HR: 16:15h
AN: P34A-02    [Abstracts]
TI: Cold-Based Tropical Mountain Glaciers on Mars: Insights From the Antarctic Dry Valleys and Implications for Mars Amazonian Climate Change
AU: * Marchant, D R
EM: marchant@bu.edu
AF: Boston University, Department of Earth Sciences, Boston, MA 02215 United States
AU: Head, J W
EM: James_Head@Brown.edu
AF: Brown University, Department of Geological Sciences, Providence, RI 02912 United States
AU: Shean, D
EM: david_shean@Brown.edu
AF: Brown University, Department of Geological Sciences, Providence, RI 02912 United States
AU: Milkovich, S
EM: s.m.milkovich@jpl.nasa.gov
AF: Jet Propulsion Laboratory, JPL, Pasadena, CA 91109 United States
AU: Fastook, J
EM: fastook@maine.edu
AF: University of Maine, Dept. of Computer Science and Climate Change Institute, Orono, ME 04469 United States
AB: Recent climate modeling on Mars and new understanding of the range of astronomical climate forcing values have shown that significant amounts of polar water ice can be mobilized and transported equatorward in the atmosphere during periods of high obliquity. Uncertain from a modeling point of view are the transit paths of this water vapor, the locales of its ultimate deposition, and the predicted maximum accumulation. Uncertainties in astronomical forcing values derive from the chaotic nature of planetary dynamics. We have examined the geological record of the equatorial region of Mars to assess evidence for the accumulation and timing of water ice to provide information to aid in reducing these uncertainties. Among the most prominent ice-related features found are vast fan-shaped deposits arrayed on the NW flanks of the Tharsis Montes, and lobate deposits at the base of the scarp on the NW flank of Olympus Mons. The Tharsis Montes fan-shaped deposits are interpreted to represent the remnants of broad piedmont-like cold-based glaciers with accumulation zones on the NW volcano flanks, each covering an area as large as 180,000 square km (Arsia). From the distal margins the deposits typically consist of concentric ridges interpreted as drop moraines formed during stages of glacial advance and retreat, a knobby facies interpreted as sublimation till formed during periods of glacial collapse and downwasting, and a lobate facies interpreted as alpine-like debris-covered valley glaciers associated with irregularities in accumulation zone topography, and representing the proximal deposits and also the most recent late stages of glacial advance and retreat. The Olympus Mons deposits consist of at least 15 individual lobes emerging from topographic alcoves at the base of the prominent basal scarp and extending up to about 100 km onto the surrounding plains. Smaller nested glacial deposits are seen within the accumulation zones of the larger lobes, suggesting the repetition of conditions leading to accumulation and flow, but under less extreme conditions. Taken together, these observations lead to some candidate constraints on Amazonian climate history: 1) water vapor can be transported to the equatorial region and deposited in large quantities during periods of high obliquity; 2) unlike homogeneous seasonal high-latitude frost deposition, accumulation is heterogeneous and localized on the NW flanks of large topographic edifices on the Tharsis rise; 3) the duration of conditions is sufficient to accumulate many hundreds of meters of ice; 4) the implied volumes of ice suggest that a significant percentage of the polar cap is mobilized during these periods; 5) the lack of significant meltwater-related features and facies suggest that the glaciers were dominantly cold-based; 6) multiple drop moraines and overlapping facies suggest duration of activity through several types of astronomical forcing cycles; 7) nested glacial deposits suggest that equatorial snow and ice deposition and accumulation recurs at these locations, but conditions are often insufficient to produce larger deposits. These observations provide important guidelines for atmospheric general circulation models during periods of high obliquity, and for models of snow and ice accumulation and flow in the Mars atmospheric and surface environment.
DE: 5416 Glaciation
DE: 5419 Hydrology and fluvial processes
SC: Planetary Sciences [P]
MN: Fall Meeting 2005