Twenty-five years ago today Mount St. Helens erupted in Washington state, prompting U. of I. graduate David Johnston of the U.S. Geological Survey to report "Vancouver, Vancouver, this is it" from inside his monitoring-station trailer. Johnston's body and trailer were never found; he was among 57 fatalities that day.
Susan W. Kieffer, now a Charles R. Walgreen Jr. Chair in the U. of I. geology department and a professor of physics at Illinois, had been on site that March and April as part of a U.S. Geological Survey team studying earlier, smaller eruptions of the long dormant volcano. On the Sunday morning of May 18, 1980, Kieffer was visiting neighbors in sunny Flagstaff, Ariz. Family plans to sell their home and build a new one would be delayed.
"The neighbor asked what we had been doing recently, and when we replied 'working at Mount St. Helens' we were told, 'Oh, it really blew up this morning!' " she recalled. "After recovering from the shock, we packed and headed back to the mountain that afternoon."
An official observer, Johnston, who had earned a bachelor's degree in geology from Illinois in 1971, had been camped on a high ridge, about 10 kilometers north of the summit of Mount St. Helens. The ridge on which he died, shortly after 8:32 a.m., is now named Johnston Ridge, and is the site of a permanent Webcam that broadcasts images every five minutes of the mountain.
"I love to log onto the Webcam when dawn opens at the mountain, and imagine what it must have been like that morning, 25 years ago," said Kieffer, who has studied the event now known as the lateral blast.
"The mountain looks so peaceful on a sunny morning, but the knowledge of how violent it turned makes it a very uneasy peace, even though now it is a relatively safe place," she said. "I had met David in the March-April work, and we enjoyed a tremendous comradeship. David was much more experienced with volcanoes than me, and because of his work with the explosive and dangerous Augustine Volcano in Alaska, he knew, and respected, the power of St. Helens probably more wisely than any of the rest of us."
Today, scientists have a lot more understanding of what happened that day, and Kieffer currently is part of a team using supercomputers to further analyze what happened and why.
In late March 1980, she said, sticky hot magma (melted rock) rose slowly into the summit of the mountain. The heat from the magma warmed the groundwater. Some of the groundwater turned to steam, and had been erupting through the top of the mountain in a series of events in March and early April. Eventually, about mid-April, the mountain "dried out," she said, and the little eruptions ceased. The weight of the mountain kept pressure on the hot water and magma, like the walls of a steam boiler keep pressure on the hot water inside and prevent it from turning into steam.
The north side of the mountain was structurally weak. Eruptions had occurred there in the 1800s, culminating in 1857 with the emplacement of a small dome called Goat Rocks. The magma under Goat Rocks had been cooling for nearly 125 years, but was still hot enough to be able to move again in 1980. On March 27, 1980, the mountain awoke with a series of summit explosions and within weeks, geologists were measuring that the north flank of the mountain was bulging outward at more than a meter per day.
"Eventually, on May 18, the bulge became so steep that the whole north flank collapsed in a series of three enormous landslides," Kieffer said. "The pressure on the hot water and magma inside the mountain was released, just like the pressure in a steam boiler is released if the walls get fractured or punctured."
The expanding steam and gases in the magma at Mount St. Helens propelled broken rock, fragmented rock and glaciers over 500 square kilometers of land, ripping up and destroying about 4 billion board feet of timber along the way, and causing nearly $1 billion in economic damage.
"These eruptions have been described as 'ash hurricanes,' " Kieffer said. "Everything in this area died, including David and the 56 others. "If it hadn't been a Sunday morning, many more people would have died because Weyerhauser Co. employees were allowed to continue logging in the area during the work week."
Kieffer has mapped the directions of blow-down of the trees and reconstructed the dynamics of the blast using rocket-engine theory. She proposed that the flow within the most highly damaged area was moving so fast that gravitational forces couldn't act to divert the flow of the "ash hurricane" down the valleys.
"The standard wisdom at the time was that you would be safe if you were on a ridge - that the flow would follow the topography down the valleys," she said. "Not so in this type of event."
Kieffer is working with Illinois colleagues S. (Bala) Balachandar, professor and associate head of the department of theoretical and applied mechanics, and Andreas Haselbacher, a research scientist at the Center for Simulation of Advanced Rockets, to use supercomputing capabilities and the university's Apple Turing Cluster computer to improve the understanding of the volcano's eruption.
"At the time of the 1980 eruption, we didn't have supercomputers," Kieffer said. "Now, we have not only the computational power for the models, but the visualization capabilities of the NCSA (National Center for Supercomputing Applications), and we're hoping to really understand and visualize these events."
The 1980 eruption, she said, was not unique. "We now know that there were nearly identical events at Bandai-San, Japan, in 1888, and Bezymianny in the Soviet Union in 1956, and probably similar events at a dozen other volcanoes around the world," she said. "The volcanoes of the Pacific Rim of Fire, including Oregon, Washington and Alaska, are particularly prone to this style of volcanism. It is important that we improve our understanding of the hazards by understanding the power of the eruptions."
