Gullies and landslides on the Moon: Evidence for dry‐granular flows

Abstract

High‐resolution images from Chandrayaan‐1 Terrain Mapping Camera and Lunar Reconnaissance Orbiter Camera reveal landslides and gully formation on the interior wall of a 7 km‐diameter simple crater emplaced in Schrödinger basin on the farside of the Moon. These features occur on the steep upper crater wall, where the slope is ~35°. The gullies show a typical alcove‐channel‐fan morphology. Some gullies incise bedrock, where impact‐related faults are present. Slope failure along the concentric faults also led to formation of landslides. Dark slope streaks are abundant at the bright gully regions, especially near the fan and channel deposits. Spectral characteristics inferred from data obtained by Hyperspectral Imager and Moon Mineralogy Mapper on board Chandrayaan‐1 show that the gullies and landslides are characterized by high optical immaturity and devoid of prominent spectral absorption features related to water or hydroxyl molecules, suggesting youthful dry‐granular flows. Mass movements on the crater wall led to the formation of arcuate ridges and ponding of fine‐grained sediments on the crater floor. Runout flows from small impact craters on the slopes indicate that impact‐induced seismic shaking was responsible for the downslope mass movements. Crater size‐frequency distributions suggest a minimum age of 18–2 Ma for the gullies and 2 Ma for the landslides, while age of the host crater ejecta was inferred to be about 175 Ma. The gullies and landslides also occur on the interior wall of other impact craters elsewhere on the Moon and probably formed by similar processes.