Weak Winds Cause Slow Dunes

Sand dunes on Mars are apparently not in any rush to get anywhere. New evidence suggests that on Mars, sand dunes move in glacier-like fashion, i.e. slowly. It takes wind up to 75mph to move a 3ft high sand dunes and this type of wind is rare on Mars. While it is a common occurrence to have windstorms on Mars, the winds are usually not strong enough to have any effect on the dunes. This is because the atmosphere on Mars is 100times less dense than the earth's atmosphere. The picture below slow dunes formed around a crater on Mars.
http://www.space.com/scienceastronomy/071113-scitues-slowpoke-mars-dunes.html