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For much of its history the U.S.--which before Mount St. Helens had largely been spared a major volcanic eruption--was complacent about this kind of devastation. After Mount St. Helens, all that changed. Hoping to improve prediction so that local populations could be evacuated before another mountain blew its top, the government set up volcano labs in Menlo Park, California; Vancouver, Washington; and Anchorage, Alaska, complementing one that already existed near the Kilauea volcano in Hawaii.
In addition, a rapid-response force known as the U.S. Volcano Disaster Assistance Program was established to act as a volcanic swat team, scrambling to the scene of an awakening mountain within days of the first sign of trouble. The group makes its services available not just in the U.S. but also overseas. It was this team that was largely behind the Mount Pinatubo success, packing hardware into suitcases and flying straight to the Philippines.
For any volcano researchers, predicting whether a smoking mountain is merely letting off steam or preparing to explode can be tricky--and often deadly. In 1993 volcanologist Stanley Williams of Arizona State University and six other scientists were working in a crater in the side of the Galeras volcano in Colombia when the mountain suddenly blew, killing all but Williams. USGS seismologist Bernard Chouet once trod so heedlessly over hot volcanic terrain that when he took off his shoes, his socks were smoking.
The stakes for the people living near the volcano can be higher still. In 1985 Colombian seismologists warned their government that the Mount Ruiz volcano was smoldering dangerously. Their data were too spotty to convince officials, however, and the government did nothing. One month later, the mountain erupted, claiming 23,000 lives.
Even when officials get it right, at least a little luck may often be involved. The first warning volcanologists got of increased seismic activity within Mount Pinatubo was not from a high-tech instrument but from a local nun who walked into the Philippine Institute of Volcanology and, begging the scientists' pardon, reported that the mountain, clearly visible from her village, had just blown up. "The challenge is to call the eruption," says USGS seismologist Dave Hill, "and that's a fine line."
One researcher who believes he may have learned to walk it is the USGS's Chouet. Originally trained as a physicist, Chouet conducts his studies with a combination of ground-based instruments and high-orbit satellites. He first positions more than 40 seismic sensors around a part of a mountain where he suspects magma might be. Next he tunes the instruments to the military's Global Positioning Satellite. As the sensors listen for subterranean rumbles, indicating the movement of materials within the mountain, the frequency of each rumble tells Chouet what those materials are. At the same time, the satellite pinpoints the position of the sensors to within an inch, allowing a computer to calculate the materials' precise location. The system provides a picture of the mountain's anatomy as revealing as any cat scan. "Volcanoes are singing when they're pressurized," Chouet says. "I can follow that process right up to the surface."