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What is the Richat Structure - "The Eye of the Sahara"?

The Richat structure, also known as the Eye of the Sahara, or Guelb er Richât, is one of the largest natural formations on our planet. It is so large that it can best be seen from space. It is a geological marvel whose history spans over more than 100 million years.


What is the Richat Structure?

The Richat Structure is a large circular geological formation in the Sahara Desert in Mauritania, Africa. It is approximately 40 km (that’s around 25 miles) in diameter. Because of its wide span, it wasn’t discovered until the beginning of space exploration.


The first people to see this geological wonder were James McDivitt and Edward White, the two astronauts of the Gemini 4 mission, in 1965. Thanks to space exploration, we are able to learn more and more about our planet and its many marvels, such as the Richat Structure. Based on its round shape with its concentric circles, you would probably first think that it’s either an ancient volcano or a crater made by the impact of some huge meteorite that hit Earth in the distant past. But none of these are the causes of the Richat structure.


How was the Richat Structure formed?

To answer that question, we have to go back in time by about 100 million years. We’re going all the way back to Pangaea. Before the continents we have today started forming and getting the shape they have today, our planet had mainly one large landmass—a supercontinent called Pangaea. When Pangea was the only continent on Earth, it was surrounded by a single ocean called Panthalassa.


Around 200 million years ago, Pangea started breaking apart. As it separated into several large landmasses, these landmasses started migrating to different areas around the globe, and they eventually became today’s continents. We now know that plate tectonics is the reason behind the breaking of Pangea.


Plate tectonics is a scientific theory that says that the lithosphere, which is the Earth’s outer layer, is made up of large rigid plates that are moving. The movement of the tectonic plates is enabled by the fact that they are sitting on a layer of magna. These plates are either moving away from one another in some regions, or coming closer in other regions, or they can be sliding along one another.


As the landmass that is currently South America started separating from the area that is present day Africa, it caused the lithosphere in that region to weaken. This happened around 100 million years ago. With the weakening of this outer layer, the magma beneath it started raising up, pushing upwards the crust above it. This lead to the creation of a geologic dome made up of the rocks that were present in the area, with the center of the dome containing the oldest rocks, and the younger ones being on the outskirts of the dome.


The shape of the Richat Structure

Over time, the dome, like every other natural formation, was subjected to different weathering conditions, such as the action of wind and water. And before you ask, "What water? It’s the Sahara desert", remember that this process started happening about 100 million years ago. At that time, the region was not a desert, but it had a much more temperate climate, water not being as scarce as it is today. So both wind and water acted as weathering agents on the rocks of the dome, forming the Richat Structure as we see it today.

The erosion of the Richat Structure happened over millions and millions of years. So nature had plenty of time to shape the dome into what it looks like today - a series of concentric circles made up of alternating ridges and valleys.

The reason behind the presence of ridges and valleys is the variation in the rock composition of the original dome that got eroded over time. The harder, igneous rocks were less affected by the weathering conditions, and thus were less eroded. Igneous rocks are rocks made of cooled and crystalized magma. Some of the igneous rocks found in the Richat structure include kimberlite, carbonatite, black basalt, and rhyolite. These igneous rocks are making up the taller areas in the Eye of the Sahara.


The valleys are regions made up of softer, sedimentary rocks, like sandstone, which are more affected by the weathering conditions. The stronger erosion of these rocks lead to the valleys int he Eye of the Sahara.


In conclusion, it took the splitting of continents, the action of magma, and the erosion of rocks by water and wind over a hundred million years to get the Richest structure to look as it does today. The Eye of the Sahara is a marvel, not just in its sight, but also in its history.