An alternative interpretation of late Amazonian ice flow: Protonilus Mensae, Mars

The morphological properties of glacial deposits located within a cirque-like alcove in eastern Protonilus Mensae, Mars (Mars grid reference: 54.55° lon, 40.80° lat), have been interpreted as indicative of an early phase of glaciation involving ice flowing out from the main glacierized valley and into a higher-elevation box canyon or alcove. This interpretation implies that the elevation of the glacial deposits currently located within the alcove mark a minimum former ice elevation in this catchment, providing a regional datum for former ice thicknesses with implications for martian climate reconstruction. Here, we raise the possibility of an alternative interpretation. Detailed geomorphological mapping and evaluation of the deposits remaining within the alcove suggest that they may have been formed by the more conventional mechanism of ice flowing out from the alcove and not into it. Both small-scale and catchment-scale morphologies, allied to the site’s location and orientation within an otherwise conventionally glacierized catchment, are consistent with outbound flow. This alternative hypothesis has important implications for ice thicknesses both in the local area and, by extension, regionally.