Caption: 
The airborne plumes of dusty material located on the downwind slope of this Martian megadune were an important clue, allowing an SwRI scientist to deduce that chunks of frozen CO2, or dry ice, slide down the gullies in the spring, kicking up sand and dust. While actively sliding CO2 ice blocks cannot be observed conclusively in this image, dense clouds of debris likely conceal mobile ice blocks. 

Credit: 
Courtesy of NASA/JPL/University of Arizona