Earth's poles shift because of dams around the world

Over the past 200 years, humans have quietly impacted the Earth's poles by building thousands of dams around the world, causing them to move more than 1 meter.

Hoover Dam and Mike O'Callaghan-Pat Tillman Memorial Bridge in the US - Photo: WIKIPEDIA

The Earth's pole shift can be traced back to two major waves of dam building around the world . The first major wave occurred in North America and Europe during the 19th and early 20th centuries. The second major wave occurred across Asia and East Africa in the second half of the 20th century.

It all has to do with the distribution of mass and moment of inertia of the planet. The Earth spins like a ball on your finger. But if the mass suddenly changes in one area, the rotation will start to wobble.

Imagine placing a lump of clay on one side of a spinning ball. To conserve momentum, the clay-covered side will move slightly outward, affecting the spin of the ball.

This is similar to how an ice skater spins faster when pulling their arms back: changing the mass distribution changes the rotational dynamics.

In Earth’s case, the mass shift comes from water trapped in giant dams. These artificial reservoirs redistribute the planet’s mass, shifting the poles slightly, according to IFLScience on July 10.

In a new study, planetary scientists at Harvard University discovered the problem by looking at global data on 6,862 dams built around the world between 1835 and 2011. From there, the team calculated how much water the dams contained, how the water reshaped the Earth's mass distribution, and whether it was enough to shift the poles.

Overall, the team found that dam construction shifted the poles by about 113cm and caused global sea levels to drop by 21mm between 1835 and 2011. In the 20th century, this shift was as high as 104cm, but not in just one direction.

Between 1835 and 1954, a wave of dam building in North America and Europe caused the poles to shift toward the equator. During this period, the North Pole moved nearly 20.5 cm toward the 103rd meridian east, a line of longitude that passes through Russia, Mongolia, China, and the Indochina peninsula.

After 1954, the dam-building wave shifted to East Africa and Asia. As a result, the pole began to shift in the other direction, about 57cm toward the 117th meridian west – the line of longitude that passes through western North America and stretches across the South Pacific .

"The fact that we're holding water in dams is not only drawing water from the ocean, which lowers global sea levels, but it's also redistributing the mass differently around the globe. We're not going into a new ice age because the poles are shifting by about a meter, but it's really affecting sea levels," said Natasha Valencic, lead author of the study and a graduate student at Harvard.

The pole shift is the cumulative effect of thousands of dams built around the world over many decades. However, in some exceptional cases, a dam itself has its own impact.

For example, China’s Three Gorges Dam, the world’s largest hydroelectric dam, is so large that it could significantly affect the Earth’s rotation. According to NASA, China’s mega-dam can hold 40 ^cubic kilometers of water, enough to shift the Earth’s poles by about 2 centimeters.

The research is published in the journal Geophysical Research Letters .

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Source: https://tuoitre.vn/cuc-trai-dat-dich-chuyen-vi-cac-dap-nuoc-tren-the-gioi-2025071113302913.htm