Aspect Asymmetry in Martian Gullies: A Topographic Signature of Their Formation Process?

Abstract On Mars, erosional‐depositional landforms named gullies provide natural experiments for studying the topographic signature of the processes that act on hillslope evolution. High‐resolution topographic data were used to quantitatively compare the steepness of opposing walls in gully alcoves incised into ice‐rich slopeside mantling deposits. We confirm the presence of an aspect‐dependent topographic asymmetry in 12 gully systems where pole‐facing alcove walls are shallower than equator‐facing walls in both the Northern and Southern hemispheres. Further 19 gully systems with an apparent topographic asymmetry display a similar trend with visually shallower pole‐facing walls. We attribute this asymmetry to landform‐scale differences in microclimates between opposing alcove walls. We argue that the shallowing of the pole‐facing alcove walls is driven by the preferential accumulation of CO 2 and H 2 O frosts, which can lead to enhanced sediment fluxes via the preferential occurrence of mass‐wasting events and CO 2 ‐driven flows on pole‐facing slopes. Exposure of subsurface ice by mass‐wasting events would likely further contribute to the shallowing of pole‐facing alcove walls. The magnitude of asymmetry is lower where alcoves incise into local bedrock and higher in the icy mantling deposits, highlighting the importance of gully substrate's resistance to erosion for the development of topographic asymmetry. Finally, we argue that the driver of asymmetry development must have been consistent between now and the recent past, as indicated by the similarities in alcove asymmetry and associated morphologies between sites with documented activity and sites with no activity observed during the monitoring period.