The Three Gorges Dam is a modern engineering marvel. Located in central China, it interrupts the flow of the Yangtze River, the longest river in Asia, and generates more electricity than any other hydroelectric power plant on the planet.
It’s so big that, according to NASA, filling it up could decelerate the rotation of the Earth. The impact would be minimal, but it would be an example of the impact of humans on planetary equilibriums.
The Three Gorges Dam. The Yangtze River is the third longest river in the world, behind the Amazon and the Nile. Also known as the “Blue River,” it drains a nearly 800,000 square miles, providing water to 40% of China’s territory. The river gets its name from the three natural gorges in the middle of the river: Qutang, Wu, and Xiling.
In 2012, nearly two decades after construction on the project began, China inaugurated the world’s largest hydroelectric power plant. It was built over the Yangtze River in the Hubei province to make use of the three gorges.
How China overshadowed Itaipú. With a generating capacity of 22,500 MW, the Three Gorges Dam is the first to generate more hydroelectric power than Itaipú, which is shared by Brazil and Paraguay and located on the Paraná River.
After intense monsoon rains in 2020, the Three Gorges Dam beat Itaipú’s annual 103 TWh electricity output record. That year, its 32 turbines of 700 MW produced nearly 112 TWh of electricity, more than some countries like Finland or Chile produce annually. The megastructure also features two smaller 50 MW generators that provide power to the plant itself and an elevator that allows ships to navigate the river.
And slowed down the Earth’s rotation. At 594 feet tall and 7,700 feet long, this colossal structure is capable of maintaining 10 trillion gallons of water. If the dam is filled up, the gigantic mass could, as NASA warned in 2005, influence the rotation of our planet in an incalculable way.
According to Benjamin Fong Chao, a former geophysicist at NASA’s Goddard Space Flight Center, filling up the Three Gorges Dam would cause Earth’s axis to shift slightly and ultimately slow its rotation. This would increase the length of the day by 0.06 microseconds.
A slightly longer day. Although it’s a small change in comparison to the melting of the polar ice caps or devasting earthquakes, it demonstrates the impact that human activities can have on our planet, affecting it on the scale of Earth’s rotation.
For reference, let’s look at the devastating 2004 tsunami in Indonesia. It was caused by an earthquake that, for its part, was caused by a compression on Earth due to the interaction between the tectonic plates of India and Myanmar. That tsunami had the opposite effect: It moved the North Pole approximately one inch to the east, which slightly accelerate the rotation of the planet. This reduced the duration of the day by 2.68 microseconds.
The key: the moment of inertia. The detonate of this effect is a physical magnitude called the “moment of inertia” that describes the resistance of an object against changes to its rotation. The moment of inertia is higher or lower depending on the mass of the object and how that mass is distributed with respect to its spin axis.
The classic example is a figure skater that increases their rotation velocity when crossing their arms and holding them close to their body. Similarly, the Earth’s rotation can be modified by changes in its mass distribution. In the Indonesia example, the movement of the tectonic plates provoked a tsunami in the Indian Ocean that modified the distribution of mass on the earth’s surface and, consequently, the planet’s moment of inertia.
The Moon has competition. The Earth isn’t a perfect sphere. Its spin axis shifts naturally due to changes in the atmosphere, the oceans, and the Earth’s crust. Since 1900, this axis has shifted about 4 inches per year. Traditionally, this shift has been attributed to glacial retreat or the Moon’s gravitational pull. But now we’re starting to understand that the role humans play in these events. The Three Gorges Dam and the melting of polar ice caps, que increases the amount of water towards the Equator, aren’t the only examples.
Wells are another example. Between 1993 and 2010, human geoengineering extracted approximately 2,150 gigatons of groundwater, which is used in production, agriculture, cattle, and industry. This massive extraction elevated the Earth’s sea level by more than 6 millimeters and, surprisingly, shifted the Earth’s spin axis about 31 inches to the east.
Is it a matter of adjusting your watch? The impact of the wells or the Three Gorges Dam on the Earth’s spin rotation, although minimal, spurs important questions about the influence of human activities on the planet. In light of these changes, some researchers are pushing to introduce a “negative leap second” in international clocks if the Earth’s rotation increases slightly because of human impact.
This would mean that a minute would only last 59 seconds to compensate for the deceleration of Earth’s rotation. Researchers say it would maintain the synchronization of atomic clocks, which are used to measure time with millimetric precision.
Images | NASA
View 0 comments