Volcano experts, speaking last week at the fall meeting of the American Geophysical Union, said they expect no less than a minor revolution in their field in the near term, as they avail themselves of rapidly advancing technologies.

Among them is the satellite, which can keep tabs on far-flung volcanic activity from the relative safety of an orbital perch. And it can do so in a way that would be otherwise too daunting a task to accomplish on Earth, where volcanoes rise everywhere from the remote Aleutians to alongside major urban centers like Mexico City.

"Its very difficult logistically and financially to go out and instrument all of them," said Howard Zebker, a Stanford University professor of geophysics. "Having spaceborne satellites, we can make these measurements with leisure."

While it doesnt take an expert to spot an erupting volcano, it does to discern the sometime subtle hints a mountain might give before blowing its top. Swarms of earthquakes, increased gas emissions and surface bulging all can herald the arrival of an eruption.

In the last example, even tiny movements on the surface can betray the presence of enormous plumes of magma rising from below. Such was the case with the bulge that Mount St. Helens sprouted prior to erupting in 1980.

Tracking less obvious bulging, like that ongoing near Mammoth Lakes in eastern California, can be a yeomans job. Thats where satellites can step in.

Using a technique called interferometric synthetic aperture radar, or InSAR, volcanologists can study even the smallest changes in surface deformation over time.

While the radar system may have limited vertical accuracy, it can successfully detect bulging as minute as a few inches (centimeters). Repeated and regular passes of the satellites allow scientists to make better predictions about future eruptions.

"Being able to look at small deformations in the surface of the Earth as stuff moves up gives us some small warning," Zebker said.

Volcanologists dream of a day when a global swarm of InSAR satellites would allow them to further their routine monitoring capabilities.

"The availability of satellite imagery in real time is becoming quite a valuable tool in disaster mitigation," said Peter Mouginis-Mark, chief scientist at the University of Hawaiis Pacific Disaster Center.