Western Sahara Desert As Seen From Orbit

The Western Sahara Desert is featured in this image photographed by an Expedition 38 crew member on the International Space Station.
The infrequent cloud bands over southern Mauritania were photographed with an oblique look angle so that the dark cloud shadows are also a prominent part of the view. Beneath the cloud the Aouker plateau of dark sedimentary rocks appears as a ragged, near-vertical escarpment at top right.

Isolated remnants of the plateau appear as dark mesas (flat-topped hills) across the top and near the center of the image. The escarpment is about 250 meters high, with a field of orange-colored dunes at the base (upper right). Prevailing winds in this part of the Sahara Desert blow from the northeast. The wavy dunes are aligned transverse to these winds.

The sand that makes the dunes is blown in from a zone immediately upwind (just out of the bottom of the image) where dry river beds and dry lakes provide large quantities of mobile sand for the wind to transport. This pattern is typical in the western Sahara Desert, where plateau surfaces are mostly dune free and dune fields are located in the surrounding lowlands where the larger rivers deposit quantities of sandy sediment on the few occasions when they flow-sometimes only once in decades.

ISS038-E-026862 (8 Jan. 2014) – Larger image