Types of Dunes

Ripples on a dune in Eureka Valley, California

Ripples on a dune in Eureka Valley, California (photograph by Terrence Moore).
A worldwide inventory of deserts has been developed using images from the Landsat satellites and from space and aerial photography. It defines five basic types of dunes: crescentic, linear, star, dome, and parabolic.

The most common dune form on Earth and on Mars is the crescentic. Crescent-shaped mounds generally are wider than long. The slipface is on the dune's concave side. 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 in China's Ningxia Province; similar rates have been recorded in the Western Desert of Egypt. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than 3 kilometers, are in China's Taklimakan Desert.
Crescentic dunes in coastal Peru

These crescentic dunes of coastal Peru are migrating toward the left (photograph by John McCauley).

Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. They may be more than 160 kilometers long. Linear dunes may occur as isolated ridges, but they generally form sets of parallel ridges separated by miles of sand, gravel, or rocky interdune corridors. Some linear dunes merge to form Y-shaped compound dunes. Many form in bidirectional wind regimes. The long axes of these dunes extend in the resultant direction of sand movement.

Linear dunes in Australia's Simpson Desert Linear dunes in desert of western Egypt

Linear dunes advance on small playas east of Lake Eyre in the Simpson Desert of central Australia (photograph by C. Twidale).

Linear dunes in the western deserts of Egypt (photograph by Carol Breed).

Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around the margins of the sand seas, particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 meters tall and may be the tallest dunes on Earth.

Star dunes in the Namib

Star dunes, such as these of the Namib, indicate the winds that formed them blew from many directions (photograph by Georg Gerster).

Oval or circular mounds that generally lack a slipface, dome dunes are rare and occur at the far upwind margins of sand seas.

U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. Sometimes these dunes are called U-shaped, blowout, or hairpin dunes, and they are well known in coastal deserts. Unlike crescentic dunes, their crests point upwind. The elongated arms of parabolic dunes follow rather than lead because they have been fixed by vegetation, while the bulk of the sand in the dune migrates forward. The longest known parabolic dune has a trailing arm 12 kilometers long.

Crescentic dunes in Saudi
Arabia's Empty Quarter Cresecentic dunes in Egypt
Small crescentic dunes occur on the crests of these complex dome dunes of Saudi Arabia's Empty Quarter (photograph by Elwood Friesen). Ripples and horns of this crescentic dune in Egypt indicate that the dune is moving right to left (photograph by John Olsen).

Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above types. These dunes typically have major and minor slipfaces oriented in opposite directions.

All these dune types may occur in three forms: simple, compound, and complex. Simple dunes are basic forms with a minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed, and complex dunes are combinations of two or more dune types. A crescentic dune with a star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed.

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Last modified 10/29/97