Southeastern Alaska is on the rebound. (Earth Science: from San Francisco, at the 2001 fall meeting of the American Geophysical Union).

Scientists using the Global Positioning System (GPS) to track ground movement along faults in southeastern Alaska have measured something entirely different--the rapid rise of parts of the region resulting from the recent melting of glaciers.

The average rate of the ground's horizontal movement along the Fairweather Fault, which runs roughly parallel to the coast in Alaska's panhandle, is one of the fastest in the world, says Jeff Freymueller, a geophysicist at the University of Alaska in Fairbanks. Recent measurements show that opposite sides of the fault slip past each other at the rate of about 4 centimeters annually. That's 13 percent faster than the slip rate along California's San Andreas Fault, Freymueller notes.

The instruments also detected rapid vertical motion in the region. Some GPS stations, especially those around Glacier Bay, measured an increase in elevation of about 36 millimeters per year--the quickest measured anywhere in the world. But hardly any of that rise is the result of motion along the fault, says Freymueller.

Most of the speedy ascent reflects to the rebound of Earth's crust after heavy coastal ice sheets melted during the past 150 years or so. The remainder, about 1 mm of rise per year, may result from the now-slowed rebound from the disappearance of continental ice sheets at the end of the last Ice Age. --S.P.