Greenland is being twisted, compressed, and stretched. This happens due to plate tectonics and movements in the bedrock, caused by the large ice sheets on top melting and reducing pressure on the subsurface.
The pressure is easing both because large amounts of ice have melted in Greenland in recent years, and because the bedrock is still affected by the enormous ice masses that have melted since the peak of the last Ice Age around 20,000 years ago.
As a result, the entire island has shifted northwest over the past 20 years by about 2 centimeters per year.
At the same time, the movements are causing Greenland to both expand and contract horizontally. The effect is that Greenland’s area is currently being ‘stretched out’ and becoming slightly larger in some regions, while others are being ‘pulled together’.
This is shown by new research from DTU Space, recently published in the Journal of Geophysical Research.
”Overall, this means Greenland is becoming slightly smaller, but that could change in the future with the accelerating melt we’re seeing now,” says DTU Space postdoc researcher Danjal Longfors Berg, lead author of the article in Journal of Geophysical Research.
The geophysical processes affecting Greenland’s shape are pulling in different directions.
”The ice that has melted in recent decades has pushed Greenland outward and caused uplift, so the area has actually become larger during this period. At the same time, we see movement in the opposite direction, where Greenland is rising and contracting due to prehistoric changes in the ice masses related to the last Ice Age and its end,” says Danjal Longfors Berg.
A very detailed model
It is the first time the horizontal movements have been described in such detail.
”We have created a model that shows movements over a very long timescale from about 26,000 years ago to the present. At the same time, we have used very precise measurements from the past 20 years, which we use to analyze the current movements. This means we can now measure the movements very accurately,” says Danjal Longfors Berg.
The new measurements are based on 58 GNSS stations (GPS) placed around Greenland. They measure Greenland’s overall position, elevation changes in the bedrock, and how the island is shrinking and stretching.
”There have not previously been such precise measurements of how Greenland is shifting. The assumption has been that Greenland is primarily being stretched due to the dynamics triggered by the ice melting in recent years. But to our surprise, we also found large areas where Greenland is being ‘pulled together’, or ‘shrinking’, due to the movements,” says Danjal Longfors Berg.
Important for surveying and navigation
The new research provides useful information about what happens when climate change hits the Arctic with accelerating speed, as is the case in these years.
”It’s important to understand the movements of landmasses. They are of course interesting for geoscience. But they are also crucial for surveying and navigation, since even the fixed reference points in Greenland are slowly shifting,” says Danjal Longfors Berg.
The GNSS stations are owned by the Climate Data Authority under the Ministry of Climate, Energy and Utilities. They are used for research purposes and operated in collaboration with DTU Space. The research is conducted under the DTU Space research center Center for Ice-Sheet and Sea-Level Predictions (CISP).
