Steep interior wall of Kepler crater, rim is to the upper left and the bottom of the crater is in the lower right. Note the exposed layering near the top, and the boulders collecting at the base of the crater wall. LROC NAC M107128381R, image width is 800 m [NASA/GSFC/Arizona State University].
Landslides are primarily caused by gravity pulling loose material down a slope. Numerous factors contribute to landslides on Earth, including water and vegetation, but these can be ignored for the Moon. However, both bodies are affected by the angle of repose which is related to the cohesiveness of the material making up the slope. Once the angle of repose is exceeded the loose material on the slope slides downhill. Since the exposed bedrock layer near the top of the wall is more cohesive it stays intact while loose rocks and dust slide from underneath. As the wall material continues to slide down, more of the resistant layer will be exposed until it is undermined and is pulled down by gravity. The boulders at the base of the landslides are probably pieces of the bedrock layer.