ISS038-E-26862

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Spacecraft nadir point: 16.9° N, 6.9° W

Photo center point: 17.2° N, 11.6° W

Nadir to Photo Center: West

Spacecraft Altitude: 225 nautical miles (417km)
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Image Caption: Western Sahara Desert, Mauritania

This astronaut photograph of infrequent cloud bands over southern Mauritania was taken from the International Space Station 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 image 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 m high, with a field of orange-colored dunes at the base (image 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 dunefields 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.