What Exactly Is the Eye of the Sahara, aka the Richat Structure?

Aerial view of red, rocky mountains in concentric circles — At first glance, the Eye of the Sahara, or Richat Structure, resembles a giant bullseye, with the sedimentary rock formation's concentric rings and circular ridges. GLF Media / Shutterstock

In the western Sahara Desert lies a natural wonder that has intrigued scientists and adventurers for centuries. Known as the Richat Structure — or, more commonly, the Eye of the Sahara — this massive geological formation resembles a giant eye.

Consisting of a series of rings on the Adrar Plateau, a prominent feature in northwestern Mauritania, the structure measures 31 miles (50 km) in diameter, making it highly visible even from high above Earth. In the local dialect of Arabic, the people refer to it as "Guelb er Richât," meaning "the eye of the Richat."

But what created the Eye of the Sahara, and what purpose does it serve today? Let's delve deeper into these mysteries to shed light on the ancient structure.

What Created the Eye of the Sahara?

At first glance, the Richat Structure resembles a giant bullseye, with its concentric rings and circular ridges. This distinctive circular shape sparked various early theories about its formation, with one theory even being that it was the site of the lost city of Atlantis.

Although some experts initially thought the Eye of the Sahara to be an enormous impact crater, subsequent studies proved the geologic curiosity had a more complex origin involving terrestrial processes.

Thanks to modern geological research, including satellite imagery provided by organizations like the NASA Earth Observatory, scientists now know it to be an uplifted geologic dome, characterized by layers of sedimentary rocks that have been exposed over millions of years by wind and water erosion.

Composition of the Eye of the Sahara

The formation's concentric rings are primarily composed of sedimentary rocks, including sandstone and limestone. The outer ring of the structure is composed of harder, more resistant rock layers, while the innermost depressions consist of softer rock layers that have eroded more rapidly over time.

These sedimentary layers offer a glimpse into the Earth's past, recording millions of years of geological history. As hard as it may be to imagine moisture in the Sahara Desert, the circular ridges of the Richat Structure have helped scientists study both wet and dry periods in the area's history.

The Eye of Sahara features an underlying alkaline igneous complex, including igneous rocks called gabbroic rocks, which form as a result of magmatic activity and hydrothermal alteration.

That's a fancy way of saying that the Earth's material became so hot it turned into magma, or liquid rock, and then forced itself into the surrounding rocks, slowly cooling into a crystalline structure.

Erosion, both by wind and water, has also helped to sculpt the Richat Structure into its present form, exposing different rock types and creating its concentric layers and circular shape. Differential erosion rates between the softer and more resistant layers have further contributed to the striking appearance of the formation today.

Scientific Significance of the Eye of the Sahara

One of the most fascinating aspects of the Richat Structure is its resemblance to an enormous eye when you view it from space. This unique feature has captured the attention of scientists and astronauts alike. The Gemini astronauts captured images on the Gemini IV mission, and astronauts on the International Space Station have photographed the Eye of the Sahara too.

The Richat Structure's geological significance extends beyond its visual appeal. It provides valuable insights into Earth's geological processes, including the effects of tectonic forces, erosion and magmatic activity. Additionally, the presence of sedimentary layers has yielded evidence of past environments and possibly even early human activity.

Some researchers speculate that the Richat Structure may have been inhabited by early hominids such as Homo erectus or Homo heidelbergensis. They've found evidence of stone tool manufacturing, including Acheulean tools (such as hand axes), in the surrounding landscape, suggesting that early people might have used this area of the Sahara Desert for short-term hunting or habitation.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.