April 24, 2000
Twenty years after big blast: Mount St. Helens leaves legacy of more accurate eruption predictions
Steve Malone began studying Mount St. Helens in 1973. He didn’t know that just seven years later he would be tracking swarms of earthquakes signaling that the mountain was about to blow its top.
Those initial studies, as a beginning geophysics researcher at the University of Washington, centered on a small seismometer network he and a colleague installed on the mountain to investigate reports of volcanic earthquakes. The two discovered the signals being recorded were generated by the sliding of glaciers that encased the peak.
Today those glaciers are gone. It has been two decades since the north face of Mount St. Helens collapsed, unleashing hot gas that melted the glacial ice and spewed a cloud of ash that blanketed much of Washington. Fifty-seven people were killed and hundreds of square miles of forest were flattened.
To Malone, a UW research professor in geophysics, one of the lasting legacies of the May 18, 1980, eruption is the improved technology that allows real-time detection and monitoring from a series of scientific instruments that beam their data directly to the UW seismology laboratory.
“It helps us to anticipate and prepare for what’s going to happen in the near future,” he said. “There were about 20 eruptions during the six years after the major eruption, and with all but two we could predict the start within hours or a day. St. Helens was certainly the first time in the United States where this was done so successfully.”
At one point Mount St. Helens held the distinction of being the most digitally wired mountain in the world. It has since been surpassed by other volcanoes, particularly in Japan, including Mount Usu on the island of Hokkaido, which recently erupted.
The first permanent seismic station was installed at Mount St. Helens in 1972. Signals from that instrument were transmitted to the university by radio and recorded on photographic film. This old-fashioned recording system was being replaced in early 1980 with a state-of-the-art digital computer system.
The computer recorder was activated on March 1 – just in time, it turned out. On March 20, it recorded a magnitude 4.2 earthquake. The next day, Malone and colleagues went to the mountain to install four more instruments.
“When we got back that night and looked at the seismograms, we saw that the aftershock pattern was not dying out,” he said. Concern mounted further the next day when the scientists realized the pattern of earthquakes was the type that could lead to an eruption.
Later analysis of the data showed that the seismic indications of the eruption actually started several days before the 4.2 earthquake was recorded. But it wasn’t until the scientists gained new knowledge from their work that they recognized those signs.
“It’s like a lot of science, there’s usually a small amount of progress with additional information,” Malone said.
And so it was two years ago, when once again there was a flurry of seismic activity under Mount St. Helens. When the earthquakes dissipated, researchers were left trying to understand how, after an eruption, a volcano replenishes its deep magma system, 4 miles or so beneath the surface. Does it happen continuously over time, in brief episodes of activity spread over many years, or all at once as a precursor to eruption?
“Studying the swarm of earthquakes in 1998 leads us to think that, at Mount St. Helens at least, it is episodic,” Malone said.
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For more information, contact Malone at (206) 685-3811 or steve@geophys.washington.edu
The U.S. Geological Survey has established a Web site that recounts, day by day, what happened at Mount St. Helens 20 years ago. It is at http://vulcan.wr.usgs.gov/News/MSH20/framework_this_week.html
Tag(s): College of the Environment • Department of Earth and Space Sciences • earthquakes & seismology • Steve Malone
