The Richat Structure, also known as the Eye of the Sahara or blue eye of Africa, is a prominent geological circular feature in the Sahara desert in Mauritania near Ouadane. From space this mysterious depression really does look like a human eye. The structure is 50 kilometers in diameter, large enough in the featureless Sahara that the earliest space missions used it as a landmark.
At first, scientists thought a meteorite had hit the Earth, causing this impression. But now it is believed to be a natural phenomenon caused by the dome shaped symmetrical uplifting of underlying geology now made visible by millennia of erosion.
Different rates of erosion on the varying rock types have formed concentric ridges; the more erosion-resistant rocks form high ridges (blue and purple), while the non-resistant rocks form valleys (yellow). No one has explained yet why it is circular. Note that this explanation is not wholly accepted by the scientific community.
Some people are amazed by the resemblance of this structure with the representation we have of Atlantis by Plato. According to Plato, the island was circular, divided into concentric circles of land and water.
The inner ring dike is about 20 m in width and lies about 3 km from the center of Richat Structure. The outer ring dike is about 50 m in width and lies about 7 to 8 km from the center of this structure. The dikes are generally about 300 m long and typically 1 to 4 m wide.
They consist of massive carbonatites that are mostly devoid of vesicles. The carbonatite rocks have been dated as having cooled between 94 to 104 million years ago. A kimberlitic plug and several sills have been found within the northern part of the Richat structure. The kimberlite plug has been dated being about 99 million years old.
July 2, 2013
I. C.
