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Retreating Glaciers Spur Alaskan Earthquakes

NASA/Goddard Space Flight Center <>

Date:   2004-08-03

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.

The study examined the likelihood of increased earthquake activity in 
southern Alaska as a result of rapidly melting glaciers. 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 

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.

\"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.

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.

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.

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.

Even though shrinking glaciers make it easier for earthquakes to occur, 
the forcing together of tectonic plates is the main reason behind major 

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.

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. 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.

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.

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.

\"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.

Editor\'s Note: The original news release can be found here 

This story has been adapted from a news release issued by NASA/Goddard 
Space Flight Center.

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