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 Desert of Egypt (photograph by Carol Breed).
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.
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).