Groundwater sapping is presumed to be able to function at low temperatures because groundwater could remain unfrozen at depth because of the high geothermal heat gradient on early Mars, and water emerging at springs might occur beneath a protective ice cap even at low temperatures. The unfrozen groundwater might be brought close to the surface by hydrothermal pumping due to water expansion accompanying igneous intrusions or heat generated by crater impacts. Similarly, upward vapor migration from a deep water table might resupply shallow groundwater supply. Initial groundwater sapping simulations examine the case where water infiltrates underground from surface recharge and emerges in lowlands. A simple model of groundwater flow assumes that the horizontal scale of flow is much greater than the vertical scale, and that the subsurface has spatially uniform properties.
Infiltrating water flows laterally and emerges in low areas.
This emerging water is assumed to erode the surface materials by the same process laws that were used for fluvial erosion simulations . Also similar to those simulations, when erosion creates slopes steeper than the the maximum stable angle for loose material, downslope slumping is assumed to occur. The first image is the same as the cratered landscape shown in the crater simulation modeling except that mass wasting of steep crater walls has occurred. In the simulation shown here the seepage rates are assumed to be low enough that no permanent bodies of water form. After a period of erosion by emerging groundwater, undermining and retreat of deeper crater rims is apparent.