NASA Photo of Sahara: Richat Structure, Mauritania

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http://www.juancole.com/2014/10/richat-structure-mauritania.html

NASA Photo of Sahara: Richat Structure, Mauritania
By contributors | Oct. 6, 2014
NASA

Richat Structure, Mauritania, Western Sahara Desert

“Richat Structure, Mauritania

This prominent circular feature in the Sahara desert of Mauritania has attracted attention since the earliest space missions because it forms a conspicuous bull’s-eye in the otherwise rather featureless expanse of the desert. Described by some as looking like an outsized fossil in the desert, the structure, which has a diameter of almost 30 miles, has become a landmark for shuttle crews. Initially interpreted as a meteorite impact structure because of its high degree of circularity, it is now thought to be merely a symmetrical uplift that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure.”