A Surprising Potential Effect Of Climate Change - Earthquakes - CSM

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"Take those powerful Alaskan earthquakes. We expect land to rise as the weight of glaciers melts away. Should we also adjust our assessment of earthquake risk? Two geophysicists say "yes." Glaciers hold down earthquake action even in a seismically active region like Alaska, argue Jeanne Sauber with NASA's Goddard Space Flight Center in Greenbelt, Md., and Bruce Molnia with the US Geological Survey in Reston, Va. They use history and current data to make their case.

For example, earthquake action picked up in places where the ice masses retreated some 10,000 years ago, Dr. Sauber notes. Scandinavia had major quakes back then. Canada also had many moderate quakes as its glaciers melted.

Melting glaciers do not cause earthquakes: Quakes are created when forces within the crust build up strain in rock until something slips. Alaska is seismically active because a North Pacific crustal plate is ramming into southern Alaska, creating pressures that must be relieved at some point. However, these pressures do push up high mountains where glaciers form - and the weight of the glaciers pushing down can stabilize the situation, if not eliminate the risk altogether. Remove that weight, and the likelihood of a quake goes up as the strain accumulates.

That's what happened with the 7.2 magnitude quake in Alaska's St. Elias region in 1979, Sauber and Dr. Molnia believe. Photographs show how glaciers in the fault area had thinned substantially during the 80 years since the previous earthquake activity. Sauber says it now is clear that "in areas like Alaska where earthquakes occur and glaciers are changing, their relationship must be considered to better assess earthquake hazard." She adds that satellites are helping seismologists do this "by tracking the changes in extent and volume of the ice and movement of the Earth."

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http://www.csmonitor.com/2004/0819/p16s01-sten.html