Scientific Symposia
for the
2nd International Maar Conference
15 – 29 September 2004
Hungary – Slovakia – GERMANY
2IMC
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Scientific Program Plenary Talk The scientific program will be opened with a plenary talk by Prof. Dr. Hans-Ulrich Schmincke. He will present an introduction to the theme and an overview on the present stage of research. The Organizing and Scientific Committee selected 13 Scientific Symposia to cover wide range of research fields dealing with monogenetic volcanic fields and maar/diatreme volcanism. The following Scientific Symposia call for presentations. On your abstract submission, please refer on these symposia numbers, to where you wish to submit your work. Symposia 1: MAARS AND THEIR TEPHRA DEPOSITS Convenor:
Michael
Ort,
(Flagstaff, Arizona, US)
– michael.ort@NAU.EDU Maars produce complex deposits both inside and outside of their craters. The record of the eruption is complicated by complex interactions between magmatic and phreatomagmatic processes in the conduit, transport processes in the vertical and lateral currents, and depositional processes. Many new and old techniques are being applied to understanding these processes. This session invites papers presenting new information on maars and their deposits. What can techniques such as particle shape and size analysis, sedimentary analysis, geophysical measurements, etc. tell us about vent dynamics and flow and depositional processes? How do we quantitatively model phreatomagmatic processes accurately? Can we design scaled experiments that elucidate real processes? How can we see through the "chaos" of the eruption to determine what processes are active at different stages? What techniques can we use to understand maar processes, and what do they tell us? Symposia 2: DIATREMES AND THEIR ROOT ZONES Convenor:
Volker
Lorenz
(Würzburg, Germany) -
vlorenz@geologie.uni-wuerzburg.de A
diatreme is the substructure of a maar crater and its tephra ring. There exist two models on the formation of maar-diatreme volcanoes: the magmatic model and the phreatomagmatic model. The magmatic model is especially concerned with ultrabasic, ultramafic and carbonatitic magmas. It invokes volatile rich fluid magmas which, close to the Earth´s surface, fragment the country rocks thus forming progressively from deeper levels to almost the surface the irregular shaped root zone. Explosive breakthrough to the surface is supposed to result in the formation of the maar crater and then via downward propagating fluidization of the root zone contents to shaping of the cone-shaped diatreme, and mixing of the diatreme clasts. The phreatomagmatic model, in contrast, invokes explosive interaction of rising magma with groundwater, originally close to the surface and then downward penetration of the sites of explosion. The various individual explosion sites or chambers jointly form the root zone. Ejection of explosively fragmented country rocks leads to a mass deficiency and consequently to collapse of the overlying rocks. Via these processes the diatreme forms and, in principle, it represents a collapse feature like a sink hole. Downward explosive penetration of the root zone on its own feeder dyke and consequent collapse phases of the diatreme leads to a growing diatreme and a growing maar crater above. Contributions are invited on all aspects of the complex physical processes resulting in the formation and evolution of diatremes and their root zones. Contributions are also invited dealing with the magmatic model and the phreatomagmatic model. Symposia 3: STRUCTURAL CONTROL ON PIPE EMPLACEMENT Convenor: Stephan
Kurszlaukis (Toronto, Canada) -
Stephan.Kurszlaukis@ca.debeersgroup.com The control on pipe emplacement is integrally linked with the understanding of the physical structure of the lower and upper lithosphere. It is generally accepted that prominent crustal discontinuities act as favorable ascent paths for the magma towards the surface. The West Eifel Volcanic Field, Germany, represents a classic example of how pre-existing country rock structures influenced and controlled the position and emplacement behavior of rising magma in the uppermost crust. The West Eifel maar-diatreme volcanoes were formed by phreatomagmatic activity on the intersections of mostly basaltic dykes with local water bearing faults or joints especially, but not exclusively, underneath fault-controlled valley floors. If meteoric water was not available, scoria cones were formed on dykes by magmatic activity, without the formation of diatremes. The internal and external geology of a maar-diatreme volcano must be carefully mapped and evaluated to understand its emplacement. Kimberlites and carbonatites also seem to follow an emplacement pattern that appears to be controlled by country rock structures. While their final emplacement mechanism is still under discussion (the major diatreme-forming process is thought to be related either to the expansion of a juvenile gas phase or to the interaction of the rising magma with groundwater), work published mainly over the last two decades has shown that the position of many of these economically important pipes is to at least some extent controlled by crustal discontinuities. Deep-seated shear zones, faults, mobile belts, transform faults, arch-style uplifts of pre-existing basement structures and the general stress field at the time of emplacement of these magma types have been quoted as being responsible, or at least as having influenced, the emplacement of pipes and dykes. Of interest, particularly for exploration purposes, is the extent to which the position and emplacement of a kimberlite pipe is controlled by country rock structures. In addition, it is important for mining purposes to define the interaction of the pipe shapes with inhomogeneities in the country rock. The morphology of root zones of maar-diatreme volcanoes seems to be particularly susceptible to country rock faults and joint patterns. Thus, we call for papers which explore whether and to what extent the position of a pipe, a pipe cluster or even a volcanic field is controlled by pre-existing country rock structures. Emphasis should also be placed on the interaction of pipe shapes with country rock discontinuities and a possible control on the style of eruptions. Symposia 4: DYKES, SILLS, PLUGS, DOMES, SCORIA CONES, AND LAVA LAKES IN MAAR-DIATREME VOLCANOES
Convenor: Jaroslav Lexa
(Bratislava, Slovak Republic) - lexa@gssr.sk Maar-diatreme volcanoes are created by phreatomagmatic eruptions arising from a contact of ascending magma with ground water in available aquifers. If this contact is eliminated magma continues its ascent towards the surface giving rise to a wide range of volcanic forms and products associated closely with maar-diatreme volcanoes. Usually this happens in the advanced or closing stage in evolution of the volcano. However, in arid regions the maar-forming eruptions were often preceded by effusive and/or Strombolian activity. Various scenarios are possible and factors controlling changes in the eruption style are understood poorly. Phreatomagmatism might be inhibited unless the magma flux is low relative to the rate of water supply and unless the top of the magma column has subsided, probably below the water table. Magma, that has not reached the surface, appears as dykes, sills and/or plugs in diatreme/maar filling. Some of them may represent feeders to surficial activity. Features relating dykes to the eruption types are open to discussion. Hawaiian to Strombolian type eruptions build up spatter, scoria and/or cinder cones. Eruption rate, volatile content, magma composition and temperature are the most obvious controlling factors. 95% of observed cinder-cone eruptions lasted less than a year in contrast to composite volcanoes formed from multiple eruptions over thousands of years – an important notion in view of the hazard assessment. Comparative morphology of scoria cones is a useful dating tool, however, new researches suggest that their erosion could be more complex. Rare basaltic Plinian eruptions are poorly known but dangerous volcanic phenomena. Outpourings of lava feed up lava flows and/or lava lakes in maar depressions, often in fully subaqueous environment. In such a case pillow lavas, hyaloclastite breccias and/or peperite breccias are present. Phreatomagmatic eruptions of the Surtseyan type due to interaction of ascending magma with water in the maar lake give rise to palagonite tuff cones. Eruption rate and water depth are factors controlling Surtseyan type eruptions and transition towards Strombolian type eruptions. Lava flows and lava lakes provide an excellent opportunity to study evolution of jointing and its relationship to the form of the lava body. They are also good objects to calibrate and compare Quaternary dating methods, remote sensing methods, and rates of geomorphic processes. Contributions to this session are expected on any subject related to the above mentioned phenomena, including understanding of fundamental processes involved in eruption styles and relationship to maars and diatremes. Presentations of new methods of dating lava flow surfaces as well as studies on radiometric age determination of magmatic systems associated with maar volcanoes are also welcomed in this session. Symposia 5: GEOPHYSICS OF MAARS AND DIATREMES Convenor:
Georg
Büchel
(Jena, Germany) -
buechel@geo.uni-jena.de Geopysical anomalies over maars and diatremes vary in their character and do not provide definitive evidence for a phreatomagmatic origin. Many known maars and diatremes are buried by post-genetic sediments. Geophysical methods resulted in their initial discovery and subsequent drilling provided geologic samples, which confirmed their phreatomagmatic origin. Interpretation of a single geophysical data set over a suspected maar or diatreme structure can be ambiguous. When combined, however, with complementary geophysical methods and the existing database over other known maar or diateme structures, a more definite assessment can be made. The most notable geophysical signature associated with maars or diatremes is a negative gravity anomaly. These gravity lows are generally circular and cover the whole structures. They are due to lithological and physical changes associated with the preatomagmatic explosion. In well-preserved maar structures, low-density sedimentary infill of the topographic depression of the crater contributes to the gravity low. In general, magnetic anomalies associated with maar or diatreme structures are more complex than gravity anomalies. Their reasons are very complex intrusion processes in the diatreme or in the sedimentary infilling of the maars. Also the development of spatter cones into the maar crater can cause a magnetic anomaly. The presence of fluids in explosion-induced fractures and pore spaces of the maar and diatreme rocks leads to decreased resistivity levels that can be mapped effectively by various electrical methods. Reflection seismic surveys allow for detailed imaging of maar structure morphology. Well logging methods are very useful for the detailed investigation of drill holes in maar and diatreme structures. Contributors are encouraged to consider these key topics. Symposia 6: PHYSICS OF MAAR-DIATREME VOLCANISM Convenor:
Ken
Wohletz, (Los Alamos,
Arizona, US) –
wohletz@lanl.gov Phreatomagmatic explosions and eruptions represent the key mechanism for the formation of maar-diatreme volcanoes, irrespective of magma composition or host rock type. However, it is environmental conditions (including magma and host-rock characteristics) that apparently cause quite a variability in size and shape of maars and the characteristics of their deposits. Furthermore, phreatomagmatism in maar volcanoes can occur with eruptive stages of purely magmatic explosivity, mixed magmatic/phreatomagmatic eruptions, or even final stages of lava lake effusion. The aim of this session is the discussion of physical processes of phreatomagmatism, how such processes lead to eruption variability, and the environmental factors that influence them. We invite experimental and theoretical contributions as well as field studies that provide insight into the physics of phreatomagmatism. From the generalized controlling parameters and processes that are common to many maar volcanoes to specific phenomena that demonstrate the range of variability in phreatomagmatism, contributed presentations will further the ability to predict the physical processes and interpret their manifestations in maar volcano structures and deposits. Contributors are encouraged to consider several key topics: 1) Environmental conditions that constrain how much water and magma interact 2) Influence of magma composition, crystal fraction, bubble fraction, and crystal-melt-bubble interfacial interaction 3) Interaction between magma and hydrothermal liquids 4) Magma-water interaction in subaqueous volcanism: the role of hydrostatic pressure 5) The potential contributing role of magmatic fragmentation in phreatomagmatic fragmentation (e.g., carbon dioxide degassing in alkaline diatremes) 6) Tephra deposit characteristics that lend quantitative interpretation to the energetics and processes of phreatomagmatism 7) Experiments: potential analogues, designs, and dimensional requirements, including industrial experience of vapor explosion 8) Computational physics: can this complex scale-dependent phenomenon be realistically simulated by numerical techniques? 9) The role of shock waves in multiphase flow and analogies to detonation 10) Field, laboratory, or theoretical analyses of phreatomagmatic fragmentation and tephra formation. Symposia 7: MAAR CRATER LAKE LIMNOLOGY AND MAAR CRATER SEDIMENTS Convenor: Kurt
Goth (Freiberg, Germany) -
Kurt.Goth@lfug.smul.sachsen.de When the phreatomagmatic explosions of a maar-diatreme volcano finally come to an end, the crater fills up with water. The resulting maar lakes are deep in relation to their diameter and damned from the surroundings by the ejected material (crater wall). This special architecture effects the lake and its sediments. These lakes trap the material of an extreme small catchment area. Allochthonous clastic material reaches the crater mainly as turbitity currents originating from the crater rim (ejected material). The autochthonous sediment in maar lakes is often dominated by algal material. Algal bloom layers alternate with the background sediment layers creating laminated deposits. And maar lakes often develop a meromiktic division of their water column providing in this way exceptional conditions for the preservation of sedimentary structures as well as fossils. We invite papers dealing with the history of maars lakes from different periods in earth history. Reconstruction of the ecology in maar lakes, comparision of the sedimentary processes and description of maar lake chemistry and other parameters should contribute to an improved understanding of these remarkable structures. We encourage speakers to consider the following key topics: 1) Post-eruptive history of maar lakes 2) Composition of maar lake sediments and their diagenesis 3) Laminated maar lake sediments with palaeo-climatic evidence (proxy-data, cyclic stratigraphy, time series) 4) Ecology of algae, reasons for algal blooms, decomposition of algae, settlement of algal remains 5) Preservation of fossils in maar lake sediments 6) Palaegeographic reconstructions of maar-diatreme volcanos 7) Field and laboratory analyses of sedimentological events in maar lakes (e.g. turbidites) 8) Chemistry of lakes: experiments and field observations 9) Meromiktic lakes: parameters, chemistry, typical sediments 10) Formation and diagenesis of siderite in maar lakes Symposia 8: PEPERITES IN MAARS AND TUFF RINGS/CONES Convenor:
Ian
Skilling (Pittsburgh,
Pennsylvania, USA)
skilling@pitt.edu Peperite results from the interaction and mingling of magma and wet sediment and commonly exhibits a range of complex textures. The occurrence of peperite demonstrates contemporaneous volcanism and sedimentation and provides important insights into subsurface magma transport, magma fragmentation, host-sediment properties and the “pre-mixing” mechanisms of FCI explosions. Recent studies demonstrate that peperite commonly occurs at the contact of lava lakes with the thephra ring of maar and tuff ring/cone volcanoes, and within the subsurface surrounding these edifices. We welcome submission of presentations that discuss peperite generation in this or other phreatomagmatic environments, and are particularly interested in any studies that address the following: links between peperite formation and eruptions, morphology of peperite domains, mingling mechanisms, influence of host sediment on peperite textures, duration of mingling and duration between host sediment deposition and magma intrusion. Symposia 9: SURTSEYAN VOLCANISM Convenor: James D.L.
White (Otago, New Zealand) -
james.white@stonebow.otago.ac.nz Surtseyan eruptions are characterized by interaction of a fluid erupting magma with abundant external water. Commonly they start in shallow subaqueous environments where accumulating tephra forms a mound-shaped volcano prior to emergence. During this subaqueous stage density currents play a significant role in shaping the edifice and imparting characteristic bedding features. Emergent to subaerial surtseyan eruptions generally produce cone-shaped edifices by accumulation of wet fall deposits with subordinate density currents. Surtseyan deposits typically consist almost entirely of glassy fragments formed by fragmentation of the erupting magma, and lack a significant country-rock component. This an important difference from deposits of maar-forming eruptions, and it indicates that in surtseyan eruptions fragmentation occurs at very shallow levels in the edifice or/and as the magma emerges from it. If or when the erupting magma no longer encounters water (e.g. by enclosure of an emergent vent, or isolation from/depletion of groundwater), both surtseyan and maar-forming eruptions may transform to strombolian or hawaiian ones. This session invites contributions on all aspects of surtseyan eruptions and their products, and particularly solicits those that address the relationship between surtseyan and maar- forming eruptions and underlying causes for the distinct eruption styles. Symposia 10: ECONOMIC GEOLOGY OF MAAR-DIATREME VOLCANOES AND THEIR ROOT ZONES
Convenor: Depending on magma-type involved, locality and state of erosion, maar-diatreme volcanoes may be of economic relevance. The economically most relevant maar-diatreme volcanoes are diamondiferous kimberlite and lamproite pipes which occur on all major cratons. The diamonds annually retrieved rank fourth in the list of mined commodities (excluding coal and oil) when assessed for value of production. Diatremes may be hosting other commodities as e.g. Au, Hg, etc., with the respective diatreme having channelled and thus having hosted fluids concentrating such commodities. Because of their Hg content, several diatremes in Palatinate, Germany, were mined for centuries. In the West Eifel, Germany, some diatremes underlying maar craters channel CO2 towards the surface which may be used in fizzy water or soft drinks, or for purely industrial purposes. The pyroclastic rocks of diatremes and maar tephra rings may represent material suitable for use as road metal and similar purposes. In the Sydney Basin, eastern Australia, pyroclastic diatreme rocks have been mined for road metal. And the basaltic lava lake rocks emplaced in many maar craters in a second non-phreatomagmatic phase are quarried for road metal, and for material used in concrete procuction.. Columnar-jointed basalts from such lava lakes were used in building dykes in the Netherlands and along the North Sea. Scoria deposited in maar craters from a second non-phreatomagmatic phase serves similar purrposes (road metal, production of light concrete, filter material, abrasives). Posteruptive crater lakes can accumulate sediments which may be quarried for their diatomite beds respectively their ”oilshale” (i.e. bituminous shales/alginite beds) for diverse uses in industry or in agriculture. When more permeable than the surrounding country rocks, diatreme rocks and the coarse marginal facies of their clastic crater lake deposits may serve as important local groundwater producers. In the West Eifel the fractured country rocks immediately surrounding two maars also produce groundwater. Young maars with their beautiful crater lakes, deep open pits (with or without a lake) left from former mining or quarrying, and pipes standing high above general ground because of greater resistance to erosion than the surrounding country rocks (e.g. Agathlan Peak, Ship Rock in the SW USA) are all attractive tourist sites and relevant in teaching the general public. Locally, in some countries, crater lakes may be relevant in respect to their fish. And last not least research on maar-diatremes with its many spin-off effects is economically relevant. Oral papers and poster presentations are invited on any of the above or additional aspects. Symposia 11: HAZARDS OF MAAR-DIATREME-VOLCANOES Convenor: Grant
Heiken (Los Alamos, New Mexico,
US) - tephra@cybermesa.com
Maar-diatreme volcanoes are the phreatomagmatic equivalent of scoria cones.
Whereas tuff-rings and tuff-cones form in shallow waterbodies and in
groundwater-rich environments maars form in rather "normal" groundwater
environments. Maars occur in volcanic fields and on foot plains and inside
calderas of polygenetic volcanoes. Only a few maars erupted in historic
times. Maars usually form when magma rises within a fissure and interacts
with groundwater. Contributors are encouraged to consider these key topics and contributions are invited on all aspects of the complexity of hazard assessment in monogenetic volcanic fields, in particular maar-diatreme-volcanoes. Symposia 12: VOLCANIC FIELDS - POLYGENETIC VOLCANOES
Convenor: Greg
Valentine,
(Los Alamos, New Mexico, US) -
gav@lanl.gov Volcanic activity in terrestrial settings often result in the formation of volcanic fields rather than single volcanic edifices. Volcanic fields, especially basaltic ones, are common volcanic systems on Earth. Monogenetic volcanic fields are those in which individual volcanoes (mainly basaltic) commonly form during single episodes of volcanic activity, without subsequent eruptions, while the volcanic field as a whole may be active for millions of years. Fundamental physical characteristics of volcanic fields that are the focus of current research include 1) the number, type and eruption history of individual vents; 2) the timing and recurrence rates of the volcanic eruptions in a given volcanic field, 3) the distribution of vents and volcanic complexes, and 4) the relationship of volcanic fields and the volcanoes within them to tectonic features such as basins, faults and rift zones. In general there are three major elements to be considered in the ascent and emplacement of magma either on Earth or other planets, and each strongly depends on the physical properties and structure of the lithosphere encountered by the magma. The three factors are: 1) magma generation and buoyancy, 2) rheological boundaries in the lithosphere and 3) density boundaries in the lithosphere. In addition to these factors, the stress field (local and regional) plays an important role in controlling magma ascent which is generally related to the structural features of the lithosphere encountered by the magma. In this session we are calling for contributions that address the following questions: What determines whether a volcanic field will consist only of scattered monogenetic volcanoes, versus development of one or a few central, polygenetic volcanoes? What are the controlling factors, how these processes can be modeled? How large can a monogenetic volcano be, and what are the criteria that distinguish, or mark the transition between, monogenetic and polygenetic volcanoes? Are all small basaltic centers monogenetic? We welcome presentations on any approach to addressing these questions, including geochemistry, high-precision geochronology, petrology, geophysics, geomorphology, and spatial analysis. A special topic for this session includes studies on the distribution characteristics of maars versus scoria cones versus polygenetic volcanoes in a volcanic field. Symposia 13: OPEN SESSION (BASALTIC VOLCANIC FIELDS INCLUDING ENVIRONMENTAL ISSUES, NATURE PROTECTION, GEOSITES, GEOPARKS AND GEOTOURISM) Convenor:
Ulrike
Mattig,
(Wiesbaden, Germany) -
u.mattig@mulf.hessen.de
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