Tharsis Montes Cold-based Glaciers: Observations and Constraints for Modeling and Preliminary Results

Introduction: Each of the Tharsis Montes volcanoes on Mars has an unusual fan-shaped deposit on the NW flank and adjacent plains. These deposits appear to be the depositional remains of massive cold-based glaciers that were present at each of the shields in relatively recent martian history [1,2]. These glaciers would have formed during periods of high obliquity (>45°), when precipitation of water ice is predicted to occur in the equatorial regions [3,4]. Reconstruction of these glaciers provides estimates for ice thicknesses and volumes, which will help delineate the thermal character of the ice (cold-based vs wetbased [1,2]). More importantly, these estimates can be compared to current polar cap volume, providing information about the amount of material removed from volatile reservoirs and the global distribution of volatiles during the time when the glaciers were present. Fan-shaped Deposits: Observations of the shape, distribution, and elevations of the fan-shaped deposits can provide important constraints for ice sheet reconstruction. In plan view, all three deposits are lobate in nature, extending onto the relatively flat plains to the WNW of each shield with thinning “horns” that taper to a point at higher elevations on the shield flanks (Fig. 1). The deposits all share similar geologic units and appear to have similar origins [5]. However, they differ greatly in size and overall trend with respect to the shield. The following table summarizes key parameters for each deposit: