Seasonal changes on Mars

From early spring, on the left, through the Martian winter, changes can be seen on the sand dunes of Mars. A layer of carbon-dioxide ice, better known to us as dry ice, about 2 feet thick, begins to crack, and exposes dark sand below, as seen in the second panel.

Rising gasses, which had been trapped below the ice layer, then bring sand and dust to the surface, where it is deposited in a fan-shaped formation downhill and downwind, exhibited in the third and fourth panels.

The final panel shows more of the exposed dark dunes as the overlying layer of seasonal ice evaporates back into the atmosphere.