By drying the Aral Sea, humanity has changed the very structure of the land – Liberation

« It seems that humanity Disturbed plates tectonics just to improve cotton yields! ” Summarizes Simon Lamb, researcher in geosciences at the University of Wellington, New Zealand. The drying up of the Aral Sea, in Central Asia, was not only an ecological disaster. It also has affected the movement of rocks tens of kilometers below the surface of the earth, according to a study published this Monday, April 7 in Nature Geoscience.

Located between Kazakhstan and Uzbekistan, the Aral Sea was until the late 1950s the fourth largest lake in the world. The diversion of its two tributaries, Syr-Daria and Amou-Daria, mainly for the cultivation of cotton and rice under the Soviet Union, essentially transformed it into a desert of sand and salt.

Between 1960 and 2018, its surface decreased by 90 % and its volume by 93 %. A « Silent Chernobyl » who had « Deep ecological and economic impacts »killing many animal species and practically ending human activities, recall the authors of the study. According to them, the consequences of this disaster were not only limited to the surface of the earth, but are also felt in the depths of the planet.

Teng Wang, lecturer at the School of Earth Sciences and Space at the University of Beijing, and his colleagues analyzed the deformation of the soil in the Aral Sea basin between 2016 and 2020. Thanks to radars, they measured with millimeter precision the differences in the position of the soil during repeated passages above the Sentinel-1 European Satellite area.

Before the Aral Sea narrowed, the weight of the water was large enough to sink the earth’s crust below. In just a few decades, 1,000 billion tonnes of water were evaporated. Scientists therefore expected the « rebounded » crust while the lake was hoped, « Like a compressed spring that has been released »explains Teng Lamb. But scientists found that the old lake bed has continued to rise at an average rate of around 7 millimeters a year, even after its drying up. And this elevation is observed in a large area extending up to 500 km from the original center of the sea.

According to their simulations, the explanation of the phenomenon is more than 150 km below the surface, in the Astenosphere, a layer of the coat located under the rigid crust of the earth. The hot rock is slowly deforming there under pressure, moving the tectonic plates that float above.

During its splendor, the long pressure exerted by the Aral Sea has moved part of the astenosphere. Having become an extremely viscous fluid, this rock is now returning to the location it occupied before the existence of the lake, at a speed comparable to the movement of tectonic plates. And it will continue for many decades. These results show how human activity can influence the earth even in the upper mantle and, therefore, cause changes to the surface, conclude the authors.