Browsing by Author "Kereszturi, Gabor"
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- ItemApproaches to forecast volcanic hazard in the Auckland Volcanic Field, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand(Massey University, 2014) Kereszturi, GaborMonogenetic basaltic volcanism is characterised by a complex array of behaviours in the spatial distribution of magma output and also temporal variability in magma flux and eruptive frequency. For understanding monogenetic volcanoes different topographic and remote sensing-based information can be used, such as Digital Surface Models (DSMs). These data are most appropriately analysed in a Geographic Information System (GIS). In this study a systematic dataset of the Auckland Volcanic Field (AVF), New Zealand, was collected and pre-processed to extract quantitative parameters, such as eruptive volumes, sedimentary unit thicknesses, areas affected, spatial locations, and topographic positions. The topographic datasets available for the AVF were Shuttle Radar Topography Mission (SRTM), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), contour-based Digital Elevation Models, and Light Detection And Range (LiDAR) datasets. These were validated by comparing their elevations to high accuracy ground control reference data from multiple Real-Time- Kinematic (RTK) Global Positioning System and Terrestrial Laser Scanning surveys. The attribute extraction was carried out on the LiDAR DSM, which had the best vertical accuracy of ≤0.3 m. The parameterisation of monogenetic volcanoes and their eruptive products included the extraction of eruptive volumes, areas covered by deposits, identification of eruptive styles based on their sedimentary characteristics and landform geomorphology. A new conceptual model for components of a monogenetic volcanic field was developed for standardising eruptive volume calculations and tested at the AVF. In this model, a monogenetic volcano is categorised in six parts, including diatremes beneath phreatomagmatic volcanoes, or crater infills, scoria/spatter cones, tephras rings and lava flows. The most conservative estimate of the total Dense Rock Equivalent eruptive volume for the AVF is 1.704 km3. The temporal-volumetric evolution of the AVF is characterised by a higher magma flux over the last 40 ky, which may have been triggered by plate tectonic processes (e.g. increased asthenospheric shearing and back-arc spreading underneath the Auckland region). The eruptive volumes were correlated with the sequences of eruption styles preserved in the pyroclastic record, and environmental influencing factors, such as distribution and thickness of water-saturated post-Waitemata sediments, topographic position, distance from the sea and known fault lines. The past eruptive sequences are characterised by a large scatter without any initially obvious trend in relation to any of the four influencing factors. The influencing factors, however, showed distinct differences between subdomains of the field, i.e. North Shore, Central Auckland and Manukau Lowlands. Based on the spatial variability of these environmental factors, a susceptibility conceptual model was provided for the AVF. Based on the comparison of area affected by eruption styles and eruptive volume, lava flow inundation is the most widespread hazard of the field. To account for this, a topographically adaptive numerical method was developed to model the susceptibility for lava flow inundation in the AVF. This approach distinguished two different hazard profiles for the valley-dominated Central Auckland and North Shore regions, and the flat Manukau Lowlands. A numerical lava flow simulation code, MAGFLOW, was applied to understand the eruption and rheological properties of the past AVF lava flow in the Central Auckland area. Based on the simulation of past lava flows, three eruptive volume-based effusive eruption scenarios were developed that best characterise the range of hazards expected. To synthesise, susceptibility mapping was carried out to reveal the patterns in expected future eruption styles of the AVF, based on the eruptive volumes and environmental factors. Based on the susceptibility map, the AVF was classified as highly susceptible to phreatomagmatic vent-opening eruptions caused by external environmental factors. This susceptibility map was further combined with eruptive volumes of past phreatomagmatic phases in order to provide an eruption sequence forecasting technique for monogenetic volcanic fields. Combining numerical methods with conceptual models is a new potential direction for producing the next generation of volcanic hazard and susceptibility maps in monogenetic volcanic fields. These maps could improve and standardise hazard assessment of monogenetic volcanic fields, raising the preparedness for future volcanic unrest.
- ItemGeothermal exploration using hyperspectral and thermal remote sensing : inferring shallow hydrology of the Waiotapu Geothermal Field, New Zealand : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Earth Sciences at Massey University, (Manawatū Campus), Palmerston North, New Zealand(Massey University, 2023) Rodriguez-Gomez, CeciliaGeothermal areas can exhibit a series of surface manifestations (e.g. mineral alteration and deposition, thermal anomalies, hot springs, and characteristic plant species) which can be directly detected with remote sensing techniques within the visible, near-infrared, and thermal ranges. These surface manifestations are, to some extent, a reflection of the subsurface activity. There is a wealth of techniques, including geological, geophysical, and geochemical methods, which can be used to explore and monitor geothermal areas; however, remote sensing techniques from airborne and spaceborne platforms can provide a cost-effective alternative. In many cases, geothermal areas are densely covered by vegetation which can further increase the time and cost of exploration. However, vegetation has the capability to reflect the environment it lives in. Here, we propose vegetation can be utilised as a proxy for subsurface geothermal activity using a combination of hyperspectral (VNIR/SWIR), thermal infrared, and LiDAR imagery with rock/soil and plant elemental concentration values. These techniques are used in geothermal areas but have rarely been employed to analyse plants growing in the area. At Waiotapu Geothermal Field, less than 10% of the surface is directly exposed, areas where the hyperspectral airborne successfully identified three main lithologies and alteration minerals; acid-sulphate alteration, “mixed” alteration, and silica-sinter deposition. While plants cover the remaining 90% of the surface, with kanuka shrub (kunzea ericoides var. microflora) as the dominant species in soils >40 °C. As such, kanuka was selected for our investigation and four geothermally relevant elements were chosen (Ag, As, Ba, and Sb). In areas with near-neutral high-chloride springs with a significant upflow (e.g. Champagne Pool), Ag, As, and Sb are enriched in rock/soil samples and are uptaken by kanuka plants. Whereas high Ba concentrations were found in plants living in peripheral areas where water mixing is taking place. The foliar element concentration zonation maps were successfully developed through classification using Random Forest and regression with Kernel Partial Least Squares. Employing ICPMS data and laboratory, airborne, and satellite hyperspectral (VNIR/SWIR) remote sensing data to create models to predict the foliar element concentrations. The results correspond well with the geology and thermal profile of Waiotapu Geothermal Field. Additionally, thermal anomalies selected from airborne TIR broadband imagery were studied using point pattern analysis such as randomness test-statistics, to map their preferred patterns and orientation, which appear to be controlled by subsurface permeability and water flow. This research opens new opportunities for geothermal exploration and monitoring through plants using hyperspectral imaging, which can overcome the limitations of geothermal exploration methods in densely vegetated areas.
- ItemMineral prospecting via biogeochemical signals and surface indicators using hyperspectral remote sensing : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand(Massey University, 2022) Chakraborty, RupsaPreliminary steps of mineral exploration have traditionally included drilling and other destructive, expensive, and time-consuming techniques. To meet the ever-increasing demand for mineral resources pertaining to the increase in population and technological demand, it is very important to develop environmentally friendly, faster, and cheaper prospecting methods. In this study, we have targeted three known regions of mesothermal gold mineralisation in the South Island, New Zealand to develop hyperspectral remote sensing-based prospect models combined with biogeochemical data. The three study sites have geological similarities around the gold mineralisation including the major pathfinder elements. On the contrary the environmental settings, and other surficial and near-surface processes including the soil and groundwater interactions with the host rock, are vastly different. This led to a wide variation in the physico-chemical properties of the soil cover and the subsequent uptake by the overlying vegetation. The Pinus radiata plantation at the Hyde-Macraes Shear Zone was the first study site to test the feasibility of using biogeochemical responses overlying the gold mineralisation through hyperspectral remote sensing for gold prospecting. Pinus radiata is known to be an accumulator of metals and metalloids with roots reaching as deep as the shear zone beneath it. The data showed a good spatial elemental trend along the shear zone for both the bark and the needle samples although the regression models performed much better with R2CV >0.7 for the bark samples. After confirming the feasibility of utilising the vegetation cover as a medium, the second site in the Rise and Shine Shear Zone was examined to assess the limits of the airborne hyperspectral data over variably exposed soil. The potentially high As anomalies indicating the gold mineralisation were classified coupled with a thorough understanding of the soil cover and its relation to the lithology. The orthogonal total variation component analysis transformed data produced the best-performing models using random forest classification with an accuracy ~50% for the high concentration As zonation. Finally, the third study site in Reefton exhibited a multi-species natural forest overlying the gold mineralisation. Apart from varying elemental responses among the different species the Reefton study area also manifested regions contaminated by previous mining activity which likely impacted the elemental uptake in the overlying vegetation. The regression models performed poorly but the spatial predictions rendered some valid correlations based on ground knowledge from previous studies.