The Richat Structure is a 50-kilometer-wide (30-mile) circular geological formation in the Sahara desert of Mauritania, often called the “Eye of Africa” or “Eye of the Sahara.” Visible from orbit as a striking bull’s-eye pattern on an otherwise featureless desert, it is not a meteorite impact crater, as scientists once suspected, but an eroded dome of ancient rock pushed upward by magmatic activity at least 100 million years ago.
Where It Is
The structure sits at 21.4 degrees North latitude, 12.0 degrees West longitude, in the central part of Mauritania’s Adrar plateaus. The nearest settlement is Ouadane, roughly 20 miles away. The ancient library town of Chinguetti lies about 76 miles to the southeast. From the ground, the feature is difficult to recognize as a circle. Its prominent outer cliffs rise about 300 meters (1,000 feet), while the central rings stand roughly 80 meters (260 feet) above the surrounding terrain. Sand dunes of similar height fill parts of the depression.
How It Formed
The Richat Structure is a domed anticline: a place where molten rock pushed the Earth’s crust upward, bowing flat-lying sedimentary layers into a broad dome. This magmatic activity occurred during the Cretaceous Period, somewhere between 145 and 66 million years ago. Over the tens of millions of years that followed, wind, sand, and water stripped away the dome’s surface layer by layer, carving out its concentric ring pattern.
The rings exist because the dome contains different types of rock stacked in alternating layers. Quartzite, which is extremely hard, resists erosion and forms the raised ridges you can see today. Softer rocks like shale and sandstone wore away much faster, leaving valleys between the quartzite rings. The result is a geological bull’s-eye where harder layers stand proud and softer layers have been carved into depressions.
The sedimentary rocks exposed by this erosion are far older than the dome itself. Some date back roughly 600 million years, to the Late Proterozoic and early Paleozoic eras, when the region was part of a vast sedimentary basin called the Taoudeni basin.
What’s Inside the Rings
The Richat Structure is more complex than a simple eroded dome. Its center contains a kilometer-scale mega-breccia, a massive jumble of shattered rock fragments cemented together. This central breccia sits within a limestone and dolomite shelf and was likely created by a collapse event tied to underground hydrothermal activity. Hot fluids circulating through the rock dissolved portions of the limestone, creating cavities that eventually caved in.
Cutting through the sedimentary layers are multiple types of igneous rock that record different episodes of magmatic activity. Two concentric ring-shaped intrusions of a dark, dense rock called gabbro were likely emplaced between 230 and 200 million years ago. These are crosscut by younger volcanic features: dikes of calcium-rich volcanic rock (carbonatites, dated to roughly 85 to 99 million years ago), a plug of diamond-bearing volcanic rock called kimberlite, and remnants of two explosive volcanic vents. An intense episode of low-temperature hydrothermal activity also altered rocks throughout the area, changing the chemistry of the gabbros and enriching the carbonatites.
Why It’s Not an Impact Crater
When geologists first studied the Richat Structure in the 1960s, its size and circular shape made a meteorite impact seem like a reasonable explanation. A French team even reported finding coesite, a mineral that forms only under the extreme pressures of an impact event. But that finding was later shown to be a misidentification: what they had actually found was barite, a common mineral with no connection to impacts.
Subsequent ground surveys found none of the signatures that define an impact crater. There were no shatter cones (cone-shaped fracture patterns in rock caused by shock waves), no overturned or upturned rock layers at the rim, no injected breccias or glassy melt rocks, and no microscopic evidence of shock metamorphism in any of the samples examined, including those from the central breccia. The scientific consensus today is clear: no evidence remains that could link the Richat Structure to an impact origin. It is a complex igneous and sedimentary feature shaped by uplift, volcanic intrusion, and millions of years of erosion.
The Atlantis Connection
The Richat Structure has become a popular candidate for the lost city of Atlantis in online communities. Proponents point to Plato’s description of a central island surrounded by concentric rings of water and land, arguing that the structure’s dimensions and geography are a match. Some cite alleged satellite surveys showing buried structures and ancient maps that place a civilization in the region.
The geological evidence doesn’t support the idea. The concentric rings are natural formations created by differential erosion of rock layers, not engineered waterways. No artifacts, building foundations, or other evidence of a large settlement have ever been found at the site. While it’s true that the Sahara was wetter thousands of years ago, with some sediments in the area dating to between 15,000 and 8,000 years before present, this doesn’t change the fact that the structure itself is a geological feature at least 100 million years old, formed by processes deep underground.
Seeing It from Space and from the Ground
Astronauts have photographed the Richat Structure repeatedly from the International Space Station, where it serves as a recognizable landmark in the otherwise monotonous expanse of the western Sahara. NASA has used satellite imagery and elevation data to produce detailed topographic views of the feature.
Visiting in person is a different experience. From ground level, the structure is too large to perceive as a circle. What you see instead are rocky ridges, desert flats, and cliff faces. The nearest town, Ouadane, is a UNESCO World Heritage Site with a centuries-old mosque, and the medieval library town of Chinguetti is also within reach. Getting there requires overland travel through remote desert, typically with a local guide and a four-wheel-drive vehicle. There is no formal visitor infrastructure at the site itself.