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Global warming
yields “glacial earthquakes,” future sea level rise
March 23,
2006
Special to World Science
In new studies, scientists report that global
warming may cause sea levels to rise dramatically in a century—and is
now producing a newfound and growing phenomenon, “glacial earthquakes.”
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A glacier in East Coast Mountains of Baffin
Island, Nunavut, Canada. (Courtesy NOAA)
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Three studies published in the March 24 issue of the research journal Science
warn of the events.
Two studies found that the Earth may be warm enough by 2100 for
widespread melting of the Greenland Ice Sheet and partial collapse of
the Antarctic Ice Sheet.
In one paper, Jonathan Overbeck at the University of Arizona in Tucson,
Ariz., and colleagues wrote that based on reconstructions of past
climates, conditions could be ripe to raise sea level by several meters
(yards) by this century’s end.
Most scientists believe the melting is due to global warming, a gradual
increase in the Earth’s temperature caused by the burning of fossil
fuels.
In a third study, seismologists reported an unexpected offshoot of
global warming: “glacial earthquakes,” in which Manhattan-sized
glaciers lurch unexpectedly. Glaciers are normally slow-moving masses of
ice.
The lurches yield temblors up to magnitude 5.1 on the moment-magnitude
scale, which is similar to the Richter scale, the researchers said.
Glacial earthquakes in Greenland, they added, are most common in July
and August, and have more than doubled in number since 2002.
The researchers, at Harvard University in Cambridge, Mass. and Columbia
University in New York, first described glacial earthquakes in 2003, but
without reporting on their seasonality or changing frequency.
“People often think of glaciers as inert and slow-moving, but in fact
they can also move rather quickly,” said Harvard’s Göran Ekström,
one of the researchers. “Some of Greenland’s glaciers, as large as
Manhattan and as tall as the Empire State Building, can move 10 meters
(11 yards) in less than a minute, a jolt that is sufficient to generate
moderate seismic waves.”
As glaciers and the snow on them gradually melt, water seeps downward.
When enough water accumulates at a glacier’s base, it can serve as a
lubricant, causing giant blocks of ice to lurch down valleys known as
“outlet glaciers,” the team explained. These funnel Greenland’s
glacial runoff toward the surrounding sea.
“Our results suggest that these major outlet glaciers can respond to
changes in climate conditions much more quickly than we had thought,”
said Meredith Nettles, a postdoctoral researcher at Columbia and member
of the research team.
“Greenland’s glaciers deliver large quantities of fresh water to the
oceans, so the implications for climate change are serious.”
Greenland is not a hotbed of traditional seismic activity associated
with the grinding of the Earth’s tectonic plates, the traditional
source of earthquakes, the scientists noted. But seismometers worldwide
detected 182 earthquakes there between January 1993 and October 2005,
they added.
They examined the 136 best-documented of these events, ranging in
magnitude from 4.6 to 5.1. All temblors were found to have originated at
major valleys draining the Greenland Ice Sheet, they said, implicating
glacial activity.
While glacial earthquakes appear most common in Greenland, the
scientists reported finding evidence of them also in Alaska and at the
edges of Antarctica.
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