English: NASA Photograph, Public Domain.

http://earth.jsc.nasa.gov/sseop/EFS/lores.pl?PHOTO=STS052-82-7

The Erg of Bilma

STS052-082-007 Sandy Desert, Eastern Chad October 1992

The scene displayed in this high-oblique, southeast-looking photograph, which points toward the Ennedi Plateau (darker structure toward the horizon) of eastern Chad, is part of the great Sahara Desert. This photograph shows vast quantities of sand and several major corridors where sand continually moves across a landscape that has little or no vegetation. The only impediments to the sand, which is moved by the prevailing northeasterly winds, are the darker, fragmented remnants of resistant sandstone rock outcrops. The reds, yellows, and oranges identify the various sand colors in the region. The somewhat linear, uniform bands are depressions where massive deposits of sand have accumulated. It is through these "sand valleys" that much of the blowing sand is channeled during sandstorms. This photograph helps explain why this hostile environment does not promote the establishment of permanent human settlements.