That Dam Water |
The hundreds of billions of gallons of water trapped behind dams have pushed Earth’s poles away from the planet’s axis of rotation, the axis around which Earth rotates. This deviation is known as true polar wander. To estimate the contribution of dammed water to polar wander, scientists reviewed almost 7,000 dams constructed from 1835 to about 2011, and calculated their effect on Earth’s poles. By 2011, the North pole was only 20.5 centimeters away from its starting location, but in that time, it had moved back and forth over a total of 113.4 cm, a little more than a meter.
How it works: As Earth rotates, the surface moves to redistribute mass and stabilize the planet’s spin. Imagine Earth 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, explains Jim Davis, a geodesist at Columbia University. On Earth, instead of a wad of gum, shifting ice sheets and movements of mantle rock cause the planet to adjust itself. Though dams move a smaller amount of mass than these other phenomena, they still have an appreciable effect.
What the experts say: “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.” For example, many tools and devices like GPS rely on high-precision measurements that might be affected by a shift in Earth’s poles, he says. —Andrea Tamayo, newsletter writer
Source :https://www.scientificamerican.com/article/earths-poles-have-shifted-because-of-water-dams/
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That Dam Water |
The hundreds of billions of gallons of water trapped behind dams have pushed Earth’s poles away from the planet’s axis of rotation, the axis around which Earth rotates. This deviation is known as true polar wander. To estimate the contribution of dammed water to polar wander, scientists reviewed almost 7,000 dams constructed from 1835 to about 2011, and calculated their effect on Earth’s poles. By 2011, the North pole was only 20.5 centimeters away from its starting location, but in that time, it had moved back and forth over a total of 113.4 cm, a little more than a meter.
How it works: As Earth rotates, the surface moves to redistribute mass and stabilize the planet’s spin. Imagine Earth 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, explains Jim Davis, a geodesist at Columbia University. On Earth, instead of a wad of gum, shifting ice sheets and movements of mantle rock cause the planet to adjust itself. Though dams move a smaller amount of mass than these other phenomena, they still have an appreciable effect.
What the experts say: “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.” For example, many tools and devices like GPS rely on high-precision measurements that might be affected by a shift in Earth’s poles, he says. —Andrea Tamayo, newsletter writer
Source :https://www.scientificamerican.com/article/earths-poles-have-shifted-because-of-water-dams/
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