On the activity of water on Mars: Investigations into the groundwater system and the stability of ice in the crater-interior environment

Water has played an integral role in geologic evolution and climate change on Mars. This thesis focuses on two key links of the martian hydrological cycle. First is the potential for interaction of groundwater with the surface, in which the implications of the current global subsurface cryosphere-hydrosphere model are tested with geologic observation. Outflow activity at Elysium is consistent with a model of cryosphere disruption due to dike intrusion, resulting in the release of water, sediment, and lava, and supporting previous interpretation of lahar deposits. The elevation dependence of outflow sources is consistent with the current cryosphere-hydrosphere groundwater model. At Lyot crater, lack of effusion of groundwater resulting from a thermally and physically disruptive impact event suggests several possible modifications and constraints to the current model. Several lines of evidence lead to the proposal that regional recharge of the groundwater system resulting from basal melting of snow on major volcanic rises, such as Elysium and Tharsis, is a viable source of water for the major outflows, in contrast to the sole, south-polar recharge area of the current model. The second focus is the stability and modification processes of ice-rich circum-polar deposits. An energy balance model of ice stability within the topographic environment of impact craters takes into special consideration the factors of surface slope, shadowing of crater walls, reflection off crater walls, and reduced emission due to a reduced visible angle of sky. Insight from this model is used in interpreting the range of morphologies of volatile-rich crater fill in both circum-polar regions. These observations suggest that fill material was deposited similarly to the PLD as part of a formerly more extensive contiguous PLD deposit. Subsequent sublimation and retreat exposed crater rims, at which point the feedback cycle of sublimation modeled within the crater topographic environment enhances the formation of wall-adjacent troughs at that location. Ice-rich crater fill material is hypothesized to have been deposited at these sub-polar latitudes as global zones of ice stability migrate latitudinally as a result of orbital variation.