The steep lee sides of the dunes are also ice-free along the crest, allowing sand to slide down the dune. Dark splotches are places where ice cracked earlier in spring, releasing sand. Soon the dunes will be completely bare and all signs of spring activity will be gone.
This image was acquired by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter on January 16, 2014. The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies, Boulder, CO. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for the NASA Science Mission Directorate, Washington.