Cracks in a Debris Apron

This observation from NASA Mars Reconnaissance Orbiter shows the nature of large fissures in a smooth apron around a mound in the Phlegra region.

The apron could be (or could have been) ice-rich, so one possibility is that the fissures are related to ice loss. Based on radar data from MRO combined with studies of the region's geology from other orbiters, scientists think that extensive glaciers covered this region several hundred million years ago.

http://photojournal.jpl.nasa.gov/catalog/PIA19307