Global Drivers and Transport Mechanisms of Lunar Rockfalls

Abstract

Lunar rockfalls are ubiquitous mass wasting features that were first observed in Lunar Orbiter high-resolution photographs in the late 1960s (Eggleston et al., 1968;Filice, 1967;Moore, 1970). Rockfall events, which have been previously referred to as block falls or rolling boulders, involve the detachment of a boulder or rock mass from an elevated source region, which then slides, bounces, and rolls down the local topographic gradient, ultimately depositing downslope. Despite the fact that these features were recognized in the late 1960's, all early studies have only examined rockfalls in relatively small geographic areas on the lunar surface, because of a lack of available high resolution imagery (e.g., Eggleston et al., 1968;Hovland & Mitchell, 1973). Due to this, the characteristics of source regions, as well as the mechanisms that govern the failure and runout of lunar rockfall remain largely unknown.

A Global Perspective on Lunar Granular Flows

“…We interpret these to reflect differences in the short‐ and long‐term drivers required for the different landslide types. Rockfall occurrence requires the release of boulders on topographic highs (typically from weathered cliffs, outcrops, or boulder fields, e.g., Bickel, Aaron et al., 2021), whereas flow occurrence requires that the regolith or a (largely) cohesionless mass is susceptible to failure. Our results indicate that these two factors rarely coincide on the lunar surface, at least on a global scale.…”

Topographic Degradation Processes of Lunar Crater Walls Inferred From Boulder Falls

“…Bickel et al. (2020, 2021) statistically compared the global distribution of boulder falls with various geophysical data such as moonquake locations and topographic features. We studied the local distribution of boulder falls associated with ground shaking due to meteorite impacts, slope angles, and surface maturity.…”

“…In steeply sloping areas, this surface layer is thin because fine regolith tends to move downward under the influence of gravity. Therefore, in such areas, the bedrock can be more easily fractured by meteorite impacts, which produce rock fragments and boulders and, therefore, upslope boulder source areas as proposed by Bickel et al (2020Bickel et al ( , 2021 (Figure 14a). These boulders move downward when ground shaking due to meteorite impacts occurs (Figure 14a).…”

“…Bickel et al. (2021) further suggested that in young terranes, solar‐driven thermal fatigue (e.g., Molaro et al., 2015), by changing bedrock conditions, can produce boulders and trigger boulder falls. Boulder falls thus have the potential to provide invaluable information on dynamic processes associated with mass wasting on the Moon but the mechanisms causing boulder falls are still under debate.…”

“…with accompanying trails (e.g., Kumar et al, 2016Kumar et al, , 2019 have been identified across the lunar surface, especially on crater walls (Bickel et al, 2020(Bickel et al, , 2021. Kumar et al (2016) investigated the detailed distribution of boulder falls in the southern part of the Schrödinger basin, about 8 km from nearby lobate scarps.…”