Slope failures and mantle degradation along the Nilosyrtis Rupes, Mars - An inventory of putative slab avalanches and sublimated terrain in the latitude-dependent mantle layer

Abstract

New data acquired from Mars orbiter and landers have led to major advances in planetary science during the last two decades, allowing for more detailed interpretations of the geological and climatic history of Mars. With the help of gamma spectroscopy, high-resolution satellite images of polygon-patterned, sorted, and sublimated ground, as well as field samples of near-surface ice, we know that much of Mars' water reservoir is bound as waterice in a thick latitude-dependent mantle layer (LDM). At latitudes poleward of 30°-45°, this ice-rich LDM covers the older terrain and is in turn overlain by a 10–20 cm thick layer of lag deposits, effectively protecting the underlying ice from fully sublimating under the low atmospheric pressure. Deposition of atmospheric ice and dust during periods of high obliquity has alternated with erosion and sublimation during periods of moderate or low obliquity during much of the Amazonian epoch. By studying the latitude-dependent mantle layer and its degradation, we may gain insight into how seasonal variations and Milankovitch cycles affect the possibility and extent of atmospheric precipitation and the stability of near-surface waterice on Mars. The aim of this study is to gain further insight into the latitudinal mantle layer properties and the spatial distribution of sublimation-induced erosion as well as the presence of mass movements of putative slab avalanches that indicate internal layering in the upper, dust- and ice-rich sediment. HiRISE and CTX data of small-scale features of the LDM-covered Nilosyrtis Rupes shows an aspect dependency of sublimated terrain and putative slab avalanches in north and northeast slope directions, which is consistent with previous mapping of glacial structures in the area (Saar, 2022). In this study, outcrops of putative sedimentary layering and large fracture lines were observed. The fracture lines predominantly lie parallel to the Nilosyrtis Rupes in a northwest and southeast direction. The orientation of these fractures favors slope instability along the ridge and cuts through both eroded and smooth terrain. Triggering factors for these relatively new fracture lines are discussed based on two hypotheses: volume collapse caused by long-term sublimation during the current moderate obliquity angle, or a geologically recent seismic event.