The Blue Eye of the Sahara, also known as the Richat Structure or the Guelb er Richat, is a geological formation in the Sahara Desert that resembles an enormous bullseye. The formation stretches across a 40 kilometer-wide region of the desert in the nation of Mauritania.

Key Takeaways: The Eye of the Sahara The Eye of the Sahara, also known as the Richat Structure, is a geologic dome containing rocks that predate the appearance of life on Earth.

The Eye resembles a blue bullseye and is located in Western Sahara. It is visible from space and has been used as a visual landmark by astronauts.

Geologists believe that the Eye's formation began when the supercontinent Pangaea started to pull apart.

For centuries, only a few local nomadic tribes knew about the formation. It was first photographed in the 1960s by the Gemini astronauts, who used it as a landmark to track the progress of their landing sequences. Later, the Landsat satellite took additional images and provided information about the size, height, and extent of the formation.

Geologists originally believed that Eye of the Sahara was an impact crater, created when an object from space slammed into the surface. However, lengthy studies of the rocks inside the structure show that its origins are entirely Earth-based.

A Unique Geological Wonder

Geologists have concluded that the Eye of the Sahara is a geologic dome. The formation contains rocks that are at least 100 million years old; some date back to well before the appearance of life on Earth. These rocks include igneous (volcanic) deposits as well as sedimentary layers that form as the wind pushes layers of dust and water deposits sand and mud. Today, geologists can find several types of igneous rock in the area of the eye, including kimberlite, carbonatites, black basalts (similar to what can be seen in the Big Island of Hawai'i), and rhyolites.

Millions of years ago, volcanic activity from deep beneath Earth's surface lifted the entire landscape around the Eye. These regions were not deserts, as they are today. Instead, they were likely much more temperate, with abundant flowing water. Layered sandstone rocks were deposited by blowing winds and on the bottoms of lakes and rivers during the temperate. The subsurface volcanic flow eventually pushed up the overlying layers of sandstone and other rocks. After the volcanism died down, wind and water erosion began to eat away at the domed layers of rock. The region began to settle down and collapse in on itself, creating the roughly circular "eye" feature.

Traces of Pangaea

The ancient rocks within the Eye of the Sahara have provided researchers with information about its origins. The earliest formation of the Eye began when the supercontinent Pangaea began to pull apart. As Pangaea broke up, the Atlantic Ocean waters began to flow into the region.

While Pangaea was slowly pulling apart, magma from deep beneath the surface began to push up from the Earth's mantle, which formed a circle-shaped rocky dome surrounded by layers of sandstone. As erosion took its toll on the igneous rocks and sandstones, and as the dome subsided, circular ridges were left behind, giving the Richat Structure its sunken circular shape. Today, the eye is somewhat sunken below the level of the surrounding landscapes.

Seeing the Eye

Western Sahara no longer has the temperate conditions that existed during the Eye's formation. However, it is possible to visit the dry, sandy desert that the Eye of the Sahara calls home—but it's not a luxurious trip. Travelers must first gain access to a Mauritanian visa and find a local sponsor.

Once admitted, tourists are advised to make local travel arrangements. Some entrepreneurs offer airplane rides or hot air balloon trips over the Eye, giving visitors a bird's-eye view. The Eye is located near the town of Oudane, which is a car ride away from the structure, and there is even a hotel inside the Eye.

The Future of the Eye

The Eye of the Sahara attracts both tourists and geologists, who flock to the Eye to study the unique geological feature in person. However, because the Eye is located in a sparsely inhabited region of the desert with very little water or rainfall, it is not under much threat from humans.

That leaves the Eye open to the vagaries of nature. The ongoing effects of erosion threaten the landscape, just as they do other places on the planet. Desert winds may well bring more dunes to the region, particularly as climate change causes increased desertification in the area. It's quite possible that, in the distant future, the Eye of the Sahara will be inundated with sand and dust. Future travelers may find only a windswept desert burying one of the most striking geological features on the planet.