Scientists have discovered a dramatic uptick in earthquakes in Greenland and they are being caused by melting icebergs.
Scientists have already documented entire meltwater lakes vanishing in a matter of hours atop the vast Greenland ice sheet, as huge crevasses open beneath them. Now scientists are discovering the mechanisms behind earthquakes being caused by the rumbling and melting of this mass of often mile-thick ice.
In a new paper in the journal Science, a team of researchers from Swansea University in the UK, the Lamont-Doherty Earth Observatory at Columbia University, and several other institutions explain how the loss of Greenland’s ice can generate glacial earthquakes. When vast icebergs break off at the end of tidal glaciers, they tumble in the water and jam the glaciers themselves backwards. The result is a seismic event detectable across the Earth.
“These are all around magnitude 4.6 to 5.2, they’re all pretty close to magnitude 5,” says Meredith Nettles of the Lamont-Doherty Earth Observatory at Columbia University, a co-author of the study. “Which is a pretty big earthquake.”
The earthquakes are caused by massive movements of ice that impact the ground beneath. Compared with the early 1990s, Nettles says, scientists are now measuring seven times as many of these glacial earthquakes coming from Greenland — the rate has dramatically increased as the ice sheet has begun to lose more mass from the calving of icebergs at the front end of glaciers.
To understand the dynamics behind how these glacial earthquakes are happening, the researchers put GPS instruments atop Greenland’s fast moving Helheim Glacier, which is located in the southeast part of Greenland. They also monitored the glacier’s calving front, where it meets the water, by camera, and used global seismic data to track earthquake occurrences.
The amount of ice mass that breaks off in large iceberg calvings from Helheim Glacier, explains Nettles, is around a gigaton, or a billion metric tons.
Measured in space rather than mass, a big iceberg breaking off Helheim can be 4 kilometers in length — or over two miles. So, it is not a surprise that a body this large can shake the Earth when it moves — and especially when it throws its weight against another solid object, as occurs during iceberg calving.