In the Sahara Desert of northwest Africa, in the country of Mauritania, lies a 25-mile-wide, bullseye-shaped “thing” carved from the very rock itself. This Saharan cyclops had scientists scratching their heads until relatively recently.
Known variously as the Eye of Africa, Eye of the Sahara, or the Richat Structure, this geologic oddity was long believed to be an ancient impact feature because of its tremendous size and crater-like shape. Research conducted in the 1960s, however, found insufficient amounts of melted rock to support that theory.
Might it be the crater of an extinct volcano, then? No, as it turns out, although volcanism is the key to understanding its origin.
It seems that about 100 million years ago,volcanic pressure deep within the earth pushed the overlying geologic layers upward - not enough to penetrate the surface as an eruption, but enough to form a large symmetrical dome.The layers of rock, some of which were harder than others, were distorted upward from their horizontal plane to form the shape of the dome. Water and wind then went to work on the exposed layers, eroding the softer layers first to create the valleys. The harder layers resisted erosion to form the ridges that define this feature’s eye-conic pattern of concentric rings. Geologists call this process differential erosion.
Astronauts have a special place in their hearts for the Eye of Africa, and have used it as a ground reference ever since the NASA Gemini missions in the mid 1960s.