HR: 17:45h
AN: P32C-08    [PDF]
TI: Did Glaciers Exist Recently on the Tharsis Montes?
AU: * Morris, A
EM: aisham@hawaii.edu
AF: Hawaii Inst. of Geophysics and Planetology, University of Hawaii, 1680 East-West Rd, POST 518B, Honolulu, HI 96822 United States
AU: Mouginis-Mark, P
EM: pmm@hawaii.edu
AF: Hawaii Inst. of Geophysics and Planetology, University of Hawaii, 1680 East-West Rd, POST 518B, Honolulu, HI 96822 United States
AU: Baloga, S
EM: steve@proxemy.com
AF: Proxemy Research, 25028 Farcroft Ln, Laytonsville, MD 20882 United States
AB: Previous studies have documented the presence of ridged features on the NW flanks of the Martian volcanoes Arsia, Pavonis, Ascraeus and Olympus Montes. Several hypotheses modes of formation for these features have been proposed, including an origin attributed to glacial activity. We examine the areographic distribution and relative age of the ridges using MOLA topography, THEMIS IR and VIS images and MOC images to assess their spatial and temporal relationships on the four volcanoes. The majority of the ridged facies have an aspect facing between 270$\deg$ and 360$\deg$. The lowest elevation reached by the distal ridge on each volcano varies between -2,100 m below Mars datum on Olympus Mons and 3,000 m above datum on Pavonis Mons. The highest elevations also exhibit a wide range, from -1,686 m for Olympus Mons, to 1,970 m (Ascraeus Mons), 4,385 m (Pavonis Mons) and 5,496 m (Arsia Mons). MOLA topography and THEMIS images of Arsia Mons and Ascraeus Mons reveal different morphologies at the same elevation and aspect on each volcano, something that is not expected if the ridges resulted from a regional climate effect. At $\sim$5,000 m above datum, there is a distinct distal ridge on Arsia Mons, whereas the flank of Ascraeus Mons is dissected by large pits and pit chains and lacking any obvious ridges. Preliminary crater counts using MOC images indicate that the ridged facies on Arsia Mons may be significantly younger than the ridged facies on Ascraeus Mons, with Pavonis Mons falling between. In all cases, the ridged lobes have some superposed impact craters, indicating that these are not extremely young. These results suggest that a purely glacial origin for the ridges on the Tharsis Montes and Olympus Mons needs to be reexamined. Objections have been raised in the literature about a conventional rapidly emplaced flow origin for the ridges because the observed periodicity and regularity is not typically associated with turbulence. However, one of the alternative mechanisms we are investigating is the rapid release of sediment-laden water. It appears possible that the ridges formed as deposits from "roll-waves" that naturally occur in high flow rate debris flows, sediment-laden floods, and long run-out fluid flows.
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5416 Glaciation
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting