A LONG LAVA FLOW IN THE THARSIS REGION OF MARS AS MAPPED USING THEMIS DATA

A long lava flow to the west of Ascraeus Mons, the northern most volcano of the Tharsis Montes volcanoes, was previously examined by Zimbelman and Peitersen using Mars Orbiter Laser Altimeter (MOLA) data. The same flow is now being mapped using the Mars Odyssey Spacecraft Thermal Emissions Imaging System (THEMIS) data, under a grant from the Planetary Geology and Geophysics program of NASA. The daytime infrared (IR) THEMIS data, at 100 m/pixel, reveal a much more detailed picture of the flow then could be inferred from MOLA shaded relief images. The entire Tharsis region is blanketed beneath at least a meter of dust, and the precise thermal attributes of THEMIS allow very subtle slopes to be revealed by small daytime temperature differences. THEMIS data have shown that the flow width appears to be narrower in places then the margins previously identified in the MOLA data. The flow extends beyond the presumed starting point from previous work. We are examining the possibility that this flow may break out into previously unrecognized flow segments. The flow contains a central channel not seen in the shaded relief data that extends at least 230 km in length. The direction of the flow is generally northward, with a turn towards the northeast near the distal end. MOLA data have shown that the flow is following the local gradient into a large topographic basin. THEMIS data have not yet covered the entire length of the flow, as of July 2004. As more THEMIS data are released, gaps previously not covered by good images should be filled in, allowing us to map the full length of the flow.