Earth’s Poles Have Shifted because of Water DamsNEWS | 15 July 2025Star trails above the Three Gorges Dam in Yichang, Hubei province, China. Large dams like this one are shifting the Earth's poles away from its axis of rotation.
When large masses of water are moved from one place to another, this changes the shape of Earth and leads to a phenomenon called true polar wander
Over the past 200 years, humans have stored hundreds of billions of liters of water in thousands of dams around the world. That shift of water is pushing Earth’s geographic poles away from its axis of rotation, a new study published in Geophysical Research Letters has found, contributing to a phenomenon called true polar wander.
In an ideal model of our planet, the axis around which Earth rotates goes through the fixed geographic poles, or what we typically call the North and South Poles. But in reality, the axis pierces through the surface of the planet at points some distance away from the geographic poles, says Jim Davis, a geodesist at Lamont Doherty Earth Observatory at Columbia University, who was not involved in the study. The distance between the two is called the polar motion, or true polar wander, and it’s crucial to know for a number of purposes.
“Astronomers need it. GPS depends on it. There’s a lot of things that depend on knowing how the Earth is rotating at the moment,” Davis says. “We have to know the polar motion accurately or else the errors will propagate into other systems on which we depend on a daily basis.”
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True polar wander happens because the surface of Earth rotates to redistribute mass and stabilize its spin. Imagine our planet as a beach ball spinning on someone’s finger. If someone stuck a wad of gum on the ball, the ball might wobble on its axis of rotation and move to adjust to the increase in mass, Davis explains. On Earth, instead of a wad of gum, there are shifting ice sheets and movements of mantle rock that cause the planet to adjust itself. Though dams move a smaller amount of mass than these other phenomena, they still have an appreciable effect.
To figure out the size of the effect, Natasha Valencic, a fourth-year Ph.D. student at Harvard University, and her team made a few minor additions to a previously developed dam database and reviewed a total of 6,862 dams constructed from 1835 to 2011. They then calculated the dams’ effect on the Earth’s poles in two time periods. From 1835 to about 1950, most dams were constructed in North America and Europe, causing the North Pole to shift away from these regions. Then, starting in the 1950s, more dams were constructed in East Africa and Asia, pulling the pole in the other direction. By 2011, the pole was only 20.5 centimeters away from its original location, but over time, it had moved back and forth over a total of 113.4 cm, a little more than a meter.
“A meter is pretty big in regards to polar motion,” Davis says. Studying polar motion reveals something about how Earth’s mass is moving, he says. “The mass motions reveal both important natural processes in the Earth system, as well as significant human-induced changes, so understanding them is important for science and society, including climate change and solutions to climate change.”Author: Andrea Thompson. Andrea Tamayo. Source
