Dams have shifted poles of Earth
Scientists have determined that the construction of dams over two centuries and the storage of vast volumes of water has slightly shifted the axis of rotation of the Earth. The research helps better understand the shifts in the poles by melting ice sheets and glaciers.
New research has revealed that the construction of nearly 7,000 dams between 1835 to 2011 have caused the poles to shift about a meter, along with a 21 millimeter drop in global sea levels. Together, these dams hold enough water to fill up the Grand Canyon twice. The study reveals another way in which human activities affect the planet, and while the shift is small, the research helps better understand how the poles of the Earth will shift from the melting of glaciers and ice sheets because of climate change. A paper describing the findings has been published in Geophysical Research Letters.
The effect of the dams on the axis of rotation of the Earth can be compared to sticking a lump of clay to a spinning ball. The portion of the ball with the clay on it will shift slightly towards its equator, and away from the axis of rotation, to maintain the momentum. A similar phenomenon occurs on a much more massive scale with the Earth itself. The solid crust on top sits on an ocean of molten rock, or magma, and moves independently. When mass is redistributed on the surface of the Earth, such as during the growth or shrinkage of ice sheets, the outermost crust wobbles and moves around, with different regions on the surface moving into the axis of rotation. The process is known as true polar wander.
How the study was conducted
The researchers used a global database of dams to map the location of each dam, and the amount of water stored in the associated reservoirs. The research revealed that the poles shifted in two distinct phases. The first, from 1835 to 1954 was a buildup of dams in North America and Europe, causing the North Pole to move eastwards by 20.5 centimetres. Between 1835 and 2011, the poles moved about 113 centimetres towards the west, as a response to dam building in Asia and East Africa. The research reveals that any forecasts on global sea level rise will have to take into account the water stored in reservoirs by dams.