EVOLUTION OF GLACIAL LANDSCAPES OF THE MARTIAN MID-LATITUDES

The mid-latitudes of Mars present a glacial landscape recording the last 3+ Ga of the planet’s climate history. The most recent history is recorded in gullies and lobate debris aprons sourced from crater rims. The interiors of mid-latitude craters host deep accumulations of ice and dust sourced both from both the crater walls and from central peaks involved in kilometers-long flows such as concentric crater fills and asymmetric lobate flows. At least three major episodes of glacial activity are recorded in crater interiors. These flows suggest a long-term decline in glacial activity, admixed with short episodes of runoff generation, fluvial incision, and alluvial fan deposition. The fraction of admixed particulates in the glacial flows may have declined with time, because sublimation has been more effective at deflating younger glacial flows. At about the ±40º latitude belt the glacial activity was locally accompanied by intra-crater lakes.

Glacial flows on the interior and exterior crater rims have been accompanied by erosion of the crater rim substrate, undercutting slopes at the flow margins. Pronounced glacial erosion of both the interior and exterior crater rims has formed “donut” craters characterized by a broad, rounded rim bordered by steep scarps.

The population of mid-latitude craters is much more degraded than equatorial craters, as measured by a degradation index, (F-D)/F, where F is the depth of a fresh crater of the same diameter as the degraded crater with depth, D. A preliminary model of glacial crater modification includes glacial flow, rock weathering, shallow solifluction mass wasting, and deep glacial flows following a Glen’s Law rheology. This modeling suggests that not only are craters infilled with hundreds of meters of ice/dust glaciers, but intercrater plains are likely encased in up to 200-300 meters of ice and dust. At present the model does not account for the observed erosive activity of the martian glaciers.