|In this photo sand and ice are cascading down the slipface of a dune,|
covering seasonal ice. The arrow points to a small cloud of dust kicked
up by this cascading.
Sand dunes have a windward side, where the sand is pushed up onto the dune, and a slip face on the lee side. Sand moves on the dunes by saltation (bouncing) and avalanching (called "grainfall" in this Science article). On earth, they have a variety of shapes and, in spite of the differences in climate, have similar morphologies on Mars.
|Kelso dunes in the Mojave desert, California,|
Photo by Mark A. Wilson, Wiki