Bumpy, Expanded Craters

Expanded craters on Mars are thought to occur when the upper slopes of an impact crater in an ice-rich target sublimate (going directly from a solid to a gaseous state). The vaporizing ice makes the walls retreat while the lower slopes are armored by dust and debris, resulting in a funnel-shaped formation. The expanded craters in this image have an unusually bumpy texture in the outer apron where the sublimation occurred. The bumps are too large to be boulders. This suggests that the ice had concentrations of other material. https://photojournal.jpl.nasa.gov/catalog/PIA25900