65 1 .206 1 .248 1 .335 1 . 1 24 1 .205 2.180 2.608 2.663 2.002 2. 1 25 1 .892 1 .498 1 .637 2.076 2. 1 21 2.073 1 .965 1 .738 2.140 1 .992 2.005 1 .090 1 .038 1 . 1 24 1 .070 1 .251 0.922 0.964 0.975 1 .054 2.025 0.245 0. 1 07 0. 1 70 0. 1 63 0. 1 28 0. 1 37 0. 1 67 0 . 1 07 0. 1 26 0. 1 1 2 0. 1 56 0. 1 37 0. 1 47 0 . 1 02 0.132 0.210 0.218 0 . 1 58 0.161 0.268 0.082 0 . 1 25 0. 1 47 0. 1 79 0. 1 66 0. 1 35 0.232 0. 1 48 0 . 1 97 0 . 1 68 0.078 0 . 1 00 0.201 0 . 1 57 0 . 1 3 1 0 . 1 29 0 . 1 57 0 . 1 56 0 . 1 4 1 0 . 1 39 0.350 0.412 0.415 0.285 0.261 0.223 0. 1 76 0. 1 92 0.289 0.265 0.299 0.097 0.036 0.335 0.303 0.223 0.1 1 8 0 . 1 34 0 . 1 70 0 . 1 92 0 . 1 37 0.003 0.043 0.044 0 . 1 05 0.298 1 .626 1 . 370 1 . 1 93 1 . 1 92 1 .3 1 8 1 .269 1 .331 1 .2 1 4 1 . 1 1 7 1 .247 1 .431 1 .268 1 .292 1 .253 1 .232 1 . 1 58 1 .386 1 .255 1 .259 1 .521 1 .307 1 .406 1 .456 1 .258 1 . 367 1 .357 1 .266 1 .3 1 2 1 .389 1 .364 1 .095 1 . 001 0.824 0.688 1 .0 1 1 1 .050 0.9 1 5 1 . 1 23 0.970 0.964 1 .660 1 .446 1 .656 1 . 393 1 .662 1 .2 1 2 1 .275 1 .295 1 .450 1 .554 1 .474 1 . 368 1 . 1 74 1 .461 1 .388 1 .403 1 . 042 0.969 0.875 1 .066 0.851 0.607 0.563 0.510 0.810 1 .504 3.779 3.353 2.829 3.086 3.389 2.775 3.419 3.041 3.290 3.71 7 3.628 3.253 3. 1 26 3.3 1 9 3.3 1 8 3.0 1 1 3.2 1 5 3.2 1 5 3.201 3.886 3.444 3.446 3.584 3.845 2.994 3.489 3.487 3.265 3.658 3.51 0 3. 1 52 3 . 1 89 2.273 2.792 3.076 3.287 3.051 3.038 2.608 2.941 3.019 3.552 2.886 4. 1 48 2.298 4.084 4 . 1 42 4.232 3.545 4.078 3.51 5 3.353 3.524 4.057 4. 1 50 3.780 3.361 3.696 3.656 2.936 3.333 3.777 3.665 3.647 3.509 3.699 2.893 3.422 3.698 3.609 3.643 3.500 3.452 3.410 3.758 3.680 3.535 3.571 3.639 3.721 3.642 3.600 3.555 3.368 3.588 2.636 3.633 2.949 3.640 3.514 3.446 3.495 3.651 2.846 3.235 3.305 3.043 3 . 1 06 3.430 3.626 2.785 2.762 2.942 2.959 2.747 3.044 3.820 3.681 3.283 2.796 2.855 3.026 2.745 2.808 3. 1 27 2.846 2.638 3.731 3.365 3.013 2.891 3.081 3.040 3.044 3. 1 24 2.710 3.0 1 5 3.707 3.718 3.972 3.291 2.830 Appendix 2: Rhyolitic glass 2 75.990 0.320 1 3.343 1 .9 1 8 0.290 1 .971 3.808 2.709 3 75.515 0.345 1 3 . 1 1 0 1 .930 0.264 1 .494 3.914 3.239 4 74. 1 76 0 . 1 34 1 2.690 1 .643 0. 1 1 3 1 .227 3.206 2.785 5 74.758 0.246 1 2.528 1 .499 0. 1 28 1 .209 3.418 2.710 6 74.677 0 . 1 45 1 2.899 1 .589 0. 1 63 1 .338 3.7 1 2 2.933 7 76.197 0.313 1 3.750 1 .942 0.293 1 .663 3.951 2.800 8 76.205 0.228 1 3.093 2.266 0.258 1 .584 3.929 2.801 Mean 75.466 0.257 1 3.089 1 .852 0.226 1 .499 3.705 2.851 Sample 1 4.22 T20/4771 1 2 72. 1 1 5 0 . 1 24 1 1 .262 1 .086 0. 1 62 1 .081 3.021 2.824 2 74.828 0 . 1 52 1 1 .671 1 . 197 0.144 1 .009 3.004 2.975 3 75.123 0 . 1 45 1 1 .833 0.949 0 . 1 50 1 .078 3.222 3.001 4 74.408 0. 1 02 1 1 .849 0.885 0.070 0.960 3.290 3.016 5 76.287 0. 1 37 1 2.317 1 .082 0. 1 1 6 1 .038 2.542 3.047 6 74.345 0. 1 65 1 1 .968 1 . 1 1 4 0. 1 1 8 0.887 2.676 2.837 7 77.982 0 . 1 21 1 2.506 1 .2 1 7 0. 1 84 1 .048 3.582 3. 1 96 Mean 75.013 0 . 1 35 1 1 .9 1 5 1 .076 0 . 1 35 1 .0 1 4 3.048 2.985 A 1 0 Appendix 3.1 : Mineralogy APPENDIX 3: ANDESITIC TEPHRAS 3.1 Ferromagnesian mineral assemblages The following table presents modal ferromagnesian mineralogy of al l the andesitic tephras sampled in this study. Counts of 400 grains were made on mineral separates. Sample Location Section Unit or correlation OPX CPX TM HB OL 93.23 T20/461 096 45 56 39 5 0 0 93.24 T20/464098 46 59 40 1 0 0 93.25 4 1 37 3 0 1 9 93.26 Marker Unit 1 8 36 1 0 56 93.27 Marker Unit 1 1 6 48 1 0 36 93.28 T20/465099 47 51 48 0 0 2 93.29 T20/4691 02 9 57 43 0 0 0 93.30 T20/466096 5 54 45 0 0 0 93.31 47 51 0 0 2 93.34 T20/4691 00 7 50 49 0 0 1 93.36 53 47 0 0 0 93.38 59 34 0 6 93.39 Marker Unit 2 39 50 1 0 2 0 93.40 56 44 0 0 0 93.41 T20/4681 02 9 44 54 0 0 2 93.42 47 52 1 0 0 93.43 57 34 9 0 0 93.44 58 33 9 0 0 93.45 57 29 14 0 0 93.46 51 31 1 8 0 0 93.47 Marker Unit 3 49 40 1 1 0 0 93.48 63 22 1 5 0 0 93.49 67 1 9 1 5 0 0 93.50 66 20 1 5 0 0 93.51 52 43 4 1 0 93.52 T20/4681 02 1 0 Marker Unit 4 54 39 6 1 0 93.53 59 41 1 0 0 93.54 55 40 2 0 3 93.55 55 42 3 1 0 93.56 58 41 1 0 0 93.57 59 29 1 2 0 0 93.58 72 1 5 1 3 0 0 93.60 T20/4771 1 2 1 4 49 51 1 0 0 93.61 (93.37) 49 43 9 0 0 93.62 (93.38) 65 28 0 6 93.63 (93.40) 58 41 0 1 93.64 (93.40) 47 52 0 93.65 (93.42) 54 44 1 0 2 93.66 65 29 5 0 1 93.67 53 43 4 0 1 93.68 68 22 1 0 0 1 93.69 66 26 8 0 0 93.70 Marker Unit 3 57 41 2 0 0 93.71 (93.48) 66 28 6 0 0 93.72 (93.49) 57 27 1 6 0 0 93.73 (93.51 ) 49 40 8 2 1 93.74 Marker Unit 4 56 39 5 0 0 93.75 52 47 1 0 0 93.76 56 42 2 0 0 93.77 62 27 1 1 0 0 93.78 75 1 2 14 0 0 93.79 59 40 2 0 0 A 1 1 Appendix 3.1 : Mineralogy 93.80 61 30 9 0 0 93.81 63 34 3 0 0 93.82 43 56 2 0 1 93.83 49 50 1 0 0 93.84 73 22 5 0 0 93.85 Marker Unit 5 50 41 9 0 1 93.86 51 37 1 2 0 0 93.87 61 36 4 0 0 93.88 60 37 3 0 0 93.89 Marker Unit 6 27 33 9 31 0 93.91 Marker Unit 7 55 39 1 5 0 94.2 T20/455088 Bullot Fm. 68 24 8 0 0 94.4 T20/4691 02 9 L 1 Bullot Fm. 69 28 3 0 0 94. 1 3 T20/4961 57 51 76 20 4 0 0 94 . 1 5 T20/463097 Bullot Fm. 47 1 0 1 5 28 0 94. 1 6 78 1 3 9 0 0 94. 1 7 66 26 8 0 0 94. 1 8 T20/4981 84 53 ?Bullot Fm. 66 24 9 1 0 94.20 T1 9/484209 54 71 22 4 0 3 94.22 T1 9/48121 1 55 {94.31 ) 36 31 7 26 0 94.31 T1 9/495220 59 {94.22) 37 14 9 40 0 94.32 T20/4771 1 2 14 Marker Unit 7 20 6 8 66 0 94.41 T1 9/491 239 Rotoaira Tephra 78 1 9 3 0 0 94 .43 T1 9/496238 66 Bullot Fm. 71 28 <1 <1 0 94.44 75 25 <1 0 0 94.45 72 24 4 <1 0 94.46 {94.22&31 ) 39 34 27 0 0 94 .79 T1 9/364544 73 Poutu Tephra 63 29 7 0 1 A 1 2 Appendix 3.2: Hornblende analyses 3.2 Hornblende analyses All analyses are l isted in a raw form (not normalised) . Sample Location Section Analysis Si02 Sample 93.39 T20/469100 7 Sample 93.48 T20/4681 02 9 Sample 93.51 T20/4681 02 9 Sample 93.52 T20/4681 02 1 0 Sample 93.55 T20/4681 02 1 0 Sample 93.71 T20/4771 1 2 1 4 Sample 93.73 T20/4771 1 2 1 4 Sample 93.75 T20/4771 1 2 1 4 Sample 93.89 T20/4771 1 2 1 4 Sample 93.90 T20/4771 1 2 1 4 44.665 2 38.562 3 39.565 Mean 40.931 1 39.885 2 38.493 41 .877 2 42.615 3 4 1 . 589 4 41 .504 5 42.194 6 40.067 7 41 .245 8 41 .473 9 41 . 1 03 Mean 4 1 .5 1 9 1 42.820 2 42.945 3 43.290 4 42.051 5 41 .725 6 40.830 Mean 42.277 35.407 2 37.31 1 3 39.803 Mean 37.507 39.540 1 40.694 2 37.426 3 40.770 4 5 6 7 8 9 10 1 1 1 2 Mean 41 .085 39.621 40.477 41 . 1 63 40.863 40.818 40.594 40.453 40.595 40.380 1 40.764 2 42.518 3 41 .933 4 43.624 Mean 42.210 1 41 .637 2 41 .062 3 4 5 6 7 8 9 1 0 Mean 40. 784 36.875 41 .979 41 .056 40. 1 59 41 .546 44.438 42.613 4 1 . 2 1 5 4 1 . 845 2 38.954 Ti02 Al203 FeO M nO M gO CaO 1 . 1 92 1 3 .032 1 3.21 5 0. 1 71 1 5.805 1 0.682 2.272 1 2.035 1 2.349 0.421 1 2.403 1 1 .56 1 2.225 1 2.821 1 2.959 1 .896 1 2.629 1 2.841 0.348 1 2.773 1 1 .694 0.313 1 3.660 1 1 .3 1 2 3.106 1 1 .854 1 2.020 0.402 1 3.520 1 1 . 1 69 2.965 1 1 .21 1 1 2.913 0.361 1 2. 903 1 1 .270 2.039 1 3.772 1 1 .474 0.089 14.617 1 0.957 1 .941 1 3.61 1 1 2. 1 09 0. 1 52 1 4. 8 1 9 1 0.824 1 .759 1 3.368 1 2.598 0.255 1 3.932 10.691 1 .7 1 0 1 3.048 1 1 .264 0.318 1 4.330 1 0.723 2. 1 26 1 3.976 1 1 .608 0.420 14.762 1 1 . 1 28 2.054 1 3.269 1 1 .321 0.260 1 3.863 1 0.574 3.305 1 1 .261 1 1 .856 0.333 1 4.673 1 1 . 1 92 3.301 1 1 .707 1 1 .459 0 . 206 1 4.344 1 1 .089 3.546 1 1 .620 1 1 . 1 1 6 0.524 1 4.282 1 1 .272 2.420 1 2.848 1 1 .645 0.284 1 4.402 1 0.939 1 . 1 68 1 2.634 1 3.569 0. 1 80 1 4 . 1 6 1 1 1 .084 1 .228 1 2 . 232 1 4. 1 41 0.387 1 3 .373 1 0 .775 1 .261 1 1 .770 1 4.338 0.579 1 3 .823 1 0 .424 1 .2 1 5 1 2.006 1 4. 5 1 5 0 . 1 72 1 3.527 1 0 .602 1 . 1 94 1 2.094 1 3.928 0.369 1 3.407 1 0.500 1 . 1 99 1 2.079 1 3.755 0.318 1 3.093 1 0 .592 1 .21 1 1 2 . 1 36 1 4.041 0.334 1 3.564 1 0 .663 2.973 1 1 .795 1 2.297 3.369 1 1 .968 1 2 . 1 02 2.930 1 3.340 1 2.406 3.091 1 2.368 1 2.268 2.967 9.925 1 1 .727 2. 1 1 0 1 3.755 1 1 .241 2. 1 53 1 2.407 1 1 .705 2.038 1 3.368 1 2.032 2.0 1 8 1 .883 2.016 1 .990 2.062 2.034 2. 1 69 3. 1 09 2.01 0 2.133 1 3. 1 1 7 1 1 .8 1 6 1 3.057 1 1 .675 1 3.542 1 0.875 1 3.481 1 1 .900 1 3.577 1 1 .505 1 3.220 1 1 .417 1 3.580 1 2.018 1 2.517 1 2.955 1 3.709 1 1 .938 1 3.278 1 1 .756 2.269 1 1 .681 1 1 .7 1 7 2 . 1 49 1 1 .900 1 2 . 1 45 3.085 1 2 . 1 50 1 1 .366 3.262 1 2.457 1 1 .954 2.691 1 2.047 1 1 .796 0.258 1 1 .878 1 2. 1 90 0.2 1 7 1 1 .708 1 2.321 0.229 1 3 . 1 37 1 1 .985 0.235 1 2.241 1 2. 1 65 0.482 1 3.630 1 0.293 0. 1 87 14.492 1 1 .052 0.31 3 1 2.793 1 0.885 0.297 1 4.674 1 0.835 0.282 1 4.543 0 . 1 92 14.477 0.196 14.468 0.342 14.677 0.451 14.756 0.306 1 4.555 0.420 14.637 0.355 1 3.446 0.266 1 4.666 0.301 14.349 1 0.556 1 0.633 1 1 .063 1 1 .266 1 1 .0 1 3 1 0.961 1 0.795 1 0.989 1 0.975 1 0.919 0.467 1 3.886 1 1 .787 0.372 1 4.661 1 1 .948 0.297 14.269 1 1 .426 0.312 14.683 1 1 .34 1 0.362 1 4.375 1 1 .626 2 . 1 80 1 3.451 1 1 . 1 5 1 0 . 1 88 1 4.937 1 2.239 2.790 1 2.499 1 2.785 0.279 1 3.272 1 1 .854 2.0 1 4 2. 1 32 2.787 2 . 1 09 1 . 971 2.490 3.081 1 .907 2.346 1 3.681 1 1 .425 1 3.902 1 2.434 1 1 .532 1 3 . 1 34 1 3.644 14.557 14.230 1 3 . 1 05 1 2.084 1 3. 1 1 3 1 0.475 1 1 .446 1 3.347 1 0.551 1 2.885 1 2.370 1 . 743 1 3. 223 1 2.900 1 .850 1 1 .738 1 3 .529 0 . 1 2 1 0. 1 51 0.373 0.380 0.206 0.423 0.421 0.212 0.275 1 3.779 1 1 .961 1 3.283 1 2.778 1 2.848 1 2.681 14.632 14.955 1 3.513 1 2.467 1 2.361 1 2.201 1 2.392 1 2.541 1 1 .795 1 1 .983 1 2.752 1 2. 259 0.250 1 3.661 1 1 .295 0.242 1 2.319 1 1 .594 A 1 3 Na20 K20 2.840 0.217 2.078 0.768 2 . 1 6 1 0.844 2.360 0.610 2.428 0.951 2.325 0.890 2.398 0.41 5 2.438 0.360 2.358 0.382 2.410 0.430 2.433 0.331 2.238 0.41 1 2.546 0.815 2.524 0.9 1 5 2.269 0.893 2.402 0.550 2.040 0.225 1 .976 0.295 1 .9 1 3 0.263 2.014 0. 1 73 1 .920 0.341 1 .873 0.325 1 .956 0.270 2.258 0.936 2.420 0.975 2.542 1 .039 2.407 0.983 2 . 1 87 2.300 1 .951 2.349 2.327 2.095 2.300 2.292 2.445 2.357 2.408 2.561 2.669 2.338 2.425 2.690 2.638 2.659 2.603 0. 758 0.387 0.297 0.348 0.340 0.371 0.398 0.350 0.308 0.317 0.313 0.844 0.324 0.383 0.749 0.743 0.730 0.759 0.745 2.565 0.856 2.493 0.884 2.358 2.332 2.625 2.607 2.487 2.665 2.395 2.580 2.51 1 0.933 0.810 0.827 0.764 0.928 0.766 0. 759 0.957 0.648 2.644 0.699 1 .855 0.767 Sample 93.91 T20/4771 1 2 1 4 Sample 94. 15 T20/463097 52 Sample 94.1 8 T20/498184 53 Sample 94.22 T19/48121 1 55 Sample 94.31 T19/495220 59 Sample 94.43 T19/496238 66 Sample 94.45 T19/496238 66 Sample 94.46 T19/496238 66 Sample 94.47 T19/496238 66 (Rhyolitic) Appendix 3.2: Hornblende analyses 3 39.785 4 38.381 Mean 39.741 1 41 .030 2 43.698 3 42.780 4 41 .701 5 42.739 6 40.861 7 42.703 8 40.427 9 43.738 10 39.626 Mean 41 .930 1 43.937 2 45.061 3 45.070 4 43.937 5 44. 144 Mean 44.430 1 41 .015 2 41 .241 3 40.385 4 41 .797 Mean 41 . 1 1 0 46.023 2 44.588 3 45.905 4 44.626 5 45.176 6 47.106 Mean 45.571 44.845 2 43.904 3 44.054 4 44.429 5 42.430 6 44.191 Mean 43.976 43.372 2 4 1 . 124 3 40.582 4 40.934 5 41 .973 6 41 .486 Mean 41 .579 1 41 .092 2 42.314 3 43. 101 4 4 1 .419 5 44.565 6 42.369 7 41 .706 Mean 42.367 1 40.721 2 41 .669 3 41 .659 4 41 .925 5 41 .017 6 40.452 7 43.502 Mean 41 .564 1 45.625 2 45. 1 1 2 3 44. 1 1 1 Mean 44.949 2.719 8.082 1 2.095 0.501 13 . 193 1 1 .323 2.579 1 2.453 13.656 0.326 1 1 .983 1 1 .090 2.223 1 1 .374 13.045 0.330 1 2.789 1 1 .326 2.489 1 1 . 101 1 2.323 0.375 13.477 1 1 .819 2.918 10.792 1 1 .713 0.504 14.527 1 1 .910 3. 1 22 1 1 .802 12 . 194 2.224 14.352 1 1 .780 2.306 14.220 1 2.205 2.281 14.028 1 2.880 3.070 1 2.369 13.065 2.055 1 2.999 1 1 .021 2.012 14.289 10 . 122 2.050 13.034 10.459 2.453 12.899 1 1 .776 2.431 10.585 1 1 .745 2.458 1 1 . 108 12 . 158 0.507 14.053 1 1 .713 0 . 173 14.632 1 2. 104 0 .145 14.032 1 2.733 0.323 1 3.433 1 2.594 0.519 13 .625 1 2.435 0.265 14.956 1 2.573 0.232 1 6.407 1 1 .372 0.063 14.600 1 2.262 0.3 1 1 14.374 1 2. 1 52 0.202 14.499 10.975 0.245 14.998 10.960 2.143 1 1 .218 1 2.341 0.224 15.053 10.931 2.314 10.900 1 2.258 0.238 14.524 1 1 . 183 2.432 1 1 .809 12.815 0. 1 63 14.491 10.953 2.356 1 1 . 1 24 12. 263 0.214 14.713 1 1 .000 2. 1 62 13.023 12 . 125 0.097 14.446 10.924 2. 1 70 13.087 1 2.021 0.21 1 14.655 1 1 .305 1 .790 1 2.656 10.906 2.074 13.057 1 2.513 2.049 1 2.956 1 1 .891 9 . 129 1 3.958 0.261 14.471 10.957 0. 1 99 14.526 10.978 0. 1 92 14.525 1 1 .041 0.407 1 3.497 10.918 1 .746 1 .685 1 .341 1 .422 1 .801 1 .299 1 .549 9.607 14.838 0.293 13.671 10.876 8.542 13.606 0.355 14. 1 1 6 10.331 9 . 156 13.824 0.369 13.607 10. 190 9.575 13. 166 0.268 14.016 10.948 7.443 1 2.733 0.280 15.729 10.568 8.909 13.688 0.329 14. 1 06 10.639 1 .204 1 1 .357 13.874 2.289 10.810 13.469 1 .319 1 2.312 13.677 1 .613 10.548 1 1 .995 1 .402 1 1 .312 1 2.043 1 .421 1 2.248 1 1 .005 1 .541 1 1 .431 1 2.677 0.484 13.982 10.677 0.276 13.91 1 10.719 0.306 13.689 10.748 0.312 14.086 10.938 0.207 14. 1 28 1 0.827 0.214 14.849 10.955 0.300 14. 1 08 10.81 1 1 . 1 95 1 2.530 14.91 7 0.948 13.144 10.51 1 1 .306 1 2.446 15.285 0.509 1 2.246 10.356 1 .523 12.809 1 2.933 0.354 13 .105 1 1 . 1 81 1 .686 13.726 1 3.974 0 .183 13 .499 1 1 .082 1 .664 9.901 14. 280 0.377 13.363 1 0.223 1 .416 10.680 13.746 0.455 1 3.325 1 0.705 1 .465 1 2.015 14. 189 0.471 13 . 1 14 10.676 1 .428 1 3.813 1 2.641 0.329 14.281 10.903 1 .553 1 3.244 13.143 0. 1 82 14.479 1 1 . 171 1 .594 1 .645 0.958 1 .256 1 .464 1 .414 13 .083 1 2. 169 13.638 1 1 .396 9.896 16.091 1 2.675 1 1 .644 14. 105 12.071 1 2.922 1 2.736 2.851 1 1 . 133 10.830 2.610 1 1 .317 1 1 .679 2.81 1 1 1 . 1 1 3 1 1 .513 2.974 1 1 .051 10.917 2.528 1 1 .049 1 1 . 1 09 2.476 1 1 .486 1 2.258 3.0 1 1 1 1 .659 1 1 .712 2.752 1 1 .258 1 1 .431 0.260 14.935 1 1 . 1 1 4 0.141 1 4.876 10.815 0.681 13.331 10.261 0.135 15.502 10.793 0.274 14.226 10.804 0.286 14.519 10.837 0.252 14.487 1 1 .597 0.316 1 5.010 1 1 .479 0.254 14.513 1 1 .326 0.233 14.910 1 1 .282 0.334 14.401 1 1 .340 0.324 13.877 1 1 .210 0.450 14.677 1 1 .333 0.309 14.554 1 1 .367 1 .330 1 .393 1 .865 1 .529 6.683 1 5.81 1 0.531 1 3.287 10 . 166 6.369 1 6.534 0.604 1 2.483 10 . 132 7.853 14.480 0.474 1 3.609 10.569 6.968 15.608 0.536 13 . 126 10.289 A 14 1 .659 0.790 2.61 5 0.733 2. 1 93 0.747 2.454 0.648 2.570 0.739 2.623 2.545 2.508 2.444 2.872 2.563 2.885 2.377 2.584 2.230 2.279 0.748 0.938 0.890 0.832 0.907 0.921 0.886 0.904 0.841 0.277 0.333 2.289 0.335 2.044 0.388 2.349 0.361 2.238 0.339 2.208 0.329 2.209 0.408 2 . 197 2.391 2.251 1 .765 0.356 0.331 0.356 0.322 1 .812 0.296 1 .400 0.416 1 .643 0.337 1 .646 0.363 1 .281 0.244 1 .591 0.330 1 .948 2.243 0.219 0.321 2.420 0.380 2 .191 0.333 2.093 0.276 2.258 0.340 2. 192 0.312 1 .932 0.381 1 .793 0.370 2. 1 22 0.310 2.401 0.337 1 .971 0.233 1 .907 0.336 2.021 0.328 2.416 2 . 173 2.264 2.31 1 1 .585 2.141 2.422 2. 1 87 2.368 2.534 2.293 2.426 2.342 2.1 1 8 0.324 0.278 0.203 0.293 0.375 0.244 0.285 0.286 0.806 0.633 0.837 0.795 0.701 0.738 2.521 0.774 2.372 0.755 1 .531 1 .436 1 .539 1 .502 0.303 0.327 0.220 0.283 Appendix 3.3: Ol ivine analyses 3.3 Olivine analyses All analyses are l isted in a raw form (not normalised). Sample Location Section Sample 93.25 T20/464098 46 Sample 93.26 T20/464098 46 Sample 93.27 T20/464098 46 Sample 93.28 T20/465099 47 Sample 93.31 T20/466096 5 Sample 93.34 T20/469 1 00 7 Sample 93.38 T20/469100 7 Sample 93.41 T20/468102 9 Analysis Si02 1 resorbed 37.947 2resorbed 39.090 39.674 2 40.235 3 40.832 4 41 .481 5 41 .462 Mean 40.737 39.200 2 39.51 2 3 39.394 4 38.805 5 39.633 6 39.686 7 39.212 8 39.354 9 39.689 10 39.370 Mean 39.386 39. 1 20 2 39.323 3 38.974 4 39.985 5 39.735 6 40.290 7 40.088 8 39.963 9 39.439 1 0 39.308 Mean 39.623 1 resorbed 37.820 2resorbed 35.922 1 38.0 1 8 2 38.001 38.200 2 38.157 3 38.036 4 35.920 Mean 37.578 1 39.006 2 39.444 3 39.159 4 40.288 Mean 39.474 1 resorbed 37.827 41 .053 2 40.307 3 39.419 4 40.048 5 39.967 Mean 40. 1 59 39.264 2 39.234 3 39. 1 52 4 38.377 5 39.733 Mean 39. 1 52 Ti02 0.01 2 0.000 0.062 0 . 1 00 0.029 0.029 0.021 0.048 0.021 0.034 0.070 0.053 0.053 0.009 0.245 0.066 0.074 0.039 0.066 0.040 0.057 0.027 0.000 0.001 0.000 0.000 0.000 0.094 0.005 0.022 0.049 0. 000 0.000 0.056 0.01 2 0.002 0.000 0.070 0.021 0.078 0.031 0.030 0.058 0.049 0.055 0. 1 23 0.061 0.005 0.048 0.01 3 0.050 0.000 0.020 0.048 0.075 0.000 0.029 A 1 5 Al203 FeO 0.000 21 .649 0.007 1 8 . 1 70 0.008 1 1 .806 0.035 1 2.237 0.049 1 5.408 0.01 5 1 2.442 0.052 1 2.876 0.032 1 2.954 0.097 14.765 0.050 1 4.514 0.083 1 5.626 0.014 1 5.306 0.045 14.676 0.055 1 3. 826 0.018 14.872 0.01 5 14.816 0.061 1 4.402 0.01 9 1 5 . 1 36 0.046 14.794 0.01 5 14.8 1 9 0.059 1 5.647 0.066 1 4.613 0.074 1 3.881 0.079 1 4.988 0.051 1 4.349 0 . 1 1 5 14.481 0.057 1 5.493 0.059 1 4.013 0.039 1 5.836 0.061 14.812 0.000 23.829 0.019 23.503 0.013 1 8 . 1 66 0.1 1 6 1 8.618 0.063 21 .276 0.076 20.525 0.043 1 9.359 0.077 20.7 1 5 0.065 20.469 0.051 1 6.481 0.01 5 1 5.039 0.018 1 5.085 0.036 1 2 .968 0.030 1 4.893 0 . 1 06 25.870 0.042 9.753 0.060 1 1 .468 0.067 1 3.450 0.012 1 1 .061 0.016 1 6.007 0.039 1 2.348 0.018 1 2.556 0.088 1 6 . 1 1 8 0.01 7 1 5.840 0.132 1 8 . 1 83 0.01 7 1 6 .6 1 1 0.054 1 5.862 M nO M gO 0.190 39.953 0. 1 25 43.692 0.284 47.596 0.331 47.465 0.260 46.610 0.266 48.663 0.228 48. 540 0.274 47.775 0.529 45.887 0.468 45.969 0.288 45.407 0. 1 59 45.285 0.027 46. 1 70 0.085 45.844 0. 1 05 45.598 0.326 44.984 0.071 46. 1 99 0.01 9 45.900 0.208 45.724 0.509 45.762 0.393 45.808 0.31 9 45.413 0.466 46.403 0.301 45.332 0.659 46.067 0.384 46.105 0.528 40.089 0.252 46.607 0.370 45.153 0.418 45.274 0.430 0.391 38.142 37.540 0.272 43.807 0. 1 74 42.628 0.358 39.613 0.318 40.809 0.378 40.925 0.304 37.892 0.340 39.810 0.31 3 47.662 0.284 46.085 0.264 47.255 0.209 46.560 0.268 46.891 0.622 36.703 0.256 49.300 0.260 47.998 0.263 46.319 0.490 48.455 0.343 45. 334 0.322 47.481 0.200 45.544 0.265 43. 1 30 0.303 44.091 0.262 4 1 . 520 0. 1 82 44.058 0.242 43.669 CaO 0.1 1 9 0 . 1 33 0 . 1 86 0.100 0. 1 53 0. 1 77 0.133 0. 1 50 0. 1 52 0. 1 78 0. 1 1 8 0. 1 46 0. 1 80 0 . 1 49 0. 1 67 0. 1 59 0. 1 29 0. 1 28 0 . 1 5 1 0. 1 58 0. 1 60 0.218 0.205 0 . 1 95 0.141 0. 1 88 0 . 1 45 0. 1 55 0 . 1 66 0. 1 73 0. 1 46 0. 1 58 0. 1 30 0. 1 39 0. 1 56 0. 1 42 0. 1 00 0. 1 56 0. 1 39 0. 1 04 0. 1 24 0. 1 49 0. 1 57 0. 1 34 0 . 1 59 0. 1 52 0. 1 99 0. 1 54 0 . 1 9 1 0.109 0 . 1 6 1 0 . 1 37 0 . 1 37 0 . 1 32 0 . 1 00 0 . 1 8 1 0. 1 37 Na20 0.005 0.058 0.050 0.035 0.051 0.049 0.005 0.038 0.031 0.090 0.013 0.057 0.035 0.029 0.002 0.068 0.001 0.005 0.033 0.002 0.000 0.044 0.031 0.005 0.037 0.001 0.008 0.000 0.000 0.013 0.005 0.000 0.083 0.01 3 0.037 0.037 0.071 0.239 0.096 0.000 0.000 0.000 0.01 1 0.003 0. 1 1 3 0.01 3 0.029 0.000 0.000 0.089 0.026 0.028 0.000 0.000 0.007 0.086 0.024 1<20 0.029 0.026 0.035 0. 1 09 0.024 0.051 0.020 0.048 0.002 0.010 0.025 0.039 0.044 0.053 0.087 0.035 0.043 0.029 0.037 0.01 5 0.031 0.037 0.008 0.01 7 0.026 0.031 0.076 0.043 0.001 0.029 0.051 0.059 0.027 0.032 0.003 0.017 0.000 0.095 0.029 0.009 0.041 0.012 0.006 0.01 7 0.053 0.039 0.053 0.026 0.027 0.01 1 0.031 0.024 0.037 0.000 0.025 0.048 0.027 Sample 93.44 T20/4681 02 9 Sample 93.54 T20/468 1 02 1 0 Sample 93.60 T20/4771 1 2 1 4 Sample 93.62 T20/4771 1 2 1 4 Sample 93.63 T20/4771 1 2 1 4 Sample 93.65 T20/4771 1 2 1 4 Sample 93.67 T20/4771 1 2 1 4 Sample 93.68 T20/4771 1 2 1 4 Sample 93.70 T20/4771 1 2 1 4 Sample 93.71 T20/4771 1 2 Sample 93.77 T20/4771 1 2 1 4 Sample 93.82 T20/4771 1 2 1 4 Appendix 3.3: Olivine analyses 1 resorbed 38.366 2resorbed 38.510 1 40.593 2 40.028 38.973 2 39.854 3 39. 1 54 4 38.293 Mean 39.069 1 39.254 2 39.982 3 39.828 4 38.610 5 38.971 1 38.619 2 38.232 3 36.979 4 37.459 5 37.612 6 36.863 Mean 37.228 36.203 2 38.549 3 36.820 4 39.259 39.778 2 40.818 3 40.050 4 39.856 Mean 40. 1 26 1 38.507 2 39.563 3 36.638 4 37.750 Mean 38. 1 1 5 1 40.023 2 39.422 3 39.460 4 37.240 Mean 39.036 1 36.074 2 35.435 3 35.566 4 35.989 5 36.485 6 34.994 Mean 35.757 35.369 2 35.460 3 35.681 4 35.256 5 35.487 6 35.540 Mean 35.466 1 41 .438 2 41 .302 3 40.576 36. 1 79 0.01 6 0.047 0.032 0.039 0.000 0.000 0.01 1 0.086 0.024 0.030 0.075 0. 1 28 0.061 0.048 0.064 0.000 0.051 0.039 0.025 0. 1 1 5 0.058 0. 1 23 0.005 0.002 0.028 0.091 0. 1 1 2 0.046 0.033 0.071 0.01 0 0.057 0.068 0.054 0.047 0.015 0.052 0.024 0.01 1 0.026 0.254 0. 1 20 0.069 0.060 0.032 0. 1 22 0 . 1 1 0 0. 1 00 0 . 1 36 0. 1 1 1 0.1 1 2 0.105 0 . 1 2 1 0 . 1 14 0 . 1 52 0.025 0.01 2 0.029 A 1 6 0.035 26.864 0.000 26.965 0.056 1 7. 205 0.01 1 1 7.300 0.016 1 3.097 0.208 1 2.091 0.014 1 3.924 0.095 1 7.940 0.083 14.263 0.009 1 2.403 0.012 1 2. 225 0.062 1 2.621 0.088 1 8.547 0.047 1 6 .325 0.01 5 0.069 8.500 8.496 0.067 1 3.970 0.055 14. 1 1 5 0.010 1 3.846 0.001 1 1 .823 0.033 1 3.439 0.045 22.252 0.046 14.057 0.000 1 3.757 0.000 1 1 .022 0.074 1 4. 1 1 5 0.069 1 4. 1 91 0.000 1 1 .890 0.000 1 1 .205 0.036 1 2.850 0.000 1 8.549 0.040 1 7.745 0.01 8 1 8. 1 3 1 0.059 1 7.386 0.029 1 7. 953 0.065 1 7.973 0 . 1 68 1 7.853 0.01 1 1 7.086 0.074 1 9.531 0.080 1 8. 1 1 1 0.293 29.819 0.014 3 1 . 1 39 0.516 29.289 0.000 27. 1 77 0.057 27. 1 46 0.204 3 1 . 220 0 . 1 8 1 29.298 0.563 3 1 . 548 0.430 31 .048 0.251 29. 746 0.325 3 1 . 056 0.465 29.998 0.402 30.157 0.406 30.592 0.01 7 1 3.766 0.01 5 1 3.691 0.069 1 2.016 0 . 1 54 1 8.471 0.429 35.010 0.532 35.077 0.346 43.407 0.295 43.016 0.231 46.030 0.203 47.247 0.199 45.506 0.268 41 .761 0.225 45. 1 36 0.224 47.222 0.277 47.632 0 . 1 97 47.547 0.252 43.273 0.269 43. 1 40 0.136 5 1 . 1 63 0.1 1 7 52.488 0.171 46.301 0.298 47.498 0.260 47.395 0.31 3 49.300 0.261 47.624 0.298 39.614 0.1 1 6 47.669 0.263 46.787 0 . 1 90 49.080 0 . 1 83 46.203 0 . 1 49 46.535 0.209 47.921 0 . 1 67 48.208 0. 1 77 47.217 0.210 43. 1 55 0 . 1 92 42.841 0.329 42.189 0.314 42.863 0.261 42.762 0.371 43.747 0.252 45.803 0.353 44.393 0.346 43.195 0.331 44.285 0.31 8 30. 8 1 3 0. 536 28.757 0.636 29.271 0.625 34.342 0.584 34.285 0.466 27.644 0.528 30.852 0.341 27. 1 34 0.51 1 27.458 0.506 30.066 0.458 29.687 0.347 29.874 0.503 29.325 0.444 28.924 0.247 46.510 0.265 46.839 1 .973 46.598 0.434 42.790 0.087 0.069 0 . 1 39 0.098 0 . 1 67 0.141 0 . 1 44 0 . 1 22 0.144 0 . 1 66 0 . 1 35 0 . 1 96 0 . 1 80 0 . 1 46 0 . 1 56 0.131 0. 1 1 4 0 . 1 69 0.147 0. 1 8 1 0. 1 53 0.099 0 . 1 1 2 0. 1 24 0. 1 25 0.081 0. 1 1 3 0. 1 35 0.092 0 . 1 05 0. 1 00 0 . 1 24 0. 1 38 0 . 1 33 0. 1 24 0. 1 23 0.421 0. 1 50 0. 1 36 0.208 0.309 0.283 0.283 0 . 1 87 0.393 0.3 1 7 0.295 0.356 0.378 0.312 0.310 0.398 0.398 0.359 0. 1 83 0.191 0.164 0.238 0.003 0.001 0.005 0.056 0.01 1 0.085 0.058 0.078 0.058 0.070 0.073 0 . 1 39 0. 1 04 0.070 0.067 0.012 0.056 0.092 0.055 0.058 0.065 0.065 0.000 0.000 0.01 1 0.066 0.013 0.000 0.000 0.020 0 . 1 0 1 0.077 0.000 0 . 1 0 1 0.070 0.050 0.030 0.084 0.073 0.059 0.053 0.004 0.402 0.084 0.200 0.168 0 . 1 52 0.084 0.095 0 . 1 38 0 . 1 06 0.068 0.098 0.098 0.037 0.045 0.042 0.088 0.031 0.047 0.016 0.041 0.023 0.01 0 0.009 0.007 0.01 2 0.037 0.043 0.045 0.064 0.043 0.052 0.047 0.002 0.000 0.01 8 0.027 0.01 2 0.044 0.004 0.002 0.027 0.018 0.000 0.007 0.01 6 0.010 0.026 0.035 0.042 0.030 0.033 0.018 0.000 0.023 0.022 0.016 0.031 0.046 0.041 0.054 0.084 0.024 0.047 0.036 0.030 0.044 0.021 0.059 0.041 0.039 0.053 0.057 1 .528 0 . 1 5 1 Appendix 3.3: Olivine analyses 2 34.925 0.028 0.040 1 9 .079 0.335 42.308 0. 1 51 0.071 0.055 3 33.552 0.01 1 0.098 21 .213 0.298 39.985 0. 149 0.091 0.01 7 Sample 93.85 T20/4771 1 2 1 4 1 36. 1 1 9 0.014 0 . 1 08 24.502 0.436 37.754 0.066 0 . 1 45 0.041 2 35.601 0.035 0.035 24.029 0.428 38.989 0 . 1 0 1 0.047 0.048 3 35.985 0.01 4 0.098 23.684 0.425 38.647 0.095 0 . 1 02 0.045 4 35.998 0.01 6 0 . 1 1 2 23.268 0.462 38.654 0.035 0.078 0.044 5 36.002 0.025 0 . 1 05 24. 1 25 0.465 38.264 0.037 0.089 0.046 6 35.654 0.056 0.065 24.517 0.425 37.724 0. 1 05 0.067 0.048 7 35.458 0.023 0.099 24.056 0.402 38.025 0.095 0.098 0.041 8 36.015 0.01 2 1 .070 24.265 0.414 37.951 0 . 1 02 0.068 0.039 Mean 35.854 0.024 0.212 24.056 0.432 38.251 0.080 0.087 0.044 A 1 7 Appendix 3.4: Titanomagnetite analyses Appendix 3.4 Titanomagnetite analyses All analyses are in a raw form (not normalised). Sample Location Section Analysis Si02 Ti02 Al203 FeO MnO MgO CaO Na20 K20 Cr203 NiO Sample 93.24 T20/464098 46 Sample 93.25 T20/464098 46 Sample 93.26 T20/464098 46 Sample 93.27 T20/464098 46 Sample 93.38 T20/469100 7 Sample 93.39 T20/469100 7 Sample 93.43 T20/468 1 02 9 Sample 93.44 T20/468 1 02 9 Sample 93.45 T20/468102 9 1 0.064 1 1 .691 3.046 72.650 0.285 2.823 0.095 0.239 0.052 0.776 0. 1 38 2 0 . 1 50 1 0.532 3 . 1 8 1 75.910 0.188 1 .4 1 5 0.148 0.300 0.000 0.081 0.047 3 0.290 1 2.030 3.351 7 1 . 1 96 0.329 3.233 0 . 1 66 0.359 0.014 0.569 0. 1 76 4 0.059 1 1 .042 3.216 72.686 0 . 1 9 1 3. 1 52 0.046 0.092 0.069 0.081 0 . 1 31 5 O.o76 1 1 .383 3.161 71 .688 0.277 2.961 0.058 0.051 0.003 0.293 0. 1 99 Mean 0 . 1 28 1 1 .336 3 . 1 9 1 72.826 0.254 2. 7 1 7 0. 1 03 0.208 0.028 0.360 0. 1 38 0.066 1 3.254 2.506 74.933 0.381 3.387 0.073 0.002 0.023 0.229 0.004 2 0.082 1 1 .627 2.232 79.062 0.658 2.204 0.083 0.227 0.029 0.444 0. 1 06 3 0. 1 28 1 3.372 2.251 75.805 0.347 3.686 0.048 0 . 1 75 0.050 0 . 1 20 0.000 4 0.097 1 5.027 2.373 76.633 0.309 2.452 0.043 0.089 0.036 0.215 0.065 5 0 . 1 2 1 1 5 . 1 25 2. 730 73.923 0.456 3.502 0.070 0.006 0.025 0. 1 30 0.064 6 0. 1 25 10.71 7 3.335 77.494 0.377 3.090 0.027 0.01 2 0.029 0.260 0.037 7 0.229 1 1 .988 2.262 77.921 0.425 2.275 0 . 1 4 1 0. 1 46 0.025 0. 1 60 0.078 8 0. 1 59 1 4.266 2.368 74.968 0.433 2.778 0.021 0.088 0.014 0. 1 67 0.056 Mean 0. 1 26 1 3. 1 72 2.507 76.342 0.423 2.922 0.063 0.093 0.029 0.216 0.051 1 0 . 1 58 2 0.256 3 0 . 1 42 4 0.1 1 1 5 0 . 1 98 6 0.225 Mean 0 . 1 82 8. 1 25 8.698 9.003 8.995 8.269 8.784 8. 646 1 0 . 1 44 9.052 2 0.388 8.458 3 0. 717 8.357 4 0.298 8.671 5 0.265 8. 798 6 0 . 1 54 9.045 Mean 0.328 8.730 2 3 4 5 Mean 0.065 0.042 0 . 1 07 0.086 0.144 0.089 8.752 8.928 9.646 9.545 9.569 9.288 2.501 80.265 0.564 2.01 3 80.999 0.441 1 .854 80.698 0.235 1 .764 8 1 . 254 0.336 1 .846 80.005 0.289 1 .655 80.568 0.364 1 .939 80.632 0.372 1 .025 0.088 0. 1 1 2 0.045 0.2 1 5 0.062 1 . 1 1 5 0.078 0. 1 65 0.088 0.258 0.098 1 .698 0.089 0. 1 88 0.068 0.232 0.254 1 .995 0.056 0. 1 65 0.035 0.247 0. 1 58 1 .654 0.021 0 . 1 2 1 0.056 0.332 0.1 1 4 1 .567 0.091 0 . 1 33 0 . 1 30 0.395 0. 1 02 1 .509 0.071 0 . 1 47 0.070 0.280 0 . 1 31 2.001 81 .051 0.429 1 .581 0.091 0.083 0.019 0.065 0.066 1 .451 80.574 0.407 1 .803 0.067 0 . 1 38 0.041 0.722 0.000 0.876 8 1 . 255 0.324 1 .225 0.094 0 . 1 34 0.035 0.205 0 . 1 74 1 .687 81 .600 0.322 1 .665 0.099 0 . 1 43 0.440 0.360 0 . 1 9 1 2.087 80.998 0.345 1 .582 0.068 0. 1 52 0.029 0.265 0.1 1 5 2.258 80.254 0.399 1 .396 0.024 0. 1 99 0.023 0.030 0.098 1 .727 80.955 0.371 1 .542 0.074 0 . 1 42 0.098 0.275 0 . 1 07 4.222 75.048 0.385 4.504 74.376 0.274 3.834 77.449 0.346 4.277 77.194 0.429 4.224 77.703 0.41 8 4.212 76.354 0.370 3.946 0.087 0.065 0.000 0.920 0. 1 70 4.050 0.069 0.000 0.021 1 .322 0. 1 05 3.083 0.042 0.000 0.031 0.632 0.055 3 . 1 9 1 0.046 0.209 0.033 0.521 0 . 1 89 2.853 0.046 0. 1 27 0.010 0.476 0.057 3.425 0.058 0.080 0.019 0.774 0. 1 1 5 1 0 . 1 02 1 5.260 1 . 201 73.025 0.531 2. 1 60 0.052 0.000 0.018 0. 1 53 0.051 2 0.050 1 5 .897 1 . 1 1 5 73.254 0.315 1 .882 0.028 0.080 0.050 0. 1 75 0.093 3 0.020 1 5.555 0.706 73.598 0.225 1 .890 0.060 0.057 0.000 0.068 0.000 4 0. 1 36 1 5.334 1 .327 73.300 0.242 1 . 1 60 0.042 0.000 0.042 0. 1 41 0.023 5 0.216 1 5 .722 1 .241 74.218 0.474 1 .258 0.038 0.000 0.023 0.089 0.033 6 0.059 1 6 .002 1 .315 72.598 0.256 1 .357 0.025 0.057 0.0 1 5 0. 1 55 0.048 Mean 0.097 1 5.628 1 . 1 5 1 73.332 0.341 1 .6 1 8 0.041 0.032 0.025 0. 1 30 0.041 1 0.096 1 3.935 2.652 71 .589 0.51 0 2.720 0 . 1 06 0. 1 88 0.000 0. 1 78 0.034 2 0.096 1 4 . 1 93 2.773 7 1 . 559 0.419 2.697 0.041 0.008 0.000 0.394 0.091 3 0. 1 57 14.225 2.765 7 1 . 904 0.4 1 5 2.643 0.067 0 . 1 1 9 0.000 0.349 0.094 4 0. 1 27 14.684 2.602 72.474 0.458 2.381 0.042 0.097 0.000 0.476 0.095 Mean 0.1 1 9 14.259 2.698 71 .882 0.451 2.610 0.064 0 . 1 03 0.000 0.349 0.079 1 0 . 1 65 9.688 3. 733 74.084 2. 783 3.382 0.055 0.008 0.770 0.085 0. 165 2 0.21 1 1 0 .425 3.843 73.270 0.403 3.214 0.008 0. 1 62 0.01 6 0.260 0. 1 98 3 0.233 1 0.363 3.946 73.948 0.334 3.235 0.032 0. 1 75 0. 1 54 0.202 0. 1 39 4 0 . 1 62 1 0 .049 4. 1 72 75.763 0.388 3. 1 57 0.051 0.073 0.048 0. 1 23 0. 1 55 5 0.261 1 0.005 3.855 72.278 0.258 3.338 0.084 0.149 0.037 0.041 0.147 6 0 . 1 68 9.801 3.979 75.587 0.323 3.260 0.056 0 . 1 9 1 0.01 3 0. 1 31 0. 1 62 Mean 0.200 1 0.055 3.921 74.155 0.748 3.264 0.048 0 . 1 26 0 . 1 73 0.140 0 . 1 61 0. 1 29 7.472 6.856 76.346 0.222 4.255 0.043 0 . 1 58 0.023 0.301 0.006 2 0. 1 32 7.468 7.068 77.093 0.31 2 3.8 1 5 0.037 0.000 0.047 0.850 0.355 3 0 . 1 94 1 2.341 3.271 78.028 0.324 2.868 0.065 0.254 0.009 0. 1 22 0.098 4 0 . 1 53 1 2.037 3.228 75. 1 30 0.398 3.006 0. 1 08 0. 1 94 0.035 0.054 0.000 A 1 8 Appendix 3.4: Titanomagnetite analyses Sample 93.46 T20/468102 9 Sample 93.47 T20/468102 9 Sample 93.48 T20/468102 9 Sample 93.49 T20/468102 9 Sample 93.50 T20/468102 9 Sample 93.51 T20/468102 9 Sample 93.52 T20/468102 10 Sample 93.53 T20/468102 10 Sample 93.54 T20/468102 10 Sample 93.55 T20/468102 10 Sample 93.57 T20/468102 10 5 0.167 12.806 2.892 76.952 0.443 2.686 0 . 109 0. 177 0.030 0 . 134 0.204 6 0. 1 14 12.664 3.066 77.152 0.476 2.609 0.052 0.087 0.037 0.141 0.072 Mean 0.157 12.462 3. 1 14 76.816 0.410 2.792 0.084 0. 178 0.028 0. 1 1 3 0.094 1 0.072 1 1 .065 2 0.075 10.459 3 0 . 178 1 1 . 1 69 4 0.181 1 1 .537 5 0 .143 1 1 .61 1 6 0.218 1 1 .046 3.446 72.767 0.383 3.050 0.000 0.269 0.000 0 . 182 0.262 3.384 72.334 0.338 2.966 0.000 0.000 0.007 0.074 0.1 16 3.404 74.536 0.417 2.907 0.010 0.012 0.005 0.267 0.007 3.388 72.604 0.456 2.800 0.01 1 0. 1 1 7 0.005 0. 147 0. 1 77 3.285 71 .670 0.395 2.781 0.000 0.057 0.015 0 . 155 0.018 3.523 74.197 0.361 3.244 0.004 0.000 0.042 0.161 0.123 Mean 0.145 1 1 . 148 3.405 73.018 0.392 2.958 0.004 0.076 0.012 0. 164 0.1 1 7 0.053 8.380 6.032 76. 190 0.31 1 3.750 0.097 0.085 0.023 1 . 1 60 0. 1 1 1 2 0.034 8. 196 6.071 77. 164 0.186 4.054 0.079 0.096 0.023 1 . 1 70 0 . 100 3 0 . 126 8.819 5.357 78.235 0.248 3.654 0.1 10 0.079 0.007 0.392 0.247 4 0.363 8.763 5.616 77.391 0.389 3.893 0.090 0.342 0.000 0.856 0.055 5 0.108 8.650 5.425 79.506 0.289 4 .139 0.128 0 . 164 0.036 0.473 0. 1 06 6 0 . 136 8.608 4.990 78.559 0.450 3.815 0.074 0.073 0.012 0.538 0.078 Mean 0.137 8.569 5.582 77.841 0.312 3.884 0.096 0. 1 40 0.017 0.765 0 . 1 16 0.226 9.423 4.627 74.929 0.284 3.509 0.036 0. 1 39 0.023 0.450 0.000 2 0.054 7. 1 77 3.467 81 .476 0.785 2.751 0.077 0.218 0.053 0 . 1 18 0.007 3 0 . 139 9.226 4.507 76.258 0.245 3.305 0.008 0.000 0.027 0. 134 0.106 4 0.192 9. 198 4.602 76.826 0.267 3.551 0.037 0.002 0.012 0.448 0.000 5 0. 134 8.969 4.477 76.863 0.301 3.488 0.079 0.013 0.01 7 0.209 0.060 Mean 0.149 8.799 4.336 77.270 0.376 3.321 0.047 0.074 0.026 0.272 0.035 1 0.062 8.734 4.358 81 .060 0.387 3.553 0.046 0 . 165 0.000 0.255 0. 103 2 0. 1 29 8.644 4.528 77.981 0.403 3.737 0.049 0.235 0.004 0.143 0.026 3 0. 159 8.594 4.609 79.361 0.337 3.590 0.054 0.265 0.019 0.448 0.030 4 0.147 8.721 4.596 78.31 1 0.438 3.550 0.049 0.208 0.000 0.224 0. 1 54 5 0 . 121 8.651 4.295 78.439 0.277 3.252 0.058 0 . 164 0.040 0.289 0.035 6 0.085 8.633 4.882 77.992 0.326 3.689 0.030 0 .134 0.021 0.1 15 0. 1 1 3 Mean 0. 1 1 7 8.663 4.545 78.857 0.361 3.562 0.048 0 . 195 0.014 0.246 0.077 0 . 166 10.861 2 0. 127 13.272 3 0.042 13.014 3.261 77.722 0.468 2.691 0.089 0 . 199 0.021 0.229 0.000 2.684 78.850 0.622 2.412 0.070 0.209 0.006 0.097 0.022 2. 782 77.845 0.583 2.161 0.024 0.003 0.058 0.217 0. 1 80 4 0. 1 24 12.987 2.881 77.854 0.382 2.617 0.070 0 . 187 0.030 0.081 0.029 5 0.036 10.829 3. 1 22 80.272 0.493 2.912 0.021 0.000 0.054 0.025 0.073 6 0.021 9.374 4.379 8 1 . 1 28 0.287 3.065 0. 1 1 6 0.000 0.014 0.093 0.071 Mean 0.086 1 1 .723 3.185 78.945 0.473 2.643 0.065 0. 100 0.031 0 .124 0.063 1 0 .108 8.397 3.879 79.537 0.323 3.334 0.044 0 . 143 0.027 0.396 0.215 2 0.137 8.868 3.746 79.203 0.424 3.245 0.000 0.082 0.055 0.203 0. 1 55 3 0.137 9.080 3.778 77.719 0.392 3.225 0.035 0.000 0.052 0.050 0.283 4 0.189 8.690 3.407 77.837 0.282 3.005 0 .105 0.000 0.042 0. 1 68 0.039 5 0.182 9.008 3.967 78.818 0.389 3.223 0.025 0.008 0.024 0. 1 84 0.225 Mean 0.151 8.809 3.755 78.623 0.362 3.206 0.042 0.047 0.040 0.200 0. 183 1 0 .167 7.828 2 0. 184 7.518 3 0.484 7.921 4.515 78.222 0.372 3.649 0. 1 1 7 0.150 0.000 0.925 0. 127 3.617 74.289 0.252 2.501 0.093 0.009 0.014 0.864 0.254 4.842 77. 1 1 3 0.338 3.883 0.045 0.605 0.022 0.577 0. 1 1 8 4 0.475 7.763 5.256 76.502 0.375 3.827 0.026 0.504 0.009 0.796 0.245 5 0.508 8.018 5.41 1 78.048 0.407 3. 730 0.091 0. 723 0.002 0.570 0.229 6 0.505 7.738 5.140 77.826 0.308 3.864 0.071 0.490 0.014 0.556 0. 174 Mean 0.387 7.798 4.797 77.000 0.342 3.576 0.074 0.414 0.010 0.715 0. 191 0 . 138 9.475 4.974 76.666 0.298 2.400 0.048 0.000 0.007 0.375 0. 1 29 2 0. 1 53 8.516 5.051 74.663 0.303 3.393 0.051 0.002 0.007 1 .050 0.091 1 0.151 9.475 2 0.147 10.259 3 0.072 9.810 3.535 71 .564 0.305 3.579 71 .035 0.332 3.549 71 .505 0.344 3.41 1 0.208 0.002 0.013 0.568 0. 1 14 3. 1 25 0.070 0 . 168 0.024 0.740 0.098 3 . 150 0.020 0.000 0.022 0.717 0.094 4 0 . 176 9.91 1 3.845 72.889 0.270 3.413 0.048 0.093 0.030 0.998 0.071 Mean 0.137 9.864 3.627 71 .748 0.313 3.275 0.087 0.066 0.022 0.756 0.094 0. 126 1 2.801 2.956 75.422 0.282 2.425 0.035 0.077 0.005 0.263 0. 1 22 2 0.281 1 2.248 3.042 75.073 0.368 2.725 0.032 0.268 0.000 0.540 0 .169 3 0. 1 89 10.243 3.336 76.203 0.222 3.016 0.025 0.251 0.000 0.477 0 .104 Mean 0.199 1 1 .764 3.1 1 1 75.566 0.291 2.722 0.031 0 . 199 0.002 0.427 0. 132 0 . 134 10. 197 3.348 74.069 0.294 2.857 0.045 0.000 0.030 0.459 0. 1 1 6 2 0 .167 10.279 3.498 74. 1 54 0.322 3.181 0.036 0 . 1 13 0.019 0.373 0.000 A 1 9 Appendix 3.4: Titanomagnetite analyses Sample 93.58 T20/468102 10 Sample 93.61 T20/4771 12 14 Sample 93.62 T20/4 771 12 14 Sample 93.63 T20/4771 1 2 14 Sample 93.65 T20/4771 1 2 14 Sample 93.66 T20/4771 1 2 14 Sample 93.67 T20/4771 1 2 1 4 Sample 93.68 T20/4771 1 2 14 Sample 93.69 T20/4771 1 2 1 4 Sample 93.70 T20/4771 1 2 14 3 0.080 10.590 3.423 73.334 0.359 3. 1 92 0.002 0.181 0.075 0.337 0.029 4 0. 129 10.068 3.608 74.440 0.425 3.216 0.026 0.000 0.023 0.368 0.000 5 0.107 10.472 3.268 73.414 0.41 1 3.057 0.038 0.013 0.065 0.201 0.020 6 0 . 158 10.095 3.417 74. 1 38 0.348 2.965 0.027 0.081 0.027 0.497 0.000 Mean 0 . 129 10.284 3.427 73.925 0.360 3.078 0.029 0.065 0.040 0.373 0.028 0.069 12 .096 2 0.060 12 . 133 3 0.039 1 1 .993 4 0.064 1 1 .659 5 0.141 1 2.279 3.033 74.382 0.344 2.382 0.054 0.336 0.060 0. 162 0. 1 1 9 3. 123 73.764 0.344 2.422 0.045 0.162 0.016 0.092 0. 1 55 3.064 72.638 0.338 2.421 0.050 0.000 0.040 0. 1 28 0.018 2.530 72.793 0.357 2. 1 80 0.073 0.000 0.062 0.091 0.064 2.801 74.147 0.348 1 .849 0.056 0.092 0.035 0.218 0.004 6 0.401 12.300 2.993 73.298 0.379 2.588 0.075 0.001 0.045 0.000 0.031 Mean 0 . 129 12.077 2.924 73.504 0.352 2.307 0.059 0.099 0.043 0. 1 1 5 0.065 0. 137 2 0 .151 3 0. 1 27 4 0.221 5 0. 1 77 9.401 9.277 8.589 8.551 9 . 104 4.246 71 .746 0.351 3.965 73.577 0.417 3.783 74.333 0.669 3.630 74.541 0.664 4.504 73.108 0.346 3. 1 29 0. 1 86 0.142 0.061 0.295 0. 134 2. 1 78 0 . 191 0 . 141 0.035 0.339 0.075 3.073 0.063 0.000 0.028 0.235 0.088 3. 127 0.059 0.201 0.067 0.300 0. 1 1 9 3. 1 75 0.026 0.000 0.065 0.672 0.093 6 0. 1 1 2 8.514 5.068 73.333 0.425 3.094 0.029 0. 128 0.055 0.412 0.000 Mean 0. 154 8.906 4. 1 99 73.440 0.479 2.963 0.092 0 . 102 0.052 0.376 0.085 1 0. 1 95 2 0. 122 3 0.056 4 0.055 8.637 8.682 9.286 9.084 4.734 71 .337 0.284 4.793 72. 131 0.323 4.422 75.708 0.422 4.398 75.206 0.260 3.716 0.251 0.075 0.017 2.231 0. 165 3.422 0.271 0.004 0.000 1 . 788 0. 169 3.365 0.090 0. 1 73 0.041 0.488 0. 1 88 3.642 0.074 0.222 0.020 0.440 0 . 108 5 0 . 100 9.060 4.386 76.958 0.472 3.095 0.108 0. 1 26 0.077 0.389 0 . 154 6 0.040 8.973 4.250 76. 123 0.243 3.578 0.1 10 0. 105 0.093 0.394 0 .146 Mean 0.095 8.954 4.497 74.577 0.334 3.470 0 . 151 0. 1 1 8 0.041 0.955 0. 155 1 0 . 194 13.461 2.468 73.919 0.428 2.540 0.047 0.013 0.01 1 0.249 0.098 2 0. 162 1 3.895 2.673 73. 194 0.362 2.644 0.024 0.1 1 2 0.000 0.234 0.084 3 0 . 177 13.097 2.464 71 .750 0.378 2.914 0 .144 0.090 0.046 0.419 0.245 Mean 0 . 178 13.484 2.535 72.954 0.389 2.699 0.072 0.072 0.019 0.301 0 . 142 1 0 . 191 1 2.698 3.074 72.225 0.414 3.525 0.073 0.003 0.006 0.335 0. 1 68 2 0.169 12.071 3.148 71 .726 0.397 3.342 0.040 0.010 0.026 0.221 0. 1 1 9 3 0.299 12.677 3.242 71 .745 0.337 3.596 0 . 108 0.083 0.025 0.358 0. 1 1 3 Mean 0.220 12.482 3. 155 71 .899 0.383 3.488 0.074 0.032 0.019 0.305 0 . 133 0.252 1 1 .207 2.977 73.905 0.427 2.857 0.080 0.1 71 0.007 0.330 0.089 2 0. 136 1 1 .361 3. 1 85 73.615 0.583 3.024 0.003 0.334 0.020 0.382 0.046 3 0.270 10.946 3.268 71 .518 0.326 2.896 0.009 0.193 0.035 0.523 0.01 1 4 0. 1 87 1 1 . 1 90 3.266 72.344 0.333 3.068 0.000 0.248 0.007 0.310 0.000 5 0.083 10.892 3.229 71 .603 0.396 2.961 0.066 0. 168 0.015 0.605 0.050 Mean 0 . 186 1 1 . 1 1 9 3 .185 72.597 0.413 2.961 0.032 0.223 0.017 0.430 0.039 1 0.093 12.469 2.997 73.785 0.292 2.522 0.092 0.013 0.018 0 . 166 0. 1 40 2 0.099 12 . 198 3.040 74.392 0.271 2.269 0.057 0. 1 92 0.016 0. 125 0. 1 30 3 0. 1 34 1 1 .603 3.065 74.805 0.343 2.486 0.075 0.060 0.008 0.000 0.245 4 0.097 9.284 4.334 72.928 0.221 3.543 0.096 0.005 0.021 0 . 125 0.149 5 0. 152 13.798 3 . 153 73.027 0.334 2.296 0.044 0.067 0.048 0.343 0.1 1 3 Mean 0. 1 1 5 1 1 .870 3.318 73.787 0.292 2.623 0.073 0.067 0.022 0 . 152 0.155 1 0 . 108 9.353 3.877 75. 147 0.266 3.505 0.054 0. 1 1 5 0.040 0.300 0.101 2 0.059 10 . 193 4.364 76. 1 34 0.344 3.328 0.072 0.009 0.006 0. 1 45 0.106 3 0 . 128 10.222 4 .100 76.229 0.366 3.313 0.075 0. 1 70 0.040 0.222 0 .149 4 0 .185 10.294 4.419 75.427 0.380 2.899 0.088 0. 1 59 0.017 0.227 0.065 5 0.076 10.097 4. 1 94 76.650 0.287 2.986 0.049 0.005 0.001 0.384 0. 124 Mean 0. 1 1 1 10 .032 4.191 75.917 0.329 3.206 0.068 0.092 0.021 0.256 0. 109 1 0.123 9.878 3.940 73.899 0.467 3.492 0.053 0.000 0.037 0.285 0.080 2 0.101 9.796 3.863 71 .916 0.358 3.470 0.017 0.095 0.033 0.492 0 . 167 3 0.086 9.792 3.888 73.193 0.415 3.522 0.060 0.053 0.038 0.221 0 . 178 4 0.244 10 . 136 4. 1 87 73.747 0.527 3.697 0.025 0.285 0.037 0.385 0 . 120 5 0.046 10. 1 1 7 3.666 72.404 0.286 3.262 0.023 0.004 0.034 0. 1 88 0.040 Mean 0. 120 9.944 3.909 73.032 0.41 1 3.489 0.036 0.087 0.036 0.314 0. 1 1 7 1 0.075 7.775 5. 1 70 76.721 0.350 3.762 0.020 0.000 0.018 1 .240 0 .149 2 0.038 6.628 5.792 76.720 0.390 3.632 0.000 0.01 1 0.021 1 .735 0. 1 46 3 0.057 4 0.088 5 0 . 137 Mean 0.079 9.048 8.662 8.275 8.078 A 20 4.610 76.465 0.372 4.638 74.720 0.362 5.554 75. 105 0.228 5. 1 53 75.946 0.340 3.704 0.016 0.064 0.037 0.679 0. 1 71 3.648 0.054 0.049 0.022 1 .008 0.144 4 .106 0.094 0.076 0.000 1 .208 0.1 1 8 3.770 0.037 0.040 0.020 1 . 1 74 0 .146 Appendix 3.4: Titanomagnetite analyses Sample 93.71 T20/4771 1 2 1 4 Sample 93.72 T20/4771 1 2 1 4 Sample 93.73 T20/4771 1 2 1 4 Sample 93.74 T20/4771 1 2 1 4 Sample 93.76 T20/4771 1 2 1 4 Sample 93.77 T20/4771 1 2 1 4 Sample 93.78 T20/4771 1 2 1 4 Sample 93.79 T20/4771 1 2 1 4 Sample 93.80 T20/4771 1 2 1 4 1 0 . 1 92 8.659 5.540 74.731 0.376 3. 1 33 0.032 0.050 0.001 0.655 0.147 2 0.248 9.062 4.349 75.6 1 7 0.414 3.127 0.075 0. 1 00 0.006 0.395 0. 1 09 3 0 . 1 00 8.862 5.916 76.227 0.376 3.398 0.045 0. 1 1 8 0.023 0.749 0.000 4 0 . 1 70 9.042 4.993 76.009 0.420 3.757 0.068 0.000 0.000 0.508 0.066 5 0. 1 1 8 8. 714 4. 767 76.283 0.362 3.486 0.043 0.000 0.008 0.692 0.055 Mean 0 . 1 66 8.868 5. 1 1 3 75.773 0.390 3.380 0.053 0.054 0.008 0.600 0.075 0.146 8.429 4. 713 73.152 0.263 3.51 1 0.092 0.060 0.072 0.201 0 . 1 66 2 0.069 9.264 4.618 73.909 0.345 3.294 0. 1 1 0 0.264 0.014 0.1 1 5 0.065 3 0 . 1 99 8.757 4.477 74.937 0.271 3.051 0.042 0.000 0.020 0.148 0.035 4 0.227 8.934 4.493 76.585 0.332 3.064 0.054 0. 1 82 0.002 0. 1 23 0.015 5 0.076 9.326 4.301 77. 1 94 0.283 2.876 0.058 0.000 0.000 0.000 0.096 6 0 . 1 41 9.245 4.657 77.033 0.31 3 3. 1 1 3 0.073 0.1 1 2 0.000 0 . 1 53 0.050 7 0.066 9.099 4.233 77.102 0.491 3.334 0.060 0.067 0.000 0.083 0.000 Mean 0 . 1 32 9.008 4.499 75.702 0.328 3. 1 78 0.070 0.098 0.015 0.1 1 8 0.061 1 0.082 1 0.606 3.0 1 5 78.327 0.516 2.358 0.055 0.1 1 6 0.030 0.082 0.032 2 0. 1 1 6 1 0.290 3. 1 38 78.353 0.497 2.387 0.054 0 . 1 29 0.000 0 . 1 76 0.026 3 0.078 9.976 3. 1 98 79.005 0.927 2.702 0.007 0.047 0.044 0.358 0. 1 29 4 0.091 9.327 3.21 7 78.979 0.449 2.771 0.044 0 . 1 07 0.0 1 2 0 . 1 94 0.039 5 0.001 8.586 3. 787 78.540 0.392 3. 1 96 0.045 0.007 0.019 0. 1 38 0. 1 1 3 6 0.068 1 0 .497 7 0.074 1 0. 3 1 5 Mean 0.073 9.942 2.835 78.635 0. 765 2.559 0.059 0. 1 70 0.000 0.229 0. 1 42 2.881 79.208 0.498 2.448 0.020 0.21 1 0.024 0. 1 1 8 0.073 3.153 78.721 0.578 2.631 0.041 0. 1 1 2 0.018 0. 1 85 0.079 1 0.1 1 2 7.572 4.908 74.600 0.272 3.664 0.036 0.005 0.000 0.905 0.231 2 0.105 7.796 5.016 74.661 0.346 3.406 0.064 0.000 0.020 0.787 0.085 3 0. 1 28 7.852 5.073 74.946 0.291 3.776 0.042 0.096 0.029 0.9 1 3 0.008 4 0.149 7.777 5.275 75.274 0.361 3.661 0.041 0.000 0.018 0.477 0.121 5 0.141 7.933 4.798 74.792 0.342 3.775 0.057 0.326 0.010 0.850 0.079 6 0.1 1 3 7.751 4.648 73.467 0.419 3.741 0.044 0.21 7 0.042 0.696 0.079 Mean 0.125 7.780 4.953 74.623 0.339 3.671 0.047 0. 1 07 0.020 0.771 0 . 1 0 1 1 0.146 8.393 4.967 73.745 0.245 3.470 0.208 0.050 0.022 1 .754 0 . 1 53 2 0.01 3 6.965 6.886 70.919 0.337 4.234 0. 1 1 0 0.003 0.000 2.954 0.038 3 0 . 1 45 1 0. 1 30 4.423 73.979 0.344 3.244 0.039 0 . 1 40 0.000 0.554 0 . 1 38 4 0.083 9.007 5.602 73.345 0.255 3.366 0.040 0.012 0.000 0.387 0 . 1 02 5 0. 1 02 9.054 6.095 73.659 0.416 3.606 0.091 0. 1 21 0.000 0.278 0 . 1 33 6 0 . 1 9 1 8.215 6.048 72.452 0.318 4.086 0.050 0.007 0.000 0.644 0.075 Mean 0. 1 1 3 8.627 5.670 73.0 1 7 0.31 9 3.668 0.090 0.056 0.004 1 .095 0. 1 07 1 0 . 1 36 9. 1 87 3.068 75.764 0.390 2.413 0.061 0.058 0.025 0.321 0 . 1 2 1 2 0 . 1 86 9.571 3.434 73.568 0.358 2.476 0.096 0.073 0.013 0.426 0.077 3 0.261 9 . 1 96 4 0. 168 9.752 5 0.217 9.468 6 0 . 1 40 9.616 Mean 0. 1 85 9.465 3.833 75.294 0.292 3.094 0.070 0 . 1 05 0.034 0.033 0. 1 27 3.51 8 74.560 0.265 2.661 0.065 0.327 0.0 1 7 0.472 0. 1 21 4.692 73.719 0.41 8 3.045 0.055 0.365 0.027 1 .045 0.000 4.51 1 74.002 0.325 2.759 0.051 0 . 1 34 0.037 0.349 0.098 3.843 74.485 0.341 2.741 0.066 0 . 1 77 0.026 0.441 0.091 1 0. 1 52 1 1 .492 3.148 7 1 .313 0.290 2.697 0.060 0.1 1 3 0.023 0.382 0. 1 00 2 0 . 1 36 1 2.317 3. 1 07 72.652 0.364 2.558 0.042 0.1 1 3 0.000 0.063 0.004 3 0.099 1 2.045 2.864 72.389 0.457 2.632 0.057 0.000 0.033 0.303 0.059 4 0. 1 02 1 2.590 2.928 71 .496 0.465 2.508 0.029 0.000 0.032 0.063 0.055 5 0. 1 58 1 2.427 2.867 75.373 0.341 1 .849 0.066 0.000 0.016 0.334 0.009 6 0.074 1 2 . 1 69 2.678 7 1 . 797 0.351 2.028 0.012 0.063 0.000 0.01 1 0.167 Mean 0. 1 20 1 2. 1 73 2.932 72.503 0.378 2.379 0.044 0.048 0.0 1 7 0. 1 93 0.066 0.020 10.905 3.931 72.338 0.360 2.622 0.000 0.000 0.01 1 0. 1 82 0.141 2 0.004 9.655 3.530 72.257 0.31 6 2.857 0.000 0.068 0.017 0.201 0.203 3 0 . 1 24 9.448 3.525 74.830 0.426 2.830 0.019 0. 1 21 0.026 0.338 0.003 4 0. 1 1 1 9.745 5 0.061 9.484 6 0.003 9.220 7 0.01 9 9.300 Mean 0.049 9.680 3.404 73.883 0.275 3.143 0.049 0.214 0.019 0 . 1 28 0.000 4. 1 05 75.692 0.248 3.308 0.024 0 . 1 93 0.016 0 . 1 63 0.000 3.866 75.772 0.541 3.31 3 0.046 0 . 1 22 0.01 3 0.371 0.057 4.098 74.945 0.413 3. 1 50 0.040 0.312 0.040 0.326 0.000 3.780 74.245 0.368 3.032 0.025 0. 147 0.020 0.244 0.058 0 . 1 27 8.383 3.774 71 .401 0.290 3.1 1 2 0.054 0.203 0.018 0.673 0.083 2 0.223 8 . 1 6 1 3.976 72.201 0.322 3.243 0.080 0.210 0.016 0.805 0.097 3 0 . 1 48 8.818 4.677 73.308 0.287 3.428 0.050 0.078 0.029 0.678 0.085 4 0. 1 31 8.843 4.676 72.237 0.31 2 3.397 0.046 0.096 0.033 0.678 0. 1 67 5 0 . 1 40 8.539 4.756 72.036 0.281 3.349 0.047 0.000 0.018 0. 734 0.045 Mean 0 . 1 54 8.549 4.372 72.237 0.298 3.306 0.055 0. 1 1 7 0.023 0.714 0.095 A 21 Appendix 3.4: Titanomagnetite analyses Sample 93.81 T20/4771 12 14 Sample 93.85 T20/4771 1 2 14 Sample 93.86 T20/4771 1 2 1 4 Sample 93.87 T20/4771 1 2 1 4 Sample 93.88 T20/4771 1 2 14 Sample 93.89 T20/4771 1 2 14 Sample 93.91 T20/4771 12 14 Sample 94.2 T20/455088 Sample 94.4 T20/469102 9 Sample 94. 1 3 T20/4961 57 51 Sample 94. 1 5 T20/463097 1 0.088 8.889 4.824 73.095 0.305 3.245 0.141 0.130 0.024 0.677 0. 1 14 2 0.206 8.894 3.850 72.533 0.568 3.190 0.209 0.000 0.034 0.641 0.234 3 0.351 8.965 4.730 72.499 0.265 3.056 0. 103 0.330 0.048 0.814 0.169 4 0.186 8.754 4.868 72.985 0.431 3.326 0. 1 26 0.228 0.01 1 0.420 0. 1 34 5 0.289 8.91 7 5.036 75.734 0.259 3.400 0.075 0.202 0.008 0.734 0.140 6 0.149 8.678 4.603 74.009 0.340 3.599 0.045 0.189 0.000 0.831 0.095 Mean 0.212 8.850 4.652 73.476 0.361 3.303 0.1 1 7 0. 1 80 0.021 0.686 0.148 1 . 1 1 8 9.482 5.579 77.683 0.442 3.234 0.026 0.000 0.053 0.613 0 .100 2 0.153 8.262 5.687 75.843 0.368 3.313 0.065 0.049 0.005 0.459 0 .155 3 0.091 7.844 5.597 77.374 0.362 3.270 0.065 0. 121 0.015 0. 1 23 0.076 4 0.108 8 . 121 5.347 74.795 0.239 3.242 0.055 0. 124 0.013 0.558 0.193 5 0. 1 30 8.253 5.457 76.605 0.232 3.189 0.074 0.000 0.000 0.300 0.122 6 0.050 8.072 7 0.149 7.689 Mean 0.257 8.246 5.369 76.567 0.450 3.1 1 3 0.030 0.000 0.015 0.321 0.170 5.206 75.524 0. 185 2.747 0.032 0.000 0.044 0.493 0.162 5.463 76.342 0.325 3.158 0.050 0.042 0.021 0.410 0.140 0.291 7.812 5.366 75.436 0.380 3.383 0.044 0.083 0.020 0.320 0.031 2 0.063 7.836 5.417 75. 190 0.350 3.273 0.051 0.000 0.024 0.227 0.004 3 0.104 8 . 156 5.358 76.492 0.250 3.480 0.047 0.009 0.013 0.306 0.000 4 0.070 7.576 5.705 76.447 0.296 3.087 0.039 0.000 0.035 0.236 0.046 5 0.121 7.835 5.249 75.392 0.361 3.283 0.066 0.000 0.039 0.196 0.042 6 0.224 8.144 5.159 75.055 0.379 3.338 0.057 0.000 0.027 0. 1 29 0.000 Mean 0 .146 7.893 5.376 75.669 0.336 3.307 0.051 0.015 0.026 0.236 0.021 0 . 166 8.675 3.260 77.240 0.207 2.251 0.083 0.000 0.065 0.189 0. 1 28 2 0 .148 8.551 3.322 75.435 0.21 7 2.258 0.058 0.005 0.020 0.196 0 .106 3 0 .185 8.566 3.431 76.824 0.395 2.290 0.086 0.001 0.028 0.549 0. 1 87 4 0 .145 8.065 3.508 77.470 0.454 2.785 0 .124 0. 103 0.018 0.293 0.090 5 0.126 8.434 3.374 75.478 0.346 2.952 0.051 0. 1 55 0.024 0. 197 0.077 6 0. 102 8.357 3.367 75.870 0.261 2.629 0.100 0.000 0.041 0.068 0.088 Mean 0.145 8.441 3.377 76.386 0.313 2.528 0.084 0.044 0.033 0.249 0.1 13 1 0.085 6.554 2.674 77.581 0.209 1 .753 0.097 0. 1 36 0.017 0.975 0.290 2 0.147 7.438 2.997 78.837 0.366 1 .912 0.070 0.000 0.041 0.337 0. 1 10 1 0.020 21 .450 0.706 68.764 0.225 1 .890 0.060 0.057 0.000 0.068 0.000 2 0.013 21 .634 0.793 67.725 0.263 1 .905 0.101 0.221 0.013 0. 1 85 0.000 3 0.045 21 .590 0.714 68.530 0 . 137 1 .971 0 . 123 0.213 0.010 0.137 0.046 4 0.026 21 .888 0.758 69.025 0 . 133 1 .912 0. 147 0.068 0.025 0.158 0.048 5 0.023 21 .368 0. 702 67.897 0.258 1 .889 0. 125 0.221 0.054 0.1 1 1 0.009 6 0.068 21 .547 0.788 67.996 0.225 1 .928 0.098 0 . 167 0.014 0.215 0.012 Mean 0.033 21 .580 0.744 68.323 0.207 1 .916 0. 109 0.158 0.019 0.146 0.019 1 0. 198 1 1 .078 3.479 75.877 0.383 2.953 0.037 0.121 0.010 0.000 0.097 2 0.067 1 1 .006 3.509 75.397 0.352 2.864 0.044 0.270 0.012 0.286 0. 1 29 1 0 .1 1 7 12. 148 2.849 75.248 0.290 2.849 0.066 0.222 0.036 0.289 0 .108 2 0.1 16 1 1 .443 3.162 74.930 0.449 2.977 0.097 0.281 0.032 0.221 0.009 3 0.387 1 1 .050 4 0.233 1 1 .356 5 0.240 1 1 .057 6 0 . 177 12.090 Mean 0.212 1 1 .524 3.804 73.801 0.341 2.949 0.069 0.288 0.026 0.063 0.092 3.484 74.641 0.409 3.327 0 . 107 0.460 0.064 0.389 0 .129 3.629 74.812 0.325 3.260 0.101 0. 1 58 0.073 0.279 0.261 3.136 75.044 0.414 2.961 0.062 0.240 0.044 0.367 0.053 3.344 74.746 0.371 3.054 0.084 0.275 0.046 0.268 0 .109 0.1 12 12.691 2.838 72.873 0.401 2.826 0.071 0.003 0.006 0.695 0. 1 59 2 0 . 134 12.725 3 0.164 12.881 4 0 . 139 12.488 5 0.1 1 1 12.685 Mean 0. 1 32 12.694 2.749 72.201 0.325 2.874 0.085 0.000 0.038 0.778 0. 157 2.857 72.826 0.451 2.854 0.061 0.012 0.024 0.967 0. 1 1 3 2.772 73.833 0.358 2.553 0.062 0.290 0.014 2. 1 59 0. 156 2.690 72.670 0.363 2.993 0.049 0.000 0.013 0.888 0 .165 2.781 72.881 0.380 2.820 0.066 0.061 0.019 1 .097 0. 150 0.341 9.784 2.863 71 .946 0.368 2.427 0. 1 77 0.1 1 9 0.040 0.359 0.082 2 0.197 9.528 3.609 75.460 0.417 3.079 0.056 0.348 0.055 0.496 0. 170 3 0.300 9.536 3.534 75.653 0.313 2.974 0.086 0.412 0.006 0.408 0. 109 4 0.370 7.653 4.963 74.810 0.545 3.597 0.032 0.504 0.081 0.260 0. 150 5 0.240 7.828 5.063 75.869 0.360 3.467 0.045 0.371 0.012 0.396 0. 1 87 6 0.398 7.838 4.721 75.828 0.347 3.449 0. 1 1 3 0.249 0.000 0.474 0. 147 Mean 0.308 8.695 4.126 74.928 0.392 3.166 0.085 0.334 0.032 0.399 0.141 1 0.131 6.964 4.255 79.809 0.415 3.231 0.030 0.001 0.002 0 .139 0.382 2 0.075 7.215 4.51 2 80.209 0.401 3.068 0.058 0.000 0.000 0 . 123 0.318 3 0.244 7.469 4.21 1 78.315 0.366 2.824 0.027 0.075 0.002 0.000 0.262 4 0.171 7 .169 4.420 80.409 0.273 3.065 0.027 0 .102 0.007 0.014 0.374 A 22 Appendix 3.4: Titanomagnetite analyses 5 0 .129 7.052 4.271 77.857 0.553 2.862 0.022 0.006 0.014 0.142 0. 1 1 9 6 0.1 14 6.926 4.440 78.167 0.329 2.857 0.048 0.000 0.023 0.050 0. 1 66 Mean 0.144 7. 133 4.352 79. 1 28 0.390 2.985 0.035 0.031 0.008 0.078 0.270 Sample 94. 16 T20/463097 0.071 8.547 3.438 80.490 0.329 2.604 0.059 0.000 0.048 0.066 0.006 Sample 94. 17 T20/463097 Sample 94. 18 T20/498184 53 Sample 94.22 T19/48121 1 55 Sample 94.31 T19/495220 59 Sample 94.45 T19/496238 66 Sample 94.79 T19/364544 73 2 0.061 9. 143 2.878 79.208 0.376 2.456 0.017 0.490 0.010 0.210 0.090 3 0. 1 54 9.500 2.728 78.471 0.381 2.218 0.026 0.008 0.022 0.058 0 . 1 10 4 0. 1 78 8.384 3.399 78.382 0.319 2.791 0.067 0. 1 38 0.009 0.092 0.045 5 0.070 8.276 3.434 77.815 0.299 2.752 0.099 0.059 0.023 0.019 0.042 6 0.230 9.220 3.449 76.361 0.269 2.881 0.058 0.408 0.038 0.000 0.000 Mean 0.127 8.845 3.221 78.455 0.329 2.617 0.054 0 . 184 0.025 0.074 0.049 1 0. 1 78 8.486 3.285 77.041 0.412 3.068 0. 1 89 0.047 0.000 0.236 0. 1 22 2 0. 124 8.730 3.262 76.470 0.436 3.034 0. 1 58 0.075 0.000 0. 1 00 0.039 3 0. 174 9.142 2.913 76.429 0.325 3.027 0.076 0.221 0.029 0. 1 63 0. 1 53 4 0 . 172 8.585 3.169 79.089 0.368 3.033 0. 121 0.000 0.01 1 0. 1 06 0.085 5 0.406 9.375 3.170 78.498 0.398 3.075 0 .139 0.076 0.009 0 . 125 0.057 Mean 0.21 1 8.864 3.160 77.505 0.388 3.047 0. 1 37 0.084 0.010 0. 1 46 0.091 0 .130 8.886 2.836 78.639 0.446 2. 1 82 0.078 0.051 0.007 0.261 0. 1 84 2 0 .147 9.101 2.853 78. 1 38 0.421 2.300 0.082 0.084 0.021 0.409 0. 184 3 0.257 9.364 2.685 77.943 0.454 2.390 0. 107 0. 165 0.017 0.346 0.213 4 0. 164 8.967 2.437 82.107 0.399 2.251 0. 1 00 0.150 0.071 0.341 0.235 Mean 0. 175 9.080 2.703 79.207 0.430 2.281 0.092 0.1 1 3 0.029 0.339 0.204 1 0.639 2 0.361 3 0.358 Mean 0.453 1 0 . 155 2 0.205 3 1 .399 6.614 6.551 4.709 5.958 5.886 6.231 6.227 2.936 78.826 0.410 2.670 80.201 0.456 3.359 79.385 0.458 2.988 79.471 0.441 3.544 79.209 0.561 3.885 79.874 0.480 3.444 76.714 0.464 2.473 0.1 10 0.876 0.049 0.956 0.233 1 .944 0.067 0.426 0.032 0.898 0.241 1 .488 0.080 0.493 0.045 0.718 0.219 1 .968 0.086 0.598 0.042 0.857 0.231 2 . 190 0.054 0.252 0.096 0. 1 83 0 .138 2.594 0.046 0.393 0.018 0.332 0.214 2.793 0. 108 0.196 0.01 1 0.327 0.230 4 0 . 109 6.561 3.376 78.639 0.887 2.069 0.050 0.013 0.302 0.386 0.362 5 0.568 6.422 3.408 79.459 0.402 1 .885 0.268 0.485 0.021 0.220 0 .135 6 0. 1 75 6.538 3.680 79.380 0.340 2.280 0.059 0.448 0.015 0 . 177 0.195 Mean 0.435 6.31 1 3.556 78.879 0.522 2.302 0.098 0.298 0.077 0.271 0.212 0.063 7.093 2.357 82.463 0.673 1 . 789 0 .137 0. 1 62 0.022 0.000 0. 1 1 5 2 0.265 7.940 1 .246 79.189 0.664 0.736 0.400 0.337 0.045 0.1 1 1 0.047 3 0.362 6.830 2.053 80.866 0.574 1 .478 0. 1 37 0.447 0.060 0.036 0 .137 4 0.717 6.262 2.360 84. 1 79 0.709 2.039 0.145 0.740 0.034 0. 1 1 6 0 .123 Mean 0.352 7.031 2.004 81 .674 0.655 1 .511 0.205 0.422 0.040 0.066 0 .106 1 0. 122 1 3.233 1 .971 75.269 0.233 1 . 1 1 8 0.089 0.000 0.026 0.376 0. 1 19 2 0.092 12.381 2.977 77.863 0.438 2.588 0.056 0. 1 1 9 0.024 0.187 0. 1 23 3 0.425 13.032 2.282 77.867 1 .022 1 .452 0.098 0.486 0.081 0.395 0 . 169 4 0.475 12.603 2.335 77.414 1 .031 1 .459 0. 1 66 0.574 0.059 0.291 0.218 Mean 0.279 1 2.812 2.391 77. 103 0.681 1 .654 0. 102 0.295 0.048 0.312 0.157 A 23 Appendix 3.5: Other phases 3.5 Analyses of other phases All analyses are in a raw form (not normalised). 3.5.1 Chromite Sample Location Section Analysis Si02 Ti02 Al203 FeO MnO MgO CaO Na20 K20 Cr203 NiO Sample 93.28 T20/465099 47 Sample 93.31 T20/466096 5 Sample 93.56 T20/468102 1 0 Sample 93.63 T20/4771 1 2 1 4 3.5.2 Cl inopyroxene Sample 93.26 T20/464098 46 Sample 93.31 T20/466096 5 Sample 93.38 T20/4691 00 7 Sample 93.39 Sample 93.54 T20/468102 1 0 Sample 93.65 T20/4771 1 2 1 4 Sample 93.72 Sample 93.75 Sample 93.76 Sample 93.85 Sample 93.89 Sample 93.90 Sample 93.91 Sample 94.31 T1 9/495220 Sample 94.43 T1 9/496238 Sample 94.45 59 66 3.5.3 Orthopyroxene Sample 93.39 T20/4691 00 Sample 93.48 T20/4681 02 Sample 93.50 Sample 93.51 Sample 93.52 T20/468 1 02 Sample 93.54 Sample 93.63 T20/4771 1 2 Sample 93.69 Sample 93.70 Sample 93.71 Sample 93.73 Sample 93.75 Sample 93.82 Sample 93.89 Sample 94. 1 5 T20/463097 7 9 1 0 1 4 0.171 3.434 1 3.774 49.795 0 . 1 79 7.638 0.030 0.064 0.057 1 9 .472 0.313 1 0.669 1 .4 1 5 1 0.371 46.440 0.295 7.401 0.096 0.314 0.046 27.857 0.247 2 0.000 1 . 1 55 9.262 42.565 0.339 6.343 0.083 0.0 1 3 0.020 31 . 1 1 2 0. 1 34 3 0.181 3.750 1 0.425 50.921 0.328 6.230 0.057 0.006 0.006 1 8.743 0.282 Mean 0.283 2.107 1 0.019 46.642 0.321 6.658 0.079 0. 1 1 1 0.024 25.904 0.221 1 0.085 5.31 7 7.478 67.042 0.486 3.951 0.082 0. 1 88 0.026 7.972 0.076 2 0. 1 62 5.579 7.548 67.921 0.267 4.267 0.109 0. 1 86 0.022 7.756 0.040 0.481 4.758 7.568 62.560 0.353 4.864 0.073 0.316 0.063 1 2 . 1 54 0.283 Si02 Ti02 Al203 FeO MnO MgO CaO Na20 K20 51 .789 0. 1 56 1 .273 4.737 0.042 1 8.744 20.089 0.225 0.046 50.273 0.399 2.459 8.477 0.395 1 5.281 20.629 0.390 0.026 49.034 0.544 3.454 9.680 0.550 14.289 20.098 0.388 0.235 2 49.818 0.577 2.331 9.350 0.552 1 5.603 1 9.059 0.361 0.01 1 46.641 0.574 2.51 1 1 1 .376 0.466 1 3.052 1 8. 1 1 9 0.381 0.026 53.070 0. 1 33 1 .558 3.871 0.084 1 9.295 1 9.650 0.316 0.043 49.828 0.684 3.655 9.689 0. 1 86 14.372 1 9.633 0.405 0.01 5 2 50. 1 54 0.513 2.070 1 0.085 0.318 14.796 1 9.494 0.401 0.032 52.596 0.666 3.226 1 0.453 0.31 2 1 5.944 1 8.81 1 0.268 0.024 51 .637 0.560 3. 793 9 . 1 9 1 0.277 1 5.501 20. 1 0 1 0.453 0.038 54.189 0.354 2.357 9.436 0.200 1 6.015 1 9.500 0.007 0.000 47.689 0.495 2.029 9.653 0.298 1 5.002 1 9.828 0.298 0.040 51 .322 0.538 2.316 10.588 0.255 1 6.235 1 7.580 0.358 0.024 45.908 0.553 0.280 1 2.020 0.378 1 3.587 1 7.229 0.000 0.065 2 47.857 0.487 2.071 1 0.000 0.000 1 4.400 1 7.842 0.397 0.077 50.916 50.541 50.433 1 51 .436 2 48.899 0.4 1 9 1 .943 9.168 0.31 4 14.616 20.208 0.471 0.036 0.374 2.076 8.763 0.436 1 3.570 20.474 0.481 0.052 0.498 1 .891 1 0 . 1 52 0.549 1 5.377 1 9.670 0.267 0.022 0.232 1 .285 9.643 0.748 1 5 . 1 6 1 20.327 0.377 0.028 0.375 2.0 1 3 8.755 0.656 1 4. 1 20 20.432 0.355 0.027 Si02 Ti02 Al203 FeO MnO MgO CaO Na20 K20 51 .508 51 .683 51 .226 52.370 1 52.755 2 52.534 51 .392 49.565 45.959 51 .294 1 52.624 2 51 .905 0. 1 83 1 .603 2 1 . 383 0.697 22.808 0.271 1 .597 1 7.540 0.595 25.643 0.278 0.872 21 .038 0.403 24.520 0.379 1 . 1 30 1 8.807 0.592 25.651 0.245 1 . 140 1 9 . 1 86 0.485 24.091 0.309 1 .453 1 6.690 0.469 26.030 0.573 4.821 1 2.719 0.263 28.184 0.246 2. 1 26 1 4.528 0.278 25.495 1 .742 1 . 786 24.686 0.457 23.476 0.262 2.018 1 7.403 0.741 25.189 0.257 1 .380 1 9.069 0.534 24.7 1 7 0.334 2.589 1 8.476 0.549 25.249 1 .298 0.012 0.021 1 .6 1 4 0.093 0.042 1 .833 0.000 0.000 1 .365 0.002 0.023 1 .692 0.044 0.010 1 .576 0.007 0.016 1 .264 0.037 0.008 1 . 1 33 0.047 0.087 1 .477 0.000 0.027 1 .463 0.278 0.038 1 .780 0 . 1 85 0.059 1 .629 0.092 0.025 3 51 .331 0. 1 70 2.109 1 8.249 0.448 23.562 1 .538 0.048 0.000 1 54.189 0.31 3 1 .406 20.280 0.508 23. 7 1 5 1 .532 0 . 1 07 0.068 2 51 .644 0.297 1 .7 1 9 1 9.747 0.575 24.244 1 .676 0.055 0.010 1 50.767 0.394 1 .268 25.532 0.721 1 9.921 1 .495 0.042 0.019 2 53.634 0 . 1 88 1 .930 1 8.272 0.551 25.270 1 .776 0. 1 68 0.042 3 53.060 0.21 1 1 .539 1 8.754 0.442 24.826 1 .795 0.039 0.027 4 51 .524 0.261 1 .416 21 .644 0.51 6 22.625 1 .652 0.376 0.040 5 52.730 0.252 1 .043 1 7.468 0.377 23.050 1 .750 0. 1 37 0.051 6 50.634 0.310 2. 1 70 1 9.01 1 0.359 23.186 1 .989 0.085 0.064 48.649 0. 1 32 1 .037 1 3.96 0.421 27.94 0. 731 0.092 0.035 52.333 0.302 1 .868 1 9.39 0.522 23.72 1 .622 0.099 0.069 53.447 0.306 1 .410 22.357 0.795 22.656 1 .440 0. 1 39 0.017 A 24 Sample 94.43 T 19/496238 66 Sample 94.45 Sample 94.46 Sample 94.79 T19/364544 73 3.5.4 Andesitic glass Sample 93.25 T20/464098 46 Sample 93.26 T20/464098 46 Sample 93.39 T20/4691 00 7 Sample 93.72 T20/4771 1 2 1 4 Sample 93.84 T20/4771 1 2 14 Sample 93.89 T20/4771 12 14 Sample 93.91 T20/4771 1 2 1 4 Sample 94.46 T19/496238 66 Sample 94.79 T19/364544 73 Appendix 3.5: Other phases 52.398 0.269 1 .212 1 9.297 0.587 24.961 1 .596 0.069 0.039 2 52.792 0.241 1 .353 23.254 0.873 20.247 1 .553 0.077 0.000 3 53.534 0 .169 0.772 1 8.897 0.708 25. 1 21 1 .439 0.033 0.020 4 54.651 0.171 0.738 14.354 0.589 27.954 1 .471 0.069 0.009 5 51 .762 0.314 1 .014 1 9.404 0.662 24.651 1 .567 0.000 0.021 1 52.439 0.161 0.673 20.360 1 . 1 80 24.009 1 .038 0.000 0.032 2 53.364 0.227 0.684 1 8.928 0.979 25.272 0.988 0.080 0.019 1 52.056 0.237 0.992 23.166 0.628 21 .032 2.829 0.080 0.000 2 53.135 0.191 2.994 1 2.737 0.224 28.448 1 .892 0.054 0.054 3 48.358 0. 1 72 0.928 25.58 0.866 20.5 0.961 0. 1 65 0.082 4 52.023 0. 156 1 . 1 64 20.51 1 0.765 23.754 1 .354 0.093 0.067 5 52. 1 56 0.295 0. 765 20.688 0.936 23.427 1 . 712 0.000 0.050 52.936 0.792 7.267 16.824 0.353 14.912 2.900 1 .283 1 .732 Si02 Ti02 Al203 FeO MgO CaO Na20 K20 68.005 2.367 1 2. 1 23 6 . 151 1 .561 2.487 1 .789 2.635 2 64.833 0.913 1 5. 185 6 . 178 1 .392 4.759 1 .885 2.082 3 69.299 0.735 14.264 4.016 0.526 2.791 2.059 2.964 4 67. 151 0.767 14.420 4.614 1 .325 4.034 4.492 1 .621 60.428 0.941 1 9.278 4.268 1 .635 7.356 4.306 2.21 7 2 60.551 0.977 1 8.865 3.938 2.077 7.103 4.212 2. 1 05 3 63.918 4 60.952 5 63.651 6 65.023 7 64.071 8 64.292 9 63.909 10 63.799 1 .258 15.276 5.341 2.778 5.504 3.896 2.766 0.886 1 8.753 4.448 1 .873 6.723 4.303 2. 1 35 1 .205 15.720 5.624 2.320 5.659 4.045 2.688 1 . 1 22 14. 108 5.501 2.319 5.548 3.852 3. 1 33 1 .023 15.507 5.080 2.553 5.066 4.264 2.999 1 .303 15.091 5.319 2.794 5. 1 06 4.069 2.945 1 . 1 74 15.255 5.748 2.541 5.412 3.855 2.817 1 .283 15.058 5.865 2.824 5.593 3.919 2.889 63.050 1 .644 13.341 1 1 .034 2.588 4.31 1 2.886 0.268 2 62.504 1 . 1 97 14.452 10 . 150 2.470 4. 102 3.025 1 .383 3 63.205 1 .845 13.987 10.955 2.251 3.204 2.204 1 .642 62.932 0.781 1 6.264 6 . 163 1 .741 5.380 3 .166 1 .531 2 61 .996 1 .077 1 5.804 4.865 2.220 5.877 4.169 2.743 3 60.875 1 . 105 14.777 5.288 3.013 5.293 3.736 2.825 59.037 1 .331 15.266 7. 1 1 2 2.661 5.629 3.055 1 .975 2 58.355 1 .062 1 6.482 5.903 2.548 5.639 3.6 17 1 .768 3 56.410 0.960 1 6.051 6.870 2.840 5.458 3.639 1 .898 4 56.791 0.940 15.904 7.238 2.923 5.935 3.699 1 .776 1 63.985 1 .024 15.363 7. 1 88 1 .758 5.766 2 63. 1 35 0.999 14.794 6.524 1 .654 5. 1 1 8 3 62.703 0.967 14.808 6 . 177 1 .757 4.805 4 63.549 0.819 15.065 6.797 1 .796 4.999 4.372 1 .919 4. 1 36 2. 1 1 8 4.283 2.056 4.326 2.221 5 62.287 1 . 1 23 14.819 6.404 1 .748 5.042 3.906 2. 1 45 1 62.077 1 .274 13.453 5.295 1 .613 4.679 3.705 2.438 2 62.485 1 . 1 30 13.950 6.390 2.221 5 . 185 3.578 2.444 3 61 .695 1 . 1 27 15.200 6.059 1 .777 5.760 4.030 2.051 4 64.966 1 .350 14.266 6.492 2.049 5.263 4.000 2.391 5 63.471 1 .233 14.760 6.260 2.097 5.480 3.707 2.407 6 63.785 1 .242 13.932 6.278 1 .905 5.215 3.877 2.526 7 64.503 1 . 1 26 13 .992 6.329 1 .960 5.091 3.734 2.396 8 62.677 1 . 1 26 14 .142 6.319 2.069 5.041 3.654 2.416 1 65.793 0.630 14.819 3.910 1 .418 3.947 3.895 2.509 2 63.858 0.968 15.335 5.788 1 .788 4.888 3.994 2.073 3 64.326 1 .043 15.060 6.358 1 .521 4.866 3.727 2.558 1 64.649 1 .213 1 2.073 6.969 2.548 2.883 2.312 2.803 2 62.324 1 .684 13.024 6.584 2.262 2.954 2.540 2. 777 3 63.709 1 .848 1 2.574 5.984 2.616 2.984 2 . 154 2.978 4 63.537 1 . 1 74 1 2.250 6.950 2.567 3.514 2.652 3.060 A 25 3.5.5 Plagioclase Sample 93.25 T20/464098 46 Sample 93.80 T20/4771 1 2 1 4 Sample 93.89 T20/4771 1 2 1 4 Sample 93.91 T20/4771 1 2 14 3.5.6 l lmenite Sample 93.25 T20/464098 46 Sample 93.51 T20/468102 9 Sample 93.88 T20/4771 1 2 1 4 Sample 94.4 T20/468102 9 Sample 94.22 T1 9/48 1 2 1 1 55 Sample 94.41 T1 9/49 1 239 Sample 94.46 T1 9/496238 66 3.5.7 Spinel Sample 93.53 T20/468102 1 0 Sample 93.83 T20/4771 1 2 1 4 Appendix 3.5: Other phases Si02 Ti02 Al203 FeO MgO CaO Na20 K20 52.067 0.036 27.982 0.423 0.075 1 1 .6 1 4 4.596 0.240 2 56.978 0. 1 33 27.224 0.833 0. 1 29 1 0.976 3.778 0.678 3 52. 744 0.078 29. 1 74 0.440 0.073 1 1 .909 4.781 0.216 1 49.899 0.039 30.6 1 6 0.748 0.057 1 4. 1 43 3.888 0. 1 1 7 2 57.891 0.358 23.944 1 . 1 02 0.321 9.998 3.145 0.684 3 48.098 0. 1 1 3 31 .247 0.608 0 . 1 31 1 5.425 2.954 0.068 4 5 1 . 8 1 9 0. 1 73 25.598 1 .498 0.091 1 0.687 5.7 1 6 0.404 1 46.220 0.077 30.989 0.655 0.081 1 6.973 2.4 1 6 0.067 2 53.316 0.060 28.289 0.619 0.221 1 0.871 4.745 0.320 3 52.697 0.088 29.794 0.743 0 . 1 0 1 1 3.221 3 . 1 94 0.293 4 52.165 0. 1 31 29.899 0.672 0. 1 95 1 3.951 3.024 0.247 5 54.062 0.050 28.227 0.635 0 . 1 00 1 1 .564 4.967 0.303 49.939 0.000 27.051 0.612 0.000 1 1 .360 4.706 0. 1 1 6 2 55.203 0. 1 21 27.331 0.550 0.065 1 0.097 4.777 0.345 3 52.148 0.000 30.480 0.281 0.009 1 3.476 4.351 0 . 1 48 Si02 Ti02 Al203 FeO MnO MgO CaO Na20 K20 Cr203 NiO 0.086 44.015 0.285 48.396 0.370 4.032 0.076 0.361 0.01 5 0.777 0.148 2 0 44.006 0.21 6 48.710 0.423 3.91 7 0.067 0.000 0.01 4 0.083 0.14 3 0. 1 1 7 46.701 0.365 44.227 0.331 6.530 0.082 0. 1 86 0.039 0.054 0. 1 56 4 0.015 43.481 0.428 48.857 0.438 4.247 0.079 0.005 0.008 0. 1 45 0. 1 1 4 5 0.052 44.531 0.270 48.483 0.359 4. 1 40 0.061 0.087 0.040 0.062 0 . 1 49 0 . 1 86 36.568 0.590 55.435 0.254 2. 705 0. 1 1 4 0.005 0.013 0.068 0.049 0.702 28.867 0.690 58.933 0 . 1 0 1 1 .603 0.377 0.010 0.020 0. 1 55 0.048 2 0. 1 06 28.968 0.536 58.457 0 . 1 34 1 .459 0 . 1 60 0.080 0.026 0.243 0.068 1 0.081 42.528 0.335 47.238 0.227 4. 1 41 0.280 0.074 0.023 0.31 1 0.265 2 0.000 46.474 0 . 1 00 46.924 2.071 0.935 0.073 0.097 0.029 0.262 0.227 1 0.262 28.556 0.633 60.858 0.234 1 .858 0 . 1 72 0.526 0.034 0.233 0. 1 1 7 2 0.1 1 0 32.024 0.652 58.834 0.182 1 .952 0.124 0.081 0.01 4 0. 1 77 0.098 1 0.071 47.027 0.227 46.423 0.474 3.342 0. 1 04 0.006 0.025 0.027 0.008 2 0.065 46.263 0. 1 88 45.401 0.428 3.348 0.076 0.000 0.027 0.249 0 3 0. 1 50 45.547 0.280 45. 1 90 0.459 3.366 0.053 0. 1 96 0.044 0.033 0.025 4 0.065 46.292 0.269 46.690 0.493 3.380 0.050 0.086 0.020 0. 1 68 0.057 5 0.01 8 45.955 0.294 45.067 0.467 3.525 0.085 0.000 0.023 0.064 0 1 0. 1 24 43.404 0.523 46.330 0.839 2.353 0.203 0.424 0. 1 1 1 0.097 0.02 2 0. 1 94 42.194 0.270 46.628 0.321 2.772 0.077 0. 1 25 0.044 0.095 0.076 3 0 . 1 5 1 44. 1 27 0.401 51 . 1 1 7 0.385 2.624 0.4 1 6 0. 1 29 0.024 0. 1 33 0. 1 09 4 0 . 1 30 45.452 0.207 49.338 0.501 2.689 0.139 0.092 0.049 0.284 0. 1 1 7 Si02 Ti02 Al203 FeO MnO MgO CaO Na20 K20 Cr203 NiO 0.000 1 . 1 67 51 .245 34. 1 08 0 . 1 74 1 2.404 0.020 0.000 0.000 0 . 1 00 0.049 2 0.000 0.975 51 .657 33.825 0.31 3 1 2.608 0.01 1 0.000 0.004 0.232 0 1 .361 0.791 42. 720 39.567 0.242 9.305 0.224 0. 1 47 0. 1 03 0.056 0.049 A 26 APPENDIX 4: SELECTED FIELD SECTION DESCRIPTIONS Of the > 1 20 sections described during the course of this study the following 60 are l isted in order to characterise the stratigraphy within each stream or sector of the ring plains studied. The sections from which samples were taken for further analysis are also l isted . The section numbers used are those assigned during the original field work and are consistent with the numbering system used throughout the thesis. The fol lowing indicates the section numbers describing each stream sector: Upper Waikato Stream Tangatu Stream Wharepu Stream Te Piripiri Stream Mangatoetoenui Stream Ohinepango Stream Waihohonu Stream Oturere Stream Makahikatoa Stream Mangatawai Stream Mangamate Stream Puketarata Stream Mangahouhounui Stream Tauhurangi Stream Tongariro River 3, 4, 5, 7, 9, 1 0 , 1 4, 45, 46, 47 1 1 1 7 , 1 8 22, 24, 26, 30 32, 34, 35, 37 38, 41 , 42 40, 44, 53 54, 56, 8 1 58, 59, 60 64, 66 68 91 93 82, 83, 88, 89 50, 51 , 72, 73, 76, 78, 95-1 05 In the "correlation and samples taken column", Marker tephra units 1 -7 from Chapter 3 , and lahar episodes R01 -R 15 and T1 -T4 from Chapter 5 are indicated as well as correlations to other, previously defined tephra formations. Samples taken and referred to in this study are a lso indicated , as are correlations between the samples. A 27 Section 3 Upper Waikato Stream T20 465095 True left bank of southern-most tributary of the Upper Waikato Stream, 50m east of State Highway 1 , approx 2 km north of Tukino Skifield access road. Unit Depth Cum. (mm) depth (m) 300-500 280 0.78 90 140 1 .01 160-190 1 1 0-140 20 1 0 90 1 30 1 80 1 .77 120 50 80 80 2 . 10 20 20 30 1 0 30 40 20 20 50 40 40 10 2.43 10 1 0 20 40 20 1 0 20 50 2.61 20 60 1 00 2.79 1 0 1 0 1 0 1 0 1 0 50 20 30 80 3.02 20 50 50 Correlation and samples taken Taupo lgnimbrite Papakai Formation Mangamate Tephra (MT), Poutu Lapilli MT, Wharepu Tephra MT, Ohinepango Tephra . MT, Waihohonu Lapilli MT, Oturere Lapilli Pahoka Tephra Bullot Formation (BT), Pourahu Member BT, M1 BT, L 1 7? BT, L 1 6? BT, M3? BT, L14? Description White fine pumice ash with intermixed pumice lapilli and blocks. Occasional charcoal fragments present. Undulating basal contact. Unconformable upper contact. Greasy, fine ash, dark greyish brown (2.5Y 4/2), with vertical crack development and evidence of root channels. Reworked red-stained, olive brown (2.5Y 4/4), and grey fine lithic and pumice lapilli Normally graded coarse ash and fine lapilli. Grey and olive brown poorly vesicular pumice. Reworked coarse ash and fine pumice and lithic lapilli grey and reddish brown, crossbedded in places. Coarse grey and olive brown ash and fine lapilli, poorly vesicular pumice. Upper contact erosive. Lower 50 mm reddish brown. Yellow brown fine ash Dark grey med-coarse ash Fine pumice lapilli, olive brown, dark grey and yellowish red (5YR 4/8) Banded layers of med-coarse lithic and poorly vesicular ash, bands dominated by grey, yellowish red, and olive brown. Dark grey, olive brown and yellowish brown (1 0YR5/6) ungraded med pumice and lithic lapilli. Dark yellowish brown fine ash with scattered yellowish brown pumice. Greyish brown coarse ash and fine lapilli, some pale brown banding evident within some of the poorly vesicular pumice. Brown and greyish brown med-fine ash with scattered lapilli interbedded. Coarse-fine pale yellow and yellowish brown pumice lapilli and grey lithic lapilli. Grey coarse ash with occasional lapilli interbedded. Yellowish brown fine pumice angular lapilli and grey lithic coarse ash. Olive grey med-coarse ash and occasional fine pumice lapilli. Yellow brown fine ash grey medium lithic ash Brown fine-med pumice lapilli and grey lithic lapilli. Yellowish brown fine angular pumice lapilli and coarse ash. Greyish brown coarse pumice ash. Yellowish red fine-med pumice lapilli and occasional grey lithic coarse ash. Dark purplish black lithic coarse ash and fine lapilli. Brown pumice med-fine pumice lapilli reversely graded with coarse ash at the base. Greyish brown med-fine ash Yellowish brown coarse ash and fine pumice lapilli. Fine-med yellowish brown ash with occasional fine pumice lapilli. Purplish black coarse lithic ash and fine lapilli. Greyish brown coarse ash and fine pumice and lithic lapilli. Purplish grey coarse ash and fine lithic lapilli. Strong brown soft pumice lapilli and coarse ash. Purplish black coarse ash and fine lithic lapilli. Strong brown med-fine pumice lapilli with occasional grey lithic fine lapilli intermixed. Strong brown pumice coarse ash and fine lapilli. Dark greyish brown coarse ash and occasional lithic lapilli. Yellowish red (5YR 5/6) pumice fine-med lapilli and few grey fine lithic lapilli. Grey med-coarse lithic ash. Greyish brown fine ash. Purplish grey med lithic ash. Strong brown fine pumice lapilli and coarse ash. Purplish black med-fine lithic lapilli. Yellowish brown coarse ash and fine pumice lapilli, reversely graded. Purplish black med-coarse ash. Greyish brown coarse-med ash and fine lithic lapilli. Yellowish red pumice fine-med lapilli with few grey fine lithic lapilli. Grey coarse lithic ash. Normally graded greyish brown coarse pumice ash and fine lapilli. Greyish brown coarse-med ash with occasional fine lapilli intermixed, lower 1 0 mm fine lapilli dominant. A 28 40 20 20 20 1 0 20 1 0 20 1 0 30 20 80 1 0 1 0 1 0 30 50 100 20 850 1 000 1200 250 3000+ Section 4 3.44 Rerewhakaaitu Tephra 3.65 BT, L7? 4.50 Hinuera Formation, Sample 93.3 5.50 R10 R10 9.95 Upper Waikato Stream, T20 466095 Dark purplish black coarse ash and fine lapilli. Yellowish brown coarse pumice ash and fine lapilli. Purplish black coarse ash and fine lithic lapilli. Greyish brown pumice coarse ash. Purplish black coarse lithic ash. Brown fine pumice lapilli. Grey med lithic ash. Yellowish brown med ash with occasional pumice lapilli. Grey med lithic ash. Greyish brown med-coarse ash mixed with many fine pumice lapilli. Brownish yellow pumice fine lapilli and coarse ash, with few grey lithic lapilli. Greyish brown coarse pumice and lithic ash and fine lapilli. White fine ash interbedded within the base 5-1 0 mm thick. grey coarse lithic ash. Greyish brown med ash and fine pumice lapilli. Grey coarse lithic ash. Yellowish brown pumice fine-med lapilli and few grey lithic fine lapilli. Grey med-coarse ash variable lower boundary. Yellowish brown coarse pumice ash to med lapilli, shower bedded. Grey med lithic ash. Bedded silts sands and pebbles, sub-rounded and poorly sorted as a whole. Dominantly greyish brown in colour with clasts of pumice and grey lithic andesite. Thin layers of reworked white and pink fine rhyolitic ash interbedded in parts of unit. Dark grey andesite lithic med-coarse sands laminated and cross? bedded. Layers and lenses of cobbles and pebbles interbedded. Lower contact is an angular unconformity. Greasy silty matrix diamicton. Matrix supported with pebble to boulder sized clasts. Clasts are heterolithologic, often soft and multi-coloured and appear hydrothermally altered. Lower part of unit contains large (1 m) diameter boulders. Matrix colour yellow to yellowish brown. Similar to unit above, except matrix is pale yellow and there are no boulder sized clasts. Bedded sands silts and gravels, in lenses and layers. Med-coarse sands and fine pebbles sub-rounded and sub angular. Base into stream. True left bank 50m downstream from Section 3. Cover-beds are the same as section 3 and this description is taken from the base of the distinctive R1 0 diamicton. Unit Depth (mm) 1 00 50 50 2000-2500 50 200 1 50 1 0 400 1 00 1 0- 150 2000 500 200 30 Cum. depth (m) c.7.0 9.65 1 0.66 Correlation and samples taken (=93.24) (=93.25) (=93.26, Marker Unit 1 ) (=93.27, Marker Unit 1 ) (=93.28 and 93.30) Description Bedded silt and sand, with yellow and greyish brown pebbly lenses. Gravels with intermixed sand. Dark red and yellowish brown coarse pumice ash and fine lapilli. Normally graded with grey lithic coarse ash interbedded toward the base. Bedded sands silts and gravels, rounded heterolithologic clasts. Cross-stratified in places, colours range from dark brown to greyish brown sands. Coarse pumice ash and fine lapilli, ungraded, soft, yellow and pale yellow. Fine grey sand with occasional interbedded pumice pebbles. Reverse graded brown and olive brown fine-med pumice lapilli. Brownish grey fine ash. Grey and pale olive brown coarse-med ash alternating layers of colour dominated by the grey lithic or olive brown pumice ash. Shower? bedded. Bedded coarse ash and fine lapilli, strong shower-bedding with grey and olive brown colours on a 30 mm scale. Yellow fine pumice lapilli. Bedded silts, gravels and sands, brown and greyish brown. Beds and lenses of sub-rounded pebbles and occasional cobbles. Multiple coloured hetero-lithologic pebbles, highly weathered. Laminated and cross bedded. Basal 200 mm gravelly. Purplish grey and purple silty matrix diamicton. Sparse multi-coloured clasts within matrix and mostly of pebble size. Few large boulders near base of unit. Strong brown and yellow, soft, pumice fine lapilli, with few intermixed grey lithics. Purplish grey fine ash. A 29 50 2000+ 1 5.44 Section 5 (=93.29 and 93.31 ) Coarse-med pumice ash, strong brown top and base mostly grey lithic ash. Silt sand and gravel beds, 50 mm scale beds mostly greyish brown and brown in colour. Lenses of pebbles and occasional small cobbles. Cross-bedded and planar bedded. Sharp contact onto lithified diamicton unit. Upper Waikato Stream, T20 466096 True left bank 1 00 m downstream from Section 4. Description taken from lowest andesitic tephra described at Section 4. Unit Depth (mm) 40 1 0 300 1 000 1 200 600 400 1 500 Section 7 Cum. depth (m) Correlation and samples Description taken 14.00 93.30 93.31 1 5.31 R1 1 1 9.01 Yellow and yellowish brown pumice fine-med lapilli. Reversely graded. Grey fine ash. Shower bedded fine-med pumice lapilli, yellowish brown and grey. 20 mm lithic rich layer of fine lapilli. Bedded silts sands and gravels, in layers and lenses. Grey and greyish brown in colour with multi-coloured pumice and lithic pebbles. Sharp upper contact. Sandy-matrix diamicton, matrix of fine-coarse sand supporting clasts of pebble to boulder in size. Yellow pumice clasts in finer size range and grey lava in larger size range. Highly lithified unit. Grey and greyish brown matrix colour. Sharp contacts with upper and lower units. Sandy matrix diamicton with maximum clast size of cobbles and pebbles. Grey and greyish brown matrix. Sandy-matrix diamicton, fine grained, clasts of mostly pebble in size. Sharp contact with units above and below. Sandy-matrix diamicton, with dominantly cobble sized clasts supported within matrix. Crude horizontal fabric preserved in the base of this bed. Grey and greyish brown in colour. base obscured by talus. Upper Waikato Stream, T20 469100 True right bank of southern tributary, 200 m upstream of junction between the two tributaries. Description taken from above Kawakawa Tephra. Unit Depth (mm) 20 30 1 0 20-200 20 1 0 1 0 50 20 40 50 250 400 500 700 350 1 200 200 1200 Cum. depth (m) Correlation and samples Description taken c. 9.0 93.32, Rerewhakaaitu Tephra 9.38 93.33, Kawakawa Tephra R10 1 1 .73 93.34 (=93.3 1 ) R1 1 Yellow brown coarse ash and fine pumice lapilli. Greyish brown and yellow brown fine lapilli and coarse ash with pocketing interbedded white fine rhyolitic ash. Yellow brown fine pumice lapilli. Pinching and swelling diamicton, coarse-fine sand matrix supporting mostly pebble clasts with occasional boulders. Unconformable lower contact, undulating. Yellow brown fine pumice lapilli. Grey medium lithic ash. Yellow brown fine greasy ash. Strong brown fine-med pumice lapilli with few grey lithic lapilli. Grey and brownish grey medium ash. Fine yellow pumice ash 20 mm at the top of the unit, underlain by 1 0 mm pink fine ash and 20 mm further pale yellow fine ash. Grey and brownish grey bedded med sand and pebbles. Yellow brown and brownish grey loose sands containing yellow pumice pebbles, unbedded. Pink and grey, greasy, silt-matrix diamicton, multi-coloured pumice and weathered lithic clasts supported in the matrix. Cobble and boulder clasts also common. Brown and dark yellow brown greasy silt-matrix diamicton, containing multi-coloured pumice pebble clasts. As above, but separated by a sharp even contact from the above unit. Shower bedded strong brown and yellow brown fine-med pumice lapilli. 1 0 mm zone of grey lithic lapilli 1 00 mm above base and reversely graded base. Grey and greyish brown silt, sand and gravel beds, 2-3 cm scale planar bedding and cross-bedded. Greyish brown and grey sandy matrix diamicton, coarse-fine sand matrix supporting pebble clasts, grey red and yellow pumice and lithic clasts. Normally graded grey and greyish brown sandy matrix diamicton, matrix supporting pebble clasts at the top and cobble clasts at the A 30 1 500 2000 1 00 500 1 50 200 200 1 000 1 50 600 300 1 500 Section 9 1 7.83 93.36 93.37 93.38 20. 1 3 93.39, Marker Unit 2 93.40 R12 Upper Waikato Stream, T20 4681 02 base. Clast rich unit with most of clasts grey and lithic, around 1 0% of clasts yellow pumice pebbles. Strongly lithified. Three to four layers of finer grained diamicton units. Sandy matrix with clasts of yellow pumice and dominantly grey lithic pebbles. Strings of cobbles seen and a horizontal fabric preserved. Strongly lithified. Sandy-matrix diamicton, no yellow pumice clasts entirely grey lithic pebbles. Strings of cobbles and occasionally huge boulders. Several units pinching in and out with sharp contacts between. Firmly lithified. Dark red and yellow pumice med-fine lapilli, very firm and cemented. Bedded grown and greyish brown med-fine sand with interbedded yellow pumice in layers and lenses. Reddish brown and red coarse pumice ash firmly cemented, and shower-bedded. Yellow brown and brown fine ash with occasional yellow pumice lapilli intermixed. Yellow brown and red stained fine-med pumice lapilli, shower-bedded with few grey lithic fine lapilli. Brown and dark brown fine ash with paleosol development evident. Greasy fine ash with abundant, finely disseminated charcoal present in the upper 300 mm. Abundant root channels seen as well as vertical cracking and coarse blocky structure. Some intermixed grey and yellow pumice and lithic lapilli near base. Grey and dark grey firmly-cemented fine ash. Extremely hard and breaks up into brittle slabs along shower bedding. Accretionary lapilli within two of the shower beds, 2-5 mm in diameter. Brown and brownish grey fine ash, firm, with little paleosol development. Yellow and strong brown fine-med pumice lapilli, soft, with occasional fine grey lithic lapilli. Uniformly fine grained diamicton. Greyish brown sandy and silty matrix with grey lithic pebble sized clasts. Distinctive content of around 20 % yellow pumice fine pebbles. Horizontal fabric observed and unit is firmly lithified. Base of section into stream. True left bank of north tributary, 40 m upstream of junction of two tributaries. Description taken from above R10. Unit Depth (mm) 1 500 600 1 500 3000 300 4000 1 500 20 20 1 20 1 000-1500 500 1 00 40 1 50 Cum. depth (m) c.5.0 10.40 15.90 R10 Correlation and samples taken 93.29 R12 93.41 R12 93.42 Description Grey and yellow brown bedded fine-coarse sands and fine gravels, unconsolidated, with planar 1 0-50 mm scale bedding. Yellow brown greasy silt-matrix diamicton. Pebble-cobble clasts supported by the matrix. Multi-coloured pumice and weathered lithic clasts. Yellow brown and pale yellow silt-matrix diamicton with large grey and red boulder clasts as well as multi-coloured pebble clasts supported by the matrix. Grey, brownish grey and brown bedded sands, silts and gravels, planar and cross bedded layers, bedding on a 1 0-100 mm scale. Yellow and yellow brown pumice pebbles common scattered within silts and sands as well as in lenses. Yellow brown and yellow fine-med soft pumice lapilli, normally graded with scattered fine grey lithic lapilli. Bedded silts, sands, and gravels, brown with grey and multi-coloured pumice and lithic pebbles. Planar and cross-bedded on a 50 mm scale. Grey and greyish brown sand- and silt-matrix diamicton. Grey lithic pebbly clasts and abundant (>20%) yellow pumice clasts supported by the matrix. Weak planar fabric and firmly lithified. Yellow brown fine ash with mixed in fine yellow pumice lapilli. Grey lithic fine lapilli with yellow brown fine ash intermixed. Strong brown and yellow brown fine pumice lapilli with intermixed grey lithic lapilli. Firmly lithified diamicton. Grey and greyish brown sandy matrix supporting huge boulder clasts. Abundant large clasts as well as up to 60% of matrix made up of yellow pumice lapilli. Yellow and yellow brown fine pumice lapilli ungraded and shower? bedded. Occasional grey lithic fine iapilli also present. Grey and greyish brown fine ash, firm. Yellow brown and strong brown fine-med pumice lapilli. Grey and greyish brown fine ash with 5% scattered fine yellow pumice lapilli. A 31 500 1 8.85 50 1 50 20 1 00 40 250 350 350 50 400 50 300 19.96 1 00 50 30 50 1 0 200 50 50 200+ 20.70 Section 1 0 93.43 93.44 93.45 R13 93.46 93.47, Marker Unit 3 93.48 93.49 93.50 93.51 Reddish brown fine ash firm with paleosol development. Abundant brown stained root channels and rare finely dispersed charcoal. Yellow and strong brown fine-med pumice lapilli with abundant dark grey lithics and coarse ash sized black free pyroxene crystals. Massive brown fine ash with few scattered fine yellow pumice lapilli, common root channels. Yellow and yellow brown fine pumice lapilli with abundant coarse black free pyroxene crystals. Reddish brown fine ash with common root channels. Yellow and yellow brown fine pumice lapilli intermixed with grey lithic lapilli, 5-10% free black coarse ash sized pyroxene crystals. Reddish brown fine ash with scattered fine yellow pumice lapilli and black free pyroxene crystals, also common root channels. Grey and greyish brown fine ash firm with common yellow pumice and grey lithic lapilli scattered throughout. Reddish brown and brown fine ash, greasy vertical cracking and some blocky structure, common root channels. Yellow and yellow brown fine pumice lapilli with intermixed grey fine lithic lapilli. Firm diamicton unit, silt and sand matrix supporting mostly grey lithic pebble clasts, also less common pebbles of red and yellow pumice. Erosive lower contact. Yellow brown and strong brown fine pumice lapilli with intermixed grey lithic lapilli. Strong brown stained fine pumice lapilli and coarse ash shower? bedded with two distinctive grey lithic dominated zones 1 0 mm thick 20 mm apart, and 50 mm from the top of the unit. Grey fine ash with scattered fine yellow pumice and grey lithic lapilli. Yellow brown and strong brown fine pumice lapilli with intermixed grey lithic fine lapilli and black coarse ash sized free pyroxene crystals. Grey fine ash, firm. Yellow brown and strong brown fine pumice lapilli with intermixed grey lithic fine lapilli and black coarse ash sized free pyroxene crystals. Brown fine ash Yellow brown and strong brown fine-med pumice lapilli with intermixed grey lithic fine lapilli and black coarse ash sized free pyroxene crystals, concentrated toward the top of the unit. Grey fine ash with scattered 5% yellow pumice lapilli and black pyroxene crystals. Yellow and yellow brown med-fine pumice lapilli with intermixed grey lithic fine lapilli. Grey and pinkish grey fine ash with scattered 5% yellow pumice lapilli and black pyroxene crystals. Base into stream. Upper Waikato Stream, T20 468103 True right bank of stream 50 m downstream of the junction of the two tributaries. Description taken from above the R13 diamicton in section 9. Unit Depth (mm) 50 50 800 1 00 200 50 1 00 50 200 50 30 70 200 1 00 Cum. depth (m) Correlation and samples Description taken c. 26.5 R13 27.65 Marker Unit 3 (=93.48) (=93.50) (=93.51 ) 93.52, Marker Unit 4 Yellow and strong brown fine pumice lapilli with grey lithic coarse ash and black free pyroxene crystals intermixed. Brown and reddish brown fine ash with root channels. Sandy-matrix diamicton. Upper 0-400 mm reworked and partially bedded lower part massive with grey lithic pebble and cobble clasts supported in matrix of grey coarse-med sand, uncemented. Olive brown and grey fine ash, firm. Strong brown fine pumice iapilli and coarse ash with distinctive 1 0 mm thick grey lithic dominated layers 20 mm apart 40 mm from the top of the unit. Grey greasy fine ash. Strong brown medium pumice lapilli with intermixed grey lithic lapilli. Grey greasy fine ash. Yellow and strong brown fine pumice lapilli with mixed grey fine lithic lapilli. Greyish brown greasy fine ash. Yellow and pale brown fine pumice lapilli with grey lithic fine lapilli and black free pyroxene crystals intermixed. Grey fine ash with scattered fine yellow pumice lapilli intermixed. Brown fine ash firm with root channels. Pale brown and strong brown med-coarse pumice lapilli with grey lithic fine lapilli and black free pyroxene crystals intermixed. A 32 200 60 1 0 30 1 50 1 50 120 200 1 200 1 00 50 1 00 90 50 200 20 1 500+ Section 1 1 93.53 93.54 31 .52 R14 93.58 33.63 R15 Tangatu Stream, T20 4701 1 0 Bedded silt and sand with intermixed yellow pumice fine lapilli. Strong brown fine pumice lapilli and coarse ash. Grey fine lithic ash. Strong brown and reddish brown coarse-med pumice lapilli. Alternating 30 mm layers of olive brown and yellow fine pumice lapilli. Grey lithic coarse ash and strong brown fine lithic lapilli. Pale brown and strong brown alternating 30 mm layers of fine pumice lapilli. Many thin ( 10 mm) layers of brown, grey, yellow, and pale brown fine pumice lapilli and coarse ash. Sandy-matrix diamicton. Matrix supporting grey clasts of pebble to small boulder in size. Brown to greyish brown clasts and matrix. Ungraded and with no bedding. Sharp planar lower contact. Dark grey and strong brown coarse-med pumice lapilli in a matrix of grey coarse ash. Grey coarse lithic ash and fine lapilli. Brown fine pumice lapilli and coarse ash. Pale brown and grey coarse ash and fine pumice lapilli. Strong brown and pale brown fine pumice lapilli with intermixed grey lithic fine lapilli. Sandy matrix diamicton, pebble clasts supported in greyish brown med-coarse sand. Pale brown and yellow fine pumice lapilli. Grey sandy-matrix diamicton, pebble and cobble clasts supported in med-coarse sand matrix, unbedded and uncemented. Base into stream. True left bank of stream, 500m downstream of state highway 1 . Unit Depth Cum. Correlation and (mm) depth (m) samples taken 400 Makahikatoa Sand 450 Taupe lgnimbrite 300 1 . 1 5 Mangatawai Tephra 1 00 Papakai Formation 30 1 .28 Waimahia Tephra 300 Papakai Formation 1 50 1 .73 Hinemaiaia Tephra within Papakai Formation 1 200-1500 1 500 500+ R10 5.23 Section 14 Upper Waikato Stream, T20 4771 12 Description Brown and greyish brown med-fine sand, present soil development. White fine ash matrix supporting white pumice block and lapilli clasts. Charcoal present near base. Brown and greyish brown fine greasy ash with several black and purplish grey fine-coarse ash beds. Yellowish brown beech leaves preserved in some of the ash layers. Brown and yellow brown fine greasy ash with strong paleosol development. Cream-cakes of fine white ash. Yellow brown fine greasy ash. Coarse white pumice ash scattered throughout brown fine ash. Unconformable lower contact. Bedded sands, silts and gravels. Greyish brown and brown, planar bedded and cross bedded, with layers and lenses of grey lithic and yellow pumice pebbles. 1 0 cm scale bedding. Brown silt-matrix diamicton. Large boulder clasts supported within matrix as well as grey pebbles and cobbles. Yellow brown sandy and silty matrix diamicton. Fine grained with dominantly pebble clasts. Firm matrix supporting multi-coloured pumice and weathered lithic clasts. Base into stream. True left bank of stream, 300 m upstream of junction with Tangatu Stream. Description taken from Bullot Formation member containing Rerewhakaaitu Tephra. Unit Depth (mm) Cum. depth (m) Correlation and samples Description taken 50 c. 7.0 93.59, Rerewhakaaitu 30 1 0 0-50 400-500 Tephra 400 93.60 2000 9.99 R1 O/R1 1 Greyish brown coarse ash and fine lithic lapilli containing cream-cakes of up to 20 mm thick of white fine rhyolitic ash. Strong brown and yellow brown fine-med pumice lapilli. Grey coarse ash. Eroded yellow brown and strong brown fine, soft pumice lapilli. Grey and greyish brown bedded sands and gravels in planar layers and lenses. Variable thickness and unconformable contacts. Yellow brown and strong brown fine-med pumice lapilli with few grey fine lithic lapilli interbedded. Brown silt and sand matrix diamicton. Matrix supports clasts of pebble to boulder in size. Multi-coloured lithic and pumice clasts abundant. A 33 1 0 20 20 30 20 30 50 200 50 1 00 1 000 1 50-200 400 1 50 200 1400 50 350 50 20 40 200 1 00 50 50 200 50 400 1 50 1 00 1 1 .49 1 3.84 1 5.00 1000-1200 16.85 20 300 300 150 200 1 7.82 70 200 50 250 70 50 1 00 50 18.66 1 0 50 200 20 200 93.61 (=93.37) 93.62 (=93.38) Marker unit 2 93.63 (=93.40) 93.64 (=93.40) R12 93.65 (=93.42) 93.66 93.67 93.68 93.69 R13 93.70 (=93.47), Marker unit 3 93.71 , (=93.48) 93.72, (=93.49) 93.73, (=93.51 ) 93.74, Marker Unit 4 93.75 Massive and unbedded, boulders concentrated toward the base. Yellow medium pumice lapilli in a matrix of brown fine ash. Dark greyish brown fine ash. Yellow coarse pumice ash and fine pumice lapilli. Grey fine ash. Yellow medium pumice lapilli. Grey fine ash. Dark greyish brown fine ash with scattered fine yellow pumice lapilli. Olive grey coarse ash, shower-bedded and ungraded. Brown fine ash with scattered yellow fine-pumice lapilli and coarse ash. Yellow brown fine and soft pumice lapilli. Brown and greyish brown fine ash, greasy and with common root channels. Finely disseminated charcoal present in the upper 200 mm. Weak blocky structure developed near top. Lower 200 mm contains scattered yellow and yellow brown fine pumice lapilli (5%). Pale grey and light brownish grey hardened fine ash tuft unit. Shower? bedded fine and med ash. Breaks into brittle slabs along beds. Yellow and yellow brown fine-med pumice lapilli with intennixed grey fine lithic lapilli. Brown fine ash with scattered yellow brown fine pumice lapilli. Yellow brown med-fine pumice lapilli and grey lithic fine lapilli. Massive diamicton. Silt and sand-matrix supporting pebble to boulder clasts. Abundant grey lithic and yellow pumice clasts. Finnly lithified. Yellow and brown fine pumice lapilli and coarse ash. Greyish brown fine ash with scattered coarse yellow pumice ash ( 10%) Yellow brown fine pumice lapilli and coarse ash. Greyish brown fine ash. Yellow and yellow brown med-fine pumice lapilli. Greyish brown fine ash with abundant root channels and few scattered yellow fine pumice lapilli. Yellow and strong brown med pumice lapilli, with grey fine lithic lapilli. Reddish brown fine ash with root channels. Yellow fine pumice lapilli with grey fine lithic lapilli and black coarse ash sized pyroxene crystals. Dark red fine ash with scattered fine yellow pumice lapilli (5%), and root channels. Yellow pumice lapilli with abundant black coarse ash grade pyroxene crystals. Dark red fine ash with scattered fine yellow soft pumice lapilli, some root channels Yellow and grey fine pumice lapilli mixed with fine brown ash. Dark red fine greasy ash with scattered fine yellow soft pumice lapilli, some root channels. Bedded silts and fine sands, laminated and cross-bedded, lenses and layers rich in pebbles. Dusky red and greyish brown. Grey and Yellow brown coarse ash. Pink fine ash, finn, and contains root channels. Firm silt matrix diamicton, grey red and yellow pebble to cobble-sized clasts supported by the matrix. Greyish brown fine ash with intennixed yellow brown fine pumice lapilli. Red coarse pumice ash and fine lapilli with grey lithic lapilli and black coarse ash grade pyroxene crystals intennixed. 3 distinctive grey 1 0 mm layers separated by 2 0 mm near the top of the unit. Grey fine ash with scattered fine yellow pumice lapilli. Strong brown and yellow brown med-fine, soft, pumice lapilli with grey lithic lapilli and black coarse ash grade pyroxene crystals intennixed. Greyish brown and grey fine ash with scattered fine yellow pumice lapilli. Yellow brown and pink fine-med pumice lapilli with grey lithic lapilli and black coarse ash grade pyroxene crystals intennixed. Grey fine ash. Yellow and yellow brown fine-med pumice lapilli. Grey and greyish brown fine ash with 5% yellow fine pumice lapilli intermixed. Yellow brown pumice lapilli with intennixed grey fine lithic lapilli. grey coarse ash. Yellow and greyish brown and black pumice and lithic fine lapilli, lithic rich unit. Brown and greyish brown fine ash with scattered fine yellow pumice lapilli. Yellow pumice coarse ash and fine lapilli with intennixed grey fine lithic lapilli. Greyish brown fine ash with scattered fine yellow pumice lapilli. A 34 20 30 1 00 1 9.29 93.76 40 50 93.77 1 00 200 30 20 30 30 30 1 0 40 1 9.87 93.78 1 0 30 40 20 40 250 20 250 1 00 20.63 93.79 200 93.80 1 0 1 00 50 93.81 1 500 R14 600 50 23. 1 4 93.82 1 00 40 93.83 400 93.84 50 20 50 93.85, Marker Unit 5 500 1 000 R1 5 200 25.50 93.86 5000 R15 2500 5000 5000 1 000 500-1 000 Brown and yellowish brown fine pumice lapilli. Grey med ash and greyish brown and black coarse lithic ash. Brown and strong brown fine-med pumice lapilli, firm lapilli. Greyish brown med-coarse ash and grey lithic fine lapilli. Yellow and yellow brown fine pumice lapilli with intermixed fine grey lithic lapilli. Brown and yellow brown fine ash with scattered yellow brown fine pumice lapilli. Brownish grey med-coarse ash with scattered grey lithic and yellow pumice fine lapilli. Brown fine ash with scattered yellow brown fine pumice lapilli Grey coarse ash. Brown coarse ash. Yellow brown fine pumice lapilli with intermixed grey coarse lithic ash. Brown coarse ash. Dark grey lithic med ash. Yellow and yellow brown fine pumice lapilli with 50% intermixed grey lithic fine lapilli. Grey fine lithic ash. Yellow and yellow brown fine pumice lapilli with intermixed grey coarse lithic ash. Grey med ash with scattered yellow fine pumice lapilli. Brownish grey fine ash with scattered yellow fine pumice lapilli. Grey med ash with scattered yellow fine pumice lapilli. Brownish grey med ash with scattered yellow fine pumice lapilli. Yellow brown fine pumice lapilli with intermixed grey lithic coarse ash. Greyish brown and grey fine-coarse ash with scattered yellow fine pumice and grey lithic lapilli. Yellow brown strong brown, greyish brown and black med-coarse pumice lapilli. Strong brown and yellow brown fine-med pumice lapilli. Brown firm, fine ash. Brown and greyish brown med-coarse ash and fine pumice lapilli. Brown and yellow brown fine-med pumice lapilli with grey fine lithic lapilli. Sandy matrix diamicton, grey and brownish grey med-coarse sand supporting grey and red lithic pebbles-boulders. Poorly sorted, unconsolidated and unbedded. Some faint planar fabric. Bedded sands and pebbles, 30 mm scale planar and cross bedding. Greyish brown with lenses of yellow and strong brown pumice pebbles. Black stained yellow fine-med pumice lapilli. Grey and brownish grey med-fine ash with scattered fine yellow pumice lapilli. Black stained, yellow brown fine-med pumice lapilli. Greyish brown, yellow and grey fine-med shower-bedded pumice lapilli. Grey med coarse-fine ash. Brownish grey fine ash. Normally graded yellow and grey pumice and lithic fine lapilli and coarse ash. Grey bedded sands and gravels in lenses and layers with yellow pumice pebbles. Grey and greyish brown diamicton. Coarse-fine sand matrix supporting pebble-cobble cfasts and some small boulders. Planar fabric preserved with cobble strings. Brown, brownish grey and yellow mad-coarse pumice lapilli, shower? bedded, lower 1 00 mm has intermixed grey med ash or sand. Several 1 m thick diamicton units interbedded with bedded silts sands and gravels in layers and cross beds. Diamictons have matrices of coarse-med sand supporting pebble-cobble cfasts with occasional boulder. Unconsolidated and overall planar fabrlc preserved with cobble strings. Dominantly grey and brownish grey lithic with occasional red lithic clasts. Coarse grained diamicton. Coarse-mad grey sand matrix supporting large grey angular boulder and cobble cfasts. Weak planar fabric. Grey and greyish brown planar diamictons and interbedded finely bedded sands and gravels. Sandy matrix supporting lithic pebble and cobble clasts. Bedded sands and gravels, grey and brownish grey, planar and cross bedded in layers and lenses. Upper half dominantly gravels and lower half dominantly sands. Pale brownish grey firm, fine sand, massive unbedded with 5 % scattered fine yellow pumice lapilli. Variable thickness dark grey diamicton. Sandy matrix supporting A 35 1 000 50 50 46. 1 0 1 00 300 20 300 40 20 1 00 1 50 1 00 400 1 000+ 48.63 Section 1 7 93.87 93.88 93.90 93.89, Marker Unit 6 93.91 , Marker Unit 7 R15 pebble-boulder lithic clasts. Grey and olive grey well sorted planar bedded med sand. Grey coarse-med ash. White and strong brown stained fine pumice lapilli. Pinkish white and grey fine pumice lapilli. Fibrous dark brown and black firm lignite. Finely bedded 10 mm scale, planar bedding. Sampled at 50 mm intervals. White and pale grey med ash. Fibrous pale brown and dark brown lignite planar laminated. Grey and pinkish grey coarse ash and fine pumice and lithic lapilli. Brown lignite. Finely laminated brown lignite and grey fine-med sand. Dark brown and pale brown laminated lignite. Grey and pinkish grey med pumice ash. Bedded fine-coarse pale grey sands. Coarse sand matrix diamicton, large boulder-pebble clasts supported within the matrix. Brownish grey unbedded, massive and very firmly consolidated. Base into stream. Wharepu Stream, T20 463122 True left bank of stream, 50 m upstream of western power pylons, approximately 500 m downstream of State Highway 1 . Unit Depth (mm) 800 1 00-250 300 1 00 20 1 50 1 00 200 40 50 30 50 500 20 1 0 260 400-500 1 50 50 1 00 50 50 50 1 0 1 0 50 30 30 40 30 Cum. depth (m) 1 .47 1 .72 1 .96 2.09 3.58 3.73 3.96 Correlation and samples Description taken Ngauruhoe Formation Taupo lgnimbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp Motutere Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli MT. Wharepu Tephra MT. Waihohonu Lapilli MT. Oturere Lapilli Pahoka Tephra Bullot Formation (BT), Pourahu Tephra BT, M1? Brown and greyish brown fine-med ash, friable, with present soil development. White fine-med pumice ash supporting ciasts of white pumice lapilli and blocks. Charcoal fragments dispersed throughout. Dark brown and brown fine greasy ash with paleosol development and paleo-root channels. The lower 1 00 mm contains several 1 0-20 mm thick fine-med purplish black and black ash beds. Yellow brown beech leaves are preserved within some of these layers. Yellowish brown fine greasy ash, friable, with paleosol development. Cream-cakes of greyish white fine ash interbedded within yellow brown greasy fine ash. Brown greasy fine ash. Scattered med-coarse white pumiceous ash within brown greasy fine ash. Brown fine greasy ash. Pale brown med-fine ash in cream-cakes within brown greasy fine ash. Brown fine greasy ash, strong brown staining at basal contact. Grey coarse ash. Strong brown and grey lithic and poorly vesicular pumice lapilii with grey coarse ash base. Shower-bedded fine-med poorly vesicular pumice and lithic lapilli. Grey, strong brown and greyish brown. Strong brown and reddish brown basal 30 mm of fine lapilli, distinctive. Yellow brown fine firm ash. Dark grey coarse ash. Grey brownish grey and strong brown fine pumice and lithic lapilli. Strong shower bedding and alternating 1 0-50 mm layers dominated by the different colours. Coarse-med grey, brownish grey and strong brown pumice and lithic lapilli, shower-bedded but ungraded. Yellow brown fine ash with yellow pumice fine lapilli scattered through a zone in the middle of the unit. Distinctive platy olive grey fine pumice lapilli. Dark yellowish brown fine ash with scattered fine yellow pumice lapilli. Pale brown coarse pumice lapilli. Normally graded coarse ash-med lapilii, yellow pumice and grey lithic lapilli intermixed. Brownish grey coarse ash and fine lapilli. Yellow brown fine ash and scattered fine pumice lapilli. Grey lithic coarse ash. Pale brown pumice and grey lithic med lapilli Grey med lithic lapilli. 10 mm olive grey med ash over 10 mm yellow fine pumice lapilii, over 1 0 mm grey coarse ash. Brownish grey fine-med iapilli. Yellowish brown fine ash with scattered coarse pumice and lithic yellow and grey ash. A 36 50 20 30 1 0 1 0 30 20 1 00 30 50 30 30 120 30 50 150 0-1 0 30 20 50 20 1 50 50 1 0 4000+ Section 18 4.30 BT, L 1 7? 4.56 BT, L 16? 4.79 BT, L 1 5? Waiohau Tephra BT, L14 9 . 10 93. 1 06 Strong brown and grey pumice and lithic med-coarse lapilli. Yellowish brown fine pumice lapilli. Grey lithic fine lapilli. Yellow brown coarse pumice ash. Grey fine lithic lapilli. Strong brown and grey med pumice and lithic lapilli. Brownish grey coarse pumice ash and fine lapilli. Strong brown and grey pumice and lithic med lapilli shower-bedded and ungraded. Brownish grey pumice coarse ash and fine lapilli. Brownish grey and grey fine pumice and lithic lapilli. Dark grey coarse ash. Brownish grey and grey coarse ash and fine lapilli. Strong brown coarse pumice lapilli with intermixed grey med lithic lapilli. Brownish grey and grey coarse pumice and lithic ash. Strong brown fine-med pumice lapilli and grey lithic fine lapilli. Strong brown and grey med pumice and lithic lapilli shower-bedded but ungraded. Pocketing fine, white ash. Brownish grey fine pumice lapilli. Grey coarse ash. Brownish grey, strong brown and grey fine pumice and lithic lapilli, normally graded. Grey coarse lithic ash. Strong brown med pumice lapilli, shower-bedded but ungraded. Brownish grey coarse-med pumice ash. Grey coarse ash. Grey andesitic lava flow. Base into stream. Wharepu Stream, T20 465123 True left bank of stream 300m downstream of Section 17. Description taken from below L 14? in Section 1 7. Unit Depth (mm) 1 000 50 200 40 1 0 1 0 30 30 1 50 20 40 200 40 400 250 50 20 30 1 50 250 50 50 20 1 00 30 1 0 30 1 0 50 1 300 Cum. depth (m) c. 5.0 5.78 6.52 7.02 7.32 Correlation and samples Description taken Reworked ash and lapilli, in cm scale beds and layers and lenses. Grey brownish grey and pale olive brown pumice and lithic pebbles. Dark purplish grey coarse ash and fine lapilli. Reworked brownish grey coarse ash and fine lapilli wavy bedding. Brownish grey fine lapilli. Grey fine lapilli. Brownish grey fine ash. Reworked Brownish grey coarse ash and lapilli, wavy, fine bedding. Strong brown and grey fine pumice and lithic med lapilli. Reworked brownish grey coarse ash and fine lapilli mm scale beds and laminations. Strong brown med pumice lapilli and grey lithic fine lapilli. Reworked brownish grey ash and lapilli. Reworked dark purplish grey coarse ash and fine lapilli, wavy and planar bedding. Pale olive brown med-fine pumice lapilli. Brownish grey reworked med-coarse ash and fine pumice lapilli mm scale wavy and planar beds. Dark purplish grey reworked coarse lithic ash in planar cm scale beds. Dark purplish grey fine lithic lapilli and olive brown pumice fine lapilli. Olive brown coarse pumice ash and grey lithic coarse ash. Grey coarse ash. Strong brown med-coarse pumice lapilli with intermixed grey lithic fine lapilli. Reworked brownish grey med-coarse pumice and lithic ash, in planar and wavy bedded layers. Pale olive brown med pumice lapilli and grey lithic fine lapilli. Grey and olive grey coarse-med ash. Grey lithic med ash. Shower-bedded olive brown and brownish grey coarse ash and fine pumice lapilli. Brownish grey med-fine pumice lapilli. Grey coarse lithic ash. Strong brown fine pumice lapilli and grey fine lithic lapilli. Brownish grey fine ash. Brownish grey coarse pumice ash and fine lapilli. Reworked grey and pale olive brown coarse ash and fine pumice A 37 1 50 1200 1 000+ Section 22 1 0.97 R10 lapilli, planar and cross bedded on a mm scale. Shower-bedded pale olive brown fine-med pumice lapilli. Grey sandy matrix diamicton. Brownish grey med-coarse sand supporting grey pebble to cobble clasts. Pinches and swells in thickness and has bouldery clasts concentrated in places. Silty matrix clast rich diamicton. Yellowish brown and pale brown firm silt matrix. Clasts mostly pebble-cobble in size and are multi-coloured pumice and lithics. Base into stream. Te Piripiri Stream, T20 453129 True right bank of southern tributary of stream, 20 m upstream of fork in southern sub-fork. Unit Depth (mm) 500 500 50 20 50 20 30 1 00 400 50 230 200 200 300 50 50 90 1 00 50 50 30 30 1 0 1 00 50 30 30 1 0 20 30 1 0 50 200 30 20 1 0 70 50 1 00 Cum. depth (m) 1 .05 1 . 1 4 1 .27 1 .72 2.84 2.99 3.21 3.64 3.92 Correlation and samples Description taken Taupo ignimbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp White and pale grey fine-coarse pumice ash with pumice lapilli and blocks. Charcoal fragments near base. Dark brownish grey and brown fine ash with paleosol development, lower half of unit contains several 1 0-30 mm thick grey and purplish grey ash beds. Abundant yellow brown beech leaves are preserved within some of the layers. Yellow brown and brown fine greasy ash with paleosol development. Strong brown and yellow fine pumice lapilli and coarse ash. Yellow brown fine ash. Cream-cakes of white, fine rhyolitic ash within yellow brown and brown fine ash. Yellow brown fine ash. White med-coarse pumice ash speckled within fine brown greasy ash. Yellow brown and brown fine ash with intermixed grey lithic and poorly vesicular pumice fine lapilli near the base. Mangamate Tephra (MT), Strong brown and grey pumice and lithic fine-med lapilli. Poutu Lapilli MT, Wharepu Tephra MT, Waihohonu Lapilli MT, Oturere Lapilli Pahoka Tephra Bullet Formation (BT), Pourahu Member Grey and brownish grey fine pumice and lithic lapilli and shower? bedded coarse ash. Distinctive strong brown basal 30 mm. Alternating coloured zones of grey and strong brown dominated coarse pumice and lithic ash, strong banded shower-bedding. Grey and strong brown fine pumice and lithic lapilli and coarse ash, shower -bedded. Brownish grey and grey fine pumice and lithic lapilli and coarse ash. Yellow brown fine ash with scattered fine yellow brown pumice lapilli. Yellow brown fine ash with grey fine ash intermixed. Olive grey platy blade like pumice fine lapilli and coarse ash. Normally graded onto olive grey and grey fine-med pumice and lithic lapilli. Yellow brown fine pumice ash with scattered yellow brown fine pumice lapilli. Pale yellow and yellow brown coarse-med pumice lapilli. Pale yellow and grey med-fine pumice and lithic lapilli and coarse ash. Greyish brown fine pumice lapilli and coarse ash with few grey lithic fine lapilli. Olive grey and grey pumice and lithic fine lapilli and coarse ash. Pale brown fine ash and scattered fine lithic lapilli. Brownish grey coarse ash with scattered med grey lithic lapilli. Olive grey and yellow fine-med coarse pumice and lithic ash. Olive brown fine ash and scattered fine pumice lapilli. Grey coarse lithic ash and fine lapilli. Olive brown coarse pumice ash and fine lapilli. Grey fine lithic lapilli. Olive brown fine-med pumice lapilli with few intermixed grey lithic fine lapilli. Brownish grey med ash with scattered fine pumice lapilli. Pale brown and yellow fine-med pumice lapilli with few grey lithic fine lapilli. Brownish grey and yellow coarse pumice ash with intermixed grey lithic coarse ash. Yellow brown fine pumice lapilli. Grey fine lithic lapilli and coarse ash. Brown fine ash. Olive grey coarse lithic ash with scattered yellow fine pumice lapilli. Strong brown and yellow fine pumice lapilli with few grey lithic fine lapilli. Brownish grey coarse ash with scattered grey fine lithic lapilli. A 38 50 1 0 1 00 30 30 20 20 50 30 20 50 30 300 1 00 500 1 00 100 1 50 50 1 000 1 000+ Section 24 4 . 14 93.6, Waiohau Tephra 4.66 5.36 R10 7.66 Yellow and pale brown fine pumice lapilli with few grey lithic fine lapilli. Grey fine lithic lapilli and coarse ash. Yellow and yellow brown fine-med pumice lapilli with few grey lithic fine lapilli. Brownish grey coarse ash with scattered yellow pumice and grey lithic fine lapilli. White fine ash, semi-continuous layer with occasional yellow fine pumice lapilli mixed in. Olive brown coarse pumice ash and fine lapilli. Dark brownish grey fine ash with scattered fine yellow pumice lapilli. Dark brownish grey fine pumice lapilli and coarse ash. Grey and olive brown fine pumice and lithic lapilli. Yellowish brown and yellow fine pumice lapilli. Dark grey lithic coarse ash and fine lapilli. Pale yellow med-fine pumice lapilli. Shower-bedded grey and pale brownish grey coarse pumice and lithic ash. Strong brown and yellow brown fine-med ungraded pumice lapilli. Reworked pale brownish grey, grey and yellow pumice and lithic med? coarse ash. Layers of yellow and grey pumice and lithic lapilli also occur. Pale olive brown med-fine pumice lapilli with scattered grey lithic fine lapilli. Greyish brown coarse lithic ash. Brownish grey coarse ash and fine pumice lapilli. Pale brown fine pumice lapilli with scattered fine grey lithic lapilli. Sandy matrix diamicton brownish grey matrix supporting clasts from pebble-boulder, clast rich in places. Silt and sand-matrix diamicton. Greyish brown and brown matrix supporting heterolithologic, multicoloured clasts from pebble to large boulder. Base into stream. Te Piripiri Stream, T20 448137 True left bank of northern tributary stream, 1 km upstream from State Highway 1 . Unit Depth (mm) 600 200 1 000 50 20 200 20 1 00 1 00 20 1 000 1 00 1 1 00 300 1 0 50 60 40 400 50 30 Cum. depth (m) 1 .85 2.09 2.29 3.41 4.81 5.37 Correlation and samples Description taken Makahikatoa Sand and Tufa Trig Formation with Kaharoa Tephra? Taupo lgnimbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli MT, Wharepu Tephra MT, Waihohonu Lapilli MT, Oturere Lapilli Brownish grey fine sand with interbedded 5-1 0 mm thick black fine? med ash beds interbedded throughout sand. At 300 mm depth white pocketing fine pumice ash preserved. Present soil development. White pumice ash with interbedded pumice lapilli and blocks. Dark brown and dark greyish brown greasy fine ash with paleosol development. In basal half of unit preserved several 1 0-20 mm black and purplish grey fine-med ash beds. Yellow brown beech leaves preserved within the ash. Greyish brown and yellow brown greasy fine ash. Strong brown and pale yellow fine pumice lapilli. Olive grey and greyish brown fine greasy ash. Pocketing fine white pumice ash within greyish brown fine ash. Greyish brown fine ash. White med-coarse pumice ash speckled within greyish brown fine greasy ash. Strong brown fine pumice lapilli. Yellow brown greasy fine ash with strong brown and grey fine pumice and lithic lapilli intermixed toward the base of the unit. Strong brown and reddish brown lithic and poorly vesicular pumice lapilli. Olive brown and greyish brown coarse pumice and lithic ash and fine lapilli. Shower-bedded and ungraded. Basal 1 00 mm strong brown fine pumice and lithic lapilli. Strong brown and grey fine-med pumice and lithic lapilli, reversely graded. Brownish grey fine ash and fine pumice lapilli. Dark grey med lithic shower-bedded ash. Yellow brown and greyish brown fine ash and interbedded strong brown fine pumice lapilli. Dark grey med-coarse lithic ash. Greyish brown, strong brown and grey fine-med pumice and lithic lapilli. Yellow brown fine greasy ash and scattered grey fine lithic lapilli. Pale yellow and grey fine pumice and lithic lapilli and coarse ash. A 39 40 50 20 1 30 1 0 500 200 50 1 00 1 000+ Section 26 5.54 6.45 7.55 Pahoka Tephra . Bullot Formation/ Pourahu Member R07 Pale brown fine ash with scattered fine yellow pumice lapilli. Olive grey platy fine pumice lapilli. Greyish brown fine ash with interbedded yellow fine pumice lapilli. Olive grey platy coarse ash and fine-med pumice lapilli, normally graded. Pale yellow and grey coarse ash. Pale greyish brown silty and sandy matrix diamicton. Pebbles? boulders supported within the matrix. Poorly sorted and unbedded, erosive angular unconformity as basal contact. Yellow brown fine ash and interbedded olive brown fine pumice lapilli. Pale yellow med pumice lapilli. Olive brown and yellow fine-med pumice lapilli and coarse ash. Grey med sandy matrix diamicton. Greyish brown coarse-med sand matrix with clasts of pebble to small boulder. Base into stream. Te Piripiri Stream, T20 435129 True left bank of main northern tributary of stream 600 m upstream of where other tributaries join the main stream. Description taken from base of Pahoka Tephra. Unit Depth (mm) 50 30 1 00 50 1 00 50 50 20 20 30 30 30 1 0 1 0 1 0 1 00 50 30 1 0 30 50 30 50 30 30 50 300 80 50 1 00 20 150 50 1 50 20 20 1 00 30 20 Cum. depth (m) Correlation and samples Description taken c. 3.0 3 . 18 Bullot Formation (BT), Pourahu Member 3.52 BT. M1? 3.79 4.28 5.02 93.8, Rerewhakaaitu Tephra Coarse pale yellow and grey pumice and lithic ash. Olive brown fine pumice lapilli. Yellow brown and pale brown fine ash with scattered grey lithic and pale brown pumice lapilli. Pale yellow and pale brown med-coarse pumice lapilli with scattered grey med lithic iapilli. Pale brown and pale yellow coarse ash and fine pumice lapilli with scattered grey coarse lithic ash. Greyish brown coarse pumice ash with grey lithic lapilli intermixed. Yellow brown and grey pumice and lithic fine lapilli. Grey lithic coarse ash. Greyish brown coarse pumice and lithic ash. Grey and greyish brown fine-med pumice and lithic lapilli. Olive grey coarse-med pumice lapilli. Grey coarse ash and fine lithic lapilli. Olive brown coarse pumice ash. fine olive grey ash. Grey bedded coarse lithic ash. Reworked pale brown and olive brown fine-med ash. Greyish brown and grey coarse pumice and lithic ash and fine lapilli. Pale olive brown fine pumice lapilli and coarse ash with scattered grey lithic coarse ash. Grey med lithic ash and scattered fine lithic lapilli. Olive brown med-coarse pumice ash with scattered fine pumice lapilli. Olive brown fine pumice lapilli with scattered grey lithic fine lapilli. Yellow brown fine ash with scattered yellow brown fine pumice lapilli. Grey and greyish brown coarse pumice and lithic ash and fine lapilli. Dark brownish grey fine-med pumice lapilli. Grey coarse ash. Greyish brown and olive brown fine-med pumice lapilli with scattered fine grey lithic lapilli. Brownish grey silty-matrix diamicton. Pebble clasts supported within the matrix, no bedding. Yellow brown and strong brown med-coarse pumice lapilli with scattered grey lithic fine lapilli. Brownish grey coarse pumice ash and fine lapilli. Yellow and grey fine-med pumice and lithic lapilli. Grey coarse lithic ash with scattered yellow fine pumice lapilli. Grey fine-med ash with scattered yellow and yellow brown fine pumice lapilli. Grey coarse lithic ash and fine lapilli. Grey and greyish brown pumice and lithic, shower-bedded coarse ash and fine lapilli. Yellow and yellow brown fine-med pumice lapilli. Grey coarse ash with scattered yellow pumice lapilli and interbedded white fine pumice ash 1 0 mm thick. Reworked purplish grey med ash to fine lithic lapilli. Grey med ash with scattered yellow fine pumice lapilli. Pale brown and yellow pumice coarse ash with grey coarse lithic ash intermixed. A 40 200 50 300 30 1 0 1 0 20 1 50 70 1 50 1 00 400 1 0 600 200 1 000 1 00 1 000+ 1 0000+ Section 30 5.72 6.26 R09 9.57 R 10 1 9.57 Te Piripiri Stream, T20 486162 Reworked grey and brownish grey fine-med ash with layers of fine? med pumice lapilli within. Yellow brown and olive brown fine-med pumice lapilli with scattered grey fine lithic lapilli. Reworked black and purplish grey coarse lithic ash and fine lapilli, 1 0- 20 mm planar bedding. Pale olive brown fine-med pumice lapilli. Grey coarse lithic ash. Strong brown and pale yellow coarse pumice ash. Greyish brown pumice med-coarse ash. Reworked purplish grey and brownish grey lithic and pumice coarse ash and fine lapilli. Strong brown and yellow fine-med pumice lapilli with scattered grey fine lithic lapilli. Brownish grey bedded med-sands, 1 0-20 mm scale beds. Pale olive brown and yellow fine pumice lapilli. Brownish grey med sands with layers and lenses of brownish grey and yellow fine pumice lapilli. Planar and cross bedded. Yellow brown silt. Dark purplish grey coarse lithic ash and shower-bedded fine lapilli. Pale olive brown and grey fine-med pumice and lithic lapilli. Brownish grey sandy matrix diamicton. Pebble-boulder ctasts supported within the matrix, grey clasts, unbedded. Angular unconformity as lower contact. Strong brown and reddish brown fine soft pumice lapilli. Yellow brown silty and sandy matrix diamicton. Pinches and swells over lava flow. Clasts of pebble to huge lava boulders contained within matrix. Grey andesite lava flow. Base into stream. True left bank of stream where four-wheel-drive track crosses lower Stream, 1 km upstream from Tongariro River. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 300 Ngauruhoe Formation Brown and brownish grey fine-med ash, present soil development. 1 000+ Taupo lgnimbrite White fine-coarse pumice ash with pumice lapilli and blocks. Charcoal fragments near base and pink staining in places. Unit ramps over a hill and thickens in paleo-valley. 300 1 .60 Mangatawai Tephra Dark greyish brown fine ash with paleosol development lower half contains several grey and purplish grey fine-med ash, 1 0-20 mm layers. 1 00 Papakai Formation (Pp) Yellow brown and brown fine ash with few scattered yellow brown fine pumice iapilli 20 1 .72 Waimahia Tephra within White fine ash cream-cakes within fine greasy yellow brown ash. Pp 30 Pp Yellow brown fine ash. 50 1 .80 Hinemaiaia Tephra within White coarse-med pumice ash scattered within yellow brown fine Pp greasy ash. 50 Pp Yellow brown fine ash. 20 Strong brown fine pumice iapilli. 1 00 Yellow brown fine ash. 20 1 .99 Motutere Tephra within Pp Pale brown and white fine pumice ash cream-cakes within yellow brown fine ash. 50 Pp Yellow brown fine ash with scattered grey pumice lapilli. Strong brown stained base. 200-400 R02 Greyish brown med-coarse and matrix diamicton, angular grey and strong brown pebble-cobble clasts supported within the matrix. Very ciast rich unit with abundant strong brown and pale brown pumice ciasts present especially concentrated near the base of the unit. 250-400 2.84 Mangamate Tephra (MT), Strong brown and greyish brown and grey fine-med pumice and lithic Poutu Lapilli lapilli, shower-bedded and ungraded. 400 MT, Wharepu Tephra Upper 200 mm grey and olive grey med-coarse pumice ash shower- bedded, next 1 50 mm fine pumice lapilii of the same colour. Lower 50 mm strong brown fine pumice lapilii and coarse ash. 1 50 MT, Ohinepango Tephra? Strong brown and grey pumice and lithic lapilli and coarse ash. 1 50 Brown and yellow brown fine, firm, greasy ash. 1 50 Grey and strong brown pumice and lithic med ash. 1 50 Grey and strong brown fine pumice and lithic lapilli and coarse ash. 1 0 Brown fine ash. 1 000 4.85 MT, Waihohonu Lapilii Alternating bands of grey and strong brown fine pumice and lithic lapilli and coarse ash. Shower-bedded but ungraded. Distinctive colour A 41 600-1 000 20 30 300 30 4000+ 3000+ Section 32 R04 MT, Oturere Lapilli 6.23 94.9, Karapiti Tephra R05-R09 13.23 banding. Grey and greyish brown fine sandy matrix diamicton. Pebble-cobble angular clasts, very clast rich almost clast supported. Unbedded, grey lithic clasts with occasional red and yellow clasts. Yellow brown coarse pumice ash. Grey lithic coarse ash. Reversely graded greyish brown, strong brown and grey fine-med pumice and lithic lapilli. Olive grey fine-med ash containing thin (5 mm) white fine pumice ash. Stacked sequence of diamicton units pinching in and out. Grey and greyish brown fine-coarse sandy matrices supporting clasts of pebble to boulders. Some of units have a horizontal fabric some are massive and unbedded. Lower units are very clast rich with huge boulders. Yellow brown matrix diamicton, silt and sand matrix with pebble to large boulder clasts, grey clasts massive and unbedded. Base into stream. Mangatoetoenui Stream, T20 445145 True left bank of stream 1500 m upstream of State Highway 1 . Description taken from below Papakai Fonnation. Unit Depth (mm) 200 1200 20 1 000-2000 1 0 30 200 1 00 3000-4000 2000+ Section 34 Cum. depth (m) Correlation and samples Description taken c. 2.0 Mangamate Tephra (MT), Strong brown and grey fine-med pumice and lithic lapilli Poutu Lapilli MT, Wharepu Tephra R03 5.56 MT, Waihohonu Lapilli R04-R09 1 1 .56 Brownish grey and grey fine pumice and lithic lapilli and coarse ash. Shower-bedded but ungraded, lower 1 00 mm strong brown fine pumice and lithic fine lapilli. Yellow brown finn, fine ash. Greyish brown diamicton. Fine-coarse sand matrix supporting clasts of pebble to boulder in size. Yellow fine pumice lapilli. Grey and strong brown coarse pumice and lithic ash. Grey and strong brown mixed fine-med pumice and lithic lapilli. Alternating layers of grey and strong brown fine pumice and lithic lapilli. Several diamicton units, greyish brown and grey sandy matrix supporting pebble to boulder clasts. Dominantly grey clasts, some units have planar fabric others are massive. Lower unit contains very large boulder clasts in a yellow brown and greyish brown silty and sandy matrix. Grey andesite lava flow Base into stream. Mangatoetoenui Stream, T20 476160 True right bank of stream, next to the four-wheel-drive track and ford across the stream, 2 km downstream of S.H. 1 . Unit Depth (mm) 400 1 00 30 1 50 1 00 80 500 150 40 1 00 200-400 20 500 Cum. depth (m) c. 1 .0 1 . 1 3 1 .38 2. 1 5 2.65 Correlation and samples Description taken Mangatawai Tephra Papakai Fonnation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp R01 Pp Motutere Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli MT, Wharepu Tephra Brown and dark brown fine ash with 20-30 mm beds of black and purplish grey med-fine ash. Yellow brown fine greasy ash with paleosol development. White fine ash cream-cakes within yellow brown fine ash. Olive brown and yellow brown greasy fine ash. White med-coarse pumice ash scattered within fine yellow brown ash. Yellow brown fine greasy ash. Yellow brown, greyish brown and grey sandy matrix diamicton. Grey and few red scoriaceous pebble to small boulder clasts supported within the matrix. Yellow brown fine ash with scattered yellow brown pumice and grey lithic fine lapilli. Fine pale brown and white pocketing pumice ash, almost a complete layer, within brown fine ash. Greyish brown fine ash with scattered grey fine lithic lapilli. Strong brown, olive brown and grey fine pumice and lithic lapilli, shower-bedded but ungraded. Grey coarse-med ash. Greyish brown and grey fine pumice lapilli and coarse ash, shower? bedded. Lower 150 mm strong brown fine pumice lapilli and coarse ash. A 42 20 3000+ Section 35 6. 1 9 R03 Yellow brown fine firm ash. Grey and pale olive grey sandy matrix diamictons. Pebble-boulder clasts supported within the matrix, mostly grey clasts, 2-3 units. Base into stream. Mangatoetoenui Stream, T20 476161 True left bank of stream, at 4WD ford in stream, 2 km downstream from State Highway 1 . Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 400 c. 1 .0 Mangatawai Tephra Brown and dark brown fine ash with 20-30 mm thick layers of black and purplish grey fine-med ash. 50 Papakai Formation (Pp) Yellow brown fine greasy ash. 20 1 .07 Waimahia Tephra within White fine pumice ash cream-cakes within fine yellow brown fine ash. Pp 50 Pp Grey fine-med ash mixed within yellow brown fine ash. 1 00 Yellow brown fine ash. 50 1 .27 Hinemaiaia Tephra within White med-coarse ash scattered within yellow brown fine ash. Pp 1 50 Pp Yellow brown fine greasy ash. 40 1 .46 Motutere Tephra within Pp Pale brown fine pumice ash cream-cakes within brown fine ash. 1 00 Pp Greyish brown fine ash. 1 00-300 1 .86 Mangamate Tephra (MT), Variable thickness strong brown and grey fine-med pumice lapilli. Poutu Lapilli 400 MT, Wharepu Tephra Upper 250 mm greyish brown and grey fine pumice and lithic lapilli and coarse ash, shower-bedded. Lower 150 mm strong brown fine pumice lapilli and coarse ash. 20 Yellow brown fine ash. Angular unconformity with sediments below. 0-1 000 R03 Grey and brownish grey sandy matrix diamicton. Pebble-boulder grey lithic clasts supported by the matrix. 1 00 3.38 MT, Ohinepango Tephra Coarse grey and strong brown ash, shower-bedded with alternating bands of colour. 800 MT, Waihohonu Lapilli Strong brown yellow brown and grey fine-med pumice and lithic lapilli and coarse ash, shower-bedded in bands of colour. 500 R04 Grey brownish grey and grey sandy matrix diamicton, faint planar fabric observed, clasts sparse and pebble-small boulders supported within the matrix. 1 000+ R05-R06 Grey sandy matrix diamictons (2 units) massive and unbedded pebble- small boulder clasts, grey lithic. 5.68 Base onto track. Section 37 Mangatoetoenui Stream, T20 465150 True left bank of stream 300 m downstream of State Highway 1 , description from Poutu Lapilli. Unit Depth (mm) 300 30 1 000 20 30 800 50 500 1 00 30 60 1 000-1500 200 300-500 400 Cum. depth (m) c. 2.0 3.03 3.88 4.43 6. 1 2 7.22 Correlation and samples Description taken Mangamate Tephra (MT), Strong brown and grey fine-med pumice and lithic lapilli, shower- Poutu Lapilli bedded. Grey lithic med ash. MT, Wharepu Tephra Brownish grey and grey fine-med pumice and lithic lapilli and coarse ash, strongly shower-bedded and ungraded. Basal 1 00 mm strong brown fine pumice lapilli. Yellow brown fine, firm ash. Grey med lithic ash. MT, Waihohonu Lapilli Grey, olive brown and strong brown fine-med pumice and lithic lapilli, shower bedded and ungraded. Banded olive grey, brown and grey coarse-med pumice and lithic ash. MT, Oturere Lapilli Grey, brownish grey and strong brown fine-med pumice and lithic lapilli, shower-bedded. Pale grey and pale brown fine ash with scattered soft pumice and lithic fine lapilli. Greyish brown med ash and scattered fine lithic lapilli. Upper half yellow brown fine-med ash, lower half yellow brown fine, soft pumice lapilli. Pahoka Tephra Over-thickened at this locality. Grey and olive grey platy coarse ash and fine lapilli, normally graded top. Lower 500-1000 mm olive grey, and pale yellow med-coarse pumice lapilli, with banded lapilli common. Yellow brown fine ash. Distinctive very pale yellow and grey pumice and lithic coarse ash and fine lapilli. Bullet Formation, Pourahu Pale yellow and pink fine ash, containing large pumice clasts of pale A 43 30 9000+ Section 38 Member R07-R09 1 6.25 Ohinepango Stream, T20 448164 yellow and pale olive, some clasts up to 250 mm diameter. Pale yellow coarse-med pumice lapilli. Grey, greyish brown and yellow brown matrix diamictons, several sandy matrix units. Pebble-boulder lithic clasts supported within matrix. Base obscured. True left bank of stream close to foot bridge across stream along track to Waihohonu Hut. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 600 Makahikatoa Sand and Brown and yellow brown fine-med sands with interbedded black and Tufa Trig Formation grey faint med-fine 5-10 mm ash layers. 200 0.80 Taupo lgnimbrite White fine-coarse pumice ash with pumice lapilli and blocks intermixed. Occasional charcoal fragments. 400 Mangatawai Tephra Dark brown and dark greyish brown fine greasy ash with soil development. Interbedded black and purplish black fine-med ash, some containing yellow brown beech leaves. 50 Papakai Formation (Pp) Greyish brown greasy fine ash. 1 0 1 .26 Waimahia Tephra within White pocketing fine ash within greyish brown fine ash. Pp 400 Pp Greyish brown and yellow brown fine greasy ash, with scattered occasional yellow brown and grey pumice and lithic fine iapilli. 50 1 .7 1 Hinemaiaia Tephra within White med-coarse pumice ash scattered within greyish brown fine ash. Pp 300 Pp Yellow brown and greyish brown fine ash. 1 0 2.02 Motutere Tephra within Pp Pale brown fine pumice ash within yellow brown fine ash. 1 50 Pp Greyish brown and yellow brown fine ash with scattered fine grey lithic iapilli. 600 2.77 Mangamate Tephra (MT), Grey, olive grey and strong brown fine-med pumice and lithic lapilli, Poutu Lapilli shower-bedded and normally graded. 1 0 Fine grey ash. 1 200 MT, Wharepu Tephra Olive grey and brownish grey fine-med pumice and lithic lapilii and coarse ash shower-bedded and ungraded. Lower 1 00 mm strong brown fine pumice lapilli. 20 Yellow brown fine, firm ash. 600 Reworked grey and strong brown med-coarse ash, planar bedded 20 mm scale. 50 MT, Waihohonu Lapilli Grey and strong brown coarse pumice and lithic ash. 400 5.05 Olive grey, strong brown and brownish grey fine pumice and lithic lapilli and coarse ash, shower-bedded and reverseiy graded, banded strong brown and grey zones near base. 1 00 R04 Pale brownish grey silly and sandy matrix diamicton. Grey pebble clasts supported within matrix. 1 0 Yellow brown fine pumice lapilli. 1 0 Grey fine ash. 20 Grey coarse lithic ash. 30 Pale brown and yellow fine ash with scattered fine pumice lapilli. 20 Olive grey fine ash. 400 5.64 MT, Oturere Lapilli Grey, brownish grey and strong brown fine-med pumice and lithic lapilli, shower-bedded but ungraded. 50 Pale yellow and grey fine-med ash grading into coarse pumice ash and lapilli of the same colours. 30 Yellow brown fine ash. 30 Yellow brown fine-med pumice iapilli with scattered grey fine lithic lapilli. 30 Greyish brown fine ash and fine lithic lapilli. 300 6.08 Pahoka Tephra Upper 50 mm normally graded, olive grey platy med-coarse ash and fine lapilli. Lower 250 mm coarse-med pumice lapilli, olive grey and pale yellow with occasional banded pumice lapilli. 20 Yellow and grey coarse pumice and lithic ash. 250 R06 Grey sandy matrix diamicton. Grey pebble-cobble ciasts supported within matrix, eroded lower contact. 20 Dark yellow brown fine ash. 1 00 Yellow brown and greyish brown fine pumice lapilli. 1 00 Yellow brown fine pumice ash. 20 Grey and greyish brown med lithic ash. 200 6.79 Bullot Formation, Pourahu Poorly sorted yellow brown and pale brown fine-coarse lapilli. Lower Member 150 mm normally graded coarse pumice ash and fine lapilli of same colours, with scattered grey lithic coarse ash. 1 500 R07 Grey and greyish brown sandy matrix diamicton. Pebble-boulder clasts supported within the matrix, grey, unbedded. A 44 2500+ Section 40 93. 1 6a 1 0.79 Grey andesite lava flow Base into stream Waihohonu Stream, T20 415815 Moraine capped ridge behind Waihohonu Hut, at top of un-vegetated part of hil l . Description taken from Oturere Lapilli. Unit Depth (mm) 500 1 00 1 00 1 0 50 50 30 300 100 30 1 00 30 50 1 0 1 00 500+ Section 41 Cum. depth (m) c. 3.0 3.20 3.34 3.96 4.56 Correlation and samples Description taken Mangamate Tephra, Greyish brown and grey fine-med pumice and lithic lapilli, shower- Oturere Lapilli bedded and ungraded. Yellow brown fine ash with scattered pale yellow and yellow brown fine pumice lapilli. Pahoka Tephra Pale olive grey and yellow fine pumice lapilli and coarse ash. Normally graded and platy coarse ash at top. Abundant yellow pumice. Grey fine ash. Brownish grey coarse pumice ash and fine pumice lapilli. Greyish brown fine ash with scattered fine yellow pumice lapilli. Bullot Formation, Pourahu Yellow brown med-fine pumice lapilli. Member? Greyish brown and grey bedded sands and pebbles. Yellow, strong brown and grey med-coarse pumice and lithic lapilli. Yellow brown and greyish brown med-coarse pumice ash. Pale brown, yellow and greyish brown fine pumice lapilli with scattered fine grey lithic lapilli. Grey and pale yellow fine pumice and lithic lapilli and coarse ash. Grey, pale brown, and brownish grey fine-med pumice and lithic lapilli. Waiohau Tephra White fine pumice ash cream-cakes. Black and greyish brown coarse lithic ash and fine lapilli. Grey and greyish brown sandy matrix diamicton or till. Grey pebble- boulder clasts. Base obscured Ohinepango Stream, T20 461 1 70 True right bank of stream in a deep rut carved by a small tributary stream. 50 m west of State Highway 1 . Unit Depth (mm) 400 500 50 1 0 200 60 250 1 0 1 50 400 20 400 1 0 1 00 1 0 80 20 20 20 500 50 50-100 30 Cum. depth (m) 0.96 1 .22 1 .48 2.03 3.21 Correlation and samples Description taken Taupo lgnlmbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp Motutere Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli MT. Wharepu Tephra MT, Ohinepango Tephra MT, Waihohonu Lapilli MT, Oturere Lapilli White fine-coarse pumice ash with intermixed pumice lapilli and blocks. Charcoal fragments contained near base of unit. Brown and dark brown fine ash with paleosol development, Lower half has several interbedded black and purplish grey 20-30 mm, fine-med ash beds. Yellow brown beech leaves contained within some of the layers. Brown fine greasy ash. Pocketing white fine pumice ash within brown fine ash. Brown and yellow brown fine greasy ash. White med-coarse ash scattered within yellow brown fine ash. Yellow brown fine ash with scattered fine yellow pumice lapilli. Pale brown fine pumice ash within yellow brown fine ash. Yellow brown fine ash with scattered grey pumice and lithic lapilli. Grey, strong brown and olive brown fine-med pumice and lithic lapilli, shower -bedded. Grey med lithic ash. Grey and brownish grey fine pumice and lithic lapilli, shower-bedded and ungraded. Lower 1 50 mm strong brown fine pumice lapilli. Yellow brown fine ash. Alternating beds of grey and strong brown coarse pumice and lithic ash. Grey fine ash. Grey and strong brown fine pumice and lithic lapilli, alternating colour layers. Black and dark grey coarse ash. Pale brown and pale yellow fine ash with soft fine-med pumice lapilli. Olive grey fine-med ash and fine lapilli, pumice and lithic. Grey, brownish grey and strong brown fine-med pumice lapilli, shower? bedded but ungraded. Pale brown fine ash. Pale yellow and grey coarse ash, pumice and lithic. Pale brown fine ash. A 45 30 Yellow and yellow brown soft pumice lapilli. 300 3.72 Pahoka T ephra Pale olive grey and pale yellow fine-coarse pumice lapilli, shower bedded and normally graded. Platy coarse ash near top. 20 Pale yellow and grey coarse pumice and lithic ash. 300-500 R06 Yellow brown fine sandy diamicton, with intermixed large pumice blocks 200 mm diameter, as well as lithic pebbles and cobbles supported within the matrix. 1 00 Yellow brown and strong brown fine pumice lapilli and coarse ash, shower -bedded. 30 Yellow brown fine ash with scattered fine pumice lapilli. 1 00 4.47 Bullot Formation, Pourahu Pale yellow and yellow brown fine-coarse pumice lapilli, with scattered Member grey fine lithic lapilli. 3000 R07 Clast rich diamicton, large boulder-pebble clasts with small amount of sandy and pebbly matrix. Grey, greyish brown and occasional red clasts and matrix. Erosive base, unconformity. 600 Bedded sands, silts and gravels planar and cross-bedded, grey, greyish brown and strong brown. 40 8. 1 1 93. 1 7, Kawakawa Tephra White fine pumice ash shower-bedded. 400 Grey and brownish grey bedded sands. 1 000 9.51 R 10 Yellow brown and pale yellow greasy silt matrix diamicton, multi- coloured pebble-large boulder, lithic and pumice clasts, highly weathered or altered clasts. 1 000 R10 Strong brown and reddish brown silty matrix diamicton, with abundant reddish and grey lava bomb clasts within it. Semi-detached bomb clasts. 450 Bedded fine sands and silts, cross-bedded. Brown and brownish grey with scattered yellow fine pumice lapilli. 80 1 1 .04 Yellow brown and strong brown med-coarse pumice lapilli. 500 Grey and olive grey bedded sands with scattered yellow brown fine pumice lapilli. 1 00 Strong brown and yellow brown fine-med pumice lapilli with scattered grey lithic lapilli. 1 000+ R1 1 Greyish brown and grey silt and sand matrix diamicton, with pebble- boulder, grey lithic clasts supported within the matrix. 1 2.64 Base into stream. Section 42 Ohinepango Stream, T20 4621 72 True right bank of stream, 50 m upstream from joining with Waihohonu Stream, immediately west of State Highway 1 . Description taken from below Papakai Formation. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 200 c. 2.0 Mangamate Tephra (MT), Strong brown and grey pumice and lithic fine-med lapilli, shower- Poutu Lapilli bedded, eroded upper contact. 500 MT, Wharepu Tephra Grey and brownish grey shower-bedded and ungraded fine-med pumice and lithic iapilli and coarse ash. Lower 200 mm strong brown fine pumice lapilli. 20 Yellow brown fine ash. 650 3 . 17 MT, Waihohonu Lapilli Grey, strong brown, and olive grey fine pumice and lithic lapilli, shower-bedded. Lower part has alternating strong brown and grey dominated bands. 1 0 Greyish brown and pale grey fine pumice lapilli. 1 0 Brownish grey med-coarse ash. 450 3.64 MT, Oturere Lapilli Grey, olive brown and yellow brown fine-med pumice lapilli, shower- bedded but ungraded. 80 Yellow brown and pink fine ash with interbedded med-coarse yellow and pale brown soft pumice lapilli. 40 Pink, grey and pale yellow med-coarse pumice ash. 1 20 3.88 Pahoka Tephra Grey and pale yellow fine pumice and lithic lapilli and coarse ash. 50 Pale yellow fine ash and fine-med pumice lapilli. 2000-3000 Grey andesitic lava flow. 2000 R10 Strong brown silty matrix diamicton, large scoriaceous bombs-pebbles supported within the matrix, grey and reddish coloured clasts. 50 Strong brown fine pumice lapilli and coarse ash. 1 000+ Brown and brownish grey bedded silts and fine sands with layers and lenses of multicoloured pumice pebbles. 9.98 Base obscured A 46 Section 44 Waihohonu Stream, T20 464174 Large road cutting on the western side of State Highway 1 , immediately north of the bridge over the Waihohonu Stream. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 400 Ngauruhoe Formation and Dark brownish grey fine-med, friable ash with indistinct 10 mm thick Tufa Trig Formation grey and black fine-med ash beds. 400-1000 1 .40 Taupo lgnimbrite White fine-coarse pumice ash with intermixed pumice lapilli and blocks, charcoal fragments also present. 450-500 Mangatawai Tephra Dark brown and greyish brown fine greasy ash with paleosol development, lower half of unit contains several black and purplish grey fine-med ash layers, often with preserved yellow brown beech leaves. 200 Papakai Formation (Pp) Brown and greyish brown fine ash with paleosol development. 50 Greyish brown fine ash with pocketing black fine-med ash. 20 2 . 17 Waimahia Tephra within Cream-cakes of fine white pumice ash within brown fine greasy ash. Pp 1 00 Pp Yellow brown fine greasy ash with scattered fine yellow brown soft pumice lapilli. 50 2.32 Hinemaiaia Tephra within White med-coarse pumice ash scattered within yellow brown fine ash. Pp 650 Pp Yellow brown greasy fine ash with scattered yellow and grey fine pumice and lithic fine lapilli, more concentrated near the base. Uneven lower contact. 350 Reworked strong brown and grey pumice and lithic fine lapilli and coarse ash, eroded upper contact, planar and cross-bedded. 400 3.42 Mangamate Tephra (MT). Strong brown and grey fine pumice and lithic lapilli, shower-bedded but Poutu Lapilli ungraded. 600 MT, Wharepu Tephra Upper 450 mm, grey, greyish brown and some strong brown fine-med pumice lapilli, shower-bedded but ungraded. Lower 1 50 mm strong brown fine pumice lapilli. 20 Yellow brown fine, firm ash. 30 MT, Ohinepango Tephra Greyish brown and strong brown med-coarse pumice and lithic ash. 30 Greyish brown reworked fine-med pumice and lithic lapilli, within med grey and greyish brown ash. 1 000 5. 1 0 MT, Waihohonu Lapilli Strong brown, grey and greyish brown fine-med pumice and lithic lapilli and coarse ash with strong shower-bedding giving a banded colour appearance. 1 50 Greyish brown fine-med sand, with mixed grey sub-rounded pebbles, and occasional cobbles. 20 Strong brown and brown coarse ash and fine pumice lapilli. 450 5.72 MT, Oturere Member Grey, greyish brown and strong brown med-fine pumice and lithic lapilli, shower-bedded but ungraded. 60 Yellow brown and pale brown fine ash with scattered grey-white soft pumice fine lapilli. 20 Yellow brown and strong brown fine pumice lapilli and coarse ash. 1 00-150 Grey and greyish brown sands and fine gravels planar bedded, sub- rounded cfasts. 1 0 Strong brown fine-med pumice lapilli. 30 Greyish brown sand and fine, sub-rounded gravel. 350 6.34 Pahoka Tephra Olive grey and pale yellow fine-med pumice lapilli and coarse ash, normally graded, upper part has very platy lapilli, and lower part contains occasional banded olive grey and pale yellow pumice lapilli. 20 Strong brown and yellow brown coarse pumice ash. 1 200 Grey and greyish brown bedded sands and fine-coarse gravels, planar bedded 1 00-300 mm scale, sub-rounded clasts. 600-1 300 8.86 R06 Greyish brown sandy matrix diamicton, abundant boulder-cobble clasts in upper half of unit and dominantly pebble clasts within the lower half, clasts supported within the matrix. Dominantly grey with occasional red lithic clasts. 50 Pale brown fine ash. 1 00 Pale brown fine-med pumice lapilli. 1 00 9. 1 1 Bullet Formation, Pourahu Pale brown and pinkish fine ash containing abundant coarse-med Member pumice lapilli within. 1 00-200 Pale yellow and pale brown fine-med pumice lapilli and coarse ash with scattered grey coarse lithic ash. 1 0 Brown fine silty layer. 3000+ R07 Greyish brown sandy and silty matrix diamicton. Pebble-large boulder cfasts supported within the matrix, dominantly grey with occasional red clasts. Diamicton pinches out over lava, laps up onto side of lava. Angular unconformity with coverbeds below diamicton. 2000+ R09ff3 Brownish grey sand and silt matrix diamicton, dominantly multi- coloured and grey pumice and lithic pebble clasts with few grey lithic A 47 400 200 50 30000+ Section 45 14.72 Kawakawa Tephra 93. 1 9 44.97 boulders, unconformable upper contact. Shower-bedded white and pale pink fine-med pumice ash. Upper 1 50 mm massive fine pale pink ash, onto 1 00 mm pale brown med ash with coarse ash horizons and accretionary lapilli present up to 1 5 mm in diameter. Onto 30 mm coarse white pumice ash, onto 20 mm pale brown fine ash, onto 30 mm fine white ash. Dark greyish brown fine-med ash. Yellow brown fine-coarse pumice lapilli intermixed within the scoriaceous top of the lava flow. Grey andesite lava flow with red scoriaceous top, highly brecciated top. Base into stream on opposite side of road. Upper Waikato Stream, T20 461096 True left bank of northern tributary 500 m upstream of State Highway 1 . Description taken from M1 marker sequence in Bullot Formation. Unit Depth (mm) 1 0 1 0 20 30 30 20 40 1 50 50 200 30 20 50 1 00 20 20 20 20 20 1 0 40 20 20 30 50 1 00 80 20 400 600 500 1 00 1 000 600 300 200 Cum. depth (m) Correlation and samples Description taken c. 4.0 Bullot formation, M1 4.55 4.75 5.02 Waiohau Tephra? 5.64 Hinuera Formation 6.74 R10 8.44 Grey fine ash. Yellow brown coarse pumice ash. Yellow brown fine ash with scattered grey coarse lapilli. Grey fine lithic lapilli and coarse ash. Yellow brown coarse pumice ash and fine iapilli. Grey coarse lithic ash. Grey and yellow brown coarse ash and fine pumice and lithic lapilli. Grey and strong brown fine-med pumice and lithic lapilli. Grey and purplish grey med ash. Strong brown fine-med pumice lapilli, shower-bedded with scattered grey lithic fine lapilli. Grey and strong brown lithic and pumice med ash. Strong brown and grey fine-med pumice and lithic lapilli. Grey and brownish grey coarse-med pumice and lithic ash. Strong brown and brownish grey fine-med pumice lapilli with scattered grey fine lithic iapilli. Brownish grey med ash. Strong brown and yellow brown fine pumice lapilli with scattered grey fine lithic lapilli. Pale grey lithic med ash. Strong brown fine-med pumice lapilli. Purplish grey lithic coarse ash. Brown coarse ash and fine pumice lapilli. Purplish grey coarse ash with scattered yellow brown fine pumice ash. Strong brown and yellow brown fine pumice lapilli with scattered fine grey lithic lapilli. Brownish grey and grey coarse lithic and pumice ash. Yellow brown and brown med pumice ash with sparse scattered grey fine lithic lapilli. Brownish grey and grey coarse pumice and lithic ash, contains a 10-20 mm pocketing white fine pumice ash. Grey and brownish grey coarse pumice and lithic ash with scattered yellow brown and strong brown fine pumice iapilli. Strong brown fine-med pumice iapilli, shower-bedded with scattered grey fine lithic lapilli. Black lithic med-coarse ash. Bedded silt, sand and gravels, wavy and planar bedding 20-100 mm scale. intermixed white fine pumice ash in places. Greyish brown and pale brown. Brownish grey sand and fine gravel. Planar and wavy bedding on a 1 0-20 mm scale, unconsolidated with pumice and lithic pebbles. Eroded upper contact. Strong brown sand and silt matrix diamicton. Multi-coloured pebble and cobble clasts supported by the matrix. Clasts highly weathered lithic and pumice, heterolithologic. Yellow brown silt matrix supporting clasts as described in the unit above. Greyish brown massive sandy matrix diamicton unit with fine pebbly clasts, dominated by grey lithic and pumice clasts with multi coloured pebbles also. Yellow brown and fine sand and silt matrix diamicton with multi? coloured cobble and boulder clasts. Bedded brown and greyish brown sands and gravels, wavy and planar bedded. Pale brown and brown fine sands and silts 1 0-20 mm scale wavy and A 48 200 700 3000 250 2000+ Section 46 R10 1 2.84 1 2.99 93.23 14.99 planar bedding. Grey and brown sands and gravels cross bedded. Pale brown and pale yellow brown silt matrix diamicton with cobble and pebble clasts supported within the matrix. Bedded fluvial sands, gravels and silt layers, grey lithic and pumice pebbles. Well developed cross-stratification in some layers. Lenses of yellow pumice lapilli interbedded in places, and some layers slightly hardened. Yellow brown pumice fine-med lapilli with few scattered fine grey lithic lapilli. Bedded silt, sand, and gravel in lenses and layers. Yellow brown and brown silts with grey and greyish brown sands and gravels. Base into stream. Upper Waikato Stream, T20 464098 True left bank of northern tributary of stream, 300 m upstream from State Highway 1 . Description taken from lowest Bullet Formation tephra preserved. Unit Depth (mm) 80 20 300 500 50-200 200 500 2500 0-50 200 200 1 0 500 20 400 500+ Section 47 Cum. depth (m) Correlation and samples Description taken c. 6.0 7.02 R10 1 0.27 93.24 93.25 1 1 . 1 8 93.26, Marker Unit 1 1 1 .20 93.27, Marker Unit 1 R1 1 1 2. 10 Yellow brown and reddish brown fine-med pumice lapilli with scattered fine grey lithic lapilli. Grey med-coarse ash. Yellow brown, bedded fine med sand and silt, with occasional yellow brown fine pumice pebbles, weak planar beds. Grey lithic, bedded sands and fine-coarse gravels, mostly grey lithic clasts with occasional red clast, cross-bedding, eroded lower contact. Variable top brown silt and sand matrix diamicton, containing multi? coloured pumice and weathered lithic pebble clasts supported within the matrix. Yellow brown silt and fine sand matrix with fine pebbles-boulders supported within the matrix. Massive pale brown silt and sand matrix diamicton with multi-coloured pumice and highly weathered lithic pebble-cobble clasts supported within the matrix. Strong brown, brownish grey and purplish grey bedded sands and gravels, well developed planar and cross-bedding on a 1 0-50 mm scale. Eroded lower contact. Strong brown and yellow brown fine pumice lapilli, soft and porous. Grey bedded sands and gravels as above. Strong brown reversely graded coarse pumice ash-med lapilli, with scattered grey lithic fine lapilli. Brown fine ash. Grey, olive grey and yellow coarse-med pumice and lithic ash, shower? bedded with distinctive banded appearance. Lower 1 00 mm coarse ash and fine pumice and lithic lapilli. Yellow fine pumice iapilli and coarse ash. Brown and greyish brown bedded sands and gravels, planar and cross-bedded with multi-coloured heterolithologic pumice and lithic pebbles in layers and lenses. Massive yellow brown and grey sand and silt matrix diamicton, grey and greyish brown lithic pebble-cobble clasts supported by the matrix. Base into stream. Upper Waikato Stream, T20 465099 True left bank of northern tributary, 1 OOm upstream from State Highway 1 , description taken from below Marker Unit 1 . Unit Depth (mm) 2000 1 000 2000 400 1 500 Cum. depth (m) c. 1 0 Correlation and samples Description taken Grey, and dark grey bedded sands and coarse gravels, wavy and planar bedding 200 mm scale beds. Grey and brownish grey bedded sands and fine gravels, cross-bedded and planar bedded on a 20-50 mm scale. Brown and strong brown bedded sands, silts and gravels, planar and cross-bedded with layers and lenses of multi-coloured pumice and lithic clasts, yellow pumice and grey lithic clasts dominant, 1 0-1 00 mm scale beds. 1 3.40 93.28 Yellow and yellow brown soft fine-med pumice lapilli, with sparse scattered grey lithic fine lapilli. Firm, bedded sands silts and gravels, grey and greyish brown planar and cross-bedded, 1 0-100 mm scale. A 49 1 000+ R1 1 1 5.90 Section 50 Tongariro River, T20 494965 Very hard grey and greyish brown sandy matrix diamicton. Grey pebble-boulder clasts supported within the matrix. Faint planar fabric. Base into stream. Road cutting and cliff exposure on the true left bank of river at the end of Waipakihi Road near the river gauging station. Unit Depth Cum. Correlation and samples Description (mm) Depth (m) taken 1 500 Taupo lgnimbrite Fine-coarse white pumice ash with mixed pumice lapilli and blocks. Charcoal fragments contained within the lower part of the unit. 300 Mangatawai Tephra Dark brown and greyish brown fine ash with paleosol development. Interbedded within this are several 10-20 mm beds of fine-med black and purplish grey ash. Some ash beds contain Yellow brown beech leaves preserved within. 600 2.40 Papakai Formation Yellow brown and brown fine greasy ash with paleosol development and scattered yellow brown and grey fine pumice iapilli. 400-500 Mangamate Tephra (MT), Variable upper contact. Yellow brown and grey fine-med poorly Poutu Lapilli vesicular pumice and lithic lapilli, shower-bedded and ungraded. 1 0 Black med lithic ash. 300-350 3.26 MT, Wharepu Tephra Grey and greyish brown fine pumice and lithic lapilli and coarse ash, shower-bedded but ungraded. Basal 50 mm strong brown fine pumice. 1 0 Yellow brown fine, firm ash. 250-300 MT, Waihohonu Lapilli Grey and strong brown alternating coloured. Shower-bands of pumice and lithic fine lapilli and coarse ash. 1 0 Brown fine ash. 250 3.83 Grey and strong brown fine pumice and lithic fine lapilli and coarse ash, shower-bedded and normally graded. 20 Pale yellow fine pumice lapilli and coarse ash. 50 Grey fine lapilli and coarse lithic ash. 20 Pale yellow and grey pumice and lithic coarse ash and fine lapilli. 1 0 Grey coarse lithic ash. 20 Yellow brown and brown fine ash with scattered fine yellow pumice lapilli. 20 Grey coarse-med lithic ash. 300 4.27 Mt, Oturere Lapilli Grey and pale yellow fine-med pumice and lithic lapilli, shower-bedded and ungraded. 50 Brown and yellow brown greasy fine ash. 200 Pahoka Tephra Grey and olive grey fine pumice lapilli and coarse ash, platy coarse ash at top of unit, normally graded. Occasional banded lapilli present, olive grey and pale yellow bands. 1 0 Pale brown coarse pumice ash. 1 0 Grey med-coarse lithic ash. 1 00-200 Yellow brown fine ash with scattered yellow fine pumice lapilli. 1 50-200 4.94 Bullot Formation, Pourahu Yellow brown and pale yellow fine-med pumice lapilli and coarse ash, Tephra normally graded. 50 Grey lithic fine lapilli. 1 500-2000 R07 Grey and yellow brown sand and silt matrix diamicton. Upper 1 000 mm grey pebble-boulder clasts, very clast rich and almost clast supported in places. Lower part finer grained with matrix mostly supporting pebble clasts, grey and olive grey lithic and sparse poorly vesicular pumice. Lower part has faint planar fabric. 800 R08-R09 Yellow brown silt and grey sand matrix diamicton, planar fabric preserved. Yellow, strong brown and grey fine pebbly pumice and lithic clasts supported by the matrix. 1 000 8.74 Yellow brown and greyish brown silt and sand matrix. Large boulder- pebble clasts supported by the matrix, reversely graded, upper part dominated by boulders and lower part by cobbles-pebble clasts. 4000-5000 Grey and brownish grey sandy and silt matrix diamicton with large boulder-pebble clasts. Massive and unbedded. Lower 2000 mm finer grained with largest clasts dominantly grey cobbles. Sharp contact to unit below. 1 000+ 14.70 Grey and greyish brown firm sandy matrix diamicton, grey angular lithic pebble-cobble clasts supported by the matrix. Faint planar fabric preserved. 5000 Obscured 2000+ 21 .70 Bedded and tilted greywacke rock, with base into river. A 50 Section 51 Tongariro River, T20 496157 Large road cutting along the Waipakihi Road, after the crossing of the unnamed stream on the top of the large high surface. Unit Depth (mm) 300 200-1 000 200-300 80 20-30 70 1 00 250 20-30 1 00 400-600 1 0 300-400 1 0 20-50 1 50 200 1 0 1 000 1 0 1 0-20 40 500 50- 100 20 50 400 1 0 40 50 50 40 40 30-40 50 20 20 20 50 1 0 40 1 0 20 30 20-50 Cum. Depth (m) 1 .60 1 .71 1 .88 2. 1 6 2.86 3.33 3.68 5.26 5.83 5.93 6. 1 7 6.39 Correlation and samples Description taken Ngauruhoe Formation Taupe lgnimbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp Motutere Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli MT. Wharepu Tephra Poronui Tephra MT, Waihohonu Lapilli MT, Oturere Lapilli Pahoka Tephra Bullet formation, Pourahu Member? Brown greasy fine-med ash with present soil development. White fine-coarse pumice ash with pumice lapilli and blocks intermixed. Charcoal fragments intermixed near base of unit. Dark brown and greyish brown fine ash with paleosol development, and several interbedded black and purplish grey fine-med ash beds, 1 0-20 mm thick, some of the beds contain yellow brown beech leaves preserved within. Brown and yellow brown fine greasy ash with occasional scattered fine yellow pumice lapilli. Pocketing white fine ash within yellow brown fine ash. Yellow brown fine greasy ash. White med-coarse pumice ash scattered within yellow brown greasy fine ash. Yellow brown greasy fine ash with scattered fine yellow pumice lapilli. Pale brown fine pumice ash cream-cakes. Yellow brown fine ash with scattered grey fine lithic and pumice lapilli. Wavy upper contact. Strong brown, grey and greyish brown fine pumice and lithic lapilli, shower-bedded and weakly reversely graded. Grey med lithic ash Grey and greyish brown fine pumice and lithic lapilli and coarse ash, shower-bedded and ungraded. Lower 1 00 mm strong brown fine pumice lapilli. Brown fine firm ash. Grey med-coarse ash containing pocketing fine white pumice ash. Alternating shower-bands of grey and strong brown med-coarse pumice and lithic ash. Strong brown, grey and greyish brown alternating bands of fine pumice and lithic lapilli. Brown fine ash. Grey and strong brown coarse ash and fine-med pumice lapilli, shower-bedded with bands of alternating colours, ungraded. Grey fine ash. Grey and yellow brown pumice and lithic med ash. Yellow brown fine ash with scattered grey and yellow brown fine pumice lapilli. Grey, greyish brown and strong brown fine-med pumice and lithic lapilli, shower-bedded but ungraded. Yellow brown fine ash with scattered fine yellow and yellow brown pumice lapilli. Yellow brown fine pumice lapilli. Yellow brown fine ash. Normally graded coarse ash-med pumice lapilli, olive grey and pale brown, with scattered banded pumice lapilli with grey and pale brown stripes. Platy pumice coarse ash at the top of the unit. Pale yellow and grey pumice and lithic coarse ash. Yellow brown fine ash. Yellow brown pumice lapilli and coarse ash. Yellow brown fine ash. Strong brown and pale yellow fine-med pumice lapilli, with scattered grey fine lithic lapilli. Grey and pale yellow coarse pumice and lithic ash. Strong brown, pale yellow and yellow brown fine-med pumice lapilli. Pale brown and pale greyish brown fine ash with scattered fine grey lithic lapilli. Pale yellow and yellow brown pumice lapilli with scattered grey lithic coarse ash. Grey fine ash. Yellow brown fine pumice lapilli with scattered fine grey lithic lapilli. Grey and greyish brown med-coarse lithic and pumice lapilli. Olive grey and brown fine ash. Greyish brown and purplish grey coarse lithic ash and fine lapilli. Pale yellow coarse pumice ash. Grey coarse lithic ash. Yellow brown fine-med pumice lapilli with scattered grey lithic fine lapilli. Grey coarse lithic ash. A 51 50 20 1 0 300 40 6.86 30 1 00 50-100 50 40 7 . 18 Waiohau Tephra 1 0 300 30 200 7.72 200 1 00 50 50 30 1 00 8.25 50 30 30 10 1 50-200 8.57 50 0-1 000 9.62 R 10 500-1 000 400 1000 12.02 20-30 1 2.05 94. 1 3 40 3000 R1 1 1 5.09 Section 53 Waihohonu Stream, T20 4981 84 Pale yellow fine pumice lapilli, reversely graded with grey coarse lithic ash. Grey coarse ash and fine lithic lapilli. Pale greyish brown and yellow brown fine ash with scattered yellow brown fine pumice lapilli. Grey and pale yellow reworked pumice and lithic coarse ash and fine lithic lapilli, wavy and planar beds. Strong brown fine pumice lapilli with scattered grey fine lithic lapilli. Greyish brown and grey coarse-med ash. Strong brown med-fine pumice lapilli with scattered grey fine lithic lapilli and med ash, shower-bedded and ungraded. Purplish black coarse lithic ash and fine lapilli. Grey and greyish brown med-coarse lithic ash. Greyish brown med ash with interbedded white fine pumice ash. Purplish grey med lithic ash. Alternating layers of greyish brown and olive grey coarse lithic and pumice ash and fine lapilli. Strong brown and pale yellow fine pumice lapilli. Purplish black coarse lithic ash. Greyish brown, grey and yellow brown fine-med shower-bedded pumice lapilli. Pale yellow brown and brown fine-med ash with scattered coarse pumice ash. Yellow and grey coarse pumice and lithic ash. Brown and greyish brown fine ash. Greyish brown and pale brown fine pumice lapilli with scattered grey lithic fine lapilli. Normally graded grey and pale olive brown coarse pumice ash and fine lapilli. Greyish brown and pale brown med-coarse pumice ash with scattered grey lithic med ash. Pale yellow pumice fine lapilli with scattered grey lithic coarse ash. Greyish brown fine ash. Purplish grey fine ash. Reversely graded yellow brown fine-med pumice lapilli with scattered fine grey lithic lapilli. Pale yellow brown normally graded coarse pumice ash and fine lapilli, with scattered grey lithic coarse ash. Brown silt and sand matrix diamicton, sparse grey angular lithic pebble-large boulder clasts supported by the matrix, angular unconformable lower contact. Brownish grey and brown sand and silt matrix firm diamicton. Weak planar fabric preserved and pebble clasts supported by the matrix. Grey lithic and yellow pumice clasts. Greyish brown bedded sands and gravels, cross-bedded, sub-rounded grey lithic gravels. Massive firm yellow brown silt and sand matrix diamicton. Pebble? cobble clasts supported by the matrix, grey lithic and abundant yellow pumice clasts. At top of unit abundant yellow pumice pebbles with a faint horizontal fabric, the rest of the unit is massive and unbedded. Yellow brown and yellow coarse pumice ash with scattered grey lithic coarse ash. Brown fine ash. Massive firm fine-grained diamicton. Brown silt and sand matrix supporting clasts of grey and red lithic and yellow pumice pebble clasts. Base obscured. True right bank of stream, 300 m upstream of where Pangara Stream meets Waihohonu Stream. Unit Depth (mm) 1 000- 1 0000 200-350 20 20 30 450 Cum. Depth (m) 1 0.35 1 0.87 Correlation and samples Description taken Taupe ignimbrite Mangamate Tephra (MT), Waihohonu lapilli MT, Oturere Lapilli White and pale grey fine-coarse ash with abundant pumice blocks and lapilli intermixed. Large charcoalised logs preserved especially near the base of the unit. Eroded angular contact into units below, angular unconformity. Strong brown, greyish brown and grey coarse pumice and lithic ash and fine lapilli, shower-bedded with alternating coloured zones. Grey and greyish brown fine-med ash. Yellow brown and strong brown fine pumice iapilli and coarse ash. Greyish brown med-coarse pumice ash. Reddish brown, and grey fine-med poorly vesicular pumice and lithic A 52 50 50 1 00 200 40 1 50 3000 1 300 40 1 00-150 5000- 1 0000 2000+ Section 54 1 1 .27 Pahoka Tephra 1 5.76 1 5.95 94. 1 8 R07-R09 27.95 Tongariro andesite Oturere Stream, T1 9 484209 fine-med lapilli, shower-bedded but ungraded. Fine yellow brown and greyish brown ash with scattered grey and yellow brown fine pumice and lithic lapilli. Yellow brown, yellow and grey coarse pumice and lithic ash. Yellow brown fine ash with scattered grey and yellow brown lithic and fine pumice lapilli. Olive grey and pale brown platy coarse pumice ash and fine-med lapilli. Normally graded, with occasional olive grey and pale brown banded pumice lapilli, shower-bedded. Brown and yellow brown fine ash. Grey med-coarse sands with scattered yellow brown fine pumice lapilli, planar bedded on a 10 mm scale. Bedded greyish brown and grey sands and fine-coarse gravels. Planar bedded on a 1 00 mm scale. Bedded grey sands with scattered common pale brown pumice fine pebbles. Wavy bedded with occasional lenses of pumice pebbles. Greyish brown and pale brown fine sand and silt, wavy bedded. Strong brown fine-med pumice lapilli, interbedded within top of diamicton and as a discrete layer on top of diamicton. Clast rich diamicton unit, dominating exposures all along this stream. Grey and occasional red lithic sub-rounded clasts, pebble-very large boulders. Matrix of greyish brown silt and fine sand, yellow pumice and grey lithic pebble clasts common. Matrix supported but very clast rich. Grey lava, base into stream Cutting on the western side of State Highway 1 , 1 00 m south of crossing of Oturere stream. True left bank of Oturere stream valley. Unit Depth Cum. Correlation and samples Description (mm) Depth (m) taken 600-1 000 400-500 1 00 20 1 50 1 00 1 50 10-20 1 00 550 40 50 1 50 600 1 0 1 0 1 0 1 0 400 1 50 1 50 50 50 1 00 1 .60 1 .62 1 .87 2.04 2.69 3.97 3.27 Taupo lgnimbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Hinemaiaia Tephra within Pp Pp Motutere Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli MT, Wharepu Tephra MT, Waihohonu Lapilli MT, Oturere Lapilli Pahoka Tephra White pumice, fine-coarse ash with mixed pumice lapilli and blocks, charcoal fragments preserved within base of unit. Dark brown and dark greyish brown fine ash with paleosol development. Interbedded black and purplish grey fine-med ash beds 1 0-20 mm thick with common pale brown beech leaves preserved within layers. Brown greasy, fine ash with paleosol development. Cream-cakes of white, fine, pumice ash within brown greasy fine ash. Dark greyish brown greasy fine ash. White, med-coarse pumice ash scattered within fine greasy greyish brown ash. Yellow brown and brown greasy fine ash with vertical cracking, and paleosol development. Pale brown pumice fine ash cream-cakes within brown fine greasy ash. Yellow brown and brown fine ash. Strong brown and grey fine-med poorly vesicular pumice and lithic lapilli, shower-bedded but ungraded. Grey coarse-med lithic ash. Strong brown fine-med pumice lapilli. Grey and strong brown 10 mm alternating layers of poorly vesicular pumice and lithic med-coarse ash. Reworked ash. Strong brown, greyish brown and grey fine-med pumice and lithic lapilli. Shower-bedded but ungraded. Lower 40 mm yellow brown pumice and lithic lapilli. Greyish brown fine ash. Grey med lithic ash. Yellow brown med-coarse pumice ash. Grey fine ash. Grey and greyish brown fine-med poorly vesicular pumice and lithic lapilli shower-bedded but ungraded. Pale brown soft greasy fine ash with interbedded yellow brown and grey fine lapilli. Grey, olive grey and pale brown fine-med pumice lapilli, shower? bedded, platy fine lapilli near top. Brown fine ash, soft and greasy with scattered yellow brown fine pumice lapilli. Pale yellow and grey coarse pumice and lithic ash. Brown and yellow brown fine ash with scattered fine, soft, brown and yellow fine pumice lapilli. A 53 50-100 3.57 Bullot Formation, Pourahu Yellow brown and pale brown fine-med pumice lapilli with scattered Member grey lithic lapilli, shower-bedded. 1 00 Grey and pale greyish brown fine ash with interbedded yellow brown and grey fine pumice and lithic lapilli. 40 Yellow brown fine-med soft pumice lapilli with scattered grey fine lithic lapilli. 1 80 Grey and greyish brown fine ash with scattered yellow brown and grey pumice and lithic lapilli. 20 Yellow brown fine pumice lapilli. 1 00 Brown and pale brown fine-med ash with scattered yellow brown fine pumice lapilli. 80 4.09 Yellow brown and strong brown fine-med pumice lapilli with scattered grey lithic fine lapilli. 1 50 Yellow brown coarse pumice ash and fine lapilli with sparse, scattered grey lithic coarse ash. 1 00 Grey and few yellow brown coarse lithic and pumice ash and fine lapilli. 50 Brown and greyish brown fine greasy ash with scattered yellow brown and strong brown fine pumice lapilli. 20 4.41 Waiohau Tephra Grey and greyish brown fine ash with pocketing white fine pumice ash. 80 Greyish brown and brown fine-coarse ash with sparse scattered fine yellow brown pumice lapilli. 1 00 Yellow brown fine pumice lapilli, shower-bedded with scattered fine grey lithic lapilli. 50 Grey fine-med ash with scattered fine yellow brown pumice lapilli. 30 Yellow brown, strong brown and grey med-coarse pumice and lithic ash. 30 Brown fine ash. 1 50 4.85 Pale brown and pale yellow pumice fine-med lapilli with scattered grey fine lithic lapilli, grey lithic rich zone in centre of unit. 40 Brown fine ash with scattered yellow brown fine pumice lapilli. 1 00 Yellow and pale yellow brown fine-med, soft pumice lapilli with scattered grey lithic coarse ash and fine lapilli. 1 0 Grey med lithic ash. 30 Yellow and pale yellow brown fine-med, soft pumice lapilli with scattered grey lithic coarse ash and fine lapilli. 1 0 Grey med lithic ash. 80 5. 1 2 Yellow brown and pale brown fine pumice lapilli with scattered grey lithic fine lapilli. 1 80 Greyish brown and grey fine ash with scattered pale brown fine pumice lapilli. 20 Pale brown and yellow brown fine pumice lapilli with scattered grey lithic fine lapilli. 200 Brown and greyish brown fine ash with scattered grey and pale brown lithic and pumice fine lapilli. 50-60 Grey and greyish brown coarse lithic and pumice ash and fine lapilli. 50 Grey and greyish brown fine-med lithic ash. 50 5.68 Pale brown coarse pumice ash and fine lapilli, normally graded, with scattered grey lithic coarse ash and fine lapilli. 30 Yellow brown fine ash. 40 Yellow brown and grey coarse pumice and lithic ash mixed in equal proportions. 1 00 Grey and greyish brown fine ash with scattered pale brown fine pumice lapilli. 20 Greyish brown and yellow brown fine pumice lapilli. 20 Purplish grey fine ash. 120 6.01 94.20 Greyish brown and pale brown med-fine pumice and scattered lithic lapilli. 350 Brown and greyish brown fine ash with scattered grey and yellow brown lithic and pumice fine lapilli. 400 Grey and greyish brown fine ash or silt with occasional interbedded cobbles and yellow brown and grey lithic fine lapilli. 2000-3000 T1 Reworked diamicton, grey clast supported with a grey sandy matrix, pebble cobble and small boulder clasts. 4000+ T2 Eroded upper contact. Yellow brown. pale brown and greyish brown silt and sand matrix diamicton. Pebble-large boulder clasts supported within matrix, massive with no bedding, multi-coloured pebble clasts, larger clasts dominantly grey. 1 3.76 Base obscured. A 54 Section 56 Oturere Stream, T19 478213 True left bank of stream 500 m upstream of previous section. Unit Depth (mm) 500-3000 800-1000 500 1 00 200 1 0-20 1 00 200-500 40 50 200-400 300 500 30 20 1 0 350-400 50 20 20 30 200 1 0 1 0 40 80 40 1 00 40 40 30 1 0 40 20 50 30 30 1 00 1 00 1 50 200 50 1 50 Cum. depth (m) 4.0 4.6 4.82 5.42 7 . 17 7.49 7.77 8.00 8.26 8.76 Correlation and sample Description taken Taupo lgnimbrite White and pale grey fine-coarse pumice ash with mixed pumice lapilli and blocks. Charcoal fragments preserved near base, thickens in paleo-valley. Mangatawai Tephra Dark brown fine ash with paleosol development, several purplish grey and black ash beds, 10-30 mm thick interbedded within. Common pale brown beech leaves preserved within black ash layers. Papakai Formation (Pp) Yellow brown and dark brown fine greasy ash with paleosol development. Hinemaiaia Tephra within White med-coarse pumice ash scattered within yellow brown fine Pp greasy ash. Pp Yellow brown fine greasy ash. Motutere Tephra within Pp Pale brown fine ash cream-cakes within yellow brown fine ash. Pp Yellow brown fine ash. Mangamate Tephra (MT), Uneven upper boundary. Strong brown and grey fine-med poorly Poutu Lapilli vesicular pumice and lithic lapilli, shower-bedded but ungraded. Grey lithic med-coarse ash. MT, Wharepu Tephra Strong brown fine pumice lapilli. MT, Ohinepango Tephra Grey and strong brown alternating layers of coarse pumice and lithic ash, shower-bedded. MT, Waihohonu Lapilli Grey, greyish brown and strong brown fine-med pumice and lithic lapilli, shower-bedded. Grey and strong brown fine poorly vesicular pumice and lithic lapilli. Grey dominated at the top and strong brown at the base. Grey lithic med ash. Strong brown coarse pumice ash. Grey coarse ash. MT, Oturere Lapilli Grey, greyish brown and strong brown fine-med poorly vesicular pumice and lithic lapilli, shower-bedded and ungraded. Greyish brown fine ash with scattered yellow brown and pale brown fine pumice lapilli. Yellow brown coarse pumice ash. Greyish brown fine ash. Strong brown and yellow brown fine pumice lapilli. Pahoka Tephra Grey and olive brown fine-med pumice lapilli, shower-bedded, with scattered banded grey and pale brown pumice lapilli. Grey coarse lithic ash. Yellow brown coarse pumice ash. Yellow brown and brown fine ash. Yellow brown and grey coarse pumice and lithic ash and fine lapilli, equal proportions of lithics and pumice. Dark brown fine ash, with scattered yellow brown and brown fine pumice lapilli. Bullot Formation, Pourahu Yellow brown, pale brown and strong brown med-fine pumice lapilli, Member with scattered fine grey lithic lapilli. Greyish brown fine ash with scattered grey and yellow brown fine lithic and pumice fine lapilli. Strong brown fine pumice lapilli. Grey lithic coarse-med ash. Yellow brown coarse pumice ash. Grey med-coarse lithic ash. Yellow brown and pale brown fine soft pumice lapilli with scattered grey lithic lapilli. Greyish brown and grey pumice and lithic med ash. Grey coarse lithic ash. Yellow brown and brown fine pumice lapilli with scattered grey coarse ash. Brown and yellow brown fine ash with scattered, sparse yellow brown and grey fine pumice lapilli. Strong brown and yellow brown med-fine pumice lapilli with scattered grey lithic lapilli. Yellow brown fine ash with abundant yellow brown and grey lithic and pumice fine lapilli. Grey, greyish brown and strong brown fine pumice and lithic lapilli, shower -bedded. Yellow brown and brown fine ash with scattered pale brown and grey pumice and lithic fine lapilli. 94.21 , Waiohau Tephra Greyish brown and grey fine-med ash with scattered occasional yellow brown fine pumice lapilli. Pocketing white fine pumice ash within A 55 1 0 20 20 1 00 50 80 40 1 00 9. 1 8 400 3000 500-1 000 200 1 000 1 000+ Section 58 centre of unit 1 0-20 mm thick. Strong brown, soft fine pumice lapilli. Grey coarse lithic ash. Yellow brown fine ash with scattered strong brown fine pumice lapilli. Strong brown fine, soft pumice lapilli. Brown and grey fine ash with scattered common grey coarse lithic ash and strong brown fine pumice lapilli. Pale yellow fine pumice lapilli with scattered grey fine lithic lapilli . Pale grey and yellow fine ash with scattered fine yellow brown pumice lapilli. Pale yellow fine soft pumice lapilli with scattered grey lithic lapilli. Grey and greyish brown bedded silts and sands with scattered and lenses of yellow brown fine pumice lapilli. T1 Eroded upper surface. Dark grey sandy matrix diamicton. Pebble? large boulder clasts supported within matrix, clasts and matrix grey, massive and unbedded. T2, pumice sample -94.22 Sharp upper contact. Pale brown and pale yellow silt and sand matrix diamicton, with clasts of yellow, yellow brown and grey pumice and lithic pebble clasts supported within the matrix. Grey and yellow pumice and lithic bedded med-fine sand, 20 mm scale. T2 Yellow, greasy silt matrix diamicton. Grey, and pinkish grey pumice and lithic pebble clasts supported within the matrix. Bright distinctive appearance. T3 Firm reddish grey lithic sand matrix diamicton, with pebble-cobble clasts supported within the matrix, massive and unbedded. Base obscured Makahikatoa Stream, T19 485221 True right bank of stream 500 m upstream of road. Description started at Mangamate Tephra. Unit Depth (mm) 300 1 50 20 300 20 1 0 1 0 60 40 30 250-300 20 50 1 0 50 50 50 20 1 0 1 0 1 0 20 40 1 0 20 50 1 00 50 20 Cum. depth (m) Correlation and samples Description taken c. 4.0 Mangamate Tephra {MT), Poutu Lapilli MT, Wharepu Tephra MT, Waihohonu Lapilli 4.57 MT, Oturere Lapilli 4.94 Pahoka Tephra 5.07 Bullet Formation, Pourahu Member 5 .17 5.46 Grey and strong brown alternating beds of coarse-med poor1y vesicular pumice and lithic ash, 30 mm shower-beds. Strong brown, grey and greyish brown pumice and lithic fine-med lapilli, shower-bedded. Strong brown fine pumice lapilli. Grey and strong brown fine pumice and lithic lapilli, shower-bedded, with grey dominated top and strong brown base. Grey coarse-med lithic ash. Strong brown coarse pumice ash. Pale olive grey med ash. Greyish brown, grey and strong brown fine-med pumice and lithic lapiili shower-bedded and ungraded. Yellow brown and pale greyish brown fine-med ash. Yellow brown and grey pumice and lithic coarse ash. Grey and olive brown fine-med pumice lapilli with scattered fine banded pumice lapilli. Shower-bedded but ungraded. Brown fine-med ash with scattered grey and yellow brown fine lithic and pumice lapilli. Yellow brown, pale brown and grey coarse pumice and lithic ash in equal proportions. Brown fine ash with scattered yellow fine pumice lapilli. Strong brown and yellow brown fine-med pumice lapilli, shower? bedded with scattered grey lithic fine lapilli. Greyish brown fine ash with scattered yellow brown and pale brown fine pumice lapilli. Strong brown and yellow brown fine-med pumice lapilli with scattered grey lithic fine lapilli. Greyish brown fine ash. Grey coarse lithic ash. Strong brown coarse pumice ash. Greyish brown fine ash. Strong brown fine pumice lapilli. Greyish brown fine ash with scattered fine strong brown pumice iapilli. Grey coarse lithic ash. Strong brown and grey pumice and lithic fine lapilli. Brown and greyish brown fine ash. Strong brown and yellow brown fine-med pumice iapiili with scattered grey fine lithic lapilli. Yellow brown fine ash with scattered strong brown fine pumice lapilli. Strong brown fine pumice lapilli. A 56 1 00 30 40 1 0 1 0 1 0 1 0 1 0 50 20 20 30 20 1 00 200 400 40 1 00 40 50 500 1 000+ Section 59 5.61 5.85 6.57 94.27 Waiohau Tephra T1 8.30 Yellow brown and strong brown fine-med shower-bedded pumice lapilli with scattered grey lithic fine lapilli. Brown fine ash with scattered yellow brown fine pumice lapilli. Greyish brown fine-med ash. Strong brown fine pumice lapilli. Grey coarse lithic ash. Greyish brown fine ash. Strong brown fine pumice lapilli. Grey fine lithic lapilli. Greyish brown fine ash. Strong brown and yellow brown coarse pumice ash. Yellow brown fine ash. Yellow brown and grey fine pumice and lithic lapilli and coarse ash. Strong brown fine pumice lapilli. Grey and dark grey fine-med lithic ash with scattered strong brown and pale brown pumice fine lapilli. Yellow brown and yellow med pumice lapilli with grey med-coarse lithic ash interbedded at the top of the unit. Distinctive unit in this area. Grey and pale greyish brown fine ash with scattered sparse yellow fine pumice lapilli. 10 mm cream-cakes of white fine pumice ash. Yellow brown coarse pumice ash. Greyish brown and yellow brown fine ash. Strong brown and yellow brown fine pumice lapilli. Yellow brown and strong brown fine ash with scattered strong brown fine pumice lapilli. Greyish brown bedded sands and silts, planar bedded on 1 0-30 mm scale with interbedded yellow brown pumice pebbles in layers and lenses. Grey and strong brown sandy matrix diamicton. Clasts of sub-rounded and sub-angular pebble-large boulders supported within the matrix, grey clasts, unbedded. Base into stream. Makahikatoa Stream, T19 495220 True right bank of stream c. 800 m downstream of State Highway 1 at crossing of power pylons. Description taken from distinctive grey topped pumice lapilli unit described near the base of the previous section (above Waiohau Tephra). Unit Depth (mm) 150 4000-5000 200-3000 200 250 20 40 50 1 00 30 400 1 50 20 40 20 250 40 50-100 1 50 50 Cum. depth (m) Correlation and samples Description taken c. 8.0 Strong brown and yellow brown fine-med pumice lapilli with scattered grey lithic fine lapilli and grey fine-med ash mixed in at the top of the unit. T1 Grey and greyish brown silty and sandy matrix diamicton, with clasts of pebble to boulder supported by the matrix. Clasts, grey and red lithic as well as abundant multi-coloured pumice and weathered lithic pebbles. T2, pumice sample - 94.31 Variable thickness, eroded top. Yellow silty matrix diamicton with grey lithic and white, pink and yellow brown pumice clasts supported by the firm silty matrix. Distinctive unit. 1 6.20 Grey mad-coarse lithic ash. Pale greyish brown fine ash with scattered fine yellow and grey pumice and lithic lapilli. Pale yellow and grey fine pumice and lithic lapilli. Pale brownish grey fine ash with scattered fine yellow pumice lapilli. 1 6.56 Pale yellow and yellow brown fine pumice lapilli, soft with scattered grey fine lithic lapilli. Pale grey fine ash, greasy. 1 6.69 94.28, Okareka Tephra Yellow brown and pale grey bedded silts, with white fine pocketing pumice ash. Pale brownish grey bedded fine silts and sands with planar and wavy bedding on a 1 0-30 mm scale. Grey fine ash with scattered fine yellow pumice lapilli. Grey and pale yellow fine pumice and lithic lapilli. Pale grey fine ash. 1 7.32 94.29, TeRere Tephra Pocketing wavy bedded fine white pumice ash. Pale yellow and yellow brown fine pumice lapilli with scattered weathered pale grey lithic lapilli. Pale greyish brown fine ash with scattered pale grey fine pumice lapilli. Pale yellow and purplish grey fine pumice and lithic weathered lapilli. Pale greyish brown fine ash with scattered grey and pale yellow fine pumice and weathered lithic lapilli. 1 7.66 White and pale yellow brown fine pumice lapilli with scattered grey lithic lapilli. A 57 1 0 30 50 Section 60 1 7.75 Greyish brown fine ash. Pale yellow and grey fine pumice and lithic lapilli. Greyish brown fine ash with scattered pale yellow fine pumice lapilli. Base into Stream Makahikatoa Stream, T19 504215 True left bank of stream c. 2 km downstream of State Highway 1 . 100 m downstream of telephone line crossing. Unit Depth (mm) 150 250 40 50 20 50 1 0 50 300 20 1 0 40 Cum. depth (m) c. 4.0 4.63 Correlation and samples Description taken Hinuera Formation Upper part obscured Strong brown fine pumice lapilli and coarse ash, with scattered grey lithic lapilli. Greyish brown greasy fine ash. Greyish brown med-coarse pumice ash. Grey med-coarse lithic ash. Yellow brown fine ash. Grey and pale yellow brown coarse pumice and lithic coarse ash. Brown fine ash. Yellow brown coarse pumice ash and fine lapilli with scattered grey coarse lithic ash. Greyish brown and brown fine ash with scattered yellow and yellow brown fine pumice lapilli. Contains white pumice ash. Yellow brown fine pumice lapilli. Grey fine ash. Yellow brown fine pumice lapilli. 1 200 6.20 Hinuera Formation Brown and pale brown bedded silt and fine pumice sand with scattered strong brown and pale brown fine pumice lapilli, also few layers and lenses of pumice lapilli. 400 6000-8000 1 0 10 1 0 20 2000- 3000+ Section 64 14.65 1 7.65 Kawakawa Tephra, Oruanui lgnimbrite Member Aokautere Ash Member T4 Strong brown and grey sandy matrix diamicton, pebble-cobble rounded clasts supported within the matrix. Grey soft fine-med ash, massive, unbedded with very occasional cobble-pebble clast of andesite supported within. Scattered white coarse pumice ash. Pinkish white fine ash. Pale brown med pumice ash. Pale yellow and white med-fine pumice ash. Pinkish brown fine pumice ash. Sharp upper contact. Brown and yellow brown silty matrix diamicton. Pebble-boulder grey lithic clasts supported by the matrix. Some sites massive and unbedded others contain fluvial lenses and planar fabric. Base into stream Mangatawai Stream, T19 490239 True left bank of stream 50 m upstream of the State Highway 1 bridge over stream. Unit Depth (mm) 200 300 1 000 1 0-20 1200 Cum. depth (m) 300 3.0 600 1 300 1500+ 6.40 Correlation and samples Description taken T2 T3 94.41 , Rotoaira Tephra Hinuera Formation T4 Top obscured, coverbeds at road section. Brown silt and sand matrix diamicton, yellow strong brown, grey angular pebbly lithic clasts supported by the matrix. Grey and greyish brown planar bedded sands and fine gravels, 30 mm scale beds. Greyish brown sand and silt matrix diamicton. Pebble-cobble clasts supported by matrix, occasional boulders also present. Dominantly grey and few red lithic clasts with pumice pebble clasts also. Unbedded, massive. Pale brown silt and fine sand. Grey, purplish grey, strong brown and brown fine-coarse sands and pebbles, pumice and lithic, planar bedded on 1 0-30 mm scale. Strong brown coarse-med pumice lapilli with scattered lithic med lapilli. Greyish brown, strong brown and grey fine-coarse bedded sands, planar bedded on a 1 0-30 mm scale. Grey and pale brown bedded sands and fine white pumice ash, planar and wavy bedded on a 1 0-30 mm scale. Greyish brown and grey sandy matrix diamicton, clast rich with cobble to boulder sized clasts supported within the matrix, grey lithic clasts. Base into stream. A 58 Section 66 Mangatawai Stream, T19 496238 True left bank of stream 600 m downstream from State Highway 1 , at crossing of westem-most power pylon line. Unit Depth (mm) 200-1000 400 1 00 1 0-20 400 300-500 4000 300 1 50 200 50 1 00 30 50 80 1 0 50 300 50 1 00 50 150 1 0 400 1 200 200-400 1200 1 500+ Cum. depth (m) 1 .50 2.42 6.87 7 . 12 7.25 7.38 7.44 7.94 8.50 12.80 Correlation and Samples Description taken Taupo lgnimbrite Mangatawai Tephra Papakai Formation (Pp) Waimahia Tephra within Pp Pp Mangamate Tephra (MT), Poutu Lapilli T1 94.43 94.44 94.45 94.46 94.47, Rerewhakaaitu Tephra T3 T3-T4 White fine-coarse pumice ash with mixed pumice lapilli and blocks, local over-thickening, contains fragments of charcoal within base. Black and purplish black 1 0-20 mm thick fine-med ash beds interbedded within dark brown, greasy, fine ash with paleosol development. Brown and yellow brown greasy fine ash. Pocketing white fine pumice ash within brown greasy fine ash. Brown and yellow brown fine ash with paleosol development, cracked vertically. Strong brown, and yellow brown fine-med poorly vesicular pumice and lithic lapilli, shower-bedded and ungraded. Grey and greyish brown silty and sandy matrix diamicton. Pebble? large boulder clasts supported by matrix, grey sub-angular lithic clasts, massive unbedded. Unconformable angular upper eroded contact. Pale purplish brown, pale brown and pale yellow bedded silt and fine sand, wavy and planar bedded on a 10 mm scale, with scattered fine pale yellow pumice lapilli. Brown and dark brown fibrous lignite, with wood fragments, wavy and planar laminations on a 5-20 mm scale. Mgt(a) taken 20 mm from top, and (b) taken 20 mm above base. Pale grey bedded silt and fine sand, planar and wavy bedded on a 1 0- 20 mm scale, with scattered pale yellow fine pumice lapilli present. Pale yellow fine, soft, pumice lapilli with scattered sparse grey lithic fine lapilli. Pale yellow and pale grey silt and fine sand, planar and wavy bedded on a 1 0-20 mm scale, with scattered pale yellow fine pumice lapilli present. Pale yellow fine pumice lapilli with few scattered pale grey lithic fine lapilli. Pale yellow and pale grey silt and fine sand, planar and wavy bedded on a 1 0-20 mm scale. Yellow and pale yellow fine pumice lapilli with few scattered pale grey lithic fine lapilli. Purplish brown firm lignite. Pale brown fine-med pumice ash. Dark brown and brown firm lignite with large (>500 mm long, >200 mm diameter) wood fragments within. Wood sampled as (c) and lignite sampled in 50 mm intervals as (d)-(h). Grey bedded fine sand planar 10 mm scale bedding. Dark brown and brown lignite planar bedded, on a 1 0-30mm scale, firm. (I) sampled near top and 0) near base. White fine -med pumice ash. Black and dark brow lignite, firm, bedded, planar and wavy bedding on a 1 0-30 mm scale. Sampled 2 cm from top and 2 cm from base. Pale brown wavy bedded fine silt. Dark brown and brown lignite and organic rich silts and fine sands. Sampled in the zones of most pure lignite. Pale grey and pale yellow bedded silts and fine sands with scattered pale yellow fine pumice lapilli. Planar and wavy bedded on a 5-30 mm scale, very finely laminated at base. Pale brown sandy matrix diamicton, pebble-cobble grey lithic clasts supported by matrix, unbedded. Massive, unbedded pale brown and pale olive silt and fine sand. Greyish brown and brown silt and sandy matrix diamicton, clasts of grey and greyish brown lithic pebble-boulders supported by matrix, unbedded. Base into stream. A 59 Section 68 Mangamate Stream, T19 505248 True left bank of stream 1 50-200 m upstream of crossing of eastern-most line of power pylons, c. 1 km downstream of State Highway 1 . Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 400 Mangatawai Tephra Dark brown fine greasy ash with interbedded purplish grey and black fine-med ash beds 1 0-20 mm thick. 1 50 Papakai Formation (Pp) Brown and yellow brown fine greasy ash. 50 0.60 Hinemaiaia Tephra within Scattered white pumice med-coarse ash within brown fine greasy ash. Pp 250 Pp Brown and yellow brown fine ash with scattered grey and strong brown pumice and lithic lapilli in base of unit. 500 1 .35 Mangamate Tephra (MT). Strong brown and grey fine-med pumice and lithic lapilli, shower- Poutu Lapilli bedded but ungraded. 1 50 MT, Waihohonu Lapilli Grey and strong brown med-coarse poorly vesicular pumice and lithic ash. 250 Strong brown and yellow brown and grey pumice and lithic lapilli. 50 Grey and greyish brown fine-med ash, 20 mm onto 30 mm of strong brown fine-med ash. 350 2 . 15 MT, Oturere Lapilli Strong brown, greyish brown and grey fine-med poorly vesicular pumice and lithic lapilli, shower-bedded but ungraded. 20 Grey fine lithic lapilli. 50 Yellow brown fine ash. 30 Strong brown fine pumice lapilli and coarse ash. 300 2.55 Pahoka Tephra Upper 1 50 mm grey and greyish brown coarse pumice ash, shower- bedded, lower 1 50 mm olive grey and pale brown fine-med pumice lapilli, with scattered banded pumice lapilli. 300 Greyish brown fine ash with scattered strong brown and grey fine pumice and lithic lapilli. 20-50 2.90 Yellow and yellow brown fine pumice lapilli, with scattered grey lithic lapilli. 50 Greyish brown and brown fine-med ash. 20 Strong brown and grey fine pumice and lithic lapilli. 50 Brown and grey fine-med ash. 10 Strong brown pumice lapilli. 50 Yellow brown and brown fine ash. 80 3. 1 8 Strong brown fine pumice lapilli, with scattered grey fine lithic lapilli. 50 Strong brown fine ash with scattered fine pumice lapilli. 250 Grey and strong brown fine pumice and lithic lapilli, shower-bedded and ungraded. 20 3.50 94.58, Waiohau Tephra Greyish brown fine-med ash with scattered grey and strong brown fine pumice and lithic lapilli, 30-40 mm cream-cakes of white fine rhyolitic ash interbedded. 300 Strong brown, greyish brown and grey med-coarse pumice and lithic ash, shower-bedded. 40 Strong brown fine ash. 1 00 3.94 Strong brown and reddish brown fine pumice lapilli with scattered fine grey lithic lapilli. 30 Strong brown and brown fine ash. 20 Strong brown fine pumice lapilli. 200 4 . 19 Rerewhakaaitu Tephra Brown and greyish brown fine ash with interbedded cream-cakes of white fine pumice ash. 1 50 Yellow brown and strong brown normally graded med ash-fine pumice lapilli, with scattered grey lithic fine lapilli and coarse ash. 50 Grey, greyish brown and strong brown fine-med pumice ash. 1 50 Strong brown fine pumice lapilli. 200 4.74 Hinuera Formation Brown, pale brown and white reworked fine ash with scattered fine strong brown pumice lapilli. 300 Grey med lithic ash with scattered strong brown fine-med pumice lapilli. 200 Pale grey soft greasy fine ash with scattered yellow brown and strong brown fine pumice lapilli. 500 5.74 Yellow brown and strong brown fine pumice lapilli, reworked, with scattered grey fine lithic lapilli. 200 Pink and pale yellow fine ash with scattered strong brown fine pumice lapilli. 1 000 T4 Grey sandy matrix diamicton, pebble to boulder clasts supported within the matrix, massive and unbedded. 3000+ Sharp upper contact. Pale greyish brown and brown silty matrix diamicton. Sparse pebbly multi-coloured lithic and pumice clasts supported by matrix, massive and unbedded. 9.94 Base into stream. A 60 Section 72 Tongariro River, T19 356556 True left bank of river immediately downstream of "Sand Pool". Unit Depth (mm) 400 400 2500-3000 4000+ Section 73 Cum. depth (m) Correlation and samples Description taken Grey bedded sand with scattered fine white pumice lapilll pebbles. Recent soil developing into top of unit, greyish brown and brown fine? coarse sand. 0.80 Taupe lgnlmbrite Fine-coarse pumice ash with mixed pumice lapilli and blocks, unconformable sharp lower contact. 3.80 7.80 Grey and pale brown diamicton, sand and fine pebble matrix supporting grey clasts of cobble to boulder size. Sub-rounded clasts, with a more well sorted matrix than unit below. Occasional interbedded lenses of sand and fine cross-bedded gravels. Greyish brown and grey sandy matrix diamicton. Surface reworked in many places by river and fines depleted. Pebble-huge sub-rounded and sub-angular boulder clasts supported by matrix. Fine clasts grey, yellow and red lithic and occasional pumice larger clasts all grey lithic. Occasional huge boulder clasts up to 3 m diameter. Very firm, cemented? matrix. Base into stream. Tongariro River, T19 364544 True left bank of river, large cliff section at "Breakaway Pool" Unit Depth (mm) 5000 300 600-800 800-1 000 800-1 200 20 1 500 100-1 50 1000 2000 150 30 30 50 10 40 200 30 50 300 0-1 700 20 Cum. depth (m) 5.30 7.10 9.82 12.97 1 3.28 14.56 Correlation and samples Description taken Taupe lgnimbrite White pumice fine-coarse ash with mixed pumice lapilli and large pumice blocks, charcoal fragments and logs near base of unit. Upper 800 mm black present soil developed. Unconformable lower contact. Mangamate Tephra, Poutu Strong brown and yellow brown fine pumice lapilli, with scattered grey Lapilli lithic lapilli, shower-bedded and ungraded, irregular upper contact. 94.79, Karapiti Tephra Yellow brown and pale yellow brown fine ash with paleosol development and paleo-root channels, white fine ash pocketing 10 mm near top. Grey sandy matrix diamicton, pebble-cobble clasts supported by matrix, cross bedded In places and with only faint planar fabric in other places. Grey and olive grey massive coarse-fine sand, poorly sorted, weak planar fabric, possible log casts present. Wavy bedded pale brownish grey silt and fine sand. Grey, olive grey and pale greyish brown coarse-fine poorly sorted matrix dlamlcton, planar fabric with occasional cobble and small boulder clasts supported by matrix, empty log casts seen. Lower 500 mm massive with no planar fabric. Pale greyish brown silt, massive with paleo-root channels. Grey and brownish grey fine-coarse sand, massive with faint planar fabric In places. Grey and greyish brown fine-coarse sand matrix dlamicton with pebbly clasts supported by matrix, grey red and yellow brown pebble clasts. Planar fabric, and poorly sorted. Pale grey fine sand, planar bedded. Dark grey fine sand and silt with scattered yellow brown fine pumice lapilli. Grey and pale brown planar bedded sand and silt. Rotoaira Tephra Strong brown and pale brown fine pumice lapllli with scattered grey lithic fine lapllli. Dark grey fine-med lithic ash. Grey, strong brown and yellow brown fine pumice and lithic lapilli, grey at top and strong brown and yellow brown soft pumice lapllli at base. Hinuera Formation Greyish brown and grey fine sand and silt with mixed in fine white pumice ash. Grey and greyish brown fine sand and silt. Pale brown fine ash with scattered grey and yellow brown fine pumice and lithic lapllli. Greyish brown and grey sand and silt, planar bedded. Kawakawa Tephra/ Pinkish pale brown fine ash with scattered coarse and med pumice Oruanui lgnimbrite ash within, occasional pumice clasts up to fine lapllll In size. Member Aokautere Ash Member Coarse white pumice ash A 61 30 40 1 0 20 200-250 1 0 4000+ Section 76 1 8.94 Pale pinkish brown fine ash with accretionary lapilli up to 1 0 mm in diameter. White fine pumice lapilli, and accretionary lapilli within white fine pumice ash. Pale brown fine pumice ash. White fine pumice lapilli. White and pale brown fine pumice ash with abundant accretionary lapilli 5-20 mm in diameter. Brown fine ash. Greyish brown sandy and silty matrix diamicton. Clasts of sub-angular pebble-boulders supported within the firmly cemented matrix. Base into river. Tongariro River, T 19 533383 Road cutting on the western side of Sate Highway 1 , 200 m south of the Trout Hatchery. Unit Depth (mm) 300-400 400-450 30 1 00 1 50 1 00 1 00 1 0 450 40 1 0 1 0 1 0 40 1 0 30 50 2000+ Section 78 Cum. depth (m) 0.85 1 .23 1 .83 1 .94 3.99 Correlation and samples Description taken Taupo lgnimbrite White and pale grey fine-coarse pumice ash with mixed white pumice lapilli and blocks, with present soil development. Mangamate Tephra, Poutu Strong brown and yellow brown fine pumice lapilli, shower-bedded and Lapilli ungraded with scattered grey fine lithic lapilli. Pale grey med-coarse lithic ash. Yellow brown and greyish brown coarse pumice ash and fine lapilli. Greyish brown and yellow brown fine-med ash. Yellow brown and strong brown fine pumice lapilli and coarse ash, with scattered grey lithic lapilli. Grey lithic fine lapilli rich zone near top of unit, 1 0 mm thick. Pale brown fine ash. Pale brown fine pumice lapilli. Pale brown and yellow brown fine ash with paleosol development and scattered grey and yellow brown fine pumice and lithic lapilli. Strong brown and yellow brown fine pumice lapiln Dark grey med-fine ash. Pale brown fine ash. Dark grey med-fine ash. Rotoaira Tephra Strong brown fine pumice lapilli and coarse ash with scattered grey fine lithic lapilli. Grey fine ash. Strong brown and yellow brown fine pumice lapilli and coarse ash. Pale brown fine ash. Hinuera Formation White, grey and pale pinkish brown pumice rich sands silts and gravels, cross-bedded and planar bedded on a 20-50 mm scale. Base obscured. Tongariro River, T1 9 404533 Disused pumice quarry at end of Admirals Reserve Road, off State Highway 1 , 2 km south of Turangi. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 1 000-6000 1 00 6.1 1 00 1200 50 1 00 500-2000+ 9.55 Taupo lgnimbrite White and pink fine-coarse pumice ash with mixed pumice lapilli and blocks and fragments of charcoal near base. Variable thickness and eroded irregular lower contact. Mangamate Tephra, Poutu Strong brown, yellow brown and grey fine pumice and lithic lapilli, Member shower-bedded and ungraded, with scattered grey fine lithic lapilli. Kawakawa Tephra/ Oruanui lgnimbrite Member Grey and greyish brown coarse pumice and lithic ash and fine lapilli. Brown and yellow brown fine ash with scattered yellow brown fine pumice lapilli, paleosol development and paleo-root channels present. Grey and strong brown fine pumice and lithic lapilli and coarse ash. Pale brown fine ash. Pinkish brown and pale brown fine-med pumice ash with scattered white coarse pumice ash, massive, unwelded but firm. Base obscured. A 62 Section 81 Oturere Stream, T19 430238 Exposure on the top of a lava flow on the true right side of Oturere valley, 500 m due west of Oturere Hut, within wilderness area. Unit Depth (mm) 1 00 400 300 20 20 1 0 1 50 200 50 1 50 50 150 20 300 50 1 0 1 0 1 0 20 1 50 1 50 20 1 0 20 1 0 30-50 1 0 1 0 1 0 1 0 1 00 200 1 0 1 000 50 30 300 1 0 200 1 0 500 20 200 1 0 30 1 0 30 20 Cum. depth (m) 0.80 1 .20 1 .92 2 . 17 2.43 3.78 4 . 16 5. 1 0 Correlation and samples Description taken Brown fine ash with scattered grey lithic coarse ash. Mangamate Tephra, Grey and greyish brown fine lithic and poorly vesicular pumice lapilli Oturere Lapilli and coarse ash, shower-bedded and ungraded. Pahoka Tephra Pale grey and pale olive brown fine-med pumice lapilli, shower- bedded, ungraded, with distinctive common banded pumice lapilli. Dark grey fine lithic lapilli. Brown fine ash. Grey med-fine ash. Yellow and grey fine pumice and lithic lapilli and coarse ash, reversely graded with equal proportions of pumice and lithics. Bullet Formation, Pourahu Greyish brown fine pumice lapilli, shower-bedded with scattered grey Member fine lithic lapilli. Brown fine ash, with scattered pale yellow brown and grey fine pumice and lithic lapilli. Greyish brown fine pumice lapilli, shower-bedded, with scattered fine grey lithic lapilli. Grey and purplish grey fine lithic lapilli and coarse ash. Pale greyish brown fine-med pumice lapilli, with scattered grey fine lithic lapilli, 10 mm grey med lithic ash zone 50 mm from top of unit. Grey and pale brown fine-med ash. Greyish brown and grey pumice and lithic coarse ash and fine lapilli. Grey and yellow brown banded 10 mm layers of alternating colour, pumice and lithic coarse ash. Yellow brown coarse pumice ash. Dark grey fine-med ash. Yellow coarse pumice ash. Grey lithic and pumice coarse ash. Yellow brown coarse pumice ash with scattered coarse lithic ash, shower -bedded. Dark grey and greyish brown alternating zones of med ash and fine pumice and lithic lapilli, shower-bedded. Yellow brown coarse pumice ash. Grey coarse lithic ash. Yellow brown coarse pumice ash. Dark grey coarse lithic ash. 95.2, Waiohau Tephra Grey med-coarse lithic ash with pocketing white fine pumice ash cream-cakes. Yellow brown coarse pumice ash. Dark grey coarse-med lithic ash. Yellow brown coarse pumice ash. Purplish grey med ash. Yellow brown and greyish brown zones of shower-bedded fine pumice lapilli. Greyish brown and grey alternating zones of fine-med pumice lapilli, shower-bedded. Greyish brown fine ash. Yellow brown, yellow and pale greyish brown fine pumice lapilli, shower-bedded with scattered grey lithic fine lapilli. Grey and greyish brown coarse pumice and lithic ash. Greyish brown fine pumice lapilli. 95.3, Rerewhakaaitu Greyish brown and grey shower-bedded coarse ash and fine pumice Tephra lapilli, alternating coloured zones, 5 mm cream-cakes of white fine pumice ash 30 mm from base. Pale grey fine ash. Greyish brown and grey coarse pumice and lithic ash and fine pumice lapilli, shower-bedded. Greyish brown fine ash. Greyish brown coarse pumice ash and fine lapilli with scattered grey fine lithic lapilli. Yellow brown fine pumice lapilli with scattered grey fine lithic lapilli. Grey and greyish brown med-coarse pumice and lithic ash, with scattered yellow brown fine pumice lapilli. Grey fine ash. Greyish brown coarse pumice ash. Brown fine ash. Greyish brown coarse pumice ash. Greyish brown and yellow brown fine pumice lapilli. A 63 1 0 1 0 1 0 70 1 0 40 300 1 0 1 00 150 200 1 00 1 50 4000+ Section 82 5.30 5.65 6. 1 1 10.36 Greyish brown coarse pumice and lithic ash. Yellow brown coarse pumice ash Dark grey fine ash. Greyish brown coarse pumice ash and fine lapilli. Brown and yellow brown fine ash. Greyish brown and yellow brown med ash and fine pumice lapilli intermixed. 20-30 mm of dark grey fine-med ash intermixed within the top of yellow brown and yellow coarse-fine pumice lapilli, shower-bedded and reversely graded, with scattered grey fine lithic lapilli. Grey fine ash. Yellow brown and strong brown fine pumice lapilli. Greyish brown and grey med-coarse sand with interbedded pale brown pumice and grey pebbles and cobbles. Strong brown and yellow brown coarse-med pumice lapilli, with scattered grey fine lithic lapilli. Olive greyish brown fine pumice lapilli, with scattered grey lithic fine lapilli. Grey and greyish brown med-coarse sands with interbedded greyish brown and grey lithic and pumice pebbles. Grey lava flow, base not seen. Mangatetipua Stream, T19 423339 Road side section on the southern side of State Highway 4 7 A, large lava flow exposure 500 m west of road bridge over Mangatetipua Stream. Unit Depth (mm) 200-3000 500 1 00 1 0-20 300 50 300 500-800 30 50-100 400 0-2000 7000+ Section 83 Cum. depth (m) 3.50 3.62 3.97 5.07 7.60 14.60 Correlation and samples Description taken Taupo lgnimbrite White fine-med pumice ash mixed with white pumice lapilli and blocks, primary in some places, bedded and reworked in other places. Mangatawai Tephra Brown and greyish brown fine ash, purplish grey and black fine ash within lower 1 00 mm. Papakai Formation (Pp) Brown and yellow brown fine ash, greasy with paleosol development. Waimahia Tephra within White fine pumice ash cream-cakes within brown fine ash. Pp Pp Yellow brown fine ash. Hinemaiaia Tephra within White coarse-med pumice lapilli scattered within fine brown ash. Pp Pp Yellow brown fine ash, greasy. Mangamate Tephra (MT). Strong brown and yellow brown fine-med pumice lapilli, shower- Poutu Lapilli bedded and ungraded, with scattered grey fine lithic lapilli, upper part mixed within lower part of Papakai Tephra. Grey med-coarse lithic ash. Brown fine ash with scattered grey and yellow brown fine lithic and pumice lapilli. MT, Te Rato Lapilli Grey and greyish brown poorly vesicular fine-med pumice lapilli, shower-bedded and ungraded. 95.6 Waiohau Tephra Variable thickness yellow brown and brown fine ash, with scattered yellow brown pumice lapilli and occasional large lava ciast, colluvial layer. Unconformable upper contact. Two apparent horizons of white fine pumice ash cream-cakes. 95.8 Grey and reddish grey scoriaceous and dense lava flow. Base obscured. Tahurangi/ Te Karo Streams, T19 448326 Large road cutting on the southern side of State Highway 47A, 500 m east of Rotoaira Trust Fishing camp jetty. Unit Depth Cum. Formation and Member Description (mm) depth (m) 200-300 Taupo lgnimbrite White fine-coarse pumice with mixed pumice lapilli. 300 Mangatawai Tephra Brown fine ash upper 1 50 mm, lower 150 mm grey and dark grey med- fine ash beds 10-30 mm thick interbedded with brown fine ash . . 200 Papakai Formation (Pp) Brown and yellow brown fine greasy ash. 50 0.85 Hinemaiaia Tephra within White mad-coarse pumice ash scattered within yellow brown fine ash. Pp 50-300 Pp Yellow brown and brown fine greasy ash. 400-700 Mangamate Tephra (MT), Variable upper contact, yellow brown, strong brown and grey fine Poutu Lapilli pumice and lithic lapilli, shower-bedded and ungraded. 30 Grey coarse-mad ash. 20 Greyish brown fine ash. 400 2.30 MT, Te Rato Lapilli Grey and pale greyish brown fine pumice and lithic lapilli, shower- A 64 1 00 200 20 20 20 150 1 0 1 0 20 40 50 1 00 150 200-250 30 80 20 100 1 00 1 0 1 0 40 400 20 400 1 000+ Section 88 2.78 95.9, Waiohau Tephra 3.00 Rotoaira Tephra 3.51 3.73 Kawakawa Tephra, Aokautere Ash Member 4.61 95. 1 0 bedded and ungraded. Pale brown and yellow brown fine ash with scattered yellow brown and strong brown fine pumice lapilli. Yellow brown fine ash. Strong brown fine pumice lapilli. Grey med-fine ash. Strong brown fine pumice lapilli and coarse ash. Greyish brown and brown fine ash with scattered strong brown fine pumice lapilli and coarse ash. Pocketing white fine pumice ash cream-cakes, within greyish brown fine ash. Black med lithic ash, pocketing within greyish brown fine ash. Brown fine ash with scattered yellow brown pumice and grey lithic coarse ash. Strong brown and yellow brown coarse pumice ash. Greyish brown and yellow brown fine ash with scattered yellow brown fine pumice lapilli. Yellow brown and strong brown fine pumice lapilli with brown fine ash intermixed toward base. Greyish brown fine-med ash. Yellow brown and strong brown fine-med, soft pumice lapilli, with scattered grey fine lithic lapilli. Black and dark grey med lithic ash. Yellow brown and strong brown fine-med pumice lapilli, with scattered fine grey lithic lapilli. Greyish brown med ash. Yellow brown sand with interbedded grey and strong brown pebbles. Pinkish pale brown fine-med pumice ash. White med pumice ash. Pale pink and pale grey fine pumice ash. Alternating layers of pale yellow and pale pink fine and med pumice ash, with basal 1 0 mm fine pale pink ash. Grey and greyish brown med sand, massive and well sorted. Strong brown soft pumice lapilli. Dark grey fine-coarse bedded sands, planar bedded. Grey lava flow, base obscured. Unnamed stream between Tahurangi and Rahuituki Streams, T19 475304 True left bank of stream 20 m upstream of forestry road bridge, Te Ngoi forestry road. Unit Depth (mm) 400 70 30 20 1 0 60 30 1 00 80 150 250 100 30 50 600 100 400 40 100 20 200 1 0 1 00 Cum. depth (m) 0.59 0.62 1 . 10 1 .88 2.42 2.75 Correlation and samples Description taken Mangamate Tephra (MT), Poutu Lapilli MT. Oturere Lapilli MT. Te Rato Lapilli Strong brown fine pumice lapilli with scattered grey lithic fine lapilli, shower-bedded and ungraded. Grey med lithic ash. Greyish brown fine ash with scattered yellow brown fine pumice lapilli. Grey med-fine ash. Yellow brown coarse pumice ash. Grey med lithic ash, grading into 30 mm yellow brown coarse pumice ash with scattered grey coarse lithic ash. Greyish brown fine ash with scattered yellow brown fine pumice lapilli. Greyish brown and yellow brown fine pumice lapilli. Greyish brown and pale brown fine ash with scattered fine grey and yellow brown pumice and lithic fine lapilli. Yellow brown and strong brown coarse pumice ash. Greyish brown fine ash with scattered yellow brown fine pumice lapilli. Strong brown fine pumice lapilli, with scattered grey fine lithic lapilli, 1 0 mm grey lithic dominated layer near top of unit. Greyish brown fine ash with scattered yellow brown fine pumice lapilli. Yellow brown fine pumice lapilli. Greyish brown fine ash with scattered yellow brown fine pumice lapilli. Yellow brown and strong brown fine pumice lapilli, soft, with scattered fine grey lithic lapilli. Greyish brown fine ash with scattered yellow brown fine pumice lapilli. Grey med lithic ash. Strong brown fine pumice lapilli with scattered grey ash. Grey med ash. Yellow brown fine-med pumice lapilli with scattered grey fine lithic lapilli. Grey med lithic ash. Yellow brown and strong brown fine pumice lapilli with scattered grey fine lithic lapilli. A 65 1 00 1 00-300 500+ Section 89 3.65 Kawakawa Tephra, Oruanui lgnimbrite Member T4 Poutu Canal, T1 9 497327 Grey med lithic ash. Pale brown fine-med massive unbedded ash with scattered coarse pale brown and white pumice ash. Boulder rich diamicton, grey sandy matrix, firm and cemented with pebble-boulder clasts supported within, large grey boulder clasts. Base into stream. True left side of canal as it flows into Poutu Dam (basal part exposed 300 m further upstream on true right side of canal). Unit Depth (mm) Cum. depth (m) Formation and Member Description 200 30 1 0 1 20 200 40 1 0 50 1 0 30 250 1 000 500 1 5000+ Section 91 c. 2.0 Rotoaira Tephra " 2.46 Hinuera Formation 4.25 Kawakawa Tephra/ Oruanui lgnimbrite Member T4 4.75 Puketarata Stream, T1 9 528289 Top Obscured. Brown fine ash with scattered strong brown and yellow brown fine pumice lapilli. Yellow brown and strong brown fine pumice lapilli. Grey med-coarse lithic ash. Strong brown and yellow brown fine pumice lapilli, with scattered grey fine lithic lapilli. Greyish brown fine ash with scattered strong brown fine pumice lapilli. Strong brown and yellow brown fine pumice lapilli. Grey coarse lithic ash. Yellow brown and strong brown fine pumice lapilli with scattered grey fine lithic lapilli, shower-bedded. Grey lithic fine-med ash. Strong brown and yellow brown fine pumice lapilli. Greyish brown with scattered grey and yellow brown fine pumice and lithic lapilli. Grey and pale brown lithic and pumice sands and fine gravels, rich in pale brown pumice ash. Grey and brown pumice and lithic gravels, fine-coarse bedded in planar layers and lenses. Pale brown and white fine pumice ash with scattered white fine pumice lapilli, massive and unbedded, uneven upper contact. Grey sandy matrix diamictons, pebble-boulder grey lithic clasts supported by matrix. Many units, some massive and unbedded others with weak planar fabric. Base obscured. True left bank of stream, below State Highway 1 bridge. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 600 20 200 50 30 50 20 50 1 0-20 50 250 1 000+ c. 4.0 4.35 Rotoaira Tephra T3/T4 5.74 Top obscured. Brown and greyish brown fine ash with scattered yellow brown fine pumice lapilli. Yellow brown and strong brown fine pumice lapilli. Greyish brown fine greasy ash. Grey and greyish brown fine-med lithic ash. Pale brown and greyish brown fine ash. Strong brown and yellow brown fine pumice lapilli with scattered fine lithic lapilli. Grey fine ash. Strong brown fine pumice lapilli with scattered grey fine lithic lapilli. Grey fine-med ash. Yellow brown and strong brown fine pumice lapilli, with scattered grey fine lithic lapilli. Greyish brown and yellow brown fine, greasy ash with paleosol development. Grey and brownish grey sandy matrix diamicton with pebble to large boulder clasts supported by matrix. Upper part reworked and fines depleted, clast supported with bedded grey and strong brown sand between grey lithic clasts. Base into stream. A 66 Section 93 Mangahouhounui Stream, T19 51 231 5 True right bank of stream where it is crossed by the Poutu canal, deep partially obscured section. Unit Depth (mm) 500 2000 2000 1 0000+ Section 95 Cum. depth (m) 14.50 Correlation and samples Description taken Mangamate Tephra, Poutu Strong brown and yellow brown fine pumice lapilli, shower-bedded Lapilli and ungraded, scattered grey fine lithic lapilli. Partially obscured ash and lapilli beds, undescribed Hinuera Formation Brownish grey, pale brown and grey bedded sands and gravels, planar and cross-bedded containing abundant pale brown and white pumice ash. T4 Greyish brown and dark grey sandy matrix diamicton, massive and unbedded, pebble-large boulder clasts, grey and reddish grey angular lava clasts supported by the matrix. Potentially several diamicton units present. Base into stream. Tongariro River, T19 540397 Stag Pool, true right bank of river. Unit Depth (mm) Cum. depth (m) Correlation and samples Description taken 4000 Taupo lgnimbrite 500-2000 0-1 500 4000 1 1 .50 Section 96 Tongariro River, T 19 549328 White fine-coarse pumice ash with mixed pumice lapilli and blocks, Charcoal fragments and logs in base of unit. Variable lower contact pinches over paleo-topography planar upper contact. Grey and greyish brown sandy matrix diamicton with pebble? boulder clasts supported within the matrix. Lenses of bedded grey and greyish brown gravels and sands, rounded grey gravels and grey and yellow brown sands. Large boulder rich diamictons. Grey and greyish brown firm sandy matrix supporting clasts of pebble-boulder, grey sub-rounded boulders, two or more units. Base into river. Road cutting along Rangipo Prison Farm road toward river, northern side of road, 300 m before bridge over river. Unit Depth Cum. Correlation and samples Description (mm) depth (m) taken 300-1000 200 200 200-400 500 200-400 1 0 30 1 0-20 50 20 20 1 0 30 40 20 1 00 500 40 1 0-200 1 .80 2.76 2.89 2.95 Taupo lgnimbrite Mangatawai Tephra Papakai Formation Hinemaiaia Tephra Papakai Formation Mangamate Tephra (MT), Poutu Lapilli Poronui Tephra MT, Te Rato Lapilli Pahoka Tephra White fine-coarse ash with mixed pumice lapilli and blocks, charcoal fragments within base. Dark brown fine ash with interbedded grey and purplish grey fine-med ash, pocketing in the base of the unit. Brown fine greasy ash with paleosol development, scattered white coarse pumice ash. White and pale brown coarse pumice ash shower-bedded occasionally over-thickened. Brown and yellow brown fine ash with grey fine pumice and lithic lapilli scattered within base of unit. Variable upper contact, strong brown and yellow brown fine pumice lapilli with scattered grey lithic lapilli, shower-bedded but ungraded. Grey med lithic ash. Greyish brown fine ash. White pocketing fine pumice ash, within grey fine greasy ash. Greyish brown fine ash. Grey med lithic ash. Greyish brown fine ash. Strong brown, yellow brown and grey fine pumice and lithic lapilli. Grey coarse ash and fine pumice and lithic lapilli. Greyish brown fine ash with scattered grey fine lithic lapilli. Grey and olive pale brown fine pumice lapilli, with scattered occasional banded lapilli. Greyish brown and brown fine, greasy ash with scattered yellow brown fine pumice lapilli. Planar bedded gravels and sands, poorly sorted coarse and fine grey gravels and sand, sub-rounded and sub-angular, with scattered yellow brown fine pumice pebbles. Greyish brown fine-med sand. Sandy matrix pebbly diamicton, lenzoidal. Grey and greyish brown A 67 50 400-700 20 20 40 600 50 40 30 60 20 1 0 250 30 200 1 5000+ Section 97 4.54 5.31 5.43 95. 1 3 Waiohau Tephra 5.91 20.91 pebbles within greyish brown sandy matrix. Greyish brown fine-med sand. Grey and greyish brown planar bedded sands and gravels, 20-30 mm scale beds, poorly sorted, pebbles rich in layers and lenses. Greyish brown fine ash. Greyish brown and yellow brown fine pumice lapilli. Greyish brown fine ash. Grey and greyish brown sandy matrix diamicton, pebble-cobble clasts supported within the matrix, clast rich unit, massive and unbedded. Brown fine ash. Yellow brown and strong brown fine pumice lapilli with scattered grey fine lithic lapilli. Brown fine ash. Grey and strong brown fine lithic and pumice lapilli. Greyish brown fine ash. White fine pumice ash, pocketing in places and a continuous layer in other places. Brown and gleyed pale brown fine ash with scattered pale brown coarse pumice ash. Strong brown and grey coarse-med pumice and lithic ash. Brown fine ash with paleosol development and root channels present. Base of section seen at road bridge across the river. Greyish brown and grey med-coarse sand-matrix diamicton, pebble-large boulder clasts, massive and unbedded, sparse large boulders, firm unit. Base into stream. Tongariro River/ Whitikau Stream, T1 9 558336 Road cutting on the western side of the Rangipo Prison farm road next to the bridge across the Whitikau Stream. Unit Depth (mm) 400 50 200 200 300 20 150 400-500 1 00 30 20 40 1 00 250 300-500 20 40 20 40 20 1 0 250 40 1 50 1 0-20 1 50 20 30 20 80 Cum. depth (m) 0.85 1 . 1 7 1 .92 2. 1 1 2.98 3.01 3.62 3.77 Correlation and samples Description taken Taupo lgnimbrite White and pale grey fine-coarse pumice ash with mixed pumice lapilli and blocks. Mangatawai Tephra Dark brown and grey fine-med ash. Papakai Formation (Pp) Brown and yellow brown fine ash Hinemaiaia Tephra Pale yellow brown med-coarse pumice ash, shower-bedded. Pp Brown fine greasy ash with occasional white med pumice lapilli. Motutere Tephra Pale brown fine pumice ash, pocketing within brown fine ash. Pp Brown fine greasy ash with scattered grey fine lithic and pumice lapilli. Mangamate Tephra (MT), Strong brown and fine pumice lapilli, shower-bedded and ungraded Poutu Lapilli with scattered grey fine lithic lapilli. Poronui Tephra Greyish brown and grey fine-med ash with pocketing 1 0 mm thick fine white pumice ash. Grey med lithic ash. Greyish brown fine ash. MT Grey and yellow brown coarse pumice ash and fine lapilli. Pahoka Tephra Grey and pale olive brown fine pumice lapilli and coarse ash. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Grey and greyish brown sandy matrix diamicton, pebble sub-angular clasts supported within the matrix, planar fabric preserved. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Strong brown and yellow brown fine pumice lapilli. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Grey and strong brown coarse pumice and lithic ash and fine lapilli. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Waiohau Tephra White fine pocketing fine pumice ash, within greyish brown fine ash. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Strong brown and grey coarse pumice and lithic ash and fine lapilli. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Yellow brown and grey fine pumice lapilli. Greyish brown fine ash with scattered fine yellow brown fine pumice lapilli. Strong brown coarse pumice ash. Grey and strong brown coarse lithic and pumice ash and strong brown fine pumice lapilli. Grey med lithic ash. Strong brown and yellow brown fine pumice lapilli with scattered grey A 68 20 1 00 600 500+ 1 0000- 1 5000 Section 98 3.99 Kawakawa Tephra, Oruanui lgnimbrite Member 95. 16 1 8.99 fine lithic lapilli. Dark brown greasy fine ash. Pale brown gleyed fine greasy ash. Brown greasy fine ash. Pale brown and pink fine pumice ash with scattered white coarse pumice ash Grey andesite lava flow. Base into stream. Tongariro River, T 19 53741 1 True right bank of river between "The Rip" and "Hydro Pool" beside the walkway. Unit Depth (mm) 400 250 300 50 200 400 300 1 000+ Section 99 Cum. depth (m) 1 .20 2.90 Correlation and samples Description taken Taupo lgnimbrite Papakai Formation (Pp) Hinemaiaia Tephra within Pp Pp White fine-coarse pumice ash with mixed white pumice lapilli and blocks. Grey and greyish brown sands and gravels. Grey and greyish brown med sands, planar and wavy bedded. Yellow brown fine greasy ash with paleosol development. White fine pumice and coarse pumice ash scattered within fine brown greasy ash. Brown and yellow brown greasy fine ash with paleosol development. Grey and greyish brown fine-med sands, planar and wavy bedded. Grey sandy matrix diamicton, pebble-boulder sub-rounded grey clasts supported within matrix, firm, massive and unbedded. Base into river. Tongariro River, T19 544423 Judges pool, exposure on true right bank of river, second terrace scarp. Unit Depth (mm) 1 500 400 1200 1 000+ Section 100 Cum. depth (m) 3 . 10 Correlation and samples Description taken Taupo lgnimbrite Grey and black med-coarse bedded sands, fine white Taupo pumice interbedded, wavy and planar bedded on a 20-50 mm scale White fine-coarse pumice ash, poorly sorted and massive, sharp upper contact. Bedded coarse-med gravels, rounded grey clasts supported, with grey well sorted sand between clasts. Grey sandy matrix diamicton, pebble-boulder sub-rounded grey clasts supported within matrix, massive and unbedded. Base obscured. Tongariro River, T19 545424 Judges Pool, True right bank of river, cliff exposure. Unit Depth (mm) 2000- 30000 1 000 400 50-100 200 1 00-1 50 300 1 000 1500 12000 Cum. depth (m) 1 6.60 Correlation and samples Description taken Taupo lgnimbrite White fine-coarse pumice ash and mixed white pumice lapilli and blocks, massive with charcoal fragments and logs near base, upper part reworked and planar and cross-bedded. Papakai Formation Yellow brown and brown fine greasy ash, with paleosol development. Mangamate Tephra, Poutu Strong brown and yellow brown fine pumice lapilli with scattered grey Lapilli fine lithic lapilli, shower-bedded and ungraded. Poronui Tephra Grey and greyish brown fine ash with pocketing fine white pumice ash. Yellow brown and brown fine ash. Grey med ash. Greyish brown fine ash. Grey and greyish brown fine grained diamicton, sands, silts and fine gravels cross-bedded and planar bedded. Sharp upper and lower contact, unit as above but only planar bedded. Greyish brown fine-coarse sand massive and unbedded with faint planar fabric, several units separated by 1 0-50 mm greyish brown silt or fine sand, fine pebbles supported within the sandy matrix. Firm and bluff forming. Base obscured. A 69 Section 1 01 Tongariro River, T19 538417 True left bank of river a t cable-way across river. Unit Depth (mm) 500 2000 1 000 Section 102 Cum. depth (m) 3.50 Correlation and samples Description taken Brownish black fine-coarse bedded sands with scattered fine white Taupo Pumice pebbles within, recent soil development in top. Clast supported pebble, cobble and small boulder deposit, sands between clasts. Pebbles of Taupo Pumice within. Grey and greyish brown sandy matrix diamicton, with pebble-boulder sub-rounded clasts supported by matrix, clast rich unit. Base into river. Tongariro River, T1 9 543427 True right bank of river, 1 00 m downstream of State Highway 1 bridge. Unit Depth (mm) 350 2100 Section 103 Cum. depth (m) 2.45 Correlation and samples Description taken Brownish grey and grey bedded sands cross and planar bedded on a 20 mm scale, Taupo Pumice fine pebbles interbedded. Grey rounded cobbles and pebble and sand, clasts supported, loose and unconsolidated, very rudimentary soil development in top. Highly rounded in places with zones devoid of matrix and zones with sand matrix between clasts although not supporting clasts. Taupo Pumice fine pebbles present within top of deposit. 80-85 % andesite clasts and remainder greywacke clasts. Base into river Tongariro River, T1 9 540429 Swirl Pool, true left bank of river. Unit Depth (mm) 500-1 500 0-500 150-250 2500+ Section 104 Cum. depth (m) 4.65 Correlation and samples Description taken Pale brown and grey fine sands and silts cross-bedded and containing Taupo Pumice fine pebbles. Alternating layers of silt and sand, bedded on a 1 0-50 mm scale. Present, recent soil development in top. Irregular lower contact. Pale greyish brown and greyish brown silt and fine sand, massive and mottled with pale greyish brown colours, structureless with common root channels. Coarse sandy matrix diamicton, pebble clasts supported within the matrix and with common scattered white fine Taupo pumice rounded pebbles, massive and unbedded. Grey and greyish brown diamicton, in places matrix supported and in some places clast supported where its upper part is reworked. Grey sandy matrix firm where it is supporting, and grey sub-rounded and sub-angular pebble-boulder clasts, firm unit, massive with no bedding in all of the unit. Base into river. Tongariro River, T1 9 541435 Upper Island Pool, true right bank of river. Unit Depth (mm) 200 400 50 50 50 1 00 Cum. depth (m) Correlation and samples Description taken Black and brown fine sand and silt, with scattered white fine rounded Taupo Pumice lapilli, present soil development within this layer, friable and unbedded. Bedded grey and greyish brown sands with scattered white fine Taupo Pumice pebbles, wavy bedded with 1 0-20 mm scale beds. Fine gravel and sand layer with andesite, greywacke and Taupo Pumice fine-med pebbles and grey sand, clast supported. Greyish brown fine sand with scattered fine Taupo Pumice fine pebbles. Fine gravel and sand layer with andesite, greywacke and Taupo Pumice fine-med pebbles and grey sand, clast supported. Greyish brown fine sand with scattered fine Taupo Pumice fine A 70 1 500+ 2.35 Section 1 05 pebbles, 1 0 mm scale wavy bedding. Grey pebbles, cobbles and boulders and coarse sand, clast supported but with matrix of coarse sand between clasts. Sparse Taupo Pumice pebbles within unit. Andesite and greywacke clasts, unconsolidated and unbedded. Base into river. Tongariro River, T19 524425 Stream running through western residential part of town, below major road culvert, highest terrace seen in town. Unit Depth (mm) 1 000 1 000 300 20 1 00 50 200 1 000 2000 1 000 Cum. depth (m) 2.3 2.57 6.57 Correlation and samples Description taken Taupo lgnimbrite Papakai Formation and Hinemaiaia Tephra White fine-coarse pumice ash with mixed white pumice lapilli and blocks, primary in places, reworked with grey sands in others. Yellow brown and brown fine ash, paleosolic and greasy, 1 00-150 mm zone in centre of unit with scattered, sparse, white fine pumice lapilli, and coarse ash Mangamate Tephra, Poutu Strong brown and yellow brown fine pumice lapilli with scattered grey Lapilli fine lithic lapilli. Mangamate Tephra, Te Rato Lapilli Greyish brown fine-med ash. Greyish brown coarse pumice and lithic ash and fine lapilli. Yellow brown fine ash. Grey, yellow brown and pale yellow fine pumice lapilli and coarse ash. Obscured. Grey and pale greyish brown fine grained diamicton. Sand and silt matrix supporting pebble clasts, planar fabric. Firm diamicton, Grey and greyish brown sandy matrix supporting clasts of pebble-cobble dominantly but also some boulders, massive and unbedded. Base into creek. A 71