Lessons learned at Mt. St. Helens could prove invaluable
What's going on at Mt. St. Helens besides an occasional eruption?
Plenty. Since the mountain broke its 123-year silence in 1980 with eruptions that included the cataclysmic May 18 blowup, it has been studied more intensively than any volcano in history.
The United States Geological Survey (USGS) has two groups totaling some 65 persons at work on the Washington State mountain. A geological division of 25 scientists, technicians, field assistants, and office workers is monitoring and studying the volcanic and seismic activity. A water resources group of about 30 specialists keeps close watch on the changing drainage systems in order to predict possible flood dangers and alert downstream residents and businesses.
In Seattle, at a laboratory of the University of Washington geophysics department, seismic data from Mt. St. Helens is interpreted. A number of other scientists have been at work on the mountain, studying biological and other phenomena.
Over the last two years, the USGS team has discovered that it can use the mountain's patterns of surface deformation and seismic activity to predict coming volcanic events. And it is felt that what is being learned here can be used elsewhere - especially where volcanoes threaten large populations -- to safeguard life and property.
Geologist Cathy Cashman, a member of the USGS team on Mt. St. Helens, recently described for the Monitor how the volcano is being studied and what the scientific and practical results have been so far.
She explained that the geological division's work is centered on the crater of Mt. St. Helens, where surface ''deformations'' caused by volcanic activity deep in the mountain are studied for indications of coming events. The scientists use electronic devices as well as common surveying tools to make precise distance measurements in the crater.
Ms. Cashman says the geologists have found that three-to-four weeks before a dome-building eruption occurs, ''we start to see an inflation of the crater floor, sometimes a swelling of the dome itself, and movement on what we call thrust faults on the floor of the crater near the dome. These thrust faults are places where one piece of the crater floor is being pushed up over another one.'' This swelling is attributed to movement of magma (molten rock) toward the surface.
The rate of deformation, she says, accelerates as the volcano ''approaches an eruption . . . It is this acceleration that we have used in our predictions.''
Also on the team is a geochemist who studies the chemistry of gasses escaping from fumaroles (vents) in the crater as well as material coming out of the dome itself. On daily flights over the volcano in a small airplane the geochemist, with an air-pollution measuring device, checks the amount of sulfur dioxide (SO2 ) in the plume. Increased presence of the SO2 in the gas from deep in the mountain could signal more discharge of magma.
The geologists study the chemistry of the material produced by each eruption to make sure nothing is changing.
''As long as the system shows the same signs, then we're pretty happy that we have a feel for what's going on,'' says Ms. Cashman. ''If we see a change in any of the patterns, whether its the chemistry, the deformation, or the seismicity - then we'll start to look more closely.''
In fact, before the last significant eruption on March 19, the USGS team noticed that the seismic activity was ''a little bit different.'' There were more tremors, and some were deeper than had been previously recorded.
These observations prompted the geologists' to warn, shortly before the eruption that was widely reported as unexpected, that ''we could have explosive activity. And we did,'' says Ms. Cashman.
The water resources division of the USGS team at St. Helens began studying changes in the drainage pattern on the mountain shortly after the May 18, 1980, eruption. Like the geological team, it has a dual role: scientific research and protection of life and property in the region.
Heavy erosion of the new material thrown out by the eruptions has caused major changes in stream beds. The USGS specialists keep close watch on whether the water-carrying capacity of streams is being diminished. They estimate flood potential and pinpoint areas of potential danger. Through a satellite hookup, the water resources team sends data through the National Weather Service system.
The close link between the volcano and the water problem was illustrated by the March eruption, Ms. Cashman points out. With a great deal of snow in the crater of Mt. St. Helens, the hot blast of the explosion generated a mud flow that went into the Toutle River. The water division was on top of the situation, monitoring the flow of the mud downstream and providing accurate information on flood and other dangers.
On the scientific side, no volcano has ever been so thoroughly studied. The geologists are using new techniques, often improvising, according to Ms. Cashman. ''We can say, 'No one has done this before; let's try this and see if it works.' Certainly there's no other place in the world where people are even trying to predict what (a volcano) is going to do, let alone being able to predict a couple of weeks ahead of time.
''I think maybe the fact that we can do it suggests a lot of hope for (mitigating the effects of) other volcanoes - others that might be more hazardous or in areas that are more heavily populated, like the one that recently erupted in Mexico.''
Last summer the USGS Mt. St. Helens team went to several other volcanoes in the Cascade Range and installed basic instrumentation that will be checked about twice a year. They will get ''an idea what these volcanoes are like when they're quiet. Then maybe we can catch some sort of change well ahead of time. It's worth doing in the event another volcano starts to become active.'