US History/US History (Bureau Development Inc.)(1991).ISO/dp/0029/00295.txt

Text File | 1990-12-23 | 34KB | 529 lines

$Unique_ID{USH00295}
$Pretitle{26}
$Title{Eruptions of Mount St. Helens:  Past, Present and Future
Comparisons With Other Eruptions}
$Subtitle{}
$Author{Tilling, Robert I.}
$Affiliation{US Geological Survey}
$Subject{helens
st
mount
eruption
eruptions
scientists
activity
dome
hazards
volcanic}
$Volume{}
$Date{1987}
$Log{Lava Dome*0029501.scf
St Helens, 1981*0029502.scf
VEI*0029501.tab
}
Book:        Eruptions of Mount St. Helens:  Past, Present and Future
Author:      Tilling, Robert I.
Affiliation: US Geological Survey
Date:        1987

Comparisons With Other Eruptions

     The May 18, 1980, eruption of Mount St. Helens was exceeded in "size" by
many other eruptions, both in historic times and in the recent geologic past.

     For the study of earthquakes, two standard measures of the "size" of the
seismic event are commonly used:  the Richter Magnitude Scale (based on energy
released as measured by seismometers) and the Modified Mercalli Intensity
Scale (based on damage caused as assessed by people).  Although some attempts
have been made to develop a scale to compare the relative sizes of volcanic
eruptions, none has yet been adopted for general use.  Volcanologists have
proposed and used various schemes to rank eruptions, and these generally
included one or more of the following factors - height of eruption column,
volume of material erupted, distance and height of hurled blocks and
fragments, amount of aerosols injected into the upper atmosphere, and duration
of eruption.  All these factors relate directly or indirectly to the total
amount of energy released during the eruption.  Perhaps the two most commonly
used and directly measurable factors are eruption volume and height of the
eruption column.

     The volcano ejected about 0.3 cubic mile of uncompacted ash, not counting
an unknown but probably much smaller amount that was deposited in the
atmosphere or too diffuse to form measurable deposits.  This volume of ash is
less than those of several earlier eruptions of Mount St. Helens and
considerably less than the ejecta volumes of some historic eruptions
elsewhere.  The 1815 eruption of Tambora (Sumbawa, Indonesia) ejected about 30
to 80 times more ash than did Mount St. Helens in 1980.  The 1815 Tambora
eruption ranks as the largest known explosive eruption in historic times.  But
even the Tambora eruption pales by comparison with the gigantic pyroclastic
eruptions from volcanic systems - such as Long Valley Caldera (California),
Valles Caldera (New Mexico), and Yellowstone Caldera (Wyoming - which, within
about the last million years, produced ejecta volumes as much as 100 times
greater.

     Some scientists recently proposed the Volcanic Exposivity Index (VEI) to
attempt to standardize the assignment of the size of an explosive eruption,
using ejecta volume as well as the other criteria mentioned earlier.  The VEI
scale ranges from 0 to 8.  A VEI of 0 denotes a nonexplosive eruption,
regardless of volume of erupted products.  Eruptions designated a VEI of 5 or
higher are considered "very large" explosive events, which occur worldwide
only on an average of about once every 2 decades.  The May 1980 eruption of
Mount St. Helens rated a VEI of 5, but just barely; its lateral blast was
powerful, but its output of magma was rather small.  The VEI has been
determined for more than 5,000 eruptions in the last 10,000 years.  None of
these eruptions rates the maximum VEI of 8.  For example, the eruption of
Vesuvius Volcano in A.D. 79, which destroyed Pompeii and Herculaneum, only
rates a VEI of 5.  Since A.D. 1500, only 21 eruptions with VEI 5 or greater
have occurred:  one VEI 7 (the 1815 Tambora eruption), four of VEI 6
(including Krakatau in 1883), and sixteen of VEI 5 (counting Mount St.
Helens). Considered barely "very large," the eruption of Mount St. Helens in
May 1980 was smaller than most other "very large" eruptions within the past
10,000 years and much smaller than the enormous caldera-forming eruption -
which would rate VEI's of 8 - that took place earlier than 10,000 years ago.

     The number of casualties and extent of destruction also have been used to
compare the "bigness" of volcanic eruptions.  For obvious reasons, such
comparisons are limited at best and misleading at worst.  Some of the most
destructive eruptions have not been in other terms "very large."  As the table
below ("VEI") clearly shows, of the six greatest volcanic disasters in terms
of casualties since A.D. 1500, only two of them (Tambora and Krakatau) qualify
as "very large" eruptions (VEI's greater than 5) in terms of their explosive
force.


[See VEI: Volcanic Explosivity Index]

     The May 1980 eruption of Mount St. Helens has a higher VEI (5) than four
of the deadliest eruptions in the history of mankind, but it resulted in the
loss of far fewer lives (60).  Loss of life would have been much greater if a
hazard warning had not been issued and a zone of restricted access had not
been established.

Subsequent Eruptions

     Since May 18, 1980, Mount St. Helens has remained intermittently active,
and at least 15 eruptions have occurred following the catastrophic activity.
The first of these smaller but significant eruptions began early Sunday
morning, May 25, 1980, when Mount St. Helens explosively erupted ash and
formed an eruption column that rose to a maximum altitude of 9 miles.  At
least one pyroclastic flow accompanied the vertical ash emission.  Although
this eruption was considerably less energetic and voluminous than that of May
18, it nonetheless caused much concern because of memories of the events of
the previous Sunday.  Variable winds dispersed ash over southwestern
Washington and neighboring Oregon, producing small to moderate ash falls in
communities that had been spared the ash fall of May 18.

     For the next 2 weeks, Mount St. Helens remained relatively quiet at its
vent, puffing steam and gas but little ash.  Meanwhile, rootless steam-blast
eruptions continued in the northern periphery of the apron of the pyroclastic
flows in the valley of the North Fork of the Toutle River.  On clear nights,
aerial observers reported seeing glows in the vent crater, interpreted to
reflect the presence of near-surface magma even though no lava was extruded.
on June 12, the volcano again erupted, generating ash falls to the
south-southwest and pyroclastic flows down the north flank.  The June 12
eruption was similar to that on May 25 in style and volume, and both eruptions
were preceded by harmonic tremor a few hours in advance of the events.

     Probably within hours following the explosive activity on June 12, but
hidden by poor visibility, pasty magma began to ascend in the vent to form a
bulbous dome of lava on the crater's floor.  Such lava domes commonly form at
stratovolcanoes following major explosive eruptions.  The formation of the
first of Mount St. Helens' many lava domes during the current activity was
confirmed by observers on June 15 when visibility over the volcano improved.

[See Lava Dome: View of the first lava dome that formed in the bottom of the
crater created by the May 18, 1980, eruption. Helicopter (circled) gives
scale. This dome was destroyed during the eruption of July 22, 1980.]

     Mount St. Helens erupted again in several pulses during the afternoon and
evening of July 22.  The July eruption was preceded by several days of
measurable swelling of the summit area, heightened earthquake activity, and
changed emission of sulfur dioxide and carbon dioxide.  Eruption plumes rose
to altitudes of between 6 and 11 miles.  The eruption destroyed most of the
dome formed in mid-June, and pyroclastic flows poured through the north breach
of the amphitheater and overrode earlier flows.  No dome developed after the
cessation of explosive activity, which ejected only about one-tenth as much
ash as that of the May 25 and June 12 eruptions.

     During the next 3 months, explosive eruptions occurred on August 7 and on
october 16-18.  These eruptions were preceded by differing combinations of the
following precursors:  increased earthquake activity, harmonic tremor, changed
gas emission, and swelling of vent area.  Both eruptions produced
ash-steam-gas clouds and pyroclastic flows, followed by the emplacement of
viscous lava domes.  Subsequent eruptions, beginning with the December 27,
1980 - January 3, 1981 eruption, have involved predominantly nonexplosive,
dome-building activity.  During the remainder of 1981, five dome-building
eruptions, accompanied by little or no ash emission, took place:  February
5-7, April 10-12, June 18-19, September 6-11, and October 30 - November 2.

     Three eruptions occurred in 1982:  March 19 - April 9, May 14-18, and
August 18-23.  In the first explosive activity since October 1980, the
March-April 1982 eruption produced an ash column 9 miles high and was
accompanied by small debris avalanches and mudflows.  Dome growth followed
this eruption.  The May and August eruptions in 1982 returned to the
nonexplosive mode and only involved dome growth.  For about a month following
the cessation of the May eruption, however, vigorous "gas-emission" events
produced spectacular vertical plumes of steam, gas, and rock debris many
thousands of feet high that were visible from Portland, Oregon (50 miles
distant) and, on occasion, even from Seattle, Washington (100 miles distant).
Scientists believed these emission were caused by steam-blast processes
triggered when cold infiltrating rain and ground water came in contact with
the subsurface hottest parts of the dome.  Gas-emission activity ceased
abruptly by late June.

     Several eruptions occurred in 1983:  one during February 7-28 and another
that began at the end of April.  The February eruption was preceded by several
gas explosions on February 2-4, the largest of which produced plumes of steam
and ash 2 to 4 miles high.  These explosions ripped open a gash on the dome's
summit through which lava extruded about February 7.  The February
dome-building eruption culminated in the formation of a spine-like protrusion
of lava that rose about 200 feet above the dome's summit.  The spine lasted
for about 2 weeks and then collapsed into a heap of rubble.  The eruption that
began at the end of April was preceded by 3 to 4 weeks of increased seismicity
as well as by internal growth of the dome at rates as great as 3 feet per day.
Slow extrusion of lava probably began between April 29 and May 4 and has
continued intermittently through February of 1984, adding several small lobes
to the dome.

     Following about 3 weeks of inactivity, the end of March 1984 was marked
by increased earthquakes, rapid swelling of the dome, and frequent rockfalls,
indicating the onset of renewed dome growth.  Extrusion of a new lava lobe was
confirmed by aerial observation on March 29.  This dome-building event, in
contrast to the preceding year-long (February 1983 - February 1984) period of
virtually nonstop extrusive-intrusive activity, ended by April 6.

     Scientists studying Mount St. Helens have called the resultant dome
structure rising in the bottom of the crater a "composite dome," because
during each eruption, material is extruded onto the surface to add another
lobe, cap, or spine to the irregular mound of viscous lava.  The composite
dome also can increase in size and change shape between eruptions when
material added does not break through to the dome's surface.  Usually,
scientists consider an "eruption" to occur only when the activity involves the
visible expulsion of material from the vent.  In this regard, the starting and
ending dates assigned to the 1983 "eruptions" are somewhat arbitrary because
of the virtually continuous, measurable internal growth of the composite dome,
punctuated by occasional outbreaks of lava through the dome's surface, which
only can be seen under clear weather conditions.  Since April 1984, Mount St.
Helens appeared to be conforming to its pre-1983 pattern of brief
dome-building eruptions, lasting only a few days, separated by relatively calm
intervals lasting several weeks or months.

     The dome-building eruptive process at Mount St. Helens may be pictured as
a periodic squeezing of an upward-pointing tube of toothpaste or caulking
compound.  It is a dynamic process involving the squeezing up of new material,
cracking and pushing aside of old material, sloughing off of material from
steep surfaces of the dome, and occasional, small violent eruptions to blast
out pieces of the dome.

     As of summer 1984, the composite dome measured about 2,880 feet long,
2,720 feet wide, and 810 feet high, comprising an aggregate volume of over 60
million cubic yards.  Thus, though growing, the composite dome still occupies
only about 2 percent of the volume of the volcano (about 3.5 billion cubic
yards) removed during the May 18, 1980, eruption.  At the present average rate
of dome construction (35 million cubic yards per year), it would take nearly a
century to fill in the summit crater and to rebuild Mount St. Helens to its
pre-1980 size.

Possible Future Behavior

     For a few intensively monitored volcanoes, scientists in recent years
have greatly improved their capability to forecast when and sometimes even
where an eruption might take place with lead times on the order of several
days or less.  For example, the current ability to forecast eruptive events at
Mount St. Helens represents a major advance; since May 1980, all eruptions
have been successfully forecasted days, or even several weeks, in advance.
Even for accurately forecasted eruptions, however, there is no way to predict
their size or duration.  Moreover, scientists are not yet able to forecast
accurately the long-term future behavior of volcanoes.  For example, for Mount
St. Helens scientists cannot answer now with any certainty the following
questions.  How long will the present intermittent eruptive activity last?
Will another large explosive eruption comparable to that of May 18, 1980, take
place within the next decade or century?  Will lava flows accompany future
eruptions?

     Most earth-science studies are concerned with past events, and the axiom
that "the present is the key to the past" is fundamental to these studies.  In
recent years, as earth scientists have been asked repeatedly to look forward
in time, the axiom that "the past and present are keys to the future" has
become increasingly significant.  Clues to the possible future behavior of
Mount St. Helens are gleaned from its past eruptive history.  During the past
4,500 years, Mount St. Helens has evolved through nine eruptive periods, not
counting the activity that began in 1980.  The most recent and best known of
these periods began with a major explosive eruption about 1800.  For the next
half century, this event was followed by intermittent relatively small
explosive eruptions, lava flows, and extrusions of lava domes.  Such activity
ceased by 1857.  Assuming that Mount St. Helens behaves as it has in the
mid-19th century, the present activity seems likely to continue intermittently
for years, possibly decades.  Such activity could include the outpourings of
lava flows, not observed to date, as well as continued dome growth and
small-to-moderate explosive events.  The probability of another catastrophic
landslide and blast comparable to that of May 18, 1980, is exceedingly low.
The past history of the volcano suggests, however, that one or more additional
explosive eruption - with heavy ash emission comparable to that of the May 18,
1980, eruption - may occur before Mount St. Helens returns to a dormant state.
This history of intermittent activity is one of the most important reasons why
scientists monitor the mountain - to detect the intensive, sustained seismic
activity and ground deformation that can be expected to accompany any massive
infusion of new magma required to feed an eruption of major proportions.

Continuing Volcanic and Hydrologic Hazards

     The present intermittent eruptive activity at Mount St. Helens poses
volcanic and hydrologic hazards for the foreseeable future.  Specific
hazards - ash fall, pyroclastic flows, mudflows, and flood - were described by
scientists years before they became stark realities on May 18, 1980.  Since
then, as the volcano settled into a pattern of episodic, moderate and
generally nonexplosive activity, the severity and regional impact of ash fall,
lateral blasts, and pyroclastic flows have diminished.  Given Mount St.
Helens' alternations between explosive and nonexplosive activity in its past,
however, the possibility of violent eruptions and attendant hazards in the
future should not be discounted.

     Considerable hazards still exist in the immediate vicinity of the
volcano's present summit - the amphitheater-like crater, with its growing and
ever changing composite lava dome.  As the composite dome enlarges, chances
increase for collapses of its steep, irregular sides.  Such collapses, in
turn, could hurl rock fragments onto the crater floor and possibly trigger
small pyroclastic flows through the crater breach and down the north flank of
the mountain toward Spirit Lake.  Rockfalls from the unstable steep walls of
the crater have been common since the formation of the huge crater, posing a
local but significant hazard to scientists working within it.  Pyroclastic
flows could also pose a serious threat in the Spirit Lake and other areas
directly downslope from the breached summit crater.

     Scientists and other people working close to or within the volcano's
crater - within the "restricted zone" established by the USFS - must remember
these hazards and take safety precautions.  Accordingly all work parties are
required to maintain radio contact with their headquarters so that they can be
notified of any increased seismicity and other precursory indicators of
possible impending activity.  Scientists working in or near the crater must
use helicopters for access; thus, they are always near a helicopter should a
quick evacuation be necessary.

     Lava flows from Mount St. Helens pose little direct hazard to people or
property because such flows are likely to be very sluggish and, therefore,
should not move very fast or far from the vent.  Anyone in good health should
be able to outwalk or outrun the flows, and no major civil works are near
enough to the volcano to be overrun by lava flows.  Such flows, however, like
other high-temperature eruptive products, melt snow and ice and thus could
cause mudflows and floods.

     Given the current, relatively quiet, eruptive behavior of Mount St.
Helens, mudflows and floods at present constitute the greatest hazards related
to volcanic activity.  The potential for mudflows and floods has been
increased by the existence of new ponds and lakes formed when the debris
avalanche of May 1980 blocked parts of the preexisting drainage to serve as
natural dams.  As these natural dams are composed of loose, easily erodible
volcanic debris, they are structurally weak and could fail, which would
trigger mudflows and floods.

     Devastating mudflows or floods or both could be triggered by any or all
of the following:  heavy rainfall during storms, melting of snow and ice by
hot eruptive products (especially pyroclastic flows), or by sudden failure of
one of the lakes impounded by the debris avalanche deposits. During winter -
the time of peak precipitation and maximum snowpack - the risks of mudflows
and floods increase significantly.  Normal precipitation in the Mount St.
Helens area is heavy, especially on the volcano's upper slopes, where the
average annual rainfall totals 140 inches.  In a normal winter, the snowpack
on the volcano's higher slopes can be about 16 feet thick.  Thus, scientists
and civil authorities are rightly concerned about the high potential for
mudflows and floods posed by the combination of abundant raw materials (rock
debris and water) and continuing eruptive activity.

     As an example of the flood hazards in the Mount St. Helens region, in
August 1980 the failure of a natural debris dam, after a heavy rainstorm,
caused the rapid draining of a 250-acre-foot lake in the Toutle River Valley
near Elk Rock.  The ensuing flood damaged heavy channel-maintenance equipment
in the North Fork of the Toutle River, but, fortunately, caused no injuries or
deaths.  For the remainder of 1980 and into the spring of 1981, there were no
major hydrologic disasters, largely because the winter and spring of 1980-1981
were exceptionally dry.  Similarly, there also were no damaging mudflows or
floods the following year because of lower than normal precipitation.  The
levels of the lakes impounded by natural dams, however, gradually rose due to
rainfall and runoff.

     By the summer of 1982, the debris dams for three of the largest lakes -
at Spirit Lake, Coldwater Creek, and South Fork Castle Creek - were becoming
substantially eroded, thereby increasing the risk of catastrophic flooding
should the dams fail or be over-topped.  The Army Corps of Engineers, in the
fall of 1982, began to control the rise of the level of Spirit Lake by pumping
and discharge into outlet channels, and the USGS and the National Weather
Service installed flood-warning systems in the Toutle and Cowlitz River
Valleys.  By March 1983, Spirit Lake had 360,000 acre-feet of water, the lake
at Coldwater Creek had 67,000 acre-feet, and that at South Fork Castle Creek
had 19,000 acre-feet.  Scientists and engineers estimate that a breach of the
natural dam at South Fork Castle Creek, the smallest of the three lakes, could
unleash mudflows and floods comparable to those triggered by the May 18, 1980,
eruption of Mount St. Helens.  The Army Corps of Engineers, the Soil
Conservation Service, and other Federal, State, and county agencies have a
variety of projects underway to mitigate the growing hydrologic hazards.
These mitigation projects require many people and much equipment to work in
the hazardous zones close to the volcano.  To ensure the safety of the
mitigation operations, scientists must redouble their monitoring efforts not
only of the volcano itself, but also of the debris-clogged drainage systems.

     Mudflow and flooding hazards should exist for many years, until such time
as the slopes and areas around Mount St. Helens, by revegetation and normal
erosion, return to or approach their pre-eruption forest cover, stream
gradients, rates of flow, discharge, and channel dimensions.  In early 1984,
the Army Corps of Engineers announced a long-term plan to cope with the
continuing hydrologic hazards.  This plan included drilling a diversionary
tunnel to lower the water level of Spirit Lake.  In the meantime, scientists
must maintain the vigil and continually assess the volcanic and hydrologic
hazards in order to provide sound recommendations and timely warnings to
public officials to lessen the impact of the hazards.  Human efforts to
control the floods and sedimentation are designed not only to gain time to
avert hydrologic disasters until natural "healing" is complete, but also to
try to guide, if possible, the healing process.

Scientists' Challenge and Opportunity

     The eruptions of Mount St. Helens have 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 eruptions also have provided scientists a
unique opportunity to learn much about the dynamics of an active composite
volcano.  The results of studies in progress should improve 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.

     When the 4.0 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 Pinchot 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 on-site, 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 Geological 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 70 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.  The
Cascades Volcano Observatory is a sister observatory to the USGS' Hawaiian
Volcano Observatory (HVO), which was founded in 1912 and has pioneered or
refined most of the modern volcano-monitoring methods used in the world today.

     As the crater of Mount St. Helens continues to fill with new lava from
successive dome-building events, the ability of scientists at CVO and the
University of Washington to provide warnings for such eruptions has been
exceptional.  Indeed, for all eruptions 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. 44) 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.

     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.

     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 eruption, 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, 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.

[See St Helens, 1981: View of Mount St. Helens from the north in April 1981,
with Spirit Lake in the middle ground.]

Mount St. Helens National Volcanic Monument

     Despite the troubled economy in the early 1980's, many thousands of
tourists flocked to Mount St. Helens.  Tens of thousands of people, especially
during the summer months, have toured the USFS Mount St. Helens Visitor Center
in Toledo, Washington.  These people see firsthand the awesome evidence of a
volcano's destruction and the remarkable but gradual healing of the land as
revegetation proceeds and wildlife returns.  On August 27, 1982, President
Reagan signed into law a measure setting aside 110,000 acres around the
volcano as the Mount St. Helens National Volcanic Monument, the Nation's first
such monument.  At dedication ceremonies on May 18, 1983, Max Peterson, head
of the USFS, said "we can take pride in having preserved the unique episode of
natural history for future generations."  The National Volcanic Monument
preserves some of the best examples and sites affected by volcanic events for
scientific studies, education, and recreation.  Intensive monitoring of the
volcano will now be all the more important to ensure the safety of the
scientists and the monument's visitors.