For some time, scientists have suspected that the filling of the reservoir behind Three Gorges Dam in China could be responsible for changing the rotation of the Earth.
The monumental dam in Hubei province, China is the world’s largest hydroelectric power station, expected to be 22,500 MW upon completion. When the water level is its maximum—574 ft above sea level and 299 ft above river level—the reservoir created by the dam is about 410 miles in length and .70 miles in width on average. It has the potential to flood 632 square kilometers of land with about 42 billion tons of water.
A shift in mass that remarkable could affect the rotation of the Earth, scientists argue, in a phenomenon known as the moment of inertia—the inertia of a rigid rotating body with respect to its rotation. The longer the distance of a mass to its axis of rotation, the slower it will spin.
As Business Insider notes, we see examples of these moments of inertia every day; it’s this precise reason why a figure skater will draw her arms into her body to spin faster or a diver with tuck his body to somersault faster.
If the Three Gorges Dam is filled to capacity at 574 above sea level, it will increase the Earth’s moment of inertia and slow its rotation—increasing the length of day by 0.06 microseconds, NASA reports. The effect would also shift the pole position by about two centimeters and make the Earth slightly more round in the middle and flat on the top.