The loss of ice masses on Greenland and other glaciers is not only causing sea levels to rise. The loss also has geological implications. This is because the missing weight causes the earth’s crust to rise again. Now researchers from the USA have discovered that the earth’s crust is not only rising, but also shifting horizontally, and that this can still be measured in distant regions.
On average, the Earth’s crust shifts up to 0.4 millimeters per year in the northern hemisphere, writes the team led by Professor Jerry Mitrovica of Harvard University’s Earth and Planetary Science Department in the published study. His graduate student Sophie Coulson, lead author of the paper, was able to show that the movement of the Earth’s crust caused by the loss of ice from the Greenland ice sheet can still be detected from the centre at a distance of over 1,000 kilometres and beyond. According to the author, how strong and how far the movements are detectable depends very much on the losses. In the record melting year of 2012, the crust in Europe and Russia shifted by up to 0.4 millimetres, whereas in 2006, with the low melting in Greenland, the shift was only 0.1 millimetres and was only detectable as far as Norway. On the other hand, in Canada and the northeastern United States, these shifts have also been shown to work.
The fact that the Earth’s crust is moving due to the loss of ice pressure is not new per se. The principle of “isostatic rebound” has been known for decades. In this process, the Earth’s surface rises after the retreat of ice sheets and glaciers that had previously pushed them down. Lateral (tangential) movements of the earth’s crust in the vicinity of such glaciers and ice sheets were also known by now. The novelty of the study, published in the journal Geophysical Research Letters, is the distance of the horizontal movements still detected and the fact that it affects all regions located within a radius of 1,000 kilometres or more from glaciers and ice sheets. With the help of satellite measurements and computer models, Sophie Coulson and the other team members succeeded in creating three-dimensional models for the regions and in calculating and displaying the movement patterns and distances of the Earth’s crust. The researchers found vertical movements of up to 0.9 millimetres per year, and horizontal movements of up to 0.45 millimetres in Europe. Especially the vertical movements, according to the team, are much higher than previously thought. On the other hand, at some of the locations studied, lateral movements are higher than vertical ones, the authors write.
The team investigated the movements not only in the northern hemisphere, but also in the south. They came to the conclusion that these do not occur to the same extent as in the northern hemisphere. Sophie Coulson and her colleagues see the reason for this in the increase in ice mass in East Antarctica at that time compared to the loss in West Antarctica.
The researchers also looked at specific locations such as London, Boston and the Falkland Islands in their work. It showed that the Falkland Islands, for example, had risen overall between 2003 and 2013, but had fallen thereafter. Instead, they shifted eastwards by 0.1 millimetres per year over the same period. On the other hand, the team was able to show that London and Siberian Norilsk had been influenced in their horizontal movements almost exclusively by the Greenland ice mass loss and had moved northwards and eastwards during the study period. The research group was thus able to show once again that impacts in the Arctic and Antarctic can have far greater and more far-reaching consequences than assumed… even if they are in the millimetre range per year.
Dr Michael Wenger, PolarJournal
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