Concentric Crater Fills as Archives of Martian Mid-Latitude Glaciation

Mars is a cold, hyperarid planet, yet it retains a water ice inventory sequestered within the polar layered deposits, widespread ground-ice reservoirs, and mid-latitude debris-covered glaciers termed Viscous Flow Features (VFFs). Because surface ice is unstable at Mars’ mid-latitudes today, VFFs are interpreted as relict landforms formed under a past climate regime. Concentric Crater Fills (CCFs) represent the most spatially extensive VFF subclass, confined within impact craters. CCF morphologies span well-preserved to degraded states, though it remains unclear whether their modern form reflects initial accumulation or subsequent post-glacial modification.
This Thesis isolates a global population of ~3,000 high-confidence CCFs and uses orbital images and elevation data to investigate the environmental gradients and mass-balance histories recorded in their current state. By treating impact craters as predictable geometric containers, my study of these CCFs separates crater-imposed topographic controls from external climatic signals. Analysis of the population reveals a decoupling that their ice volume generally increases with host-crater diameter, but their surface geometry (elevation deficit below crater rim or “apparent depth”, surface slope, and slope aspect) exhibits coherent, latitude-dependent variations that are largely independent of host-crater capacity.
I argue that CCF surface geometry primarily records the effect of post-glacial ablation rather than initial accumulation. The poleward decrease in apparent depth and slope is consistent with insolation-mediated downwasting, where reduced solar forcing at higher latitudes favours the preservation of ice which fills craters closer to the rim level. A fundamental hemispheric asymmetry is identified: northern CCFs possess lower apparent depths, possess no surface aspectual bias and are more numerous, whereas southern CCFs exhibit lower volumes and stronger pole-facing aspect biases. This suggests an asymmetry in CCF evolution, where the northern mid-latitudes experienced more effective ice preservation. Collectively, these findings establish CCFs as systematic environmental archives.