Volatile Ice Presence Analysis through Mass Wasting Events Mapping in Lunar Permanently Shadowed Regions

Mass wasting events on the Moon have been documented since the Apollo era and are distributed across its surface. On Earth, the morphology and runout distance of landslides, particularly flowlike landslides such as debris and mud flows, are strongly influenced by the mobilized soil and bedrock properties, notably the water content.

Despite the absence of widespread, liquid surface water on the Moon, previous surveys identified numerous lunar flow events across the Moon’s equatorial regions (± 60° latitude), termed “granular flows” or “flows”, in short, excluding the polar regions due to unfavorable illumination conditions. The recent release of ShadowCam images now enables the extension of past mapping efforts to the shadowed portions of the lunar polar regions (> 80° latitude).

Here, we perform a thorough, manual search for flows in polar region craters using images from the Korean Pathfinder Lunar Obiter (KPLO) ShadowCam and the Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC). We analyzed three regions for comparison: the Equatorial Region (Eq) (±60°), the South Pole Region (Sp) (80°–90° S), and the North Polar Region (Np) (80°–90° N). We focused our mapping efforts on flows in craters where more than 1% of the internal area has slope angles exceeding 30°. We utilized 131 ShadowCam images and 84 processed NAC images to map flows. Additionally, 100 random highland events from the Eq region were manually mapped for comparison with polar events.

We identified 23 Sp and 99 Np flows, distributed across 3 and 16 craters, respectively. A significant disparity emerged between the Eq and polar regions. While 38.7% of craters with slopes exceeding 30° in the Eq region contained flows, the percentages dropped to 33.3% in Np and 16.6% in Sp. Consequently, the likelihood of developing flows in Np and Sp with the same distribution as the Eq region is only 8.02% and 0.59%, respectively. Notably, Sp flows occur in areas with relatively lower LPNS-derived Water Equivalent Hydrogen (WEH) and outside permanently shadowed regions (PSRs) compared to Np flows. We observe no significant differences in geomorphic flow characteristics between the three regions. Flow efficiency (flow height/length, or H/L) averaged ~0.6, and the median source angle was ~32° across all regions.

Our results suggest that flows are 1) scarce in the polar regions, yet 2) do not exhibit anomalous geomorphologic properties in comparison to equatorial (dry) flows. This suggests the presence of an inhibitory factor - or the absence of the pre-conditions required for flow formation. Ongoing work is investigating whether our observations could be explained by a cementing effect caused by (near-)surface volatiles. The accumulation of volatiles might strengthen the regolith, reducing the probability of flow initiation due to meteorite-induced seismicity or moonquakes. Our observations might also indicate that potentially large quantities of subsurface volatiles are not shallow enough to cause and/or become mobilized in flow events. It is also possible that the observed flows formed before volatiles accumulated.