2003 Fall Meeting          
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Cite abstracts as Eos Trans. AGU, 84(46),
Fall Meet. Suppl., Abstract xxxxx-xx, 2003
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marchant

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HR: 17:30h
AN: P32C-07 INVITED
TI: Tropical Cold-Based Mountain Glaciers on Mars: Evidence for Significant Amazonian Climate Change
AU: * Head, J W
EM: James_Head_III@brown.edu
AF: Dept. of Geological Sciences Brown University, Box 1846, Providence, RI 02912 United States
AU: Marchant, D R
EM: marchant@bu.edu
AF: Dept. of Earth Sciences Boston University, 685 Commonwealth Avenue, Boston, MA 02215 United States
AU: Shean, D E
EM: David_Shean@brown.edu
AF: Dept. of Geological Sciences Brown University, Box 1846, Providence, RI 02912 United States
AU: Milkovich, S M
EM: Sarah_Milkovich@brown.edu
AF: Dept. of Geological Sciences Brown University, Box 1846, Providence, RI 02912 United States
AB: Surface environmental conditions on Mars are presently extremely cold and hyper-arid, most equivalent to polar deserts on Earth. Coupling newly acquired Mars MOLA, THEMIS and MOC data with field-based observations regarding the flow, surface morphology, and depositional history of polar glaciers in Antarctica, we show that the multiple facies of extensive fan-shaped deposits on the western flanks of the Tharsis Montes and Olympus Mons, Tharsis Rise, are consistent with deposition from cold-based mountain glaciers. An outer ridged facies that consists of multiple laterally extensive, arcuate and parallel ridges, resting without disturbance on both well-preserved lava flows and impact craters, is interpreted as drop moraines formed at the margin of an ablating and predominantly receding cold-based glacier. Inward of the ridges lies a knobby facies that consists of irregular and closely spaced equidimensional knobs, each up to several kilometers in diameter; this facies is interpreted as a sublimation till derived from {\it in situ} downwasting of sediment-rich glacier ice. A third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock-glacier deposits, some of which may still be underlain by a core of glacier ice, particularly at Olympus Mons. Taken together, these surficial deposits show that the western flanks of these volcanoes were occupied by extensive mountain glacial systems accumulating on, and emerging from, the slopes of the volcano in the case of the Tharsis Montes, or at the basal scarp in the case of Olympus Mons, and spreading downslope to form piedmont-like fans. These deposits occur in equatorial and near-equatorial regions where surface water ice is not currently stable. The presence of the tropical mountain glacier deposits suggests that several phases of late Amazonian-aged glaciation occurred in the equatorial Tharsis region. Recent climate models suggest that at obliquities approaching 45 degrees and greater, water ice is stable in tropical regions. Thus, these tropical mountain glaciers may record periods of unusually high obliquity in the recent history of Mars.
DE: 5416 Glaciation
DE: 6207 Comparative planetology
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting


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