Icy Earthquakes: Warming Planet Shakes Up Glaciers

Researchers setting up GPS equipment next to the north side of Helheim Glacier in Greenland.

(Image credit: Nick Selmes, Swansea University)

When large chunks of ice break off of a glacier and plop with a giant splash into the chilly water, the result can be lots of thunderous shaking. These mysterious glacial quakes have increased seven-fold in Greenland in the past two decades, according tonew research.

Now, scientists think they've figured out the cause of the rumbling phenomenon, at least in Greenland.

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The scientists discovered that, when a big chunk of ice splits, or "calves," from a massive glacier and tips forward into the ocean, it could force the glacier not only to stop inching forward, but also to push it backward. The backward movement and the subsequent change in water pressure cause glacial earthquakes, which can trigger massive tsunami waves and thunderous rumbling. [See Photos of Greenland's Gorgeous Glaciers]

As a recently calved iceberg begins to topple over into the ocean, it displaces a lot of water, Nettles said. Simultaneously, water rushes in to fill the space between the iceberg and the remaining glacier. That water motion causes a low-pressure zone behind the iceberg (the one that just plunged into the water) strong enough to suck water up from the ocean floor. The upward force on the Earth and the force of the falling iceberg produce a measurable seismic wave, Nettles explained.

Glacial earthquakes induced by calving occur seven times more frequently than they did in the early 1990s, according to Nettles. "Calving is such an important component of the mass loss in both Greenland and Antarctica — it's really important to try and understand how calving actually works," Nettles said. This fast pace "is very human in its timescale," she said, linking it to anthropogenic climate change.

"The difficult thing about Greenland is, it's so important for sea level rise because [compared to other countries with massive ice sheets] it's quite far south," said study co-author Timothy James, a professor of geography at Swansea University in the United Kingdom. Watching a glacial earthquake unfold back in 2010 for a prior mission to study glacial earthquakes "was a really lucky experience," he said. "Every once in a while, you'd hear a crack and a bang," he added, "but by the time the sound actually got to you, you turned and didn't really see anything."

Elizabeth is a staff writer for Live Science. She enjoys learning and writing about natural and health sciences, and is thrilled when she finds an evocative metaphor for an obscure scientific idea. She researched ancient iron formations in China for her Masters of Science degree in Geosciences at the University of California, Riverside, and went on to Columbia Journalism School for a master's degree in journalism, focusing on environmental and science writing.