GLACIAL FLOW MODELING ON MARS

Modeling ice sheets on Mars with the University of Maine Ice Sheet Model (UMISM) can help to explain and interpret various deposits observed by orbiting space craft. Models can quantify the spatial and temporal response to changing environmental conditions, assess how reasonable various GCM reconstructions of Martian climate are during periods of differing obliquity, and aid in assigning ages to observed stratigraphic chronologies. UMISM is an adaptation of a thermo-mechanically coupled shallow-ice approximation terrestrial ice sheet model used for time-dependent reconstructions of Antarctic, Greenland, and paleo-ice sheet evolution on Earth.

Amazonian deposits on the flanks of the Tharsis Montes volcanos are recognized to be of glacial origin. A GCM run for a high-obliquity (45 degrees) climate produces snow deposition due to upwelling and cooling of polar air as it rises up the slopes of the volcanos. Using these predicted accumulation rates to drive UMISM and comparing the resulting ice sheets to the geological evidence allows us to describe the temporal response (how long the high obliquity climate must exist to produce ice sheets matching observed landforms), as well as to provide an estimate of the volume of water contained in the ice sheets.

Further to the north and at lower elevations in the Deuteronilus-Protonilus Mensae region along the dichotomy boundary, a valley typical of many in this region displays an integrated system with glacial features such as alcoves from which emanate lobate flows interpreted to be remnants of debris-covered glaciers, horseshoe-shaped ridges upstream of topographic obstacles, and convergence and merging of lineated valley fill fabric in the down-valley direction. A GCM for a dusty-atmosphere Mars with obliquity set to 35 degrees and a water source in the Tharsis region generates a pattern of ice accumulation in good agreement with these geological observations. This climate is what one might expect to follow a high-obliquity excursion of the sort that built ice sheets on the Tharsis volcanos. Comparison of geologic features with results from UMISM supports the glacial interpretation of these features and also allows speculation as to the timing and processes responsible for their formation.