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Mount St. Helens erupts

Mount St. Helens erupts

At 8:32 a.m. PDT, Mount St. Helens, a volcanic peak in southwestern Washington, suffers a massive eruption, killing 57 people and devastating some 210 square miles of wilderness.

Called Louwala-Clough, or “the Smoking Mountain,” by Native Americans, Mount St. Helens is located in the Cascade Range and stood 9,680 feet before its eruption. The volcano has erupted periodically during the last 4,500 years, and the last active period was between 1831 and 1857. On March 20, 1980, noticeable volcanic activity began with a series of earth tremors centered on the ground just beneath the north flank of the mountain. These earthquakes escalated, and on March 27 a minor eruption occurred, and Mount St. Helens began emitting steam and ash through its crater and vents.

Small eruptions continued daily, and in April people familiar with the mountain noticed changes to the structure of its north face. A scientific study confirmed that a bulge more than a mile in diameter was moving upward and outward over the high north slope by as much as six feet per day. The bulge was caused by an intrusion of magma below the surface, and authorities began evacuating hundreds of people from the sparsely settled area near the mountain. A few people refused to leave.

On the morning of May 18, Mount St. Helens was shaken by an earthquake of about 5.0 magnitude, and the entire north side of the summit began to slide down the mountain. The giant landslide of rock and ice, one of the largest recorded in history, was followed and overtaken by an enormous explosion of steam and volcanic gases, which surged northward along the ground at high speed. The lateral blast stripped trees from most hill slopes within six miles of the volcano and leveled nearly all vegetation for as far as 12 miles away. Approximately 10 million trees were felled by the blast.

The landslide debris, liquefied by the violent explosion, surged down the mountain at speeds in excess of 100 miles per hour. The avalanche flooded Spirit Lake and roared down the valley of the Toutle River for a distance of 13 miles, burying the river to an average depth of 150 feet. Mudflows, pyroclastic flows, and floods added to the destruction, destroying roads, bridges, parks, and thousands more acres of forest. Simultaneous with the avalanche, a vertical eruption of gas and ash formed a mushrooming column over the volcano more than 12 miles high. Ash from the eruption fell on Northwest cities and towns like snow and drifted around the globe for two weeks. Fifty-seven people, thousands of animals, and millions of fish were killed by the eruption of Mount St. Helens.

By late in the afternoon of May 18, the eruption subsided, and by early the next day it had essentially ceased. Mount St. Helens’ volcanic cone was completely blasted away and replaced by a horseshoe-shaped crater–the mountain lost 1,700 feet from the eruption. The volcano produced five smaller explosive eruptions during the summer and fall of 1980 and remains active today. In 1982, Congress made Mount St. Helens a protected research area.

Mount St. Helens became active again in 2004. On March 8, 2005, a 36,000-foot plume of steam and ash was expelled from the mountain, accompanied by a minor earthquake. Another minor eruption took place in 2008. Though a new dome has been growing steadily near the top of the peak and small earthquakes are frequent, scientists do not expect a repeat of the 1980 catastrophe anytime soon.

READ MORE: The Deadliest Volcanic Eruption in History


1980 eruption of Mount St. Helens

On March 27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of phreatic blasts occurred from the summit and escalated until a major explosive eruption took place on May 18, 1980. The eruption, which had a Volcanic Explosivity Index of 5, was the most significant to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California. [2] It has often been declared the most disastrous volcanic eruption in U.S. history.

The eruption was preceded by a two-month series of earthquakes and steam-venting episodes caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain's north slope. An earthquake at 8:32:11 a.m. PDT (UTC−7) on Sunday, May 18, 1980 [3] caused the entire weakened north face to slide away, creating the largest landslide in recorded history. [4] This allowed the partly molten rock, rich in high-pressure gas and steam, to suddenly explode northward toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the landslide. An eruption column rose 80,000 feet (24 km 15 mi) into the atmosphere and deposited ash in 11 U.S. states [5] and two Canadian provinces. [6] At the same time, snow, ice and several entire glaciers on the volcano melted, forming a series of large lahars (volcanic mudslides) that reached as far as the Columbia River, nearly 50 miles (80 km) to the southwest. Less severe outbursts continued into the next day, only to be followed by other large, but not as destructive, eruptions later that year. Thermal energy released during the eruption was equal to 26 megatons of TNT. [7]

Approximately 57 people were killed, including innkeeper and World War I veteran Harry R. Truman, photographers Reid Blackburn and Robert Landsburg and geologist David A. Johnston. [8] Hundreds of square miles were reduced to wasteland, causing over $1 billion in damage (equivalent to $3.5 billion in 2020), thousands of animals were killed and Mount St. Helens was left with a crater on its north side. At the time of the eruption, the summit of the volcano was owned by the Burlington Northern Railroad, but afterward the land passed to the United States Forest Service. [9] The area was later preserved in the Mount St. Helens National Volcanic Monument.


Mount St. Helens erupts - HISTORY

Mount St. Helens, located in southwestern Washington about 50 miles northeast of Portland, Oregon, is one of several
lofty volcanic peaks that dominate the Cascade Range of the Pacific Northwest the range extends from Mount
Garibaldi in British Columbia, Canada, to Lassen Peak in northern California. Geologists call Mount St. Helens a
composite volcano (or stratovolcano), a term for steepsided, often symmetrical cones constructed of alternating layers
of lava flows, ash, and other volcanic debris. Composite volcanoes tend to erupt explosively and pose considerable
danger to nearby life and property. In contrast, the gently sloping shield volcanoes, such as those in Hawaii, typically
erupt nonexplosively, producing fluid lavas that can flow great distances from the active vents. Although Hawaiian-type
eruptions may destroy property, they rarely cause death or injury. Before 1980, snow-capped, gracefully symmetrical
Mount St. Helens was known as the "Fujiyama of America." Mount St. Helens, other active Cascade volcanoes, and
those of Alaska form the North American segment of the circum-Pacific "Ring of Fire," a notorious zone that produces
frequent, often destructive, earthquake and volcanic activity.

Some Indians of the Pacific Northwest variously called Mount St. Helens "Louwala-Clough," or "smoking mountain." The
modern name, Mount St. Helens, was given to the volcanic peak in 1792 by Captain George Vancouver of the British
Royal Navy, a seafarer and explorer. He named it in honor of a fellow countryman, Alleyne Fitzherbert, who held the
title Baron St. Helens and who was at the time the British Ambassador to Spain. Vancouver also named three other
volcanoes in the Cascades--Mounts Baker, Hood, and Rainier--for British naval officers.

Indians on the Cowlitz River watching an eruption of Mount St. Helens, as painted by Canadian artist Paul Kane
following a visit to the volcano in 1847 (Photograph courtesy of the Royal Ontario Museum).

The local Indians and early settlers in the then sparsely populated region witnessed the occasional violent outbursts of
Mount St. Helens. The volcano was particularly restless in the mid-19th century, when it was intermittently active for at
least a 26-year span from 1831 to 1857. Some scientists suspect that Mount St. Helens also was active sporadically
during the three decades before 1831, including a major explosive eruption in 1800. Although minor steam explosions
may have occurred in 1898, 1903, and 1921, the mountain gave little or no evidence of being a volcanic hazard for
more than a century after 1857. Consequently, the majority of 20th-century residents and visitors thought of Mount St.
Helens not as a menace, but as a serene, beautiful mountain playground teeming with wildlife and available for leisure
activities throughout the year. At the base of the volcano's northern flank, Spirit Lake, with its clear, refreshing water
and wooded shores, was especially popular as a recreational area for hiking, camping, fishing, swimming and boating.

The tranquility of the Mount St. Helens region was shattered in the spring of 1980, however, when the volcano stirred
from its long repose, shook, swelled, and exploded back to life. The local people rediscovered that they had an active
volcano in their midst, and millions of people in North America were reminded that the active--and potentially
dangerous--volcanoes of the United States are not restricted to Alaska and Hawaii.

Previous Eruptive History

The story of Mount St. Helens is woven from geologic evidence gathered during studies that began with Lieutenant
Charles Wilkes' U.S. Exploring Expedition in 1841. Many geologists have studied Mount St. Helens, but the work of
Dwight R. Crandell, Donal R. Mullineaux, Clifford A. Hopson, and their associates, who began their studies in the late
1950's, has particularly advanced knowledge of Mount St. Helens. Their systematic studies of the volcanic deposits,
laboratory investigations of rock and ash samples, and radiocarbon (carbon-l4) dating of plant remains buried in or
beneath the ash layers and other volcanic products enabled them to reconstruct a remarkably complete record of the
prehistoric eruptive behavior of Mount St. Helens.

Ancestral Mount St. Helens began to grow before the last major glaciation of the Ice Age had ended about 10,000
years ago. The oldest ash deposits were erupted at least 40,000 years ago onto an eroded surface of still older
volcanic and sedimentary rocks. Intermittent volcanism continued after the glaciers disappeared, and nine main pulses
of pre-1980 volcanic activity have been recognized. These periods lasted from about 5,000 years to less than 100
years each and were separated by dormant intervals of about 15,000 years to only 200 years. A forerunner of Spirit
Lake was born about 3,500 years ago, or possibly earlier, when eruption debris formed a natural dam across the
valley of the North Fork of the Toutle River. The most recent of the pre-1980 eruptive periods began about A.D. 1800
with an explosive eruption, followed by several additional minor explosions and extrusions of lava, and ended with the
formation of the Goat Rocks lava dome by 1857.

The post-A.D. 1400 segment of the 50,000-year eruptive history of Mount St. Helens (after USGS Bulletin 1383-C).

Mount St. Helens is the youngest of the major Cascade volcanoes, in the sense that its visible cone was entirely
formed during the past 2,200 years, well after the melting of the last of the Ice Age glaciers about 10,000 years ago.
Mount St. Helens' smooth, symmetrical slopes are little affected by erosion as compared with its older, more glacially
scarred neighbors--Mount Rainier and Mount Adams in Washington, and Mount Hood in Oregon. As geologic studies
progressed and the eruptive history of Mount St. Helens became better known, scientists became increasingly
concerned about possible renewed eruptions. The late William T. Pecora, a former Director of the USGS, was quoted
in a May 10, 1968, newspaper article in the Christian Science Monitor as being "especially worried about snow-covered
Mt. St. Helens."

On the basis of its youth and its high frequency of eruptions over the past 4,000 years, Crandell, Mullineaux, and their
colleague Meyer Rubin published in February 1975 that Mount St. Helens was the one volcano in the conterminous
United States most likely to reawaken and to erupt "perhaps before the end of this century." This prophetic conclusion
was followed in 1978 by a more detailed report, in which Crandell and Mullineaux elaborated their earlier conclusion
and analyzed, with maps and scenarios, the kinds, magnitudes, and areal extents of potential volcanic hazards that
might be expected from future eruptions of Mount St. Helens. Collectively, these two publications contain one of the
most accurate forecasts of a violent geologic event.

Reawakening and Initial Activity

A view to the north of the "two-tone" mountain--an appearance produced by prevailing easterly winds during the initial
activity of Mount St. Helens. Mount Rainier is visible in background (Photograph by C. Dan Miller).

A magnitude 4.2 (Richter Scale) earthquake on March 20, 1980, at 3:47 p.m. Pacific Standard Time (PST), preceded
by several much smaller earthquakes beginning as early as March 16, was the first substantial indication of Mount St.
Helens' awakening from its 123-year sleep. Earthquake activity increased during the following week, gradually at first
and then rather dramatically at about noon on March 25. The number of earthquakes recorded daily reached peak
levels in the next 2 days, during which 174 shocks with magnitudes greater than 2.6 were recorded. Many hundreds of
smaller earthquakes accompanied these larger events, the largest of which were felt by people living close to the
volcano. Aerial observations of Mount St. Helens during the week of seismic buildup revealed small
earthquake-induced avalanches of snow and ice, but no sign of an eruption.

With a thunderous explosion, or possibly two nearly simultaneous ones, widely heard in the region at about 12:36 p.m.
PST on March 27, Mount St. Helens began to spew ash and steam, marking the first significant eruption in the
conterminous United States since that of Lassen Peak, California, from 1914 to 1917. The crown of the ash column
rose to about 6,000 feet above the volcano. The initial explosions formed a 250-foot-wide crater within the larger,
preexisting snow- and ice-filled summit crater, and new fractures broke across the summit area.

View of the "bulge" on the north face of Mount St. Helens, from a measurement site about 2 miles to the northeast
(Photograph by Peter Lipman). The drawing above the photograph illustrates, in a highy exaggerated fashion, the
nearly horizontal movement--about 85 feet in 20 days--of one of the measured points on the "bulge."


I went into reading this book knowing nothing about Mount St. Helens except that it’s located in Washington state and it erupted in the 1980s. This book does a fabulous job of not only explaining the science behind volcanic eruptions, tectonic plate movement, and how exactly Mount St. Helens erupted, but it also delves into the rich history of the logging industry that plays a massive part of the pacific northwest’s history. The book pays homage to those who fought to conserve the forest lands in the late 1800s and early 1900s and gives a wonderful history lesson on why we have our forestlands today under the Department of Agriculture. It pays respect to those who passed during the eruption, explaining who they were and why they were located in the places they were during the explosion. Olson does a great job of writing on the search and rescue efforts taken place, as well as looking at the impact of the eruption on several different communities.

The Pacific Northwest has a rich logging history, much of which is and was controlled by the Weyerhaeuser logging company. Olson goes very in-depth explaining the long history behind this company and how it eventually became the predominant logging company in the US. This logging history, combined with railroad history, played an important part in designating the “safe zones” and “danger zones” for the future eruption of Mount St. Helen’s in the 1980s. In the 1890s, Weyerhaeuser began to look towards the rich forestland of the PNW and eventually became a monopoly in that regional as well. The deep explanation of this history gives reason as to how Weyerhaeuser owned so much land near Mount St. Helen’s, why it was hell-bent on logging, and why it carried such political weight when it came time to draw danger zone boundaries.

The mountain is a relatively young stratovolcano with a history of being the most active and explosive volcano in the US. With scientific study, discoveries of past “laterally directed explosions” and thick layers of ash from the mountain hundreds of miles away gave support to this claim. With eruption, it was predicted that mudslides , landslides, and floods would happen. Dangerous pyroclastic flows, fast moving currents of hot gas and volcanic matter, would kill many. Over the past millennium, the mountain has erupted about once every one hundred years, with the last eruption being in 1857. So come 1980, that next eruption time had passed. Previous eruptions were depicted by writers and artists as violent, and scientist Mullineaux of the US Geological Survey warned the Forest Service of this in a 1980 conference. At this point in time, earthquakes had begun and the mountain was deemed no longer dormant.

Around April of 1980, a great bulge had formed on the north side of the mountain over 300 feet outside the normal contour of the side. Geologists again warned that this bulge of built-up pressure and steam exploding.

-go into those who lived there, Sprit lake, blast zone reasons, media coverage

Geologists who knew how dangerous and eruption could be urged the state to keep people out of designated potential blast zones around the volcano. The state worked to create a “red zone” and “blue zone” designations, the red zone only allowing permitted workers and scientists and the blue zone being a limited access for logging and camping were allowed. However, due to Weyerhaeuser’s power and influence on politics, the government decided they could not designate Weyerhaeuser land as prohibited areas. Thus, a large area of land in projected-danger zones was not sanctioned off. Of course, the public was enraged about not being able to camp, hike, or even go to their property in these blocked off zones. Tourists wanted to come see the volcano and it’s bulging side (filling up with highly pressurized, and soon to be dangerous steam). Washington governor, Dixie Lee Ray, did not support these zoned- off areas and did not encourage people to stay away from the mountain. A man named Harry Truman owned a lodge on Spirit Lake (which is now obliterated due to the eruption) and he adamantly refused to leave his property. With the angry citizens, a protesting Truman, and a governor who seemed to applaud those who stood against the law, it is no surprise that blockades were not followed, police were unable to enforce prohibiting access, and citizens took Weyerhaeuser logging roads up the mountain instead.

Not everyone ignored the rules and warnings of the eruption though. Weyerhaeuser loggers were being sent to work in dangerous blue zones, and they protested such safety issues. Unfortunately they were brushed off by a bureaucrat who thought they were just trying to get unemployment. It is a miracle that the eruption happened on a Sunday when the loggers’ presence was much less than a weekday.

57 people were killed in the Mount St. Helen’s eruption early Sunday morning on May 18, 1980. Frequently the victims are blamed for “going around roadblocks” or “otherwise breaking the law to get where they were”. In reality, nobody was acting illegally because there was no law to break. The governor of Washington, Dixie Lee Ray, did not believe in the blue zone regulations and did not sign an extension of the blue zone. None of the people who were camping that morning went around the Spirit Lake Highway roadblock, and since the red and blue zones ended on Weyerhaeuser property, the police did not try to stop people from entering this land. Only three people were in the red zone, two of which were authorized to be there. The only person who died in the eruption by breaking a law was Harry Truman, who refused to leave his property on Spirit Lake. The governor commended him for his fortitude and he became something of a celebrity for his stubbornness, which ended up causing his death.

While it is heartbreaking that this many lives were lost, it is amazing that only 57 were killed by Mount St. Helen’s. Had the eruption been on Saturday or Sunday afternoon, or on Monday, the number of deaths would have been several times greater. Just Saturday afternoon, people with property off of the red-zoned Spirit Lake Highway were allowed to quickly go back in and retrieve their belongings. They would’ve been killed had the eruption been earlier. There would have been many more hikers had it been during the daytime. Had the eruption been on Monday, the Weyerhaeuser logging zone would have been densely populated with workers, most of which would have died.

This website does a great job of explaining the eruption.

Several people lived, often by luck and pure grit carrying them out of the ashes. Some campers in the Green River Zone were lucky and were not blasted by the eruption based on the contours of the land. Others walked miles on severely burnt and broken extremities, losing copious amounts of blood and breathing in air thick with ashes. What was interesting about the eruption is that since it came off of the side of the mountain, not the top, and was caused by built up pressure beneath “the bulge”, the eruptive forces drove their way down

138 people were rescued by helicopters after the eruption, and shockingly nobody was further injured in rescue attempts. Miraculously, two reserve Air Force units were conducting training near Mount St. Helens that weekend. The National Guard was also training at the Yakima Firing Center east of the volcano as well. When they saw the smoke plume and the downfall ashes following it, they mobilized as many helos as they could. Helicopter Rescue attempts were largely on the northwest side of the mountain, where the blast hit most severely.

-Ash attracts large amounts of static electricity due to the friction caused by the densely packed ash particles rubbing against one another. This causes lighting storms within the ash, which can make helicopter rescues difficult. Not to mention the severely limited visibility due to the ashes.

In 1982, president Ronald Regan signed a bill making Mt. St. Helen’s a National Volcanic Monument. The monument’s creation has provided scientific research on how landscapes recover from disaster. The area around the volcano was expected to recover from the outside in, but the inverse happened. Plants and animals became established in the inner zone, and from these tiny bubbles of life more colonization would happen. A plant crucial to the area’s regrowth and population was the prairie lupine, a legume that does not need nitrogen from the soil. Small nodules in the prairie legume’s roots make it possible for the plant to not be dependent on the soil, and thus grow anywhere. Although these plants died within a few years, their death and remains provided the necessary nitrogen for future plant growth. What also was discovered during this growth period was that areas left on their own had the best regrowth. The less human intervention the better. For example, downed trees not removed from the renewal area are able to rot and provide soil for new plants.

-Susan Saul: worked for the Fish and Wildlife Service pushed hard before and after the eruption to have Mount St. Helen’s become a protected area helped create the Washington Wilderness Act of 1984 which created new wilderness areas and expanded existing ones

-Dave Johnston: volcano expert, the first to make a public statement on Mt. St. Helen’s reawakening

-Gifford Pinchot: the father of American Forestry

-Frederick Weyerhaeuser: from Illinois, “self-made 19 th -century American tycoon”. He became head of the largest logging conglomerate in America by merging with Chippewa Falls lumbermen in 1880. Weyerhaeuser used generosity and cooperation with his competitors when retribution was expected, thus gaining respect and eventually business from and with adversaries.

-George Weyerhaeuser: in charge of Weyerhaeuser logging when the eruption occurred was kidnapped in 1935

-phreatic eruptions: molten gas or rock inside a volcano that heat up the surface, heating up ground water in the volcano’s surface rocks so much that is flashes into steam through a newly formed crater


Volcano World

The eruptive history of Mount St. Helens began about 40,000 years ago with dacitic volcanism, which continued intermittently until about 2,500 yr ago. This activity included numerous explosive eruptions over periods of hundreds to thousands of yr, which were separated by apparent dormant intervals ranging in length from a few hundred to about 15,000 yr. The range of rock types erupted by the volcano changed about 2,500 yr ago, and since then, Mount St. Helens repeatedly has produced lava flows of andesite, and on at least two occasions, basalt. Other eruptions during the last 2,500 yr produced dacite and andesite pyroclastic flows and lahars , and dacite, andesite , and basalt airfall tephra . Lithologic successions of the last 2,500 yr include two sequences of andesite-dacite-basalt during the Castle Creek period, and dacite-andesite-dacite during both the Kalama and Goat Rocks periods. Major dormant intervals of the last 2,500 yr range in length from about 2 to 7 centuries.

During most eruptive periods, pyroclastic flows and lahars built fans of fragmental material around the base of the volcano and partly filled valleys leading away from Mount St. Helens. Most pyroclastic flows terminated with 20 km of the volcano, but lahars extended down some valleys at least as far as 75 km. Fans of lahars and pyroclastic flows on the north side of the volcano dammed the North Fork Toutle River to form the basin of an ancestral Spirit Lake between 3,300 and 4,000 yr ago during the Smith Creek eruptive period, and again during the following Pine Creek eruptive period.

ERUPTIVE PERIODS AT MOUNT ST. HELENS

The eruptive history of Mount St. Helens is subdivided here into nine named eruptive "periods," which are clusters of eruptions distinguished by close association in time, by similarity of rock types, or both. The term "eruptive period" is used in an informal and largely arbitrary sense to divide the volcano's history into convenient units for the purpose of discussion. The periods are as much as several thousand years in duration, and include what may have been a single group of eruptions as well as extended episodes of volcanism , during which there were tens or possibly hundreds of eruptions. Eruptive periods are separated by apparently dormant intervals, which are inferred chiefly from buried soils and absence of eruptive deposits. However, some dormant intervals may span times of minor activity that did not produce deposits which can now be recognized. Fine-grained, air-laid volcanic detritus was deposited during some dormant intervals, but these deposits are not known to have originated directly from eruptions they might be material reworked from the flanks of the volcano.

The stratigraphic record of eruptive activity during the last 13,000 yr is believed to be reasonably complete. Parts of the older record, however, apparently are missing because of glacial and stream erosion during the last major glaciation (the late Pleistocene Fraser Glaciation) of the region.

APE CANYON ERUPTIVE PERIOD

The first stratigraphic evidence of the existence of Mount St. Helens consists of voluminous dacitic deposits of slightly vesicular to pumiceous air-fall tephra and pyroclastic flows , and at least one pumice-bearing lahar . These deposits overlie extensively weathered glacial drift formed during the next-to-last alpine glaciation of the Cascade Range. The volcanic deposits were formed during at least four episodes, separated by intervals during which very weak soils developed. The entire eruptive period may have extended over a time span as long as 5,000 yr. One pumiceous tephra deposit produced during the period probably had a volume as great as that of any subsequent tephra erupted at Mount St. Helens.

The Ape Canyon eruptive period was followed by a dormant interval which may have lasted from about 35,000 to 20,000 yr ago. Most of this 15,000-yr interval coincided with climates which, at times, were evidently somewhat cooler than those of the present (Alley, 1979, p. 233).

The second eruptive period probably began about 20,000 yr ago, and was characterized by the eruption of small volumes of pumiceous dacite tephra it also produced lahars , pyroclastic flows of pumiceous and lithic dacite , a few lava flows of dacite or high- silica andesite (C.A. Hopson, written commun., 1974), and perhaps one or more dacite domes. Several different eruptive episodes can be identified during the period. At least one pumiceous pyroclastic flow moved southward to at least 16 km from the center of the present volcano about 20,350 yr ago (Hyde, 1975, p. B11-B13). Two sequences of air-fall tephra that followed (sets M and K) are separated by a two-part deposit of fine air-laid sediment that locally is a meter or more thick, and that contains at least one weakly developed soil. After another quiet interval during which there was a small amount of soil development, at least two more pyroclastic flows moved south and southeast from the volcano between about 19,000 and 18,000 yr ago. The Cougar eruptive period occurred during the Frasier Glaciation when alpine glaciers in the Cascade Range were at or near their maximum extents, and the products of eruptions generally are poorly preserved.

One lahar that apparently occurred early in the Cougar period is of special interest because of some similarities to the debris avalanche of May 18, 1980, that swept down the North Fork Toutle Valley. The lahar of Cougar age consists of an unsorted and unstratified mixture of gray dacite fragments in a compact matrix of silt and sand as much as 20 m thick. Locally, it contains discrete texturally similar masses of red dacite many meters across. The iron-magnesium mineral content of rocks in the lahar is similar to that of the Ape Canyon period, suggesting that the lahar might have been derived from older parts of the volcano. The lahar was recognized in the Kalama River drainage 8 km southwest of the center of the modern volcano, and on both walls of the Lewis River valley near Swift dam (Hyde, 1975, p. B9-B11). It has not been recognized elsewhere thus, little is known of its original extent. Its local thickness and heterolithologic character suggest that the lahar might have originated in a large slope failure on the south side of the Mount St. Helens of early Cougar time.

There is no stratigraphic record of volcanism at Mount St. Helens between about 18,000 and 13,000 yr ago.

SWIFT CREEK ERUPTIVE PERIOD

The third eruptive period was characterized by repeated explosive eruptions that initially produced many pyroclastic flows as well as pumiceous air-fall tephra deposits, some of which had large volumes and extended at least as far east as central Washington. These eruptions of dacite pumice were followed by many lithic pyroclastic flows, which are believed to have been derived from domes at least one of these pyroclastic flows reached a point 21 km from the center of the present volcano. The pyroclastic flows were followed, in turn, by another series of explosive eruptions that produced the voluminous tephra set J. One coarse pumice layer of set J extends west-southwest from Mount St. Helens, and is as much as 20 cm thick as far as 20 km from the volcano. The layer represents the only coarse and thick pumice known to have been carried principally in a westerly direction. The sequence of explosive eruptions that formed set J apparently ended the Swift Creek eruptive period sometime before 8,000 yr ago, and was followed by a quiet period of at least 4,000 yr.

SMITH CREEK ERUPTIVE PERIOD

Multiple explosive eruptions of the Smith Creek eruptive period, which began about 4,000 yr ago, initiated at least 700 yr of intermittent and at times voluminous eruptive activity. Three coarse pumice layers at the base of tephra set Y are overlain by layers of denser, somewhat vesicular tephra. Deposition of these units was followed by an interval during which a soil began to develop on the tephra. The next eruption of the period produced the most voluminous and widespread tephra deposit of the last 4,000 yr it is one of the largest, if not the largest, in the history of the volcano, and has an estimated volume of at least 3 km. The resulting pumice layer, Yn, has been found nearly 900 km to the north-northeast in Canada (Westgate and others, 1970, p. 184). The formation of this layer was followed shortly by another voluminous eruption of tephra, which resulted in layer Ye (Mullineaux and others, 1975, p. 331), then by a pumiceous pyroclastic flow and a coarse lithic pyroclastic flow. The lithic pyroclastic flow was accompanied by clouds of ash that spread at least a kilometer beyond the sides of the flow and as much as 2 km beyond its front. Many smaller eruptions of lithic and moderately vesicular ash and lapilli followed, perhaps within a few years or tens of years.

Lahars and pyroclastic flows of Smith Creek age formed a fan north of the volcano, and lahars extended down the North Fork Toutle River at least as far as 50 km downvalley from Spirit Lake. An ancestor of the lake probably came into existence at this time, dammed in the North Fork valley by the fan of lahars and pyroclastic-flow deposits. It is not known if the lake ever existed before Smith Creek time.

A dormant interval of apparently no more than a few hundred years followed the Smith Creek eruptive period.

PINE CREEK ERUPTIVE PERIOD

Although only a short time elapsed between the Smith Creek and Pine Creek periods, eruptive products of Pine Creek age contain an iron-magnesium phenocryst assemblage that is distinctly different from those of Smith Creek age. During the Pine Creek eruptive period, large pumiceous and lithic pyroclastic flows moved away from the volcano in nearly all directions. The lithic pyroclastic flows , some of which extended as far as 18 km from the present center of the volcano, are believed to have been derived from dactic domes. Eruptions of dactic airfall tephra were of small volume, but at least four formed recognizable layers as far away as Mount Rainier (Mullineaux, 1974, p. 36).

During this time, lahars and fluvial deposits aggraded the valley floors of both the North and South Fork Toutle River, and created the basin of Silver Lake 50 km west-northwest of the volcano by locking a tributary valley (Mullineaux and Crandell, 1962). Similar deposits also formed a contiguous fill across the floor of the Cowlitz River valley near Castle Rock that was about 6 m above present river level this fill probably extended 209 km farther to the mouth of the Cowlitz River. Lahars and fluvial deposits formed a similar fill in the Lewis River valley which, near Woodland, was about 7.5 m higher than the present flood plain (Crandell and Mullineaux, 1973, p. A17-A18).

The eruptions of Pine Creek time extended over a period of about 500 yr. No single eruption of very large volume has been recognized from deposits of Pine Creek age, and the period seems to have been characterized by many tens of eruptions of small to moderate volume and the growth of one or more dacite domes. Some radiocarbon dates on deposits of Pine Creek and Castle Creek age overlap, and if the two eruptive periods were separated by a dormant interval, it must have been short.

CASTLE CREEK ERUPTIVE PERIOD

The next period of activity marked a significant change in eruptive behavior and variety of rock types being erupted at Mount St. Helens. During the Castle Creek eruptive period, both andesite and basalt were erupted as well as dacite , and these rock types evidently alternated in quick succession. The overall sequence includes, from oldest to youngest, andesite, dacite, basalt, andesite, dacite, basalt.

Thus, the stratigraphic sequence of Castle Creek time is complex, and not all stratigraphic units are represented on all sides of the volcano. Northwest of Mount St. Helens, in the Castle Creek valley, the sequence preserved includes the following:

Lava flow of olivine basalt (youngest)

Lava flow of hypersthene-augite andesite

Tephra deposit of olivine-augite andesite scoria (layer Bo)

Pyroclastic-flow deposits of hypersthene-dacite pumice

Tephra deposit of hypersthene-augite andesite scoria (layer Bh)

Lava flow and lahars of hypersthene-augite andesite (oldest)

The pumiceous pyroclastic-flow deposits have a radiocarbon age of 2,000-2,200 yr. Deposits and rocks of Castle Creek age on the south and east flanks of the volcano include pahoehoe basalt lava flows whose radiocarbon age is about 1,900 yr, and pumiceous dacite tephra whose age is about 1,800 yr (layer Bi.). East of the volcano, layer Bi overlies a pyroclastic-flow deposit of pyroxene andesite, and directly underlies thin olivine basalt lava flows which probably are correlative with the uppermost unit in the Castle Creek valley. The Dogs Head dacite dome was extruded before those thin olivine basalt flows, probably during the Castle Creek eruptive period. Layer Bu is the youngest tephra of Castle Creek age it underlies a deposit whose radiocarbon age is about 1,620 yr. This tephra is basaltic and probably was formed when thin olivine basalt lava flows were erupted near the end of the Castle Creek period.

Castle Creek time marked the start of eruptions that built the modern volcano. It is interesting to note that the change in eruptive behavior from that of the preceding 35,000-plus years did not follow a long period of dormancy like several that occurred during Mount St. Helens' earlier history. The dormant interval that followed Castle Creek time apparently lasted about 600 yr.

SUGAR BOWL ERUPTIVE PERIOD

During the next 1,200 yr, the only eruptions recorded at Mount St. Helens are those associated with the formation of Sugar Bowl, a dome of hypersthene-homblende dacite at the north base of the volcano. During extrusion of the dome, a directed blast carried rock fragments laterally northeastward in a sector at least 50 degrees wide and to a distance of at least 10 km. The resulting deposits are as much as 50 cm thick and consist of ash , lapilli , and breadcrusted blocks of dacite from the dome, fragments of charcoal, and stringers of material eroded from the underlying soil. A single fragment of charcoal from within the deposit has a radiocarbon age of about 1,150 yr, whereas a sample of wood charred and buried by the deposit has an age of about 1,400 yr (Hoblitt and others, 1980, p. 556). We provisionally assign an age of about 1,150 yr to the blast deposit the older date may have been obtained from a fragment of a mature tree that was overridden by the blast.

A pyroclastic flow deposit of breadcrusted blocks, as well as prismatically jointed blocks of dacite of the same composition as the dome, was found on the north slope of Mount St. Helens downslope from Sugar Bowl this pyroclastic flow may have occurred at the time of the lateral blast. Three lahars containing breadcrusted blocks of similar dacite were formerly exposed in the North Fork Toutle River valley west of Spirit Lake. These lahars may have been caused by melting of snow by the lateral blast or by the pyroclastic flow.

East Dome, a small dome of hypersthene-homblende dacite at the east base of the volcano, may have been formed at about the same time as the Sugar Bowl dome. East Dome is overlain by tephra of the Kalama period but not of the Castle Creek period, and could have been formed any time between the Castle Creek and Kalama eruptive periods, a time span of about 1,200 yr.

Most of the rocks visible at the surface of the volcano before eruptions began in 1980 were formed during the Kalama eruptive period. Although the range in radiocarbon dates and ages of trees on deposits of Kalama age suggest that the eruptive period lasted from nearly 500 to 350 yr ago, all the events described here probably occurred during a shorter time span, perhaps less than a century.

The Kalama eruptive period began with the explosive eruption of a large volume of dacite pumice (layer Wn) which forms the basal part of tephra set W. Layer Wn was deposited northeastward from the volcano across northeastern Washington and into Canada (Smith and others, 1977, p. 209) and was followed by additional pumice layers. At about the same time, pyroclastic flows of pumiceous and lithic dacite moved down the southwest flank of the volcano. The relative timing of these events is poorly known because most of the air-fall tephra was carried eastward and northeastward, whereas the pyroclastic flows have been found only on the southwest flank of Mount St. Helens.

A short time later, scoriaceous tephra of andesitic composition was erupted. In addition, andesite lava flows extended down the west, south, and east slopes of the volcano, and andesite pyroclastic flows moved down the north, west, and south flanks.

These eruptions of andesite were followed by the extrusion of the dacite dome that formed the summit of the volcano before the May 18, 1980, eruption. Avalanches of hot debris from the dome spilled down over the upper parts of the preceding lava flows, and some of this hot debris partly filled channels between levees of the andesite lava flows on the south side of the volcano (Hoblitt and others, 1980, p. 558). Late in this eruptive period, a pyroclastic flow of pumiceous dacite moved northwestward from the volcano down the Castle Creek valley and covered lahars of summit-dome debris. Charcoal from the pyroclastic-flow deposit has a radiocarbon age of about 350 yr (Hoblitt and others, 1980, p. 558).

The Kalama eruptive period was characterized by frequent volcanism of considerable variety rock types being erupted alternated from dacite to andesite and back to dacite, and the volcano grew to its pre-1980 size and shape. The eruptive period was followed by a dormant interval of about 200 yr.

GOAT ROCKS ERUPTIVE PERIOD

The Goat Rocks eruptive period began about A.D. 1800 with the explosive eruption of the dacitic pumice of layer T. This pumice was carried northeast-ward across Washington to northern Idaho (Okazaki and others, 1972, p. 81) and apparently was the only eruptive product of that time. Many minor explosive eruptions of the Goat Rocks period were observed by explorers, traders, and settlers from the 1830's to the mid-1850's. The Floating Island Lava Flow (andesite) was erupted before 1838 (Lawrence, 1941, p. 59) and evidently was followed by extrusion of the Goat Rocks dacite dome on the north flank of the volcano (Hoblitt and others, 1980, p. 558).

The last eruption of the Goat Rocks eruptive period was in 1857, when "volumes of dense smoke and fire" were noted (Frank Balch, quoted in Majors, 1980, p. 36). A recent study of old records has suggested that minor eruptions of Mount St. Helens also occurred in 1898, 1903, and 1921 (Majors, 1989, p. 36-41). The published descriptions of these events suggest that they were small-scale steam explosions, and none produced deposits that were recognized in our studies.

One of the most interesting features of Mount St. Helens' history is the change in eruptive behavior that occurred about 2,500 yr ago. Eruptions of dacite had characterized the volcano for more than 35,000 yr. Then, with virtually no interruption in eruptive activity, andesite and basalt began to alternate with dacite, and not always in the same order. The chemical composition of eruptive products changed gradually during some episodes and abruptly during others. Thus, basalt followed dacite and dacite succeeded basalt andesite followed dacite of considerably different SiO2 content, and vice versa. Some of these changes in composition of eruptive products are not adequately explained as results of eruption of cyclic sequences of compositionally different magmas derived from successively deeper levels in a larger magma body that differentiated at shallow depth, as proposed by Hopson (1971) and Hopson and Melson (19800. An alternative explanation that fits the stratigraphic record better, suggested by R.E. Wilcox (oral commun., 1974), is that some changes resulted from repeated contributions from more than one magma body, or from different parts of an inhomogeneous magma.

Explosive eruptions of volumes on the order of 0.1 to 3 km have occurred repeatedly at Mount St. Helens during some eruptive periods in the past. This record suggests that a similar sequence could occur during the present period of activity and could result in one or more explosive magmatic eruptions of similar or larger volume than the eruption of May 18. If the lengths of the last two eruptive periods are a valid guide to the future, we might expect intermittent eruptive activity to continue for several decades.

Eruptive History References

Alley, N.F., 1979, Middle Wisconsin stratigraphy and climatic reconstruction, southern Vancouver Island, British Columbia: Quatermary Research, v. 11, no. 2, p. 213-237.

Carithers, Ward. 1946. Pumice and pumicite occurrences of Washington: Washington Division of Mines and Geology Report of Investigations 15, 78 p.

Crandell, D.R., and Mullineaux, D.R., 1973, Pine Creek volcanic assemblage at Mount St. Helens, Washington: U.S. Geological Survey Bulletin 1383-A, 23 p.

_______ 1978, Potential hazards from future eruptions of Mount St. Helens volcano, Washington: U.S. Geological Survey Bulletin 1383-C, 26 p.

Crandell, D.R., Mullineaux, D.R., Miller, R.D., and Rubin, Meyer, 1962, Pyroclastic deposits of Recent age at Mount Rainier, Washington, in Short papers in geology, hydrology, and topography U.S. Geological Survey Professional Paper 450-D, p. D64-D68.

Crandell, D.R., Mullineaux, D.R., and Rubin, Meyer, 1975, Mount St. Helens volcano recent and future behavior: Science, v. 187, no. 4175, p. 438-441.

Fulton, R.J., and Armstrong, J.E., 1965, Day 11, in Schultz, C.B. and Smith, H.T. UY., eds, International Association (Union) of Quatemary Research Congress, 7th, 1965, Guidebook of Field Conference J., Pacific Northwest p. 87-98.

Greeley, Ronald, and Hyde, J.H., 1972, Lava tubes of the /ave Basalt, Mount St. Helens, Washington geological Society of American Bulletin, v. 83, no. 8, p. 2397-2418.

Hoblitt, R.P., Crandell, D.R., and Mullineaux, D.R., 1980, Mount St. Helens eruptive behavior during the past 1,500 years: Geology, v. 8, no. 11, p. 555-559.

Hopson, C. A., 1971, Eruptive sequence at Mount St. Helens, Washington: Geological Society of America Abstracts with Programs, v. 3, no. 2, p.138.

Hopson, C. A., and Melson, W. G., 1980, Mount St. Helens eruptive cycles since 100 A. D. [abs.]: EOS, v. 61, no. 46, p.1132-1133.

Hyde, J. H., 1975, Upper Pleistocene pyroclastic-flow deposits and lahars south of Mount St. Helens volcano, Washington: U.S. Geological Survey Bulletin 1383-B, 20 p.

Lawrence, D. B., 1939, continuing research on the flora of Mount St. Helens: Mazama, v.12, p. 49-54.

_______ 1941, The 'floating island" lava flow of Mount St. Helens: Mazama, v. 23, no. 12, p56-60.

_______ 1954, Diagrammatic history of the northeast slope of Mount St. Helens, Washington: Mazama, v. 36, no. 13, p. 41-44.

Mullineaux, D. R., 1974, Pumice and other pyroclastic deposits in Mount Rainier National Park, Washington: U.S. Geological Survey Bulletin 1326, 83 p.

Mullineaux, D. R., and Crandell, D. R., 1960, Late Recent age of Mount St. Helens volcano, Washington: U.S. Geological Survey Professional Paper 400-B. p. 307-308.

_______ 1962, Recent lahars from Mount St. Helens, Washington: Geological Society of America Bulletin, v 73, no. 7, p. 855-870.

Mullineaux, D. R., and Hyde, J. H., and Rubin, Meyer, 1975, Widespread late glacial and post glacial tephra deposits from Mount St. Helens, Washington: U.S. Geological Survey Journal of Research, v. 3, no. 3, p. 329-335.

Okasaki, Rose, Smith, H. W., Gilkeson, R. A., and Franklin, Jerry, 1972, Correlation of West Blacktail ash with pyroclastic layer T from the 1800 A. D. eruption of Mount St. Helens: Northwest Science, v. 46, no. 2, p. 77-89.

Smith, H. W., Okasaki, Rose, and Knowles, C. R., 1977, Electron microprobe analysis of glass shards from tephra assigned to set W, Mount St. Helens, Washington: Quaternary Research, v. 7, no. 2, p. 207-217.

Verhoogen, Jean, 1937, Mount St. Helens, a recent Cascade volcano: California University, Department of Geological Sciences Bulletin, v. 24, no. 9, p. 236-302.

Westgate, J. A., Smith, D. G. W., and Nichols, H., 1970, Late Quaternary pyroclastic layers in the Edmonton area, Alberta, in Symposium on pedology and Quaternary research, Edmonton, 1969, Proceedings: Alberta University Press, p. 179-187.


1980 Cataclysmic Eruption

Magma began intruding into the Mount St. Helens edifice in the late winter and early spring of 1980. By May 18, the cryptodome (bulge) on the north flank had likely reached the point of instability, and was creeping more rapidly toward failure.

Annotated seismogram indicates the signals for a Low-Frequency (LF) volcanic earthquake, relative quiescence, and then harmonic tremor as the eruption of May 18, 1980 accelerated. Each horizontal line represents 15 minutes of time. (Public domain.)

Summary of Events

On May 18, 1980, a magnitude-5+ earthquake was accompanied by a debris avalanche, which in turn unloaded the confining pressure at the top of the volcano by removing the cryptodome. This abrupt pressure release allowed hot water in the system to flash to steam, which expanded explosively, initiating a hydrothermal blast directed laterally through the landslide scar. Because the upper portion of the volcano was removed, the pressure decreased on the system of magma beneath the volcano. A wave of decreasing pressure down the volcanic conduit to the subsurface magma reservoir, which then began to rise, form bubbles (degas), and erupt explosively, driving a 9-hour long Plinian eruption.

Steam-blast eruption from summit crater of Mount St. Helens. Aerial view, April 6, looking southwest, showing a roiling, gray-brown, ash-laden cloud that envelops and almost completely hides an initial fingerlike ash column, and an upper white cloud formed by atmospheric condensation of water vapor in the convectively rising top of the eruptive column. Image and caption taken from Professional Paper 1250 and not scanned from original slide. (Credit: Moore, James G.. Public domain.)

Precursory Activity

On March 16, 1980, the first sign of activity at Mount St. Helens occurred as a series of small earthquakes. On March 27, after hundreds of additional earthquakes, the volcano produced its first eruption in over 100 years. Steam explosions blasted a 60- to 75-m (200- to 250-ft) wide crater through the volcano's summit ice cap and covered the snow-clad southeast sector with dark ash.

Within a week the crater had grown to about 400 m (1,300 ft) in diameter and two giant crack systems crossed the entire summit area. Eruptions occurred on average from about 1 per hour in March to about 1 per day by April 22 when the first period of activity ceased. Small eruptions resumed on May 7 and continued to May 17. By that time, more than 10,000 earthquakeshad shaken the volcano and the north flank had grown outward about 140 m (450 ft) to form a prominent bulge. From the start of the eruption, the bulge grew outward—nearly horizontally—at consistent rates of about 2 m (6.5 ft) per day. Such dramatic deformationof the volcano was strong evidence that molten rock (magma) had risen high into the volcano. In fact, beneath the surficial bulge was a cryptodome that had intruded into the volcano's edifice, but had yet to erupt on the surface.

Debris Avalanche

With no immediate precursors, a magnitude 5.1 earthquake occurred at 8:32 a.m. on May 18, 1980 and was accompanied by a rapid series of events. At the same time as the earthquake, the volcano's northern bulge and summit slid away as a huge landslide—the largest debris avalanche on Earth in recorded history. A small, dark, ash-rich eruption plume rose directly from the base of the debris avalanche scarp, and another from the summit crater rose to about 200 m (650 ft) high. The debris avalanche swept around and up ridges to the north, but most of it turned westward as far as 23 km (14 mi) down the valley of the North Fork Toutle River and formed a hummocky deposit. The total avalanche volume is about 2.5 km 3 (3.3 billion cubic yards), equivalent to 1 million Olympic swimming pools.

A "bulge" developed on the north side of Mount St. Helens as magma pushed up within the peak. Angle and slope-distance measurements to the bulge indicated it was growing at a rate of up to five feet (1.5 meters) per day. By May 17, part of the volcano's north side had been pushed upwards and outwards over 450 feet (135 meters). (Lipman, Peter. Public domain.)

Bulge (right) and small crater, Mount St. Helens summit. Crater area dropped in relation to the summit, and bulge shows pronounced fracturing because of its increased expansion. View looking south. (Credit: Krimmel, Robert M.. Public domain.)

Lateral Blast

Blowdown of trees from the shock-wave of the directed (lateral) blast from the May 18, 1980 eruption of Mount St. Helens. Elk Rock is the peak with a singed area on the left.

(Credit: Topinka, Lyn. Public domain.)

The landslide removed Mount St. Helens' northern flank, including part of the cryptodome that had grown inside the volcano. The cryptodome was a very hot and highly pressurized body of magma. Its removal resulted in immediate depressurization of the volcano's magmatic system and triggered powerful eruptions that blasted laterally through the sliding debris and removed the upper 300 m (nearly 1,000 ft) of the cone. As this lateral blast of hot material overtook the debris avalanche it accelerated to at least 480 km per hr (300 mi per hr). Within a few minutes after onset, an eruption cloud of blast tephra began to rise from the former summit crater. Within less than 15 minutes it had reached a height of more than 24 km (15 mi or 80,000 ft).

The lateral blast devastated an area nearly 30 km (19 mi) from west to east and more than 20 km (12.5 mi) northward from the former summit. In an inner zone extending nearly 10 km (6 mi) from the summit, virtually no trees remained of what was once dense forest. Just beyond this area, all standing trees were blown to the ground, and at the blast's outer limit, the remaining trees were thoroughly seared. The 600 km 2 (230 mi 2 ) devastated area was blanketed by a deposit of hot debris carried by the blast.

Plinian eruption column from May 18, 1980 Mount St. Helens. Aerial view from the Southwest. (Credit: Krimmel, Robert. Public domain.)

Plinian Eruption

Removal of the cryptodome and flank exposed the conduit of Mount St. Helens, resulting in a release of pressure on the top of the volcano's plumbing system. This caused a depressurization wave to propagate down the conduit to the volcano's magma storage region, allowing the pent-up magma to expand upward toward the vent opening. Less than an hour after the start of the eruption, this loss of conduit pressure initiated a Plinian eruption that sent a massive tephra plumehigh into the atmosphere. Beginning just after noon, swift pyroclastic flows poured out of the crater at 80 - 130 km/hr (50 to 80 mi/hr) and spread as far as 8 km (5 mi) to the north creating the Pumice Plain.

The Plinian phase continued for 9 hours producing a high eruption column, numerous pyroclastic flows, and ash fall downwind of the eruption. Scientists estimate that the eruption reached its peak between 3:00 and 5:00 p.m. When the Plinian phase was over, a new northward opening summit amphitheater 1.9 x 2.9 km (1.2 x 1.8 mi) across was revealed.

Ash cloud from Mount St. Helens over Ephrata, Washington (230 km (145mi) downwind), after May 18, 1980 eruption. (copyright by Douglas Miller)

Over the course of the day, prevailing winds blew 520 million tons of ash eastward across the United States and caused complete darkness in Spokane, Washington, 400 km (250 mi) from the volcano. Major ash falls occurred as far away as central Montana, and ash fell visibly as far eastward as the Great Plains of the Central United States, more than 1,500 km (930 mi) away. The ash cloud spread across the U.S. in three days and circled the Earth in 15 days.

During the first few minutes of this eruption, parts of the blast cloud surged over the newly formed crater rim and down the west, south, and east sides of the volcano. The turbulently flowing hot rocks and gas quickly eroded and melted some of the snow and ice capping the volcano, creating surges of water that eroded and mixed with loose rock debris to form lahars. Several lahars poured down the volcano into river valleys, ripping trees from their roots and destroying roads and bridges.

The largest and most destructive lahar occurred in the North Fork Toutle and was formed by water (originally groundwater and melting blocks of glacier ice) escaping from inside the huge landslide deposit through most of the day. This powerful slurry eroded material from both the landslide deposit and channel of the North Fork Toutle River. Increased in size as it traveled downstream, the lahar destroyed bridges and homes, eventually flowing into the Cowlitz River. It reached maximum size at about midnight in the Cowlitz River, about 80 km (50 mi) downstream from the volcano.

Nearly 135 miles (220 kilometers) of river channels surrounding the volcano were affected by the lahars of May 18, 1980. A mudline left behind on trees shows depths reached by the mud. (Credit: Topinka, Lyn. Public domain.)


Mount St. Helens and the Worst Volcano Eruption in U.S. History

I t was small by volcanic standards, but massive by human ones: on this day in 1980, Mount St. Helens erupted in what the National Oceanic and Atmospheric Administration calls “the deadliest and most economically destructive volcanic event in the history of the United States.”

Though the blast generated “about 500 times the force of the atomic bomb dropped on Hiroshima,” TIME reported in a cover story, it was seen as a “middling” explosion for a volcano. Still, it killed 57 people and thousands of animals and left the mountain itself 1,300 feet lower. As TIME reported:

Clouds of hot ash made up of pulverized rock were belched twelve miles into the sky. Giant mud slides, composed of melted snow mixed with ash and propelled by waves of superheated gas erupting out of the crater, rumbled down the slopes and crashed through valleys, leaving millions of trees knocked down in rows, as though a giant had been playing pick-up sticks.

Today, National Geographic reports, a “baby volcano” is growing inside the crater as magma builds up in its center. While that doesn’t pose an immediate threat to the region, it is indicative that the volcano is alive and well&mdasha fact that may be troubling to residents of the Pacific Northwest.

“The volcano is still living and breathing,” Smithsonian volcanologist Stephanie Grocke told National Geographic.


The Eruption of Mount St. Helens: The Untold History of this Cataclysmic Event

Robin Lindley is a Seattle-based writer and attorney, and the features editor of the History News Network (hnn.us). His articles have appeared in HNN, Crosscut, Salon, Real Change, Documentary, Writer’s Chronicle, and others. He has a special interest in the history of conflict and human rights. You can find his other interviews here. His email: [email protected]

If you’re over age 40 or so and lived in Washington State in 1980, you probably have a story about the eruption of Mount St. Helens.

On Saturday, May 17, 1980, my wife Betsy and I were married on a bright, warm day in Spokane, Washington. The following morning, oblivious to any news, we saw a dark bank of what we thought were thunderhead clouds approaching Spokane from the southwest.

It turned out that the inky clouds carried volcanic ash from the 8:33 a.m. eruption of Mount St. Helens, more than 250 miles away. By afternoon, the Spokane sky was dark as night and a steady downpour of the powdery ash obscured the sun through the day.

Many of our wedding guests that Sunday were caught in the blinding ash storm as they drove west, toward Seattle. Several holed up in motels or emergency shelters in churches or schools for the day and sometimes longer.

Our friends eventually made it home unscathed but that wasn’t the case for everyone. The massive volcanic blast from Mount St. Helens left 57 people dead, dumped ash on eight U.S. states and five Canadian provinces, and caused more than a billion dollars of damage.

Acclaimed author Steve Olson deftly interweaves the history and science of this cataclysmic event in his groundbreaking new book Eruption: The Untold Story of Mount St. Helens (Norton). Based on exhaustive research, his book tells the story not only of the eruption and its toll, but also looks back at economic and political developments that determined the fate of those near the mountain when it blew, particularly the cozy relationship of the powerful Weyerhaeuser lumber company and some government bodies.

Mr. Olson’s book is a work of investigation as well as vivid storytelling that takes readers from the world of logging and railroad barons more than a century ago to the lives of scientists, loggers, government officials and many others at the time of the eruption. His book demonstrates how history is a constant presence in our lives as he illuminates fateful decisions that preceded the eruption and shares in evocative prose the previously untold stories of those who perished as well as those who survived this massive volcanic explosion. Mr. Olson also describes the aftermath of the eruption: the resilience of nature, scientific advances, policy changes, and the creation of a national monument—and he shares ideas on preparedness for natural disasters to come.

Mr. Olson is a Seattle-based science writer. His other books include Mapping Human History: Genes, Race, and Our Common Origins, a finalist for the National Book Award and recipient of the Science-in-Society Award from the National Association of Science Writers Count Down: Six Kids Vie for Glory at the World’s Toughest Math Competition (Boston: Houghton Mifflin), named a best science book of 2004 by Discover magazine and, with co-author with Greg Graffin, Anarchy Evolution. His articles have appeared in The Atlantic Monthly, Science, Smithsonian, The Washington Post, Scientific American, and many other magazines. Mr. Olson also has served as a consultant writer for the National Academy of Sciences and National Research Council, the White House Office of Science and Technology Policy, the President’s Council of Advisors on Science and Technology, the National Institutes of Health, and many other organizations.

Mr. Olson generously responded by email to a series of questions about his new book on Mount St. Helens.

Robin Lindley: You’re an accomplished author Steve, and you’ve written on a wide array of science topics. What inspired you to research and write about the Mount St. Helens’ eruption of May 1980?

Steve Olson: I grew up here in the Pacific Northwest, in a small farming town about 100 miles downwind of Mount St. Helens, but I went east for college in the 1970s and stayed there after meeting my future wife in the back of an English class (though I was a physics major in college who only later got interested in writing). In 2009, she got a job in Seattle, so we moved back to my native state. I’d written several previous trade books on mostly scientific topics, but when we got here I decided to write a book about the most dramatic thing that had ever happened in Washington – and the eruption of Mount St. Helens was the obvious choice.

Robin Lindley: Where were you when the mountain erupted? Did you know any people affected by the eruption?

Steve Olson: On May 18, 1980, I was living outside of Washington, DC, working as a freelance science and technology policy writer and editor, and was three weeks away from getting married. My grandmother, who still lived in the small town where I grew up, brought a jar of ash that she’d scraped from her driveway to the wedding as a conversation starter.

Robin Lindley: Much has been written about the eruption but you have done exhaustive research to revisit the history of the mountain and its explosion. What was your research process and how did the book evolve from the time you began working on it to its publication?

Steve Olson: Lots of previous books had been written about Mount St. Helens, but as I started doing research on the book I discovered that many parts of the story had never been written about before. In particular, I got interested in the 57 people who had been killed by the eruption. Why were they so close to such a dangerous volcano – some just three miles away from the summit?

It turned out that the danger zones were much too close to the mountain, running along the border between land owned by the Weyerhaeuser timber company to the west and the Gifford Pinchot National Forest to the east. I decided that I needed to tell why the border was there and not somewhere else, and that required telling the stories of both Weyerhaeuser and land use in the western United States.

Robin Lindley: You set forth the historical context of the eruption in 1980, and the Northwest was a much different place than now, 36 years later. What are few things you’d like readers to understand about that time?

Steve Olson: When I left the Pacific Northwest in 1974, there was little to keep an ambitious person who was curious about the world here. Weyerhaeuser and Boeing were the two big companies in the state. The economy was stagnant, the culture was idiosyncratic and isolated, and the rest of the United States seemed far away. All of that began to change in the 1980s, and the Northwest is now completely different than when I was growing up – except, of course, for the profound natural beauty surrounding us on all sides.

Robin Lindley: How does the violence of the eruption of Mount St. Helens compare with other volcanic eruptions?

Steve Olson: In a global and geological context, the 1980 eruption of Mount St. Helens was not particularly large.

As I write in the book, more than 20 larger eruptions have occurred around the world in the past 500 years. Mount St. Helens has had much larger eruptions in the past. When Mount Mazama erupted in Oregon about 7,000 years ago, it released 100 times as much ash as Mount St. Helens did in 1980 before collapsing to form what is today Crater Lake. That said, the avalanche that destroyed the northern flank of Mount St. Helens in 1980 was the largest in recorded human history (so over the past few thousand years), and the blast that destroyed 230 square miles of forest and took 57 lives was largely unexpected by geologists, so it was a major event.

Robin Lindley: How was the mountain and its vicinity changed by the eruption? What was the area destroyed by the volcano, flora and fauna lost, and the amount of ash strewn to the east?

Steve Olson: The 1980 eruption emitted about a cubic kilometer of ash, which fell across the United States from Washington to New York State and eventually traveled all the way around the world on high-altitude winds. In addition to the people killed, many thousands of animals in the surrounding forests died, along with almost all the plant life in the blast zone, including gigantic old growth trees that had been growing for centuries.

Robin Lindley: The mountain rumbled and bulged in March and April 1980. Did scientists predict the lateral blast to the north that actually occurred by then or were they convinced the mountain would blow out the top and upward?

Steve Olson: They didn’t predict a lateral blast to the north, but they knew it was possible. Mount St. Helens had blown out to the side before, and they knew of other volcanoes that had done so. Still, the size of the blast did take them by surprise. Volcanoes in Russia and in Japan had erupted laterally, but the size of the devastated zone was not as great as at Mount St. Helens. However, once Mount St. Helens erupted that way, volcanologists took a look at deposits by other volcanoes in the past and realized that the 1980 eruption was not a geologically unusual event. On the contrary, some volcanic avalanches and lateral blasts have been much larger.

Robin Lindley: Your book serves as a tribute to the 57 people lost in the eruption. You took great pains to collect their stories from archives and from friends and family members, among others. For you, it seems, the roots of their demise may rest in the history of logging and railroads a century earlier? Why is that?

Steve Olson: I think of those 57 people as victims of history. Some of the history was short-term and personal, related to their specific circumstances and decisions, but other parts of the history that came into play at Mount St. Helens extended decades or centuries into the past.

Robin Lindley: How did Weyerhaeuser acquire vast timberlands in the Cascades and on the Olympic Peninsula and what was the role of railroad magnate James J. Hill?

Steve Olson: To me, this was the most interesting part of the historical story. As I said, the danger zone on the western and northwestern sides of the mountain was drawn along the boundary between Weyerhaeuser land and the Gifford Pinchot National Forest.

How did Weyerhaeuser, a company formed on the banks of the Mississippi River in the 19th century, come to own so much land in southwestern Washington state? It’s not an overstatement to say that it arose in large part because Frederick Weyerhaeuser, the German immigrant who started the company, happened to buy the house in 1891 next to Jim Hill on Summit Avenue in St. Paul, Minnesota.

Hill, who was the owner and driving force behind the Great Northern Railway from St. Paul to Seattle, had recently acquired control of the Northern Pacific Railroad, which was built, starting in 1870, from Duluth to Tacoma. In the 1890s, Hill wanted to buy the rail line from Chicago to Burlington, Iowa (which is why it’s called the Burlington Northern Santa Fe railroad today), and needed money to do so. To raise the money, he sold much of the Northern Pacific’s land grants in Washington State to his next door neighbor Frederick Weyerhaeuser, who realized that the forests of the upper Midwest were being depleted and needed new sources of timber. It’s a rich, convoluted, intricate history that had direct consequences for the people around the mountain on May 18, 1980.

Robin Lindley: Many people may not realize that logging was allowed on the mountain. What was happening with the Weyerhaeuser operation there at the time of the eruption? Did logging interests ignore scientists and the Forest Service on safety?

Steve Olson: Weyerhaeuser had been logging the land west of Mount St. Helens hard for the eight decades before 1980. When the mountain began to shake in March, two months before the big eruption, the company continued to log its land, despite the hazards of working near the volcano. If the mountain had erupted on a weekday rather than a Sunday morning, hundreds of Weyerhaeuser loggers in the surrounding woods likely would have died.

Robin Lindley: What was the role of Washington state and Governor Dixy Lee Ray in creating danger zones at Mount St. Helens?

Steve Olson: The state appears not to have wanted to interfere with Weyerhaeuser’s operations west of the mountain. The easy way to do that was to avoid drawing the danger zones on Weyerhaeuser property. The governor of Washington State in 1980, Dixy Lee Ray, signed the order establishing the danger zones knowing that they were too small. But the geologists’ predictions of what the mountain would do were uncertain, and Ray was the kind of person who believed that people should simply be sensible enough to stay away from the mountain on their own. (Though she had toured it several times from aircraft overhead.)

Robin Lindley: You believe the people who died and were injured in the blast got a bad rap as risk takers or scofflaws. What would you like readers to know about these people?

Steve Olson: After the eruption, Dixy Lee Ray insinuated that the people killed in the eruption were in the danger zones illegally, and Jimmy Carter, who flew over the blast zone a few days after the eruption, repeated the accusation. But only 3 of the 57 people killed were in the designated off-limits zone – and two of them had permission to be there. The only person in the danger zone illegally was the one person people tend to remember from the eruption – Harry R. Truman, who refused to leave his lodge on the south end of Spirit Lake, right beneath the mountain’s northern flank.

Robin Lindley: How did most of the deaths occur? Were fatalities caused by heat or suffocation or burial in ash or other reasons?

Steve Olson: The majority of the victims suffocated when they were caught in the blast cloud, which consisted of ash, hot rock, and volcanic gases. But others were blown off ridge tops, hit by falling trees, and carried away by mudflows. The bodies of nearly half the people killed were never found and remain buried around the mountain.

Robin Lindley: Lodge owner Harry Truman is probably the best known person who died in the eruption. Did you learn anything new about the steadfast and stubborn Mr. Truman?

Steve Olson: In the weeks before the eruption and after his death, Harry Truman was often portrayed by the media as a hero who proudly and defiantly held out against a nanny state government that wanted to remove him to safety. But up close the situation was more complicated. Harry’s presence near the mountain gave other people a bargaining chip to pressure law enforcement personnel to let them enter the danger zones, and those who succeeded in getting in are lucky the blast occurred when it did.

Harry knew that he was in great danger and was scared of what the mountain might do to him. But after being built up in the media, he had a reputation to uphold. Also, he was 83, his wife had died suddenly a few years before, he was drinking heavily. It’s probably fair to say that Harry Truman met the fate he would have hoped he would meet.

Robin Lindley: Was there ever a formal investigation of why people were on the mountain on May 18 and how the restricted zones were created and enforced?

Steve Olson: There were hearings at which geologists and public officials testified. But probably the most consequential follow-up was a lawsuit brought by several families of victims against the state (which was dismissed) and against Weyerhaeuser. The case against Weyerhaeuser went to trial in King County in 1985 and ended in a hung jury. The majority of the jurors were convinced that Weyerhaeuser was not at fault in not providing its employees with more information about the dangers of working so close to the mountain, but a solid minority disagreed. Instead of insisting upon a new trial, the families settled for a small amount of money, saying that their intention was more to clear the names of the dead than to reap a large settlement.

Robin Lindley: Did the state breach its responsibility to keep citizens safe?

Steve Olson: Yes. The danger zones to the west and northwest of the mountain were too small, and the state was aware of that. In the week before the May 18 eruption, a concerted effort, led by local law enforcement officials, was under way to expand the danger zone to the west, which would have encompassed much of the area where the 57 victims were killed. A proposal to do so was put on Dixy Lee Ray’s desk on Saturday, May 17, but she was at a parade that weekend and did not go to her office. The proposal was still sitting on her desk when the volcano erupted Sunday morning.

Robin Lindley: Mount St. Helens is now a national monument in part because of the efforts of conservationists and environmentalists. Didn’t commercial interests resist this designation? Can logging, mining or other interests still exploit the monument?

Steve Olson: Weyerhaeuser and the other companies that owned land in the area protected their interests, as would be expected. But they also cooperated with the state and federal governments in establishing the monument, exchanging land they owned inside the monument for land outside the monument. Today, Weyerhaeuser is still logging the land it owns around the monument, and exploratory shafts are still being drilled on old mining claims, which could result in large open air mines right on the border of the monument.

Robin Lindley: You note that scientists have learned a great deal about volcanoes and more from the Mount St. Helens’ eruption. What are some of those lessons from this massive event?

Steve Olson: For one thing, public safety officials will never let people get so close to a dangerous volcano, though every volcano is different, and they all have the capacity to surprise. Scientifically, U.S. geologists have been studying Mount St. Helens carefully ever since the eruption and have learned much more about the signs that precede an eruption, so much so that they have been able to predict every eruption of Mount St. Helens that has occurred since that date. The technology is also so much more sophisticated now than it was then, which has further increased understanding of volcanic behavior.

Robin Lindley: What have you been learning from your readers and people acquainted with the story of the eruption since your book came out?

Steve Olson: People have been contacting me to tell me their stories of that day. I haven’t yet heard of anything that would require me to make changes in the paperback edition of the book, but I hope I do. I tried to get the history just as accurate as I possibly could, but I know that written histories are only an effort to get close to the truth, not to capture it completely.

Robin Lindley: Thanks Steve for your insights and thoughtful comments. And congratulations on your groundbreaking and revelatory new book.

Steve Olson: Thanks, Robin. It’s a fascinating story. I always enjoy talking about it.


Mount St. Helens erupts - HISTORY

The story of Mount St. Helens is woven from geologic evidence gathered during studies that began with Lieutenant Charles Wilkes' U.S. Exploring Expedition in 1841. Many geologists have studied Mount St. Helens, but the work of Dwight R. Crandell, Donal R. Mullineaux, Clifford P. Hopson, and their associates, who began their studies in the late 1950's, has particularly advanced knowledge of Mount St. Helens. Their systematic studies of the volcanic deposits, laboratory investigations of rock and ash samples, and radiocarbon (carbon-l4) dating of plant remains buried in or beneath the ash layers and other volcanic products enabled them to reconstruct a remarkably complete record of the prehistoric eruptive behavior of Mount St. Helens.

Ancestral Mount St. Helens began to grow before the last major glaciation of the Ice Age had ended about 10,000 years ago. The oldest ash deposits were erupted at least 40,000 years ago onto an eroded surface of still older volcanic and sedimentary rocks. Intermittent volcanism continued after the glaciers disappeared, and nine main pulses of pre-1980 volcanic activity have been recognized. These periods lasted from about 5,000 years to less than 100 years each and were separated by dormant intervals of about 15,000 years to only 200 years. A forerunner of Spirit Lake was born about 3,500 years ago, or possibly earlier, when eruption debris formed a natural dam across the valley of the North Fork of the Toutle River. The most recent of the pre-1980 eruptive periods began about A.D. 1800 with an explosive eruption, followed by several additional minor explosions and extrusions of lava, and ended with the formation of the Goat Rocks lava dome by 1857.

The post-A.D. 1400 segment of the 50,000-year eruptive history of Mount St. Helens (after USGS Bulletin 1383-C).

Mount St. Helens is the youngest of the major Cascade volcanoes, in the sense that its visible cone was entirely formed during the past 2,200 years, well after the melting of the last of the Ice Age glaciers about 10,000 years ago. Mount St. Helens' smooth, symmetrical slopes are little affected by erosion as compared with its older, more glacially scarred neighbors--Mount Rainier and Mount Adams in Washington, and Mount Hood in Oregon. As geologic studies progressed and the eruptive history of Mount St. Helens became better known, scientists became increasingly concerned about possible renewed eruptions. The late William T. Pecora, a former Director of the USGS, was quoted in a May 10, 1968, newspaper article in the Christian Science Monitor as being "especially worried about snow-covered Mt. St. Helens."

On the basis of its youth and its high frequency of eruptions over the past 4,000 years, Crandell, Mullineaux, and their colleague Meyer Rubin published in February 1975 that Mount St. Helens was the one volcano in the conterminous United States most likely to reawaken and to erupt "perhaps before the end of this century." This prophetic conclusion was followed in 1978 by a more detailed report, in which Crandell and Mullineaux elaborated their earlier conclusion and analyzed, with maps and scenarios, the kinds, magnitudes, and areal extents of potential volcanic hazards that might be expected from future eruptions of Mount St. Helens. Collectively, these two publications contain one of the most accurate forecasts of a violent geologic event.


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