Convenor: Ian Skilling (Pittsburgh, Pennsylvania, USA) — skilling@pitt.edu
Co-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 groundwater 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
com-position 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 dan-gerous 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 joint-ing and its relationship to the form of the lava body. They are also good objects to calibrate and compare Quaternary dat-ing methods, remote sensdat-ing methods, and rates of geomorphic processes.
Peperite results from the interaction and mingling of magma and wet sediment and commonly exhibits a range of com-plex 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-mix-ing” 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 envi-ronments, 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 tex-tures, duration of mingling and duration between host sediment deposition and magma intrusion.
Contributions to this session are expected on any subject related to 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.
Oral Presentations of Symposium 4 23 September
10.50–11.10 C. M. White; B. D. Brand
MAGMATIC AND PHREATOMAGMATIC DEPOSITS AT SINKER BUTTE, A LARGE PLEISTOCENE VOLCANO IN THE WESTERN SNAKE RIVER PLAIN,
IDAHO, USA p. 101
11.10–11.30 U. Martin; K. Németh
SHALLOW SUBSURFACE SILL AND DYKE SYSTEMS ASSOCIATED WITH AN ALKALINE BASALTIC INTRACONTINENTAL VOLCANIC FIELD,
WESTERN PANNONIAN BASIN p. 74
11.30–11.50 N. A. Van Wagoner;R. W. D. Lodge; K. A. Dadd
CONTROLS ON MAAR VOLCANISM: EVIDENCE FROM SILLS AND DYKES
OF THE SILURIAN EASTPORT FORMATION, MAINE, USA p. 99 11.50–12.10 K. Balogh; V. Koneèn ; D. Vass; J. Lexa; K. NØmeth
METHODICAL RESULTS OF K/Ar DATING OF POST-SARMATIAN ALKALI BASALTS
IN THE CARPATHIAN BASIN p. 41
13.40–14.00 U. Martin; K. Németh
MAGMA/WET SEDIMENT INTERACTION IN CRATER LAKES AND VENT ZONES OF MONOGENETIC VOLCANOES IN MIO/PLIOCENE VOLCANIC FIELDS
OF WESTERN HUNGARY p. 73
14.00–14.20 I. P. Skilling
MECHANISMS OF FORMATION OF CORED ASH-LAPILLI AND ELONGATE FLUIDAL
ASH-LAPILLI DURING HYDRODYNAMIC MINGLING WITH SEDIMENT p. 91 14.20–14.40 V. Koneèn; J. Lexa
A COMPLEX EVOLUTION OF THE BULHARY MAAR, SOUTHERN SLOVAKIA p. 67
Poster Presentations of Symposium 4 22 September: 17.00–18.00 and
23 September: 17.00–18.00
J. Wijbrans; K. Németh; U. Martin; K. Balogh
40AR/39AR GEOCHRONOLOGY OF A MIO/PLIOCENE PHREATOMAGMATIC VOLCANIC FIELD
IN THE WESTERN PANNONIAN BASIN, HUNGARY p. 103
K. Birkenmajer;Z. Pécskay;M. W. Lorenc; P. P. Zagozdzon
RECENT GEOCHRONOLOGICAL AND GEOCHEMICAL STUDY OF ALKALI BASALTIC ROCKS IN LOWER SILESIA,
POLAND p. 43
K. Birkenmajer;M. W. Lorenc;Z. Pécskay; P. P. Zago¿d¿on
SPATIAL DISTRIBUTION AND PETROGRAPHIC DIFFERENTIATION OF BASALTIC ROCKS IN LOWER SILESIA,
POLAND p. 43
K. Gméling;K. Németh; U. Martin; N. Eby
BORON CONCENTRATION IN DIFFERENT MAAR-DIATREME VOLCANIC ENVIRONMENTS p. 59 I. Seghedi;A. Szakács; A. H. Pacheco; J-L. B. Matesanz
MIOCENE ULTRAPOTASSIC VOLCANOES IN SOUTH-EASTERN SPAIN — AN ASSOCIATION OF PHREATOMAGMATIC
AND MAGMATIC PRODUCTS p. 90
U. Martin;K. Németh
GROWTH OF SCORIA CONES FROM THE WESTERN TRANSMEXICAN VOLCANIC BELT, NEAR VOLCÁN CEBORUCO,
MEXICO p. 75
A. Y. Rotman
PHANEROZOIC VOLCANIC ASSOCIATIONS OF THE SIBERIAN PLATFORM’S EAST p. 86 W. J. W. Williams;E. Y. Anthony; J. Poths; W. C. McIntosh; T. B. Housh
PLEISTOCENE POTRILLO VOLCANIC FIELD, SOUTHERN RIO GRANDE RIFT, U.S.A. AND MÉXICO: SPATIAL AND
GEOCHEMICAL DISTRIBUTIONS THROUGH TIME p. 104
Symposium 5
GEOPHYSICS OF MAARS AND DIATREMES Convenor: Georg Büchel (Jena, Germany) — buechel@geo.uni-jena.de
Co-Convenor: Peter Suhr (Freiberg, Germany) — Peter.Suhr@lfug.smul.sachsen.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 diatreme 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 anom-alies. 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 have been encouraged to consider these key topics.
Oral Presentations of Symposium 5 23 September
14.40–15.00 H. Buness; H. Wiederhold
DETAILED IMAGING OF MAAR-DIATREME STRUCTURES BY REFLECTION
SEISMIC SURVEYS p. 46
15.00–15.20 H. de Wall; T. Nitzsche; C. Rolf ; T. Wonik
MAGNETIC SUSCEPTIBILITY LOGGING IN MAAR-DIATREM VOLCANOES–
WHAT IS IT GOOD FOR? p. 50
15.20–15.40 G. Gabriel;R. Pucher; W. Jacoby; H. Wallner
INTERPRETATION OF THE POTENTIAL FIELD ANOMALIES ABOVE THE MAARS
OF BARUTH (SAXONY/GERMANY) AND MESSEL PIT (HESSE/GERMANY) p. 57 16.00–16.20 C. A. Locke; S. J. France; J. Cassidy
CONTRASTING GEOPHYSICAL CHARACTERISTICS OF MAAR VOLCANOES
IN THE AUCKLAND VOLCANIC FIELD, NEW ZEALAND p. 71
16.20–16.40 T. Nitzsche; C. Rolf; H. de Wall
ORIGIN OF MAGNETIC ANOMALIES IN VOLCANICLASTIC UNITS
OF THE MESSEL MAAR-DIATREME (GERMANY) p. 81
16.40–17.00 R. Schulz; H. Buness; G. Gabriel; R. Pucher; C. Rolf; H. Wiederhold; T. Wonik DETAILED INVESTIGATION OF PRESERVED MAAR STRUCTURES
BY COMBINED GEOPHYSICAL SURVEYS p. 89
Poster Presentations of Symposium 5
22 September: 17.00–18.00 and 23 September: 17.00–18.00 J. Cassidy; C. A. Locke, S. J. France
THE AUCKLAND VOLCANIC FIELD, NEW ZEALAND: INSIGHTS FROM AEROMAGNETIC DATA p. 48 G. Gabriel; H. Wiederhold; T. Wonik; J. Rohrmüller; E. Geiss
GEOPHYSICAL INVESTIGATIONS OF A TERTIARY MAAR NEAR BAYERHOF (BAVARIA/GERMANY) p. 57 G. Büchel; G. Hesse
HYDROGEOLOGICAL POTENTIAL OF MAAR VOLCANOES DERIVED FROM THE GEES MAAR,
WEST EIFEL VOLCANIC FIELD, GERMANY p. 45
S. Senitz; G. Hesse; M. Pirrung; G. Büchel
PROSPECTION OF THE PRODUCTIVE GROUNDWATER POTENTIAL OF MAAR VOLCONOES AND SCORIA CONES
IN THE WESTEIFEL VOLCANIC FIELD (GERMANY) WITH GRAVITY AND GEOMAGNETIC SURVEY p. 91 A. Goepel; S. Senitz M. Pirrung; G. Büchel
GEOPHYSICAL, GEOMORPHOLOGICAL, AND LITHOLOGICAL IMPLICATIONS FOR A SPECIAL TYPE
OF PHREATOMAGMATIC VOLCANOES p. 60
P. Kubeš;V. Koneèn ;V. Syèev;J. Zuberec
GEOLOGICAL-GEOPHYSICAL EXPLORATION OF MAAR STRUCTURES IN SLOVAKIA p. 68 H. Lindner; R. Käppler; C. Pretzschner; P. Suhr
GEOPHYSICAL EXPLORATION OF MAAR LOCALITIES IN UPPER LUSATIA, GERMANY p. 70
T. Lipovics; A. Csontos; L. Lenkey
PRELIMINARY RESULTS OF GEOPHYSICAL STUDIES OVER THE TIHANY VOLCANO
AT THE TIHANY PENINSULA, HUNGARY p. 70
B. Zec;V. Sycev
GEOLOGICAL AND GEOPHYSICAL EVIDENCES OF VOLCANIC PRODUCTS
OF THE KOSICKÝ KLECENOV TUFF CONE, SLANSKE VRCHY MTS, SLOVAKIA p. 105 P. Schulze; P. Suhr
DISCUSSION OF THE DIATREM UNDER THE MAAR OF KLEINSAUBERNITZ IN EAST-SAXONY
BY GRAVIMETRICAL CALCULATIONS p. 89