Frosty Alcoves on Kaiser Crater Dunes

Kaiser Crater hosts a large field of sand dunes. Every winter the dunes are covered with a layer of seasonal carbon dioxide ice (dry ice). In early spring the ice begins to sublimate (going directly from solid ice to gas).

In this image, the dunes are partially free of seasonal ice, with the contrast making it easy to see the ripples. Deep alcoves have been carved at the crest of the dune. We hypothesize that this is the result of the gas coming from the dry ice, destabilizing the sand at the crest. As blocks of ice protected in the cold shadows of the alcove break off they slide downslope, carving the channels we see.

http://photojournal.jpl.nasa.gov/catalog/PIA21038