Science Snap (#28): The Eye of the Sahara

Originally posted on the EGU blog network

Eye of the Sahara, Geology
The Eye of the Sahara. Image credit: NASA

Surrounded by thousands of square miles of ubiquitous desert, the “Eye of the Sahara” peers out from the Earth’s surface and at nearly 50 km wide, its easily visible from space too. The “Eye of the Sahara” is known as a Richat Structure, a geological feature consisting of a series of alternating circular layers of sedimentary, igneous and metamorphic rock, exposed by erosion.

The “Eye of the Sahara” is located in central Mauritiana and is also known as Guelb er Richat. The sheer size of the Eye meant it wasn’t discovered until space exploration took off. So here’s a challenge, find it on Google Earth.

The “Eye of the Sahara” was formed by a magmatic intrusion, which forced its way up and warped the overlying rock layers into a dome shape. The intrusion initially never reached the surface, but now erosion has effectively sliced dome’s top off, exposing its inner structure.

The Eye is extremely symmetrical, a striking feature that led scientists to interpret it as an impact crater. This idea was dismissed, however, when scientists began researching its structure. Nevertheless, scientists still can’t explain exactly why the Eye is so symmetrical.

The layers of rock inside the eye are visually distinct as each varies in colour, composition, and resistance to erosion. Inside the Eye there is a rich variety of geological rocks, including rhyolites, gabbros, carbonatites and kimberlites. Quartzite layers are highly resistant, but breccias and volcanic rocks are more prone to weathering and erosion. Intrusive kimberlite plugs beneath the Eye suggest the presence of deep and large alkaline magmatic intrusions and was likely responsible for uplifting the Eye.

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