STS-099 Earth Sciences and Image Analysis Photographic Highlights

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STS099-729-45

STS099-729-45         Click the photo number to access all resolutions available and the database record.

Erg Chech Dunes, Algeria: Linear dunes in the Algerian Saharan sand sea known as the Erg Chech, have been built up over thousands years into masses elongated roughly parallel with the prevailing northeast winds. Dune chains in the northern (upper) half of the view are 5-8 km apart. A slight change in orientation and an increase in the density of dunes appears across the middle of the view. Such changes usually relate to changes in sand supply, and also to topographic scarps over which the dunes pass. Obstacles like scarps and hills locally cause a leftward deflection (in the northern hemisphere) in wind direction, an effect which can be seen here in the dune orientation in the middle of the photo. Dunes in the lower part of the view are 2-5 km apart. White patches are small dry lakes at low points in the underlying rock surface. The strong red color in some dunes near the edge of the dune field (left margin) is iron staining derived from sand particles blown into the dunes from the underlying iron-rich soils. A dune free area appears in the lower left corner.

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