Image:Dune in Namibia.jpg

Crescent Dune, Namibia

These dunes form under winds that blow from one direction,
and they also are known as barchans, or transverse dunes.
Some types of crescentic dunes move faster over desert
surfaces than any other type of dune. A group of dunes
moved more than 100 meters per year between 1954 and 1959.