The rotation of the Earth appears constant and unchanging, as it determines our days. Yet, even we as humans influence it.
The title image is a symbolic image. It does not depict the Three Gorges Dam.
How can China influence the Earth’s rotation? In a scientific paper NASA published about 20 years ago the fluctuations that the Earth’s rotation is subjected to. Events or even structures created by humanity cause a slowdown in the Earth’s rotation around its own axis. This makes the days longer.
Earthquakes are primarily responsible for this, but a famous project in China is also mentioned: the Three Gorges Dam.
The Earth as an Ice Dancer
How can a dam slow down the Earth’s rotation? The principle of a dam is to dam one or more rivers in mountainous terrain by building a wall that is several hundred meters high.
This accumulates enormous amounts of water in a reservoir, in the case of the Three Gorges Dam in China, up to about 40 cubic kilometers. For comparison: Lake Constance in Germany holds around 48 cubic kilometers (via Thurgau Office for the Environment and The Three Gorges Dam – a sustainable undertaking?
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Due to its location in a mountain range and relatively far above the equator (30° 49′ 23″ northern latitude), this artificially created water mass slows down the Earth’s rotation.
The principle behind it is similar to that of an ice dancer, who can control her spinning speed by extending and pulling her arms in. The more extended, the slower; the closer to the body, the faster the rotation will be.
By how much does that shorten the day? However, even with maximum filling, the Earth day would reportedly only be shortened by 0.06 microseconds according to NASA. This maximum water mass is generally not reached (via CNN). Thus, the effect is likely to be less pronounced in everyday life – but still present. A day currently lasts 86.4 billion microseconds.
What impact do earthquakes have? Earthquakes can have far stronger consequences, such as the infamous one from Christmas 2004, which also caused a tsunami. This resulted in around 230,000 casualties (via Welthungerhilfe).
Its mass displacement away from the center resulted in a lengthening of the day by 2.68 microseconds. NASA used the earthquake as a basis for the above calculations.
Completely uncontrolled masses of water have often brought disaster to humanity. Historically, there have been devastating storm surges, including in January 1624. An anniversary of one of these occurred recently when a company is still paying interest for the consequences: 400 years ago, a dike broke in the Netherlands – A company is still paying interest for the consequences
