Sand dunes

Sand dunes can range from 3 feet (1 meter) to greater than 650 feet (200 meters) in height. Star dunes, which have one central peaked mound with radiating ridges, can grow as high as 1,000 feet (300 meters).

The type of dune that most people are familiar with from photographs and motion pictures is the barchan dune. Barchan dunes are formed by winds blowing in a nearly constant direction and moderate speed across relatively flat land with only a shallow layer of sand. These dunes, when viewed from above, resemble crescent moons, with the tips of the crescent pointing downwind. They have convex (curved outward) backs and steep, concave (curved inward) faces. A barchan dune may grow as tall as a several-story building.