The rotation of the earth is constant and unchanging, as it determines our days. But even we as humans influence them.
The cover image is a symbolic image. It does not depict the Three Gorges Dam.
How can China influence the Earth’s rotation? Around 20 years ago, NASA published a scientific paper about the fluctuations the Earth’s rotation is subject to. Human events or structures cause the earth’s rotation around its own axis to slow down. This makes the days longer.
Earthquakes are mainly responsible for this, but a famous project in China is also mentioned: the Three Gorges Dam.
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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 sometimes several hundred meters high.
Enormous amounts of water accumulate in a reservoir, in the case of the Three Gorges Dam in China a maximum of around 40 cubic meters. For comparison: Lake Constance in Germany has a capacity of around 48 cubic kilometers (via the Thurgau Environment Agency and the Three Gorges Dam – a sustainable venture?).
Due to its location in a mountain range and relatively far above the equator (30° 49′ 23″ north latitude), this artificially created water load slows down the earth’s rotation.
The principle behind it is similar to that of an ice dancer, who can control her rotation speed by extending and contracting her arms. The more stretched out, the slower, the closer to the body, the faster the rotation.
How much does that shorten the day? However, even at maximum filling, Earth’s day would only be shortened by 0.06 microseconds, according to NASA. This maximum water load is usually not reached (via CNN). The effect is likely to be smaller in everyday life – but still exists. A day currently lasts 86.4 billion microseconds.
What effect do earthquakes have? Earthquakes can have far greater consequences, such as the infamous one at Christmas 2004, which also caused a tsunami. This caused around 230,000 deaths (via Welthungerhilfe).
Its mass shift away from the center resulted in a day lengthening of 2.68 microseconds. NASA used the earthquake as a reason for the above calculations.
Completely uncontrolled masses of water have often been the downfall of humanity. There have been devastating storm surges several times in history, including in January 1624. One consequence of this was recently the anniversary of a money handover: 400 years ago, a dike broke in the Netherlands – a company is still paying interest for the consequences to this day