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During the
1980-86 eruptions of Mount St. Helens,
hazards information was
quickly disseminated through a U. S. Geological Survey Cascades Volcano
Observatory - U. S. Forest Service notification system. Written and verbal
statements issued jointly by the Cascades Volcano Observatory (CVO) and
University of Washington (UW)
were released to the U. S. Forest Service (USFS) for telephone
call-down to governmental agencies and private interests. Once the call-down
was underway, public and media information tapes were updated and press
releases were issued. Because most of these eruptions had recognizable
precursors, a series of information statements and eruption forecasts was issued
during the weeks to hours before and eruption, thus providing advance warning of
volcanic activity and associated hazards.
Hundreds of small gas and ash emissions also occurred during 1980-86, most
without recognizable precursors. The lack of precursors made advance warning of
these events impossible; instead, information statements
were issued after the larger, more visible events. ...
When Mount St. Helens awoke in March 1980, there was an immediate need for the
rapid dissemination of information about volcanic events and hazards. An
emergency coordination center (ECC) was established at the U.S. Forest Service
(USFS) facility in Vancouver, Washington. The facility was staffed 24 hours a
day by USFS personnel experienced with emergency response. During critical
times, the ECC was also staffed by representatives of the U.S. Geological Survey
Cascades Volcano Observatory, emergency management agencies, and private
companies. A communications network and telephone call-down
procedures were developed to facilitate rapid dissemination of information about
the activity of the volcano. Information was also disseminated through public
meetings, press conferences, and briefings with governmental agencies and
private businesses (Miller and others, 1981). Written "volcanic and seismic
activity reports" were issued daily. These "daily updates" provided information
on the status of the volcano and any significant changes or observations during
the previous 24 hours. ...
Since May 18, 1980, 21 magmatic eruptions have occurred at Mount St. Helens; 5
were predominantly explosive, and 16 were predominantly non-explosive,
dome-building eruptions. Several eruptions involved both explosive and
dome-building activity. The last magmatic eruption was a dome-building
eruption in October 1986. Scientists at CVO in Vancouver, Washington, and at
the University of Washington Geophysics Program in Seattle were able to
predict most of these eruptions based on evaluation and interpretation of data
from an extensive monitoring network (Swanson and others, 1985). Initially,
these predictions were issued as verbal statements, but, after December 1980,
they were issued as written statements. Both types of statements were
distributed by the U.S. Forest Service through the Emergency Coordination Center.
For most eruptions, a series of statements was issued, usually
beginning with an "extended outlook advisory" predicting an eruption within
several weeks. As the levels of precursory activity increased, the predicted
eruption window was fine-tuned to days or hours, and "eruption advisories" and
"eruption alerts" were issued. After an eruption began, factual statements were
issued regarding the character and effects of the eruption, and, finally, a
statement was issued declaring the eruption to be over. The "daily updates" and
information tapes for the public and media provided additional information on a
daily basis.
Example of statements by CVO and UW released by USFS/ECC during the March-April
1982 eruptive period of Mount St. Helens, and "daily updates" about Mount St.
Helens issued by CVO and UW after the March 15, 1982 advisory and before the
March 19, 1982, alert.
Mount St. Helens Volcano Updates:
March-April 1982
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| Type of Notice and When Issued |
Statements |
March 5, 1982 - 0900 PST;
EXTENDED OUTLOOK ADVISORY
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Seismicity at Mount St. Helens increased around February 21 and has remained at
a level somewhat above background since that time. Approximately 100
earthquakes that occurred during this period have been located. These
earthquakes fall into two groups: (1) a "deep" group of very small earthquakes
with centers at 6- to 11-kilometer depths, and (2) a shallow group of somewhat
larger (magnitude 1 or less) earthquakes located at 3-4 kilometers us to the
surface. There is a pronounced lack of seismicity at a depth of 4-6 kilometers.
Although poor weather during the past week has hampered observations and
monitoring on the mountain itself, measurements made last week show only slow
ground deformation in the immediate vicinity of the dome and no significant
increase in gas emissions.
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March 12, 1982 - 0800 PST;
EXTENDED OUTLOOK ADVISORY
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Seismicity beneath Mount St. Helens continues at elevated levels, but
individual earthquakes are of low magnitude. Earthquakes have been occurring in
1-2-day-long episodes separated by 1-2-day intervals of decreased activity. The
earthquakes are occurring between the surface and a depth of about 6 miles.
Rates of ground deformation in the crater area have increased during the last
two weeks, and they are similar to patterns observed before previous
dome-building eruptions.
Based on rates of deformation, an eruption is likely within the next 3 weeks.
Deformation is confined to the crater areas, suggesting that renewed dome growth
will occur. The current seismic patterns differ from any observed before
1980-81 eruptions, however, and raise the possibility of more hazardous
variations in eruptive behavior. If there were to be any pyroclastic flows,
from either and explosive eruption or collapse of the steep north face of the
dome, the possibility of rapid snowmelt would be a concern.
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March 15, 1982 - 1900 PST;
ADVISORY
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Accelerating rates of ground deformation in the crater of Mount St. Helens
suggest that an eruption, most likely of the dome-building type, will probably
begin within 1 to 5 days. Deep earthquakes have almost ceased, and shallow
earthquakes continue at a moderate rate. A further increase in shallow
seismicity is likely before the eruption starts.
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March 16, 1982 - 0800 PST:
"Daily Update"
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Geologists and hydrologists form the Geological Survey performed on-site
monitoring in and around Mount St. helens on March 15, 1982. Measurements
showed accelerated rates of ground deformation on thrusts and cracks in the
crater. University of Washington-USGS reports seismicity remains at a slight
increase over the weekend's activity. Shallow earthquakes continue at a
moderate rate (see Mount St. Helens Advisory, 7:00 p.m., March 15, 1982).
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March 17, 1982 - 0800 PST;
"Daily Update"
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Good weather permitted on-site monitoring in and around Mount St. Helens by
geologists and hydrologists of the U.S. Geological Survey. Measurements showed
continued acceleration of ground deformation localized around the lava dome.
Overflights of the volcano the last two days have shown an increase in the
number of incandescent areas on the dome. University of Washington-USGS reports
seismicity remains at a moderate rate.
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March 18, 1982 - 0800 PST:
"Daily Update"
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Continued good weather enabled monitoring to be carried out in the crater of
Mount St. Helens for the third day in a row. Measurements performed by
geologists from the U.S. Geological Survey continued to document accelerating
ground deformation rates. Airborne gas monitoring around the volcano during the
past several days has shown that a moderate increase in the rate of SO2
emissions has occurred. The University of Washington-USGS seismic lab reports a
slight increase in the level of seismicity over that of yesterday, but it still
can be described as a moderate level.
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March 19, 1982 - 0900 PST;
ERUPTION ALERT
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Seismicity at Mount St. Helens has increased significantly during the past
day. This indicates that an eruption will begin soon, probably within the next
24 hours. The character of both the seismicity and deformation in the crater
area indicated the the most likely type of activity is dome growth.
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March 19, 1982 - 1933 PST;
ERUPTION ALERT
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Verbal statement that eruption had begun at 1927. (Significant increase in
seismicity and pilot and radar reports of an ash plume indicated start of
eruption.)
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March 19, 1982 - 2025 PST;
ERUPTION UPDATE
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The eruption has subsided for the time being, and an ash plume is blowing to
the SSE. and S. with a lesser amount to the SSW. The size of the eruption and
the amount of the ash appear to be like those of the summer 1980.
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March 21, 1982 - 0900 PST;
ERUPTION UPDATE
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There is a new lobe being added to the SE. side of the lava dome in the
crater of Mount St. Helens. The new extrusion began during the night.
Seismicity and tilt are now following patterns observed during other recent
periods of dome growth.
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March 24, 1982 - 1730 PST;
ERUPTION UPDATE
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Growth of the new dome lobe has slowed significantly over the past 2 days,
but rates of deformation on the north side of the dome have increased over the
same period. Until additional measurements are made, it would be premature to
declare this eruption over. Seismometers are recording decreasing numbers of
avalanches as growth of the new lobe slows.
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April 5, 1982 - 0100 PST;
ERUPTION UPDATE
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Seismicity still continues at moderate to high levels. Fluctuations in
seismicity correspond to pulses of gas and ash, the largest of which began at
1237 a.m. and rose to a maximum of about 32,000 feet. There does not appear to
be much ash in the plume, but minor ashfall was reported earlier tonight at
Packwood. No increases have been reported in river levels.
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April 5, 1982 - 1800 PST;
ERUPTION UPDATE
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Seismicity is continuing at a moderate to high level. The status of the
volcano remains unchanged since the previous advisory (1 a.m., April 5, 1982).
Some additional dome growth and (or) small-scale explosive activity is likely;
larger explosive activity is less likely but cannot be ruled out.
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April 6, 1982 - 0915 PST;
ERUPTION UPDATE
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Another new lobe is being added to the dome. This reduced the immediate
likelihood of larger explosive activity, but small, intermittent gas and ash
pulses may continue to occur.
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April 12, 1982 - 1515 PST;
ERUPTION UPDATE
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Seismicity, deformation and gas emissions at Mount St. Helens have returned
to low levels, indicating that the eruption that began on March 19, 1982 is over.
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