A team of Earth scientists affiliated with Peking University and the Southern University of Science and Technology, both in China, and a researcher from the University of Southern California, in the U.S., have found that the land below parts of the Aral Sea that have dried up over the past several decades is slowly rising.

In their paper published in the journal Nature Geoscience, the group describes how they used satellite-based radar readings to monitor the change in altitude of the areas where the Aral Sea used to be filled with water. Simon Lamb, with Victoria University of Wellington, in New Zealand, has published a News & Views piece in the same journal issue, outlining the work done by the team on this new effort.

The Aral Sea straddles the border between Uzbekistan and Kazakhstan—it was once the fourth largest saline lake in the world. But since the 1960s, it has been shrinking because water from the rivers that once filled it was shunted off for irrigation. Just 10% of its surface area remains, with the rest now a salty desert.

Prior research had suggested that the rock beneath the lake had likely been compressed when the lake formed, suggesting that it may now be rebounding as the lake has dried. To determine if that is the case, the research team obtained radar-based satellite data for the years 2016 through 2020. Such radar is able to measure ground height to the millimeter.

In comparing ground height for the parts of the lake that are now nothing more than salt beds, the research team found that the ground has indeed been rising—an average of 7 millimeters a year. It was also rising as far as 500 kilometers from what was once the original center of the sea.

The research team used the data they obtained to create simulations showing the initial depression of the rock below the lake and then as it has been rebounding. For such activity to occur, they note, the rock below the lake would have to be behaving as a viscous fluid; otherwise, the rebound would have taken place much more quickly. Thus, the rock is in essence flowing upwards very slowly, at approximately the pace of tectonic plates. That means the uplift will continue for many decades to come.

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