Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
Browse
3 results
Search Results
Item Pitfalls in erosion level calculation based on remnants of maar and diatreme volcanoes(Groupe Francais de Geomorphologie, 2007) Nemeth K; Martin U; Csillag GErosion estimates based on geometrical dimension measurements of eroded maar/diatreme volcanoes are useful methods to determine syn-volcanic surface level and syn-volcanic bedrock stratigraphy. However, such considerations on volcanic architecture should only be employed as a first-order approach to determine the state of erosion. We demonstrate, on both young and eroded maar/diatreme volcanoes, that establishing the volcanic facies architecture gives vital information on the environment in which the volcano erupted. In ‘soft’ rocks, maar volcanoes are broad and underlain by ‘champagne glass’-shaped diatremes. In contrast, the crater wall of maar volcanoes that erupted through ‘hard rocks’ will be steep, filled with lacustrine volcaniclastic deposits and underlain by deep diatremes.Item Eroded porous-media aquifer controlled hydrovolcanic centers in the South Lake Balaton region, Hungary: The Boglar volcano(Akad�miai Kiad�, 1999) Nemeth K; Martin U; Philippe MThe volcanic centers next to Balatonboglar township represent 3.5 Ma old products of post-extensional alkaline basaltic volcanism in the Pannonian Basin (eastern Central Europe). They are small, eroded volcanic centers located on the southern shore of Lake Balaton and genetically related to the Bakony-Balaton Highland Volcanic Field eruptive centers. The relatively small area (500 m x 500 m) contains at least 2 eruptive centers, which are probably related to each other and have built up a complex volcano, called the Boglar Volcano. The volcanic rocks overlie the older Pannonian clastic sedimentary sequence and represent the topographic highs in this area. The areas of lower elevation around the eruptive centers are covered by Pleistocene to Holocene swamp, lake and river clastic sediments, which strongly suggest intense erosion during the last few million years. All volcanic rocks around Balatonboglar are volcaniclastic. There is no evidence of lava flow occurrence. The volcaniclastic sediments have been divided into two lithofacies associations. The largest amount of volcaniclastic rocks is located in the center of the local hills and has been interpreted as a phreatomagmatic crater fill lapilli tuff. They contain large amphibole megacrysts and small olivine crystals. The second lithofacies association is interpreted as lahar deposits. This sequence contains an unusually large amount of fossil tree trunks, which are identified as Abies species. Within a small area in the western hills small outcrops show evidence of maar-lake clastic sediment occurrence. On the hilltops debris shows intimate interaction processes between clastic sediments and basaltic melt. We interpret this to mean that the eruptive centers of Boglar Volcano were formed under subaerial conditions, with explosions fueled by intensive interaction between water-saturated Pannonian sand and uprising basaltic magma.Item Deltaic density currents and turbidity deposits related to maar crater rims and their importance for palaeogeographic reconstruction of the Bakony-Balaton Highland Volcanic Field, Hungary(Massey University., 2001) Nemeth KThe Bakony-Balaton Highland Volcanic Field (BBHVF), active in the late Miocene, is located in the Central Pannonian Basin and consists of around 100 mostly alkaline basaltic eruptive centers. After volcanism, lake deposition took place inside the maar craters. Above the primary volcaniclastic deposits, thick maar-lake volcaniclastic sediments occur. The steeply dipping (25-35o), 25-30 cm thick, coarse-grained, inverse-to-normal graded beds of reworked tuff represent the foresets of large Gilbert-delta fronts built into the maar crater lakes of the BBHVF. The coarse-grained beds were deposited by low-density granule debris flows and grain flows. 10-15 cm thick beds of fine-grained, cross-bedded reworked volcaniclastic sandstone and mudstone beds are interbedded, probably deposited by turbulent sediment gravity flows. The delta fronts usually indicate transportation from north to south, suggesting a strong north-south trending fluvial system, active during or, shortly after volcanism in the BBHVF. The juvenile fragments of the deltaic sediments are often highly vesiculated, rounded/semirounded glassy lapilli. These suggest that the maar volcanism was related to widespread Strombolian-type explosive volcanism after the maar-forming phreatomagmatic events. Deposits derived from scoria cones were easily washed into the steep walled maar basins and deposited by debris flows into the maar lakes.