The eruptive activity of Mount St. Helens has provided a good test for scientists who faced the challenge of obtaining, relaying, and explaining in easily understandable terms the information needed by the Federal, State, and local officials charged with land management and public safety. It should be reemphasized, however, that a quick response at Mount St. Helens was possible only because decades of systematic research before 1980 had contributed to a good understanding of the volcano's eruptive behavior and potential hazards. Additionally, the Mount St. Helens activity also has provided scientists a unique opportunity to learn much about the dynamics of an active composite volcano. The results of studies completed and in progress have improved the understanding of eruptive mechanisms and should refine a forecasting capability not only for Mount St. Helens but also for similar volcanoes in the United States and elsewhere.
Scientists of the David A. Johnston Cascades Volcano Observatory (CVO) collecting gas samples in Mount St. Helens as part of the geochemical monitoring program (Photograph by Kathy Cashman).
When the 4.2-magnitude earthquake occurred on March 20, 1980, seismologists of the University of Washington and the USGS began a round-the-clock effort to expand the monitoring and to evaluate the seismic activity. As the number of earthquakes increased over the next few days, USGS and other scientists discussed with officials of the Gifford Pin chot National Forest the significance of the seismic activity, the safety of USFS facilities near the volcano, and the need to close its upper slopes because of snow avalanche and other hazards. USGS scientist Donal Mullineaux arrived on the scene the evening of March 25, and an emergency coordination center was set up at the USFS headquarters in Vancouver. The next day, Mullineaux--one of the foremost experts on Mount St. Helens--described the possible types of eruptions and associated volcanic hazards at a meeting of representatives from government and industry. Following the meeting, the USFS, State, and county officials decided to extend the area of closure beyond the immediate flanks of the volcano. The same day (March 26), the general nature of potential eruptive activity and volcanic hazards was discussed again at a joint USFS-USGS press conference. An official announcement of a Hazard Watch for Mount St. Helens was issued by the USGS at 8 a.m. PST on March 27. By 12:36 p.m. that day, the first eruption of Mount St. Helens in over a century had begun.
By the time the eruptive activity was into its second week, 25 to 30 scientists were on hand carrying out a wide variety of monitoring and volcanic-hazard-assessment studies. These scientists participated in daily meetings and briefings with USFS and other officials and provided advice on the locations of hazardous zones for use, such as the selection of sites for roadblocks to control access around the volcano. All decisions regarding access and restricted areas, however, were the sole responsibility of the USFS, State of Washington, and other land managers for the Mount St. Helens region. Ironically, in 1980 the section of land containing the summit crater was owned by the Burlington Northern Railroad; it has since been acquired by USFS by land exchanges. On March 31, an onsite, comprehensive, volcanic-hazards assessment was presented at another meeting of agencies responsible for public safety. On April 1, a large-scale volcanic-hazards map was prepared for use by these agencies. A news release was issued by the USGS on what might be expected should the activity develop into a "major eruptive phase." Scientists contributed geotechnical and volcanic-hazards information essential for preparing the "Mount St. Helens Contingency Plan" issued by the USFS on April 9. Although the possibility that the collapse of the rapidly deforming "bulge" on the north flank could trigger a magmatic eruption was considered and discussed with officials at various meetings in late April, scientists could not be sure that such an event would actually occur, let alone estimate its timing or size.
The early recognition of the potential hazards of the bulge on Mount St. Helens' north slope and the systematic measurement of its extremely rapid growth led scientists to advise the USFS that hazards were increasing. Accordingly, the USFS, State, and county officials enforced closure zones. Had these access-control measures not been taken, the catastrophic events of May 18 would have resulted in considerably more human deaths and injury. An element of luck also saved many lives. The catastrophe began hours before the scheduled departure of a caravan of landowners permitted by officials to enter the controlled access area to inspect their properties and cabins. Also, had the eruption occurred on any other day than Sunday, many more people authorized to enter the restricted areas (such as loggers, USFS personnel, and government officials) would have been at work and exposed to the danger.
Legislation passed by Congress in 1974 made the Geoiogical Survey the lead Federal agency responsible for providing reliable and timely warnings of volcanic hazards to State and local authorities. Under this mandate, and recognizing the need to maintain systematic surveillance of Mount St. Helens' continuing activity, the USGS established a permanent regional office at Vancouver, Washington, after the May 18, 1980, eruption. On May 18, 1982, the office at Vancouver was formally designated the David A. Johnston Cascades Volcano Observatory (CVO), in memory of the Survey volcanologist killed 2 years earlier. Staffed by about 90 permanent and part-time employees--geologists, geophysicists, hydrologists, geochemists, technicians, and supporting personnel--the CVO not only maintains a close watch on Mount St. Helens but also serves as the headquarters for monitoring other volcanoes of the Cascade Range in Washington, Oregon, and northern California. In recent years, the CVO staff has also participated in studies of eruptions or unrest at other volcanoes in the western United States and elsewhere in the world. The Cascades Volcano Observatory is a sister observatory to two other volcano observatories operated by the USGS: the Hawaiian Volcano Observatory, founded in 1912, has pioneered or refined most of the modern volcano-monitoring methods used in the world today; and the Alaska Volcano Observatory, established jointly by the USGS and the state of Alaska in 1988, studies the volcanoes of the Alaskan Peninsula and Aleutian Islands.
CVO scientist making
a ground-deformation measurement as a small explosion takes place. This
photograph shows the laser beam transmitter positioned atop a heavy 12-foot-high
steel tower centered over a benchmark used as the measurement reference
point. Such towers allow measurements to be made at Mount St. Helens during
the winter despite deep snow (Photograph by Lyn Topinka).
Throughout the 1980s, the ability of scientists at CVO and the University of Washington to provide warnings for dome-building eruptive episodes has been exceptional. Indeed, for all episodes (except for one small event) since May 1980, scientists using data from seismic, ground deformation, and volcanic gas monitoring have provided reliable forecasts from several hours to several days, even weeks, in advance of these events. The table (p. 50) gives a typical example of the timely information for one 1982 eruption given to government officials charged with emergency management and to the general public via news releases.
Sketch map showing the close-in monitoring network at Mount St. Helens. The seismic network, jointly operated by the USGS and the University of Washington, covers an area much larger than that shown in the diagram--encompassing the entire State of Washington. EDM stands for electronic distance monitoring.
At Mount St. Helens, the track record for predicting eruptions, especially dome-building ones, is better than any previously accomplished for any volcano in the world. Our improving predictive ability, however, has not been tested by any large explosive eruptions.
August 18-23, 1982, Eruption of Mount St. Helens
Type of Notice and When Issued
Extended Outlook Advisory
|"an eruption will probably begin within the next 3 weeks." ". . . the eruption will consist primarily of dome growth."|
|"eruption will begin within the next 4 days, possibly within 2 days . . . the eruption will consist primarily of dome growth, but as with all dome growth, minor explosive activity is also possible."|
|"Seismicity and rates of deformation in the crater have accelerated sharply . . . the expected eruption will probably begin within the next 24 hours."|
Updated Eruption Alert
|"The dome is already growing internally, but we have not seen any discrete event yet, for example, an explosion, a change in the character of seismicity or deformation . . . or gas emissions, that in other eruptions has signaled the onset of . . . eruptions. We still expect lava to eventually work its way through the dome and to be extruded as a new lobe on the surface of the dome."|
|"Lava finally broke through to the top of the dome this morning, and a new lobe is flowing slowly onto the western and southern sides of the dome."|
|"Deformation and gas emissions have returned to their background levels, so this eruption is essentiaily over. Minor sagging and spreading of the new lobe may continue for a few days, accompanied by occasional rockfalls and dust plumes. "|
Mount St. Helens has provided, and will continue to provide, an unprecedented
opportunity for scientific research on volcanism. Relatively easy accessibility
and a dense network of monitoring instruments have made Mount St. Helens
a natural laboratory at which scientists can study processes typical of
volcanoes elsewhere along the circum-Pacific "Ring of Fire." As
Mount St. Helens is monitored continuously before, during, and after each
eruptive episode, and its eruptive products are regularly sampled for chemical
and other laboratory analyses, the information being compiled and interpreted
yields a better understanding of Mount St. Helens in particular, and other
composite volcanoes in general. Moreover, the monitoring techniques now
being used at Mount St. Helens and other Cascade volcanoes are the same
as, or variations of, those used to monitor the active Hawaiian volcanoes.
Thus, in the rather young science of volcanology, there is a rare opportunity
to compare the effectiveness of these techniques on two contrasting kinds
of volcanoes--the Hawaiian shield volcanoes, which typically erupt nonexplosively,
and the Cascade composite volcanoes, which typically erupt explosively.
Scientists have learned that data from all types of monitoring are helpful
regardless of the type of volcano. From such comparative studies, they will
be able to determine which techniques are the most effective and reliable
for monitoring each type of volcano. With such tools and broadened knowledge,
scientists may be entering a new epoch in volcanology, in which significant
advances in understanding volcanic phenomena will be achieved, accompanied
by a sharpened ability to forecast and mitigate volcanic hazards.
Continuing Volcanic and Hydrologic Hazards
Mount St. Helens National Volcanic Monument
Contact: John Watson
Last updated: 06.25.97