The Richat Structure, Mauritania – April 24th, 2009
The Ras Nouadhibou Peninsula (upper left) marks the border Morocco’s Western Sahara (above) and Mauritania (below). The Gulf of Arguin, lies just south of the peninsula.
Another border, between Mauritania and Senegal, is marked by the Senegal River.
Moving inland from the Atlantic Ocean into Mauritania, an odd, circular feature can be observed (open full image for best view). This is the Richat Structure, a prominent ringed indentation in the Sahara desert near Ouadane.
It 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. The structure has a diameter of almost 50 kilometres (30 miles).
Initially interpreted as a meteorite impact structure because of its high degree of circularity, it is now thought to be a symmetrical uplift (circular anticline or dome) that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure.
The close-up image is a false-colored topographic reconstruction from satellite photos. The false coloring shows the geological composition and vegetation of the area using the following color scheme: bedrock is brown, sand is yellow or white, vegetation is green, and salty sediments are blue.