Richat Impact Structure of Mauritania from the Space Station by Astronaut Chris Hadfield. He tweeted this photo on 16 Jan: “Undoubtedly one of the coolest space sights on Earth.” Image © Chris Hadfield/NASA
The Richat Structure, also known as the Eye of the Sahara and Guelb er Richat, is a prominent circular feature in the Sahara desert of west–central Mauritania near Ouadane. Initially interpreted as an asteroid impact structure because of its high degree of circularity, it is now argued to be a highly symmetrical and deeply eroded geologic dome.
This structure is a deeply eroded, slightly elliptical, 40-km in diameter, dome. The sedimentary rock exposed in this dome range in age from Late Proterozoic within the center of the dome to Ordovician sandstone around its edges. The sedimentary rocks comprising this structure dip outward at 10°-20°. Differential erosion of resistant layers of quartzite has created high-relief circular cuestas. Its center consists of a siliceous breccia covering an area that is at least 3 km in diameter.