- Greenbelt MD (SPX) - In a
new study, NASA and United States Geological Survey (USGS) scientists found
that retreating glaciers in southern Alaska may be opening the way for
future earthquakes.
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- The study examined the likelihood of increased earthquake
activity in southern Alaska as a result of rapidly melting glaciers.
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- As glaciers melt they lighten the load on the Earth's
crust. Tectonic plates, that are mobile pieces of the Earth's crust, can
then move more freely. The study appears in the July issue of the Journal
of Global and Planetary Change.
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- Jeanne Sauber of NASA's Goddard Space Flight Center,
Greenbelt, Md., and Bruce Molnia, a research geologist at USGS, Reston,
Va., used NASA satellite and global positioning system receivers, as well
as computer models, to study movements of Earth's plates and shrinking
glaciers in the area.
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- "Historically, when big ice masses started to retreat,
the number of earthquakes increased," Sauber said. "More than
10,000 years ago, at the end of the great ice age, big earthquakes occurred
in Scandinavia as the large glaciers began to melt. In Canada, many more
moderate earthquakes occurred as ice sheets melted there," she added.
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- Southern Alaskan glaciers are very sensitive to climate
change, Sauber added. Many glaciers have shrunk or disappeared over the
last 100 years. The trend, which appears to be accelerating, seems to be
caused by higher temperatures and changes in precipitation.
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- In southern Alaska, a tectonic plate under the Pacific
Ocean is pushing into the coast, which creates very steep mountains. The
high mountains and heavy precipitation are critical for glacier formation.
The colliding plates create a great deal of pressure that builds up, and
eventually is relieved by earthquakes.
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- The weight of a large glacier on top of these active
earthquake areas can help keep things stable. But, as the glaciers melt
and their load on the plate lessens, there is a greater likelihood of an
earthquake happening to relieve the large strain underneath.
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- Even though shrinking glaciers make it easier for earthquakes
to occur, the forcing together of tectonic plates is the main reason behind
major earthquakes.
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- The researchers believe that a 1979 earthquake in southern
Alaska, called the St. Elias earthquake, was promoted by wasting glaciers
in the area. The earthquake had a magnitude of 7.2 on the Richter scale.
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- Along the fault zone, in the region of the St. Elias
earthquake, pressure from the Pacific plate sliding under the continental
plate had built up since 1899 when previous earthquakes occurred.
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- Between 1899 and 1979, many glaciers near the fault zone
thinned by hundreds of meters and some completely disappeared. Photographs
of these glaciers, many taken by Molnia during the last 30 years, were
used to identify details within areas of greatest ice loss.
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- Field measurements were also used to determine how much
the glacier's ice thickness changed since the late 19th century. The researchers
estimated the volume of ice that melted and then calculated how much instability
the loss of ice may have caused. They found the loss of ice would have
been enough to stimulate the 1979 earthquake.
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- Along with global positioning system measurements made
by Sauber and Molnia a number of NASA satellites were used to document
glacier variability. Data from Landsat-7 and the Shuttle Radar Topography
Mission (SRTM) were used to study glacier extent and topography. Currently,
NASA's ICESat satellite is being used to measure how the glacier thicknesses
are changing.
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- "In the future, in areas like Alaska where earthquakes
occur and glaciers are changing, their relationship must be considered
to better assess earthquake hazard, and our satellite assets are allowing
us to do this by tracking the changes in extent and volume of the ice,
and movement of the Earth," Sauber said.
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- http://www.spacedaily.com/news/iceage-04f.html
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