Sahara

Although we tend to think that the unknown is in space and we focus our exploration on what is outside the Earth, our planet continues to surprise us: from the 50,000 volcanoes hidden in the seabed to shapes and constructions that seem too curious to have appeared out of nowhere… especially when we see them from space. It is the case of Great Dam of Zimbabwe (which by the way, is not a dam). We are not leaving the African continent because there is another scar of land with a shape so precise that it is disconcerting. It can’t be seen from the ground, but as you gain height it can be seen better. However, it is from space where it is best appreciated, as NASA has already photographed. There it is simply shocking: it is the inexplicable eye of the Sahara. It is a kind of giant eye that looks at the sky engraved in the rock of the Sahara, it is actually called Richat structure. As says French astronaut Thomas Pesquetalmost all astronauts have taken a photo of it from space simply because it can’t be missed. The Britannica Encyclopedia assures that World War II pilots used it as a reference point. Tap to go to the post After all, they are almost 50 kilometers in diameter. To get an idea, if we moved it to Madrid, it would cover the entire city and reach surrounding municipalities. However, it is in Mauritania, at the western end of the Sahara. More specifically, it sits on the Adrar plateau, on the northwestern edge of the Taoudenni basin, about 500 meters above sea level and in an inhospitable area. As a curiosity, the closest town is Ouadane, it is about 17 kilometers from the edge of the structure and it is not just any city: it was founded in 1147 by the Idalwa el Hadj Berber tribe and its old part has been a UNESCO World Heritage Site since 1996. The first time we “discovered” it (that is to say, because it was already there) was in the 1930s and 1940s and the person who studied it in depth at that time was the French geographer Jacques Richard-Molard. Later, astronauts James McDivitt and Ed White, aboard the Gemini IV mission, were the first to photograph it from space in 1965. However, the image that illustrates the cover was taken on July 10, 2020 by an astronaut aboard the International Space Station, during the Expedition 63 mission, with a Nikon D5 camera with a 50 millimeter lens. Richat’s structure from the inside. Clemens Schmillen What is the Richard Structure and how was it formed? From that orbital height the image shows something that would be impossible to capture from the ground: a series of perfect concentric rings, like the waves left by a stone when it falls into water, but petrified in the desert. The tones of that figure range from ocher to bluish gray, from almost pristine white to rusty red. Each color is a different rock and belongs to a different era. Surrounding the structure, a sea of ​​dunes: on the right, longitudinal dunes that stretch in long parallel tongues and on the left, transverse dunes, wider and more arched. The set is truly strange to have formed naturally. POT Because it is not a lake that has dried up over time. It is neither a volcano nor the crater of a meteorite (the hypothesis which was most popular initially). It’s something much slower but just as violent: is the result of millions of years of geological forces working silently beneath the planet’s surface. And although the group as such was formed about 100 million years ago, those rocks are up to 2.5 billion years old. Or in other words, the Eye of the Sahara was forged in the Cretaceous, but the rocks belong to the time when there were no animals, only bacteria and algae. The Richat Structure is a deeply eroded geological anticline dome that was formed by a subsurface igneous intrusion, which deformed the overlying sedimentary rock layers, exposing concentric rings with the oldest rocks in the center. In a simplified way, a bubble of rock that never burst: the magma from inside the Earth pushed up the layers of rock above it and cooled without reaching the surface. The passage of time eroded that bubble as if it were an onion, exposing the rings of each layer. The hardest rocks resisted and formed the relief, the soft ones disappeared. Hence the circles. The most recent studies They confirm that there was also hot water circulating inside the structure, which accelerated and modeled the final shape. In Xataka | A 2.5 billion-year-old geological wonder: Zimbabwe’s Great Dam seen by NASA from space In Xataka | This is the impressive interactive map to see the Earth in 4K live from space and monitor satellites Cover | POT