Where is the largest desert in the world? You might answer without hesitation: the Sahara Desert in Africa. Yes, the desert across the North African continent is too big. But did you know that in this desolate desert, there are many unknown secrets hidden. Among them, a circular landscape known as the "Eye of the Sahara" is full of mysterious and eerie colors.
How did this circular geological landscape come about? Why is it called the Eye of the Sahara?
< h1 class= "pgc-h-arrow-right" > astronauts' discovery</h1>
It is the largest desert in the world, the Sahara Desert. It is 5,600 kilometers long from east to west and 1,600 kilometers wide from north to south, with a total area of 9.065 million square kilometers, accounting for 32% of Africa's total area. This huge "bunker" is large enough to accommodate the entire United States.
In the early 1960s, an American space shuttle traveled through space. As they passed over Africa, the astronauts observed a strange phenomenon in space hundreds of kilometers from Earth: a circular object appeared in the southwest of the Sahara Desert that looked like a round eye, staring at people in space. After the Sahara Desert disappeared from their eyes, the astronauts still felt that the "eyes" were firmly staring at them.
This "eye" is known as the "Eye of the Sahara" of the peculiar landscape. In fact, it had long been present in the Western Sahara Desert and had been sleeping in the wilderness and desolation for several years. If the astronaut doesn't "wake up" it in space, it may continue to sleep.
< h1 class= "pgc-h-arrow-right" > huge concentric circles</h1>
Well, let's go and look at that big "eye" now.
The Eye is located in Mauritania in the southwest of the Sahara Desert. It is a huge concentric circle that appears on the ground of the desert. From the air, it is shaped like a rounded eye, and its height is about 400 meters. In the past, it was deserted. Even if someone happens to pass by, it is only "ignorant of the true face of Lushan Mountain only because he is in this mountain." Because "this circle" is so big, it's about 50 kilometers in diameter, and when you're in it, you can't tell if it's a circle or a square. Only astronauts in space or satellites in the sky can see the panorama.
This "concentric circle" resembles an eye, or rather, like an ammonite. Judging from the satellite photographs, it is divided into three layers: the circle in the center resembles an eyeball, and its edges are slightly damaged, but it does not hinder its overall effect; the "eye circumference" is a larger circle, which closely surrounds the central circle, which is the indisputable "pupil"; the outer circle is naturally the "eyelid". What's more, there is also something like a ring on the outer edge of the large circle, like eyelashes.
In the distance of the Sahara Desert, there is a very shallow place surrounded by yellow hills. Standing on the edge of the "Eye", the "Eye of the Sahara" is like a large wooden basin carved from mountain stone, and like a large plate. People walk on the edge of the "eye" like a small ant walking on a huge blue disc.
So, how did this strange landscape come about?
< h1 class="pgc-h-arrow-right" > large craters formed by meteorite impacts? </h1>
Ever since astronauts discovered the "Eye of the Sahara," there has been an endless stream of tourists here. Scientists are trying to uncover the causes of this mysterious landscape.
At first, scientists thought it was a crater formed by a meteorite impact. Because in the Sahara Desert, someone once found a huge crater, 45 meters wide, the deepest point 16 meters above the ground. It is estimated that the meteorite that hit the earth weighed about 5000-10000 kg and fell at a speed of more than 3500 m/ s, and the "Eye of the Sahara", although shallow in depth, had very obvious traces on the ground. According to the analysis, only meteorites can leave a "circle" with a diameter of 50 kilometers on the earth. When a meteorite hits the Earth, the largest side of the surface first touches the ground, forming a large diameter crater, but not deep.
<h1 class= "pgc-h-arrow-right" > look closely at the "Eye of the Sahara."</h1>
However, after further investigation, the scientists found that the theory of meteorite impacts was untenable. Because the terrain at the center of the circle is too flat, there is no geological evidence of high temperatures and effects on the ground.
< h1 class="pgc-h-arrow-right" > the crater formed by a volcanic eruption? </h1>
So, can it be formed by volcanic eruptions?
When a volcano erupts, due to the large amount of karst material erupted, the center of the eruption often forms a circular or oval crater. The largest volcanic crater in the world is located in Mount Aso in Japan. It is 24 km long from north to south, 18 km wide from east to west, and covers an area of 250 square kilometers. It was formed during a violent volcanic eruption 33,000 years ago. There has been speculation that the "Eye of the Sahara" may be similar to the crater of Mount Aso due to the violent eruptions.
However, when scientists analyzed the causes of the volcano, they found that this speculation was untenable. Because volcanoes on Earth generally appear in the cracking and plate subduction zones of the Earth's crust (including the oceanic crust); the location of the "Eye of the Sahara" is part of the Great Desert and is neither a crevasse nor a plate subduction zone, so it is not eligible for volcanic eruptions.
After further investigation, the scientists also found that there are no traces of volcanic eruptions, the local rock is not volcanic rock, and more importantly, there is no dome-like igneous rock accumulation.
< h1 class= "pgc-h-arrow-right" > the result of terrain uplift and erosion</h1>
What was the reason for the formation of the "Eye of the Sahara"? Over the years, people have had different opinions. Some say it's a trace of an alien visit to Earth; some say it's the product of secret nuclear tests by superpowers; others say it's a masterpiece by the Hand of God.
Later, geologists, through extensive exploration, saw this as the result of simultaneous uplift and erosion.
It turned out that beneath the long yellow sand of the Sahara Desert, there were hard rock formations. Hundreds of thousands of years ago, due to geological movements, rocks under the desert were lifted up and stood out from the sand. After the rock formation is exposed to the ground, it gradually forms a huge depression under the erosion of natural wind and sun. Due to the different structures of rock formations, some rocks are very hard and some are relatively soft. Under the same natural conditions, the erosion degree of hard rock is relatively low, especially some Paleozoic quartzites with high hardness and are not easily eroded are basically preserved. Coincidentally, these quartzites form three concentric circles. So, this strange terrain appeared.
However, why is this "eye" so big and so round? Also, why does Paleozoic quartzite appear alone in concentric arcs? Scientists have yet to give a reasonable explanation for these puzzles.