Greenland Icequakes as possible warming evidence.

[Hill]

A recent report shows strong evidence that the margins of the Greenland icecap are melting at a much faster rate than they did as little as five years ago. Glaciers produce "glacial earthquakes" and these quakes provide further evidence for global warming according to seismologists Göran Ekström and Victor C. Tsai at Harvard and Meredith Nettles at the Lamont-Doherty Earth Observatory.

"People often think of glaciers as inert and slow-moving, but in fact they can also move rather quickly," says Ekström, professor of geology and geophysics at Harvard who will be moving to Lamont-Doherty in the spring. "Some of Greenland’s glaciers, as large as Manhattan and as tall as the Empire State Building, can move 10 meters in less than a minute, a jolt that is sufficient to generate moderate seismic waves."

As glaciers and the snow atop them gradually melt, water seeps downward. When enough water accumulates at a glacier’s base, it can serve as a lubricant, causing blocks of ice 10 cubic kilometers in size to lurch down valleys known as "outlet glaciers," which funnel all of Greenland’s glacial runoff toward the surrounding seas.

"Our results suggest that these major outlet glaciers can respond to changes in climate conditions much more quickly than we had thought," says Nettles, a postdoctoral researcher at Lamont-Doherty. "Greenland’s glaciers deliver large quantities of fresh water to the oceans, so the implications for climate change are serious. We believe that further warming of the climate is likely to accelerate the behavior we’ve documented."
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Although glacial earthquakes appear to be most common in Greenland, Ekström, Nettles and Tsai have also found evidence of glacial earthquakes originating from mountain glaciers in Alaska and at glaciers located in ice streams among the edges of Antarctica.

Source: Glacial Earthquakes Point to Rising Temperatures in Greenland -- The Earth Institute at Columbia University
Other links: Geotimes - December 2003 - Glacial earthquakes and
Glacial earthquakes rock Greenland ice sheet - earth - 24 March 2006 - New Scientist


A screen capture of the location of icequakes in Greenland from Google Earth.

A closeup of the icecap at site JI showing melt pods and surface runoff.

Google Earth Community Forum link: Google Earth Community: "Glacial earthquakes" provide warming evidence