HR: 1340h
AN: P23B-0188    [Abstracts]
TI: Tharsis Montes Mars: Evidence of Massive Recent Erosion Caused by Volcano-Ice Interactions
AU: * Helgason, J
EM: jhelgason@simnet.is
AF: National Land Survey of Iceland, Stillholt 14-16, Akranes, 300 Iceland
AB: The Tharsis Montes volcanoes, Arsia, Pavonis and Ascreus, share many volcano-tectonic features, including fissure swarms that extend NE and SW away from their centers. Lavas and sedimentary deposits have built up fan shaped aprons that overlie or partly bury the fissures swarms to a distance of over 500 km from the volcano massifs. The pattern with depressions observed on the NE and SW sides of the Tharsis Montes suggests a common origin. The fissure swarms coincide with large-scale negative landforms, some 25 km wide and over 2 km deep. These negative landforms can further be divided into lineated channels and isolated circular depressions or pit craters. While tectonic movements have surely been a major factor in forming the depressions the overall character of this network resembles erosional channels. Volcanism culminated most likely within the fissures swarms where surface lavas are visibly draped by a cover of sedimentary origin. Teardrop shaped crater remnants with erosional collar grooves are found in these deep depressions, e.g. Pavonis Mons. The derived teardrop orientation is downstream within the depressions and oblique to local wind directional pattern. The volcano-tectonic pattern, erosional morphology and pit craters all conform to an origin where volcanism has produced meltwater that in turn has led to jokulhlaups, both within the Montes calderas, the fissure swarms and even on the flank volcano slopes. Research has shown that the age of volcano units, based on crater counting, is lowest on the fissure swarm floors. Volcano-ice interactions within the calderas are likely to have forced copious quantities of melt water into the fissures swarms and caused large-scale erosion there. A genetic relationship is suggested between the erosional valley systems and the locus of maximum volcanism within the fissures swarms. The process of jokulhlaups resulting from magma-ice interactions can account for the generation of this erosional pattern. Large scale melting of ice within Tharsis calderas and leakage of meltwater from there through fissure swarms can account for the erosional phenomena observed within the NE-SW Montes depressions.
DE: 5415 Erosion and weathering
DE: 5419 Hydrology and fluvial processes
DE: 5480 Volcanism (6063, 8148, 8450)
SC: Planetary Sciences [P]
MN: Fall Meeting 2005