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Crumbling Glacier Quakes as It Breaks

Michael Reilly, Discovery News

But after studying the glacier for the past two melt seasons, Amundson thinks that's unlikely. "We found that after a calving event, there's only a small acceleration in sliding in the main glacier, not enough to cause the seismic signal we see."

Instead, he noticed that the quakes coincided with large calving events. The glacier edge sits in the water, resting against the bottom of the fjord. So when a berg calves and starts to roll, it scrapes hard against solid ground.

"Picture a box against a wall at a 45-degree angle: As the box rolls, the corner scrapes along the floor," Amundson said.

Victor Tsai of Harvard University agrees that calving, rather than sliding of the main glacier, is the likely cause of the quakes. "They physically observed one of the icebergs rolling over and recorded seismic waves that look a lot like the glacial earthquakes we've seen," he said.

"This is important to understanding ice sheet stability," Amundson said. "Changes in calving affect how the glacier responds to climate," making understanding the strange quakes crucial to studying the effects of climate change on the world's glaciers.

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