This Chinese Dam Is So Big That It Changed The Rotation Of The Earth

In the long, slow process of man over the years, we have built some great buildings, and China in particular is no stranger to great engineering works. The Great Wall is approximately 13,166 miles long, built over a period of 2,300 years (from the 3rd century BC to the 17th century AD). Although you can’t see it with your own eyes from the ground (however, there are five things you can do), its scale is still quite impressive.

Over the millennia, we have stored hundreds of billions of gallons of water behind thousands of dams around the world. That had a measurable effect on the position of the Earth’s poles. And now it seems that the Three Gorges Dam hydroelectric project on the Yangtze River in China’s Hubei province is changing the world’s orbit itself.

Since construction began in 1994 and was completed in 2006, the dam contains approximately 44 billion tons, the weight of which has taken 0.06 microseconds off the Earth’s rotation, according to NASA scientists. It measures 607 meters in length, spans about 1.5 kilometers across the Yangtze, and can generate 22,500 megawatts (three times that of the largest dam in the US, Grand Coulee). About 3.67 million people were displaced, and nearly 55 million were affected as 13 cities and more than 1,300 villages were submerged, along with countless archaeological sites and hazardous waste dumps.

The Earth completes one rotation on its axis as it orbits the Sun every 24 hours, but no two rotations (or two days for that matter) are ever exactly the same length. Therefore, the 0.06 microseconds a dam pulls is very small compared to other natural one-time events. For example, the 9.1 magnitude earthquake that struck off the coast of Japan in 2011 (which caused the Fukushima nuclear accident) actually accelerated its rotation by 1.8 million parts of a second. And the 2004 Sumatran earthquake changed Earth’s mass enough to shorten the length of the day by 2.68 seconds.

The Three Gorges Dam – the largest in the world – is not going anywhere, so it will continue to change the geophysics of the world. When water converges, the earth’s inertia changes, causing a very small but measurable decrease in circulation. It’s like a skater moving their arms in and out to control the speed of their rotation.

When large volumes of water are moved from one place to another, the shape of the Earth changes, leading to what is known as “true polar wander,” something that happens because the Earth rotates to redistribute weight and strengthen its rotation. A report published in Geophysical Research Letters says that all of this water has been thrown slightly off the planet’s spin axis by about a meter in the past few decades. If the Earth continues to move slowly, several catastrophic events may occur in a short day. Fortunately, there’s no need to worry about it for the foreseeable future, but it’s something we need to keep an eye on.