Monitoring Nature's Big Blow-Up
THE catastrophic eruption of Washington's Mount St. Helens on May 18 blasted a cubic mile of mountainside tens of thousands of feet into the air, reducing the mountain's previous 9,677-foot elevation by more than 2,000 feet. The explosion caused more than a billion dollars' worth of damage and took dozens of lives. It also opened up a "window into the earth," Dartmouth geologist Richard Stoiber '32 said recently, and it gave volcanologists an opportunity to refine their admittedly crude tools for predicting when a volcano will blow.
Professor Emeritus Stoiber and two graduate students, Stanley Williams and Larry Malinconico '74, were among the 40 volcanologists who kept a watch on the mountain last spring and summer and studied the series of eruptions. "When a volcano erupts, particularly in North or South America, I like to go see it," Stoiber said shortly after his return to Hanover last June. He added that "there is actually less interest among American scientists in the active volcanic process than you might think, especially if one excludes the interest in Hawaii, where the process is somewhat different. Geologists tend to be interested in what volcanos produce - the rocks that are left behind as the result of a volcanic explosion."
The Dartmouth Earth Sciences Department, which offers an undergraduate major as well as a graduate degree in geology, has been one of the few centers of interest and research in volcanology. In fact, about one quarter of the scientists who congregated at Mount St. Helens had studied or taught at the College. One of the first research papers based on studies of the St. Helens eruption was published by Stoiber, Williams, and Malinconico in the June issue of Science magazine.
Stoiber noted that there had been two distinct phases of volcanic activity at the mountain last spring. Starting in late March, there were a series of giant steam explosions followed by a couple of weeks of relative quiet. The cataclysmic May 18 eruption and a lesser outburst a few days later emitted magma, gas, pumice, and ash. Volcanic ash, Stoiber explained, consists either of fragments of volcanic rock already present at the throat of the volcano "cold" rock blasted out during the eruption or particles of solidified magma. The liquid magma cools and turns into rock after it has been in the air for a time. If there are enough gas bubbles in the magma, the bubbles blow the walls of the rock apart and the fragments form the variety of ash that blanketed Eastern Washington, Idaho, and Montana.
The sulfur dioxide gas emitted by a volcano is of particular interest to the Dartmouth researchers. "It tells you if there is magma contributing gas to the eruption," Stoiber explained. "The early phase at Mount St. Helens didn't have much sulfur dioxide but the later phase did," he noted. "That tells us that the early part didn't have much magmatic component while the later part had quite a bit. If you have enough experience with a volcano's plumbing system, an increase in gas might tell you the volcano is about to go off. It doesn't do that for St. Helens yet because we don't have that much experience. One of my students, however, went to Mount Etna a .couple of years ago and found that an increase in sulfur dioxide there preceded an eruption by about 48 hours. That doesn't seem like very much advance warning, but for us it was a milestone. We haven't had anything to go on, so any indication is a plus. We're in such an inelegant state with this that anything looks good." The gas measurements are taken with a
correlation spectrometer, an instrument originally designed for studying emissions from coal-burning industrial plants. Although the spectrometer can be used from a stationary position on the ground or from a moving car, a plane is the favored site because more accurate readings can be obtained. By using a plane it is possible to avoid the distorting interference of a smog layer, to get closer to the plume of a volcano, and to take a series of measurements rapidly. The problem is the expense. Fortunately, the group from Dartmouth was able to use a plane at Mount St. Helens through a cooperative arrangement with the National Broadcasting Corporation. An NBC camera crew had a plane available but couldn't obtain a clearance to fly close to the volcano. The scientists had the necessary clearances but no plane, and the authorities raised no objections to the two groups working together.
Following the explosions in May, several scientists were quoted as welcoming the presence of lava in the crater as a signal that the explosive stage of the eruption had passed. A lava "dome" lava that stays put and plugs the hole, Stoiber explained - could be good or bad. "It's good while it's plugging the hole, but it might act as a cap to hold in the pressure until it bursts. I would like to see a dome with a lot of fumaroles emitting gas, which seems to be what is happening now. That is what didn't happen before the May 18 explosion."
Before that explosion, he recounted, there was almost no gas coming out, and observers thought that the gas was either being held inside the volcano or that there wasn't that much gas to begin with."Most of us thought the latter," Stoiber admitted. "To hold all that in was amazing. That's partly why the May 18 explosion was such a surprise. Because they're so dumb, volcanologists have to have three or four scenarios of what can happen. One of the scenarios was that Mount St. Helens was going to blow up, but that wasn't very high on the list."'
One of the most surprising features of the big explosion was that instead of the hot gasses coming down the side of the mountain into the valleys and forming socalled "glowing clouds," the force of the blast was directed out the side of the mountain. Stoiber said "that was one of the least likely scenarios. The pressure was a lot greater than we thought, and the pattern of earthquakes, it turned out, contributed directly to the whole side of the mountain blowing out. Now we can see how it happened." He predicted that the volcano would probably continue to erupt periodically.
The scientists from Dartmouth found the atmosphere among observers at the site "amazingly cooperative." Although scientists rushed to the site of the eruption from all over the country, they weren't engaged in the competitive, secretive races to capitalize on their findings that one might expect. That is partly explained by the nature of the event, Stoiber said, and by the relatively small number of geologists who specialize in volcanology. There was more than enough of Mount St. Helens for everybody.
Stoiber commended the United States Geological Survey for "stepping in to run the show." "They had good people in charge of the environmental-hazards and science aspects of the situation," he said, "and they welcomed outsiders with something to offer. They helped to provide clearances, and there was a great deal of cooperative effort and sharing. The USGS was so good to the Dartmouth people you wouldn't believe it." He noted, however, that there were perpetual logistical problems, "a constant merry-go-round with the press, the government, the scientists, and the planes." He said he had never been on a job where there was so much to keep on top of. "It was nobody's fault, it was just the nature of the situation." Another non-science "part of the business" Stoiber described was the search for research money. The trips to St. Helens depleted his N.A.S.A. funding for volcanic studies and he was looking for further government sponsorship. If the right sort of grant could be obtained, he said, he was hoping to include undergraduates as well as graduate assistants in some of the follow-up research.
Reflecting on the value of the work that was accomplished at Mount St. Helens, Stoiber observed that it was the first time he had seen an eruption without magma change into a magmatic explosion. "The ones I'm most familiar with are magmatic right along. This was particularly rewarding scientifically because it changed from one kind of eruption into another. We learned that sulfur dioxide is a good tool for telling when the change occurs, and the rock fragments back up our observations. For some scientists, this was a first experience dealing with the active eruptive process in the circum-pacific. Scientifically, this was a good experience for volcanologists."
The portrayal of scientists as delighted by the eruption and oblivious to the destruction that resulted is a distortion, however. Stoiber seemed very much in awe of the power of the volcano and sensitive to the cost of the blow-up. One of his associates, David Johnston, a U.S.G.S. scientist who was operating the correlation spectrometer, was buried by mud and ash. What Stoiber seemed happy about was the chance to improve the methods for predicting an eruption in order to give a vulnerable population some advance warning.
"Every volcano we study we get a better idea of what is happening," Stoiber added. "Until we study quite a few, we won't be able to forecast with much accuracy. We need to establish a pattern and to follow a lot of case histories. We've hardly begun. The best tool for forecasting is probably seismic measurements. One can also look at how the area is tilting and at the pattern of volcanic history. Gas measurements are just one very interesting way of looking at things. It has been a fantastic opportunity for us to learn."
At Mount St. Helens
Stoiber (wearing oxygen mask) and Williams during a flight over Mount St. Helens.
