Morphology and dynamics of steep-fronted glaciers around Alba Mons, Mars

Martian ice-rich landforms, generically referred to as Viscous Flow Features (VFFs), are key to understanding the Late Amazonian climate history of Mars, as its evolution may be recorded in the internal structure and dynamics of these deposits. In this study, we report the occurrence of 29 steep-fronted, pole-facing lobate deposits identified within craters (24) and pits (5) larger than 2 km in diameter in the Alba Mons region of Mars. We interpret these deposits, which extend 1-3 km downslope and can reach thicknesses exceeding 200 m at their termini, as debris-covered glaciers. Their most distinctive feature is a steep (up to 42°) terminal scarp, tens to hundreds of meters high, which truncates surface flow features. This morphology has not been previously described for Martian debris covered glaciers, but resembles the steep termini of some debris-covered or rock glaciers on Earth. We propose that these steep-fronts result from sublimation-driven retreat of ice at the glacier termini. The steep fronts exhibit two superposed textural units. We argue that these do not reflect internal layering, but instead correspond to distinct components of the glacier system: a lower, rougher and steeper unit that we interpret as a debris accumulation (moraine-like), and an upper, smoother unit corresponding to the ice-rich body of the glacier. This debris accumulation is likely sourced from the degraded crater headwalls and transported by the flowing glacier before accumulating at the front as ice sublimates. Finally, our comparison with a debris-covered glacier in northern Iceland reveals similar frontal morphologies, supporting the interpretation of the two textural units of the Martian deposits. Combined with glacial flow model and climate model outputs, our results suggest that these deposits represent the remnants of ice deposits formed during a recent colder, high-obliquity period and preserved under favorable topographic conditions on pole-facing crater slopes. Although their present-day geometry indicates a state of disequilibrium, characterized by mass deficits in the distal regions and excess ice in the source areas, our results show that their distinctive steep-fronted morphology arises from the combined effects of ice flow and sublimation-driven marginal ablation. These findings underscore the critical roles of local topography and debris-ice interactions in governing the preservation, evolution, and geomorphic expression of ice-rich deposits on Mars.