#PPOD: In this HiRISE image of #Mars, many sand dunes are visible. They have an elongated crescent form and are called "barchan dunes." They are formed by the continuous action of the wind, blowing in the same direction, giving this particular shape.
The orientation of these dunes tells us that the prevailing wind blows from the right to the left (east to west). The wind continuously moves sand grains up the longer dune slope towards the top.
