Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p52b..01w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P52B-01
Physics
5480 Volcanism (6063, 8148, 8450), 6225 Mars, 8425 Effusive Volcanism, 8428 Explosive Volcanism, 8429 Lava Rheology And Morphology
Scientific paper
We focus on six separate, but physically close, vent systems in eastern Tharsis, Mars, just to the east of the volcano Jovis Tholus. The vents are typically linear fissures a few to 20 km in length that have built small shields rising to 50-85 m above the level of the surrounding topography. Typical lengths of individual lava flows from these fissures are 15-20 km, with a maximum of 30 km. Mapping of the vent complexes reveals smooth material, interpreted to be spatter from fire fountaining, located on the rims of some of the fissures. In some places this spatter fed individual short (less than 5 km) lava flows; elsewhere spatter from segments of the fissure coalesced to form longer flows. Temporal evolution of the flow fields is indicated: the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows. In places activity was locally focussed and formed lava ponds and channelized flows from central vents. MOLA topographic data and photoclinometry topographic profiles made from THEMIS VIS images show that the flows are typically less than 5 m thick, 8-15 times thinner than flows elsewhere on Mars. We used standard models of magma rise through dikes, lava flow emplacement, and fire-fountain behavior to find lava viscosities and yield strengths (100 Pa s and 100 Pa, respectively), eruption rates (5,000 m3/s), flow speeds (1-2 m/s), durations of emplacement of individual flow units (5 hours), and an equivalent magma water content (0.1-0.2 mass percent). These eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions. Small vents like those studied here have been identified elsewhere in Tharsis (particularly just to the east of Olympus Mons), and the eruption conditions described above may characterize a previously poorly recognized style of volcanism on Mars only identifiable in images with spatial resolutions better than 10 m/pixel.
Garbeil Harold
Mackown Jennifer
Mouginis-Mark Peter J.
Tyson Shelly
Wilson Leslie
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