I'm 65 years old & fascinated by photography, geology, Africa & space. And yet, in all my life, I've never ever before come across the Eye of the Sahara until this evening.
It is about 40 km in diameter, and best seen from space (west–central Mauritania). It seems to be entirely home-grown (not caused by asteroid impact, but rather both igneous--volcanic--and hydrothermal in origin). Magnificat.
The picture above was taken by Chris Hadfield from the International Space Station.
--------- Alex Kemp