Influence of Target Properties on Wall Slumping in Lunar Impact Craters Within the Simple-To-Complex Transition

The 15-20 km crater diameter range on the Moon spans simple to transitional to complex crater morphologies. Simple craters in this range are only in the highlands. Transitional craters that contain localized slumps are scattered across the lunar surface. Most craters with localized slumps in the highlands superpose pre-impact topography with obvious slope breaks. We interpret this as a condition favorable for post-excavation internal slumping. However, some of these craters formed on terrains with topographic variation like the settings of simple craters: flat or gradually sloping surface, or degraded structures of older craters such as rims and terraces. To resolve the conundrum of two morphologies on one terrain type, we performed investigations of the local geology and topography of the inferred pre-impact terrains. We assessed if the localized slumping in the craters happened during or well after crater formation, looked for spatial variations in the strength of the highlands crust, detected topographic breaks (through elevation data) that were unnoticeable in the optical data, and examined rim circularity. Our findings corroborate the influence of pre-existing slopes on mass wasting along crater walls. Most of the craters with localized slumps have walls superposing topographic breaks that slope toward the crater interior. These walls are located near the uphill sector of the rims which initiated localized slumping. Most simple craters were found to have formed on surfaces with topographic breaks/slopes that face away from the adjoining crater walls, so that any immediate mass wasting would likely be outside the crater cavity.