China's Three Gorges Dam is a symbol of human ingenuity, providing hydroelectric power and flood control. But there's something less well-known: it can slightly adjust the Earth's rotation.
According to NASA, the massive amount of water the mega-dam holds could unbalance the rotation of our planet. While the change is small, it serves as a powerful reminder of how much we can impact natural systems.
Located on the Yangtze River in Hubei Province, China, the Three Gorges Dam is considered the largest hydroelectric power plant on the planet. It took nearly 18 years to build and was completed in 2012. The massive structure is 2,335 meters long and 185 meters high, holding 40 cubic kilometers of water - that's about 40 trillion liters.
The main purpose of the Three Gorges Dam is to generate hydroelectric power and control floods, but there is much more to it than that. As water builds up behind this massive dam, it displaces a huge amount of mass that can even change the Earth's rotation by changing the way the mass is distributed.
The whole idea stems from the physics of mass distribution and moment of inertia. It gained traction after NASA published a study in 2005 on the effects of the massive earthquake and tsunami in the Indian Ocean in 2004. That event changed the mass of the Earth and adjusted its moment of inertia, making the day shorter by about 2.68 microseconds.
Similar things happen when humans do big things like fill up giant dams, says Dr Benjamin Fong Chao of NASA’s Goddard Space Flight Center. Theoretically, moving that much water could push the Earth’s poles about 2cm and lengthen a day by about 0.06 microseconds.
Building large dams isn’t the only way humans are affecting the Earth’s rotation. Climate change can have a similar effect as melting polar ice caps. Natural forces like the pull of the Moon have been slowing the planet’s rotation for thousands of years.
But throwing mega-projects like the Three Gorges Dam into the mix adds another layer to those impacts.
To account for these small variations in the Earth's rotation rate, some experts have proposed using something called a "negative leap second." This would mean occasionally dropping a second from atomic clocks to keep them in line with the Earth's slightly changing rotation rate.
China is not alone in harnessing hydropower through mega-dams. Countries like the US, Brazil and India are also building massive projects that could shift the Earth’s mass in similar ways.
