When I was wandering aimlessly through the desert of west–central Mauritania (via Google) I stumbled upon this massive round structure and immediately assumed it was an impact crater.
The huge 40-kilometer diameter circular structure is also known as the Eye of the Sahara or Guell al-Richat. The eye emerged from differential erosion.
For a while, scientists did think that the Eye of the Sahara was an impact crater. But they didn’t find enough melted rock to make that guess hold water. Current theories suggest a much more complicated story behind this incredible natural formation.
The main ring structure of the Eye is the eroded remains of what was once a dome of layers of the Earth’s crust.
The current theory on how it formed
Scientists still have questions about the Eye of the Sahara. But two Canadian geologists have a working theory about its origins.
They think the Eye’s formation began more than 100 million years ago, as the supercontinent Pangaea was ripped apart by plate tectonics and what are now Africa and South America were being torn away from each other.
Molten rock pushed up towards the surface but didn’t make it all the way, creating a dome of rock layers, like a very large pimple. This also created fault lines circling the Eye and crossing it. The molten rock also dissolved limestone near the center of the eye, which collapsed to form a special type of rock called breccia.
A little after 100 million years ago, the Eye erupted violently. That collapsed the bubble partway, and erosion did the rest of the work to create the Eye we know today. The rings are made of different types of rock that erode at different speeds. The paler circle near the center of the Eye is volcanic rock created during that explosion.
Modern astronauts are fond of the Eye because so much of the Sahara Desert is an unbroken sea of sand. The Eye is one of the few breaks in the monotony, and now it’s become a key landmark for them.
http://gizmodo.com/the-eye-of-the-sahara-is-an-enigmatic-desert-landmark-1607604961
