December 1, 1995
Web posted at: 10:33 a.m. EST
From Correspondent Miles O'Brien
MOUNT ST. HELENS, Washington (CNN) -- The chopper ride to the summit of Mount St. Helens takes only 15 minutes, but landing on the rocky lava dome inside the crater seems more like a descent onto another planet. There are clearly no aliens there, except for humans who are themselves alien to such an environment. Except, perhaps, for these people, scientists from the U.S. Geological Survey on a routine mission to install and service a slew of sensors that monitor the vital signs of the still-active volcano.
The volcanologists are there because over the past few months they have noted increased seismic activity beneath the volcano. During the month of September, they recorded 100 earthquakes. Although that number still indicates only mild earthquake activity for a volcano, the scientists nevertheless would like to know more about what is going on.
"We use whatever tools work best, and we have a varied tool kit," said the scientist in charge, Dan Dzurisin. He says it takes a blend of high-tech and low-tech tools to do the job right.
Volcanologists use a laser rangefinder to measure the lava dome to see if it is moving relative to a fixed point. A tiltmeter senses even the slightest surface movement -- a clue that molten rock, or magma, may be on the move below. Volcanologist John Ewert likens the tiltmeter to "an electronic carpenter's level." They also use a device that measures any widening or narrowing of surface cracks.
Data gathered by the tilt- and crackmeters are automatically transmitted every 10 minutes to the Geological Survey's Cascades Volcano Observatory 50 miles away in Vancouver, Washington. There it is compiled by computers and compared with data from the most important sensors of all: seismometers. Volcanologists say earthquake activity is the single best indication a volcano may be coming to life.
"Volcanoes are fundamentally places where magma from within the earth manages to force its way up through the crust of the earth and reach the surface, and that process always breaks rocks, and that by definition is an earthquake," Dzurisin explained.
In the past 10 years, researchers from the Geological Survey office have responded on a moment's notice to a dozen restless volcanoes all over the world. They fly in with a full array of sensors, radios and computers to help local officials make evacuation decisions. When the team responded to the 1991 eruption of Mount Pinatubo in the Philippines, their advice led to the largest evacuation ever.
But eruption prediction is limited. "We can tell them, 'You are getting into a dangerous phase,' but you can't predict the moment or the day of an eruption," said volcanologist Andy Lockhart. The uncertainties are underscored by the death toll. At least 13 volcano researchers have died in the line of duty over the past 15 years, including Dave Johnston, who perished in the avalanche unleashed by Mount St. Helens.
"The risks we take are calculated. They are not excessive.," said Dzurisin. "We try very much to make measurements with remote instruments rather than with staff and we're constantly learning. But it's a sense of mission, and it's certainly an exciting career. There's no denying that."
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