When wind drops its load of sand, it can form a hill called a dune. Dunes are mounds or ridges of sand that are formed by the action of wind. They can be found in many different environments, including deserts, beaches, and coastal areas. Dunes are formed when wind picks up sand and carries it away from its source. The sand is then deposited in a new location, where it can accumulate and form a dune. The shape and size of a dune depend on a number of factors, including the strength and direction of the wind, the amount of sand available, and the presence of vegetation.