The Three Gorges Dam It is a marvel of modern engineering. Located in central China, it interrupts the passage of the Yangtze River, the longest in Asia, generating more electricity than any other hydroelectric plant on the planet. It is so large that, according to NASA, filling it can slow down the Earth’s rotation. With a minimal impact, but highlighting the human influence on planetary balances; even the most fundamental ones.
The Three Gorges Dam. The Yangtze River is the third longest in the world, behind the Amazon and the Nile. Also called the Blue River, it drains a basin of almost two million square kilometers, feeding 40% of Chinese territory with water. In the middle course of the river there are three natural gorges called Qutang, Wu and Xiling: the Three Gorges.
In 2012, almost two decades after the start of construction, China inaugurated the largest hydroelectric power plant in the world, built on the Yangtze River in Hubei province to take advantage of the Three Gorges waterfall.
How China overshadowed Itaipu. With a power of 22,500 MW, the Three Gorges Dam is the first to generate more energy than the Itaipú hydroelectric plant, shared by Brazil and Paraguay on the Paraná River.
In 2020, the Three Gorges Dam broke Itaipú’s 2016 record of 103 TWh after intense monsoon rains. That year, its 32 700 MW turbines produced almost 112 TWh of electricity, more than what entire countries, such as Finland or Chile, consume annually. The megastructure is completed by two smaller 50 MW generators, which provide power to the plant itself, and a boat lift that allows navigation on the river.
And it slowed down the Earth’s rotation. With a length of 2,335 meters and a height of 185, this colossal structure is capable of retaining up to 40 cubic kilometers of water, or in other words: 40 billion liters. A gigantic mass that, as NASA warned in 2005 and was evaluated laterif filled, it could have a calculable influence on the rotation of our planet.
According to geophysicist Benjamin Fong Chao of NASA’s Goddard Center, filling the Three Gorges Dam would slightly shift the Earth’s axis to slow its rotation, increasing the length of the day by 0.06 microseconds.
A slightly longer day. Although it is a small change compared to the melting of the polar caps or large earthquakes, demonstrates the impact that human activities can have on our planet, even on a scale as large as the Earth’s rotation.
Take the devastating Indonesian tsunami of 2004. It was caused by an earthquake which, in turn, was due to a compaction of the Earth due to the interaction between the tectonic plates of India and Myanmar. That tsunami had the opposite effect: it moved the North Pole about 2.5 cm to the east, which slightly accelerated the planet’s rotation, reducing the length of a day by 2.68 microseconds.
The key: the moment of inertia. The trigger for this effect is a physical magnitude called “moment of inertia” that describes the resistance of a body to changes in its rotation. The moment of inertia is greater or less depending on the amount of mass of the object and how that mass is distributed with respect to its axis of rotation.
The classic example is a figure skater who, by crossing his arms close to his body, increases his rotation speed. Similarly, the Earth’s rotation can be modified by changes in its mass distribution. In the example of Indonesia, the movement of tectonic plates caused a tsunami in the Indian Ocean that modified the distribution of masses on the Earth’s surface and, consequently, the planet’s moment of inertia.
The Moon has competition. The Earth is not a perfect sphere; Its axis of rotation shifts naturally due to changes in the atmosphere, oceans, and Earth’s crust. Since 1900, this axis has moved about 10 centimeters per year. Traditionally, this displacement was attributed to the retreat of glaciers or the gravitational pull of the Moon. Now we are beginning to understand the hand of man, and the Three Gorges Dam or the melting of the poles, which increases the water level towards the equator, are not the only examples.
Another example is wells. Between 1993 and 2010, human geoengineering extracted approximately 2,150 gigatons of groundwater, used for consumption, agriculture, livestock, and industry. This massive extraction raised sea levels by more than six millimeters and, surprisingly, shifted the Earth’s axis of rotation by 80 centimeters east.
Question of adjusting the clock? The impact of the wells or the Three Gorges Dam on the Earth’s rotation, although minimal, raises questions about the influence of human activities on our planet. For years, some researchers have advocated introduce a negative leap second in international time if the Earth’s rotation becomes slightly faster.
As we saw a few months agothis idea is becoming progressively outdated. A Nature study suggests that the melting of the poles is already offsetting the hypothetical (and tiny) acceleration of the Earth due to human causes. The leap second was going to be introduced in 2026… And for now it has been postponed to 2029. It is possible that it will never be introduced.
Short record. The impressive magnitude of the Three Gorges Dam can be put into perspective in two ways. The first is by observing the works that China is undertaking in the future Medog hydroelectric power stationin Tibet, located on the Yarlung Tsangpo River. Its works began in 2025 and, once it is completed, in 2035, it will be the most powerful dam on the planet, three times more than that of the Three Gorges.
The second is with a fact: despite its brutal dimensions, the Three Gorges only produce 1% of China’s annual electricity. A testament to the country’s energy voracity.
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