Russell Crater Dunes
Russell Crater is one of many craters in the southern highland region of Mars that contain large areas of sand dunes. The sand in these dunes has accumulated over a very long time period - perhaps millions of years - as wind blows over the highland terrain, picking up sand in some places and depositing in others.
The topography of the craters forces the wind to blow up and over the crater rims, and the wind often isn’t strong enough to keep the tiny grains suspended. This makes the sand fall to the ground and gradually pile up, and over time the surface breezes shape the sand into ripples and dunes.
Credit: NASA/JPL/University of Arizona