Retreating Glaciers spur Alaskan Earthquakes
- After reading the article that follows, can anyone be confident in saying that global warming had NO association to the Dec 26, 2004 earthquake off Indonesia?
RETREATING GLACIERS SPUR ALASKAN EARTHQUAKES
This story has been adapted from a web publication issued by the NASA/GSFC Public Affairs Office.
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. (Image right: Landsat Keeps an Eye on the Bering Glacier, 1986 - 2002. Roll your mouse over the image to see the difference in the Bering Glacier from October 1986 to September 2002. Click on image to view animation. These images were derived from the Landsat 5 and Landsat 7 satellites, respectively. Credit: NASA/USGS.)
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 Change.
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. A Decade of Earthquakes in Southern Alaska. Click on one of the images on the right to see all earthquakes between magnitude 2 and 6 that have occurred in southern Alaska since 1993. In this image series the size of the ring around each earthquake represents its relative magnitude. Credit: NASA/USGS.
"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 earthquakes.
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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