1980 eruption of Mount St. Helens
Template:Short description Template:Redirect Template:Pp-move-indef Template:Use American English Template:Featured article Template:Use mdy dates Template:Infobox eruption In March 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 for nearly two months until a major explosive eruption took place on MayTemplate:Nbs18, 1980, at 8:32Template:Nbsa.m. The eruption, which had a volcanic explosivity index ofTemplate:Nbs5, was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California.Template:Sfn It has often been considered the most disastrous volcanic eruption in U.S. history.
The eruption was preceded by a 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 8:32:11Template:Nbsam PDT (UTC−7) on May 18, 1980,<ref>Template:Cite web</ref> caused the entire weakened north face to slide away, a sector collapse which was the largest subaerial landslide in recorded history.<ref>Template:Cite web</ref> 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 Template:Convert into the atmosphere and deposited ash in eleven U.S. states<ref name="WashPost2005"/> and various Canadian provinces.<ref>Template:Cite web</ref> 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 Template:Convert 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. The thermal energy released during the eruption was equal to 26 megatons of TNT.<ref>Template:Cite web</ref>
About 57 people were killed, including innkeeper and World War I veteran Harry R. Truman, photographers Reid Blackburn and Robert Landsburg, and volcanologist David A. Johnston.<ref>Template:Cite news</ref> Hundreds of square miles were reduced to wasteland, causing over $1Template:Nbsbillion in damage (equivalent to $Template:Inflation billion in Template:Inflation/year), 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 United States Forest Service acquired the land from the railroad.<ref name="TillingPastClimactic">Template:Cite web (adapted public domain text).</ref><ref>Template:Cite journal</ref> The area was later preserved in the Mount St. Helens National Volcanic Monument and, due to the eruption, the state recognized the month of May as "Volcano Awareness Month" and events are held at Mt. St. Helens, or within the region, to discuss the eruption, safety concerns, and to commemorate lives lost during the natural disaster.<ref>Template:Cite news</ref>
Build-up to the eruption
Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980.<ref>Template:Cite news</ref> Several small earthquakes, beginning on March 15, indicated that magma might have begun moving below the volcano.<ref name="PrecursorMar15-21" /> On March 20, at 3:45Template:Nbspm Pacific Standard Time, a shallow, magnitudeTemplate:Nbs4.2 earthquake centered below the volcano's north flank,<ref name="PrecursorMar15-21" /> signaled the volcano's return from 123Template:Nbsyears of hibernation.Template:Sfn A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale among a total of 174 shocks of magnitudeTemplate:Nbs2.6 or greater.<ref>Template:Cite news</ref><ref name="PrecursorMar22-28">Template:Cite web</ref>
Shocks of magnitude 3.2 or greater occurred at a slightly increasing rate during April and May, with five earthquakes of magnitudeTemplate:Nbs4 or above per day in early April, and eight per day the week before May 18.Template:Sfn Initially, no direct sign of eruption was seen, but small earthquake-induced avalanches of snow and ice were reported from aerial observations.
At 12:36 pm on March 27, phreatic eruptions (explosions of steam caused by magma suddenly heating groundwater) ejected and smashed rock from within the old summit crater, excavating a new crater Template:Convert Template:Nowrap and sending an ash column about Template:Convert into the air.<ref name="PrecursorMar22-28" /> By this date, a Template:Convert eastward-trending fracture system had also developed across the summit area.Template:Sfn This was followed by more earthquake swarms and a series of steam explosions that sent ash Template:Convert above their vent.Template:Sfn Most of this ash fell between Template:Convert from its vent, but some was carried Template:Convert south to Bend, Oregon, or Template:Convert east to Spokane, Washington.Template:Sfn
A second, new crater and a blue flame were observed on March 29.Template:Sfn<ref name="PrecursorMar29-Apr4">Template:Cite web</ref> The flame was visibly emitted from both craters and was probably created by burning gases. Static electricity generated from ash clouds rolling down the volcano sent out lightning bolts that were up to Template:Convert long.Template:Sfn Ninety-three separate outbursts were reported on March 30,Template:Sfn and increasingly strong harmonic tremors were first detected on April 1, alarming geologists and prompting Governor Dixy Lee Ray to declare a state of emergency on April 3.<ref name="PrecursorMar29-Apr4" /> Governor Ray issued an executive order on April 30 creating a "red zone" around the volcano; anyone caught in this zone without a pass faced a $500 fine (Template:Inflation) or six months in jail.<ref name="hzcarmtn">Template:Cite news</ref><ref name="vbgrows">Template:Cite news</ref> This precluded many cabin owners from visiting their property.<ref name="SpokaneMay17">Template:Cite news</ref>
By April 7 the combined crater was Template:Convert and Template:Convert deep.<ref name="PrecursorApr5-11">Template:Cite web</ref> A USGS team determined in the last week of April that a Template:Convert section of St. Helens' north face was displaced outward by at least Template:Convert.Template:Sfn For the rest of April and early May, this bulge grew by Template:Convert per day, and by mid-May, it extended more than Template:Convert north.Template:Sfn As the bulge moved northward, the summit area behind it progressively sank, forming a complex, down-dropped block called a graben. Geologists announced on April 30 that sliding of the bulge area was the greatest immediate danger and that such a landslide might spark an eruption.<ref name="vbgrows" /><ref name="hhofmtn">Template:Cite news</ref> These changes in the volcano's shape were related to the overall deformation that increased the volume of the volcano by Template:Convert by mid-May.<ref name="Reawakening">Template:Cite web</ref> This volume increase presumably corresponded to the volume of magma that pushed into the volcano and deformed its surface. Because the intruding magma remained below ground and was not directly visible, it was called a cryptodome, in contrast to a true lava dome exposed at the surface.
On May 7, eruptions similar to those in March and April resumed, and over the following days, the bulge approached its maximum size.<ref name="PrecursorMay3–9" /> All activity had been confined to the 350-year-old summit dome and did not involve any new magma. About 10,000 earthquakes were recorded before the May 18 event, with most concentrated in a small zone less than Template:Convert directly below the bulge.<ref name="Reawakening"/> Visible eruptions ceased on May 16, reducing public interest and consequently the number of spectators in the area.<ref name="PrecursorMay10–17">Template:Cite web</ref> Mounting public pressure then forced officials to allow 50 carloads of property owners to enter the danger zone on Saturday, May 17, to gather whatever property they could carry.<ref name="PrecursorMay10–17"/><ref name="hnvch">Template:Cite news</ref> Another trip was scheduled for 10Template:Nbsam the next day,<ref name="PrecursorMay10–17" /><ref name="hnvch" /> a Sunday, when more than three hundred loggers who would normally be working in the area were not present.
By the time of the climactic eruption, dacite magma intruding into the volcano had forced the north flank outward nearly Template:Convert and heated the volcano's groundwater system, causing many steam-driven explosions (phreatic eruptions).
Landslide and climactic phase
As May 18 dawned, Mount St. Helens' activity did not show any change from the pattern of the preceding month. The rates of bulge movement and sulfur dioxide emission, and ground temperature readings did not reveal any changes indicating a catastrophic eruption. USGS volcanologist David A. Johnston was on duty at an observation post around Template:Convert north of the volcano. At 6:00Template:Nbsam Johnston's measurements did not indicate any unusual activity.<ref name="TillingPastClimactic" />
At 8:32 am, a magnitude 5.1 earthquake centered directly below the north slope triggered that part of the volcano to slide,Template:Sfn approximately 7–20Template:Nbsseconds after the shock,<ref name="TillingPastClimactic" /> followed a few seconds later by the main volcanic blast. The sector collapse, the largest subaerial landslide in recorded history, traveled at Template:Convert and moved across Spirit Lake's west arm. Part of it hit a Template:Convert ridge about Template:Convert north.<ref name="TillingPastClimactic" /> Some of the slide spilled over the ridge, but most of it moved Template:Convert down the North Fork Toutle River, filling its valley up to Template:Convert deep with avalanche debris.Template:Sfn An area of about Template:Convert was covered, and the total volume of the deposit was about Template:Convert.<ref name="TillingPastClimactic" />
Scientists were able to reconstruct the motion of the landslide from a series of rapid photographs by Gary Rosenquist, who was camping Template:Convert away from the blast Template:Coord.<ref name="TillingPastClimactic" /> Rosenquist, his party, and his photographs survived because the blast was deflected by local topography Template:Convert short of his location.Template:Sfn Template:Listen Most of St. Helens' former north side became a rubble deposit Template:Convert long, averaging Template:Convert thick; the slide was thickest at Template:Convert below Spirit Lake and thinnest at its western margin.<ref name="TillingPastClimactic" /> The landslide temporarily displaced the waters of Spirit Lake to the ridge north of the lake, in a giant wave about Template:Convert high.Template:Sfn This, in turn, created a Template:Convert avalanche of debris consisting of the returning waters and thousands of uprooted trees and stumps. Some of these remained intact with roots, but most had been sheared off at the stump seconds earlier by the blast of superheated volcanic gas and ash that had immediately followed and overtaken the initial landslide. The debris was transported along with the water as it returned to its basin, raising the surface level of Spirit Lake by about Template:Cvt.<ref name="TillingPastClimactic" />
Four decades after the eruption, floating log mats persist on Spirit Lake and nearby St. Helens Lake, changing position with the wind. The rest of the trees, especially those that were not completely detached from their roots, were turned upright by their own weight and became waterlogged, sinking into the muddy sediments at the bottom where they are in the process of becoming petrified in the anaerobic and mineral-rich waters. This provides insight into other sites with a similar fossil record.<ref>Template:Cite journal</ref>
Pyroclastic flows
Initial lateral blast
The landslide exposed the dacite magma in Mount St. Helens' neck to much lower pressure, causing the gas-charged, partially molten rock and high-pressure steam above it to explode a few seconds after the landslide started. Explosions burst through the trailing part of the landslide, blasting rock debris northward. The resulting blast directed the pyroclastic flow laterally. It consisted of very hot volcanic gases, ash, and pumice formed from new lava, as well as pulverized old rock, which hugged the ground. Initially moving about Template:Convert, the blast quickly accelerated to around Template:Convert, and it may have briefly passed the speed of sound.<ref name="TillingPastClimactic" />Template:Sfn
Pyroclastic flow material passed over the moving avalanche and spread outward, devastating a fan-shaped area 23 miles across by 19 miles long (37Template:NbskmTemplate:Nbsby 31Template:Nbskm).Template:Sfn In total, about Template:Convert of forest were knocked down,Template:Sfn and extreme heat killed trees miles beyond the blow-down zone. At its vent, the lateral blast probably did not last longer than about thirty seconds, but the northward-radiating and expanding blast cloud continued for about another minute.
Superheated flow material flashed water in Spirit Lake and North Fork Toutle River to steam, creating a larger, secondary explosion that was heard as far away as British Columbia,Template:Sfn Montana, Idaho, and Northern California, yet many areas closer to the eruption (Portland, Oregon, for example) did not hear the blast. This so-called "quiet zone" extended radially a few tens of miles from the volcano and was created by the complex response of the eruption's sound waves to differences in temperature and air motion of the atmospheric layers, and to a lesser extent, local topography.<ref name="TillingPastClimactic" />
Later studies indicated that one-third of the Template:Convert of material in the flow was new lava, and the rest was fragmented, older rock.Template:Sfn
Lateral blast result
The huge ensuing ash cloud sent skyward from St. Helens' northern foot was visible throughout the quiet zone. The near-supersonic lateral blast, loaded with volcanic debris, caused devastation as far as Template:Convert from the volcano. The area affected by the blast can be subdivided into roughly concentric zones:<ref name="TillingPastClimactic" />
- Direct blast zone, the innermost zone, averaged about Template:Convert in radius, an area in which virtually everything, natural or artificial, was obliterated or carried away.<ref name="TillingPastClimactic" /> For this reason, this zone also has been called the "tree-removal zone". The flow of the material carried by the blast was not deflected by topographic features in this zone. The blast released energy equal to Template:Convert.
- Channelized blast zone, an intermediate zone, extended out to distances as far as Template:Convert from the volcano, an area in which the flow flattened everything in its path and was channeled to some extent by topography.<ref name="TillingPastClimactic" /> In this zone, the forces and direction of the blast are strikingly demonstrated by the parallel alignment of toppled large trees, broken off at the base of the trunk as if they were blades of grass mown by a scythe. This zone was also known as the "tree-down zone". Channeling and deflection of the blast caused strikingly varied local effects that still remained conspicuous after some decades. Where the blast struck open land directly, it scoured it, breaking trees off short and stripping vegetation and even topsoil, thereby delaying revegetation for many years. Where the blast was deflected so as to pass overhead by several metres, it left the topsoil and the seeds it contained, permitting faster revegetation with scrub and herbaceous plants, and later with saplings. Trees in the path of such higher-level blasts were broken off wholesale at various heights, whereas nearby stands in more sheltered positions recovered comparatively rapidly without conspicuous long-term harm.
- Seared zone, also called the "standing dead" zone, the outermost fringe of the impacted area, is a zone in which trees remained standing, but were singed brown by the hot gases of the blast.<ref name="TillingPastClimactic"/>
By the time this pyroclastic flow hit its first human victims, it was still as hot as Template:Convert and filled with suffocating gas and flying debris.Template:Sfn Most of the 57 people known to have died in that day's eruption succumbed to asphyxiation, while several died from burns.<ref name="TillingPastClimactic" /> Lodge owner Harry R. Truman was buried under hundreds of feet of avalanche material Template:Coord. Volcanologist David A. Johnston, who was stationed at Observation post Coldwater II Template:Coord, located just six miles (ten km) north of the mountain, was one of those killed Template:Coord, as was Reid Blackburn Template:Coord, a Vancouver Columbian and National Geographic photographer who was situated near Coldwater Creek Template:Coord, Template:Convert from the volcano, on the day of the eruption.<ref> Robinson, Erik (April 1, 2010). "Volcano's toll hits close to home". The Colombian. Retrieved May 20, 2011.</ref> Robert Landsburg, another photographer, who was within a few miles of the summit Template:Coord, was killed by the ash cloud. He was able to protect his film with his body, and the surviving photos provided geologists with valuable documentation of the historic eruption.<ref>Robert Coenraads (2006). "Natural Disasters and How We Cope", p.50. Millennium House, Template:ISBN.</ref> Another eruption victim, amateur radio operator Gerry Martin, located near the Coldwater peak and farther north of Johnston's position Template:Coord, reporting his sighting of the eruption enveloping the ColdwaterTemplate:NbsII observation post. As the blast overwhelmed Johnston's post, Martin declared solemnly: "Gentlemen, the camper and car that's sitting over to the south of me is covered. It's going to hit me, too." before his radio went silent.<ref>Template:Cite news</ref><ref>Template:Cite web</ref>
Later flows
Subsequent outpourings of pyroclastic material from the breach left by the landslide consisted mainly of new magmatic debris rather than fragments of pre-existing volcanic rocks. The resulting deposits formed a fan-like pattern of overlapping sheets, tongues, and lobes. At least 17 separate pyroclastic flows occurred during the May 18 eruption, and their aggregate volume was about Template:Convert.<ref name="TillingPastClimactic" />
The flow deposits were still at about Template:Convert two weeks after they erupted.<ref name="TillingPastClimactic" /> Secondary steam-blast eruptions fed by this heat created pits on the northern margin of the pyroclastic-flow deposits, at the south shore of Spirit Lake, and along the upper part of the North Fork Toutle River. These steam-blast explosions continued sporadically for weeks or months after the emplacement of pyroclastic flows, and at least one occurred a year later, on May 16, 1981.<ref name="TillingPastClimactic" />
Ash column
As the avalanche and initial pyroclastic flow were still advancing, a huge ash column grew to a height of Template:Convert above the expanding crater in less than ten minutes and spread tephra into the stratosphere for ten straight hours.Template:Sfn Near the volcano, the swirling ash particles in the atmosphere generated lightning, which in turn started many forest fires. During this time, parts of the mushroom-shaped ash-cloud column collapsed, and fell back upon the earth. This fallout, mixed with magma, mud, and steam, sent additional pyroclastic flows speeding down St. Helens' flanks. Later, slower flows came directly from the new north-facing crater and consisted of glowing pumice bombs and very hot pumiceous ash. Some of these hot flows covered ice or water, which flashed to steam, creating craters up to Template:Convert in diameter and sending ash as much as Template:Convert into the air.Template:Sfn
Strong, high-altitude wind carried much of this material east-northeasterly from the volcano at an average speed around Template:Convert. By 9:45Template:Nbsam, it had reached Yakima, Washington, Template:Convert away, and by 11:45 it was over Spokane, Washington.<ref name="TillingPastClimactic" /> A total of Template:Convert of ash fell on Yakima, and areas as far east as Spokane were plunged into darkness by noon, where visibility was reduced to Template:Convert and Template:Convert of ash fell.Template:Sfn Continuing eastward,<ref name=mapcloud>Template:Cite news</ref> St. Helens' ash fell in the western part of Yellowstone National Park by 10:15Template:Nbspm, and was seen on the ground in Denver the next day.Template:Sfn In time, ash fall from this eruption was reported as far away as Minnesota and Oklahoma, and some of the ash drifted around the globe within about two weeks.
During the nine hours of vigorous eruptive activity, about 540,000,000 tons (Template:Cvt) of ash fell over an area of more than Template:Convert.<ref name="TillingPastClimactic" /> The total volume of the ash before its compaction by rainfall was about Template:Convert.<ref name="TillingPastClimactic" /> The volume of the uncompacted ash is equivalent to about Template:Convert of solid rock, or about 7% of the amount of material that slid off in the debris avalanche.<ref name="TillingPastClimactic" /> By 5:30Template:Nbspm on May 18, the vertical ash column declined in stature, but less severe outbursts continued through the next several days.Template:Sfn
Ash properties
Generally, given that the way airborne ash is deposited after an eruption is strongly influenced by the meteorological conditions, a certain variation of the ash type will occur, as a function of distance to the volcano or time elapsed from eruption. The ash from Mount St. Helens is no exception, hence the ash properties have large variations.<ref name="1980taylor">Template:Cite journal</ref>
Chemical composition
The bulk chemical composition of the ash has been found to be about 65% silicon dioxide, 18% aluminum oxide, 5% ferric oxide, 4% each calcium oxide and sodium oxide, and 2% magnesium oxide. Trace elements were also detected, their concentrations varying as 0.05–0.09% chlorine, 0.02–0.03% fluorine, and 0.09–0.3% sulfur.<ref name="1980taylor" />
Index of refraction
The index of refraction, a measure used in physics to describe how light propagates through a particular substance, is an important property of volcanic ash. This number is complex, having both real and imaginary parts, the real part indicating how light disperses and the imaginary part indicating how light is absorbed by the substance.
The silicate particles are known to have a real index of refraction ranging between 1.5 and 1.6 for visible light. However, a spectrum of colors is associated with samples of volcanic ash, from very light to dark gray. This makes for variations in the measured imaginary refractive index under visible light.<ref name="1981patterson">Template:Cite journal</ref>
In the case of Mount St. Helens, the ash settled in three main layers on the ground:<ref name="1980taylor" />
- The bottom layer was dark gray and was found to be abundant in older rocks and crystal fragments.
- The middle layer consisted of a mixture of glass shards and pumice.
- The top layer was ash consisting of very fine particles.
For example, when comparing the imaginary part of the refractive index k of stratospheric ash from Template:Cvt from the volcano, they have similar values around 700Template:Nbsnm (around 0.009), while they differ significantly around 300Template:Nbsnm. Here, the Template:Cvt sample (k was found to be around 0.009) was much more absorbent than the Template:Cvt sample (k was found to be around 0.002).<ref name="1981patterson" />
Mudslides flow downstream
The hot, exploding material also broke apart and melted nearly all of the mountain's glaciers, along with most of the overlying snow. As in many previous St. Helens eruptions, this created huge lahars (volcanic mudflows) and muddy floods that affected three of the four stream drainage systems on the mountain,Template:Sfn and which started to move as early as 8:50Template:Nbsam.Template:Sfn Lahars travelled as fast as Template:Convert while still high on the volcano, but progressively slowed to about Template:Convert on the flatter and wider parts of rivers.<ref name="TillingPastClimactic" /> Mudflows from the southern and eastern flanks had the consistency of wet concrete as they raced down Muddy River, Pine Creek, and Smith Creek to their confluence at the Lewis River. Bridges were taken out at the mouth of Pine Creek and the head of Swift Reservoir, which rose Template:ConvertTemplate:Sfn by noon to accommodate the nearly Template:Convert of additional water, mud, and debris.<ref name="TillingPastClimactic" />
Glacier and snowmelt mixed with tephra on the volcano's northeast slope to create much larger lahars. These mudflows traveled down the north and south forks of the Toutle River and joined at the confluence of the Toutle forks and the Cowlitz River near Castle Rock, Washington, at 1:00Template:Nbspm. Ninety minutes after the eruption, the first mudflow had moved Template:Convert upstream, where observers at Weyerhaeuser's Camp Baker saw a Template:Convert wall of muddy water and debris pass.Template:Sfn Near the confluence of the Toutle's north and south forks at Silver Lake, a record flood stage of Template:Convert was recorded.Template:Sfn
A large but slower-moving mudflow with a mortar-like consistency was mobilized in early afternoon at the head of the Toutle River north fork. By 2:30Template:Nbspm the massive mudflow had destroyed Camp Baker,Template:Sfn and in the following hours, seven bridges were carried away. Part of the flow backed up for Template:Convert soon after entering the Cowlitz River, but most continued downstream. After traveling Template:Convert further, an estimated Template:Convert of material were injected into the Columbia River, reducing the river's depth by Template:Convert for a Template:Convert stretch.Template:Sfn The resulting Template:Convert river depth temporarily closed the busy channel to ocean-going freighters, costing Portland, Oregon, an estimated $5 million (equivalent to $Template:Inflation million Template:Inflation/year).Template:Sfn Ultimately, more than Template:Convert of sediment were dumped along the lower Cowlitz and Columbia Rivers.<ref name="TillingPastClimactic" />
Aftermath
Direct results
The May 18, 1980, event was the most deadly and economically destructive volcanic eruption in the history of the contiguous United States.<ref name="TillingPastClimactic"/> About 57 people were killed directly from the blast, and 200 houses, 47 bridges, Template:Convert of railways, and Template:Convert of highway were destroyed; two people were killed indirectly in accidents that resulted from poor visibility, and two more suffered fatal heart attacks from shoveling ash.<ref name="OregonStateEffects">Template:Cite web</ref> U.S. President Jimmy Carter surveyed the damage, and said it looked more desolate than a moonscape.<ref name="Senate 25th anniversary">Template:Cite web</ref><ref>Template:Cite news</ref>
A film crew was dropped by helicopter on Mount St. Helens on May 23 to document the destruction, but their compasses spun in circles and they quickly became lost.<ref>Template:Cite web</ref> A second eruption occurred the next day (see below), but the crew survived and was rescued two days after that.<ref>Template:Cite web</ref> The eruption ejected more than Template:Convert of material.Template:Sfn A quarter of that volume was fresh lava in the form of ash, pumice, and volcanic bombs, while the rest was fragmented, older rock.Template:Sfn The removal of the north side of the mountain (13% of the cone's volume) reduced Mount St. Helens' height by about Template:Convert and left a crater Template:Convert wide and Template:Convert deep with its north end open in a huge breach.Template:Sfn
More than Template:Convert of timber were damaged or destroyed, mainly by the lateral blast. At least 25% of the destroyed timber was salvaged after September 1980. Downwind of the volcano, in areas of thick ash accumulation, many agricultural crops, such as wheat, apples, potatoes, and alfalfa, were destroyed. As many as 1,500 elk and 5,000 deer were killed, and an estimated twelve million Chinook and Coho salmon fingerlings died when their hatcheries were destroyed. Another estimated 40,000 young salmon were killed when they swam through turbine blades of hydroelectric generators after reservoir levels were lowered along the Lewis River to accommodate possible mudflows and flood waters.<ref name="TillingPastClimactic" />
In total, Mount St. Helens released 24 megatons TNT of thermal energy, seven of which were a direct result of the blast. This is equivalent to 1,600 times the size of the atomic bomb dropped on Hiroshima.<ref>Template:Cite web</ref>
In 2024, a study was conducted that provided an explanation for the observed phenomenon of an increase in the duration of the Lamb waves compared to the expected.<ref>Ponomarev, O.V. An analytical near-source shock wave model explaining anomalous periods of volcanic lamb waves: evidence from the 2022 hunga tonga eruption. Pure Appl. Geophys. (2025). https://doi.org/10.1007/s00024-025-03738-7</ref>
Uncertain death toll
The death toll most commonly cited is 57, although two points of uncertainty remain.
The first point regards two officially listed victims, Paul Hiatt and Dale Thayer. They were reported missing after the explosion. In the aftermath, investigators were able to locate individuals named Paul Hiatt and Dale Thayer who were alive and well. However, they were unable to determine who reported Hiatt missing, and the person who was listed as reporting Thayer missing claimed she was not the one who had done so. Since the investigators could not thus verify that they were the same Hiatt and Thayer who were reported missing, the names remain listed among the presumed dead.<ref name="HiattAndThayer">Template:Cite news</ref><ref name="MissingPersons">Template:Cite news</ref>
The second point regards three missing people who are not officially listed as victims: Robert Ruffle, Steven Whitsett, and Mark Melanson. Cowlitz County Emergency Services Management lists them as "Possibly Missing — Not on [the official] List". According to Melanson's brother, in October 1983, Cowlitz County officials told his family that Melanson "is believed [...] a victim of the May 18, 1980, eruption" and that after years of searching, the family eventually decided "he's buried in the ash".<ref name="MissingPersons" />
Taking these two points of uncertainty into consideration, the direct death toll could be as low as 55 or as high as 60. When combined with the four indirect victims (two dying from vehicle accidents due to poor visibility, and two dying from heart attacks triggered by shovelling ash)<ref name="OregonStateEffects" /> those numbers range from 59 to 64.
A year and a half after the eruption, the bodies of two young women, Marsha Anne Weatter and Katherine Jean Allen, 18 and 20 years old respectively, were discovered. They were believed to have been murdered six weeks before the eruption, rather than being killed by the events. Backpacks belonging to them had been found in July 1980, but a layer of ash deposited by the eruption may have hidden the bodies, also preventing animals disturbing the remains. An autopsy showed they had each been shot once.<ref>Template:Cite news</ref> The murders of Weatter and Allen were later linked to serial killer Martin Lee Sanders.<ref>Template:Cite news</ref>
Ash damage and removal
The ash fall created some temporary major problems with transportation, sewage disposal, and water treatment systems. Visibility was greatly decreased during the ash fall, closing many highways and roads. Interstate 90 from Seattle to Spokane was closed for a week and a half. Air travel was disrupted for between a few days and two weeks, as several airports in eastern Washington shut down because of ash accumulation and poor visibility. Over a thousand commercial flights were cancelled following airport closures. Fine-grained, gritty ash caused substantial problems for internal combustion engines and other mechanical and electrical equipment. The ash contaminated oil systems, clogged air filters, and scratched moving surfaces. Fine ash caused short circuits in electrical transformers, which in turn caused power blackouts.<ref name="TillingPastClimactic"/>
Removing and disposing of the ash was a monumental task for some Eastern Washington communities. State and federal agencies estimated that over Template:Convert of ash, equivalent to about 900,000 tons in weight, were removed from highways and airports in Washington. The ash removal cost $2.2Template:Nbsmillion and took ten weeks in Yakima.<ref name="TillingPastClimactic" /> The need to remove ash quickly from transport routes and civil works dictated the selection of some disposal sites. Some cities used old quarries and existing sanitary landfills; others created dump sites wherever expedient. To minimize wind reworking of ash dumps, the surfaces of some disposal sites were covered with topsoil and seeded with grass. In Portland, the mayor eventually threatened businesses with fines if they failed to remove the ash from their parking lots.<ref>Painter, John Jr. The 1980s. The Oregonian, December 31, 1989.</ref>
Cost
A refined estimate of $1.1 billion ($Template:Inflation billion in Template:Inflation/year) was determined in a study by the International Trade Commission at the request of the U.S. Congress. A supplemental appropriation of $951Template:Nbsmillion for disaster relief was voted by Congress, of which the largest share went to the Small Business Administration, the U.S. Army Corps of Engineers, and the Federal Emergency Management Agency.<ref name="TillingPastClimactic" />
Also, indirect and intangible costs of the eruption were incurred. Unemployment in the immediate region of Mount St. Helens rose 10-fold in the weeks immediately following the eruption, and then returned to near-normal levels once timber-salvaging and ash-cleanup operations were underway. Only a small percentage of residents left the region because of lost jobs owing to the eruption. Several months after May 18, a few residents reported suffering stress and emotional problems, though they had coped successfully during the crisis. Counties in the region requested funding for mental-health programs to assist such people.<ref name="TillingPastClimactic"/>
Initial public reaction to the May 18 eruption dealt a nearly crippling blow to tourism, an important industry in Washington. Not only was tourism down in the Mount St. Helens–Gifford Pinchot National Forest area, but conventions, meetings and social gatherings also were cancelled or postponed at cities and resorts elsewhere in Washington and neighboring Oregon not affected by the eruption. The adverse effect on tourism and conventioneering, however, proved only temporary. Mount St. Helens, perhaps because of its reawakening, has regained its appeal for tourists. The U.S. Forest Service and the State of Washington opened visitor centers and provided access for people to view the volcano's devastation.<ref name="TillingPastClimactic"/>
Later eruptions
St. Helens produced an additional five explosive eruptions between May and October 1980. Through early 1990, at least 21 periods of eruptive activity had occurred. The volcano remains active, with smaller, dome-building eruptions continuing into 2008.
1980–1991
An eruption occurred on May 25, 1980, at 2:30am that sent an ash column Template:Convert into the atmosphere.Template:Sfn The eruption was preceded by a sudden increase in earthquake activity, and occurred during a rainstorm. Erratic wind from the storm carried ash from the eruption to the south and west, lightly dusting large parts of western Washington and Oregon. Pyroclastic flows exited the northern breach and covered avalanche debris, lahars, and other pyroclastic flows deposited by the May 18 eruption.Template:Sfn
At 7:05 pm on June 12, a plume of ash billowed Template:Convert above the volcano. At 9:09 a much stronger explosion sent an ash column about Template:Convert skyward.Template:Sfn This event caused the Portland area, previously spared by wind direction, to be thinly coated with ash in the middle of the annual Rose Festival.<ref name="Oregonian2007" /> A dacite dome then oozed into existence on the crater floor, growing to a height of Template:Convert and a width of Template:Convert within a week.Template:Sfn
A series of large explosions on July 22 broke more than a month of relative quiet. The July eruptive episode was preceded by several days of measurable expansion of the summit area, heightened earthquake activity, and changed emission rates of sulfur dioxide and carbon dioxide. The first hit at 5:14Template:Nbspm as an ash column shot Template:Convert and was followed by a faster blast at 6:25 that pushed the ash column above its previous maximum height in just 7.5 minutes.Template:Sfn The final explosion started at 7:01 pm, and continued over two hours.Template:Sfn When the relatively small amount of ash settled over eastern Washington, the dome built in June was gone.Template:Sfn
Seismic activity and gas emission steadily increased in early August, and on August 7 at 4:26Template:Nbspm an ash cloud slowly expanded Template:Convert into the sky.Template:Sfn Small pyroclastic flows came through the northern breach and a weaker outpouring of ash rose from the crater. This continued until 10:32, when a second large blast sent ash high into the air, proceeding due north.Template:Sfn A second dacite dome filled this vent a few days later.
Two months of repose were ended by an eruption lasting from October 16 to 18. This event obliterated the second dome, sent ash ten miles in the air, and created small, red-hot pyroclastic flows.Template:Sfn A third dome began to form within thirty minutes after the final explosion on October 18, and within a few days it was about Template:Convert wide and Template:Convert high. In spite of the dome growth next to it, a new glacier formed rapidly inside the crater.
All of the post-1980 eruptions were quiet dome-building events, beginning with the December 27, 1980, to January 3, 1981, episode. By 1987 the third dome had grown to be more than Template:Convert wide and Template:Convert high.Template:Sfn
Further eruptions occurred over a few months between 1989 and 1991.
2004–2008
The 2004–2008 volcanic activity of Mount St. Helens has been documented as a continuous eruption with a gradual extrusion of magma at the Mount St. Helens volcano. Starting in October 2004, a gradual building of a new lava dome happened. The new dome did not rise above the crater created by the 1980 eruption. This activity lasted until January 2008.
- Satellite images before and after 1980 eruption
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Satellite image of Mount St. Helens before eruption (July 23, 1975) -
Satellite image of Mount St. Helens crater June 30, 1980 (color infrared) -
Satellite image of Mount St. Helens crater (July 22, 1982)
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_satellite_image_of_Mount_St,_Helens_1980_color_infrared..jpg)
_satellite_image_of_Mount_St,_Helens_crater_.jpg)
- Elevation models and landscape (lava domes) change models of Mount St. Helens (crater) between 1982 and 2017
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Digital elevation model (DEM) of Mount St. Helens (1982) -
DEM of Mount St. Helens (2003) -
DEM of Mount St. Helens (2017) -
Lava domes growth and landscape change of Mount St. Helens 2002-2017 -
Lava domes growth and landscape change of Mount St. Helens 1982-2003 -
Lava domes growth and landscape change of Mount St. Helens 1982-2017
.jpg){kind=link}
Summary table
| Eruption summary May 18, 1980, eruption of Mount St. Helens | ||
|---|---|---|
| Elevation of summit: | Before eruption: | Template:Convert |
| After eruption: | Template:Convert | |
| Total removed: | Template:Convert | |
| Crater dimensions: | East-West: | Template:Convert |
| North-South: | Template:Convert | |
| Depth: | Template:Convert | |
| Crater floor elevation: | Template:Convert | |
| Eruption | Date: | May 18, 1980 |
| Time of initial blast: | 8:32 am Pacific Daylight Time (UTC−7) | |
| Eruption trigger: | A magnitude 5.1 earthquake about Template:Convert beneath the volcano | |
| Landslide and debris avalanche | Area covered: | Template:Convert |
| Volume: (uncompacted deposits) |
Template:Convert | |
| Depth of deposit: | Buried North Fork Toutle River to average depth of Template:Convert with a maximum depth of Template:Convert | |
| Speed: | Template:Convert | |
| Lateral blast | Area covered: | Template:Convert; reached Template:Convert northwest of the crater |
| Volume of deposit: (uncompacted deposits) |
Template:Convert | |
| Depth of deposit: | From about Template:Convert at volcano to less than Template:Convert at blast edge | |
| Speed: | At least Template:Convert | |
| Temperature: | As high as Template:Convert | |
| Energy release: | 24 megatons thermal energy (7 by blast, rest through release of heat) | |
| Trees blown down: | Template:Convert of timber (enough to build about 300,000 two-bedroom homes) | |
| Human fatalities: | 55-60 (direct); four (indirect); 59-64 (total) | |
| Lahars | Speed: | About Template:Convert and over Template:Convert on steep flanks of volcano |
| Damaged: | 27 bridges, nearly 200 homes: Blast and lahars destroyed more than Template:Convert of highways and roads and Template:Convert of railways. | |
| Effects on Cowlitz River: | Reduced carrying capacity at flood stage at Castle Rock from Template:Convert per second to less than Template:Convert per second. | |
| Effects on Columbia River: | Reduced channel depth from Template:Convert; stranded 31 ships in upstream ports | |
| Eruption column and cloud | Height: | Reached about Template:Convert in less than 15 minutes |
| Downwind extent: | Spread across U.S. in 3 days; circled Earth in 15 days | |
| Volume of ash: (based on uncompacted deposits) |
Template:Convert | |
| Ash fall area: | Detectable amounts of ash covered Template:Convert | |
| Ash fall depth: | Template:Convert at Template:Convert downwind (ash and pumice) Template:Convert at Template:Convert downwind Template:Convert at Template:Convert downwind | |
| Pyroclastic flows | Area covered: | Template:Convert; reached as far as Template:Convert north of crater |
| Volume and depth: (volume based on uncompacted deposits) |
Template:Convert; multiple flows Template:Convert thick; cumulative depth of deposits reached Template:Convert in places | |
| Speed: | Estimated at Template:Convert | |
| Temperature: | At least Template:Convert | |
| Other | Wildlife: | The Washington State Department of Game estimated nearly 7,000 big game animals (deer, elk and bear) perished as well as all birds and most small mammals. Many burrowing rodents, frogs, salamanders and crawfish managed to survive because they were below ground level or water surface when the disaster struck. |
| Fisheries: | The Washington Department of Fisheries estimated that twelve million Chinook and Coho salmon fingerlings were killed when hatcheries were destroyed. Another estimated 40,000 young salmon were lost when forced to swim through turbine blades of hydroelectric generators as reservoir levels along the Lewis River were kept low to accommodate possible mudflows and flooding. | |
| Brantley and Myers, 1997, Mount St. Helens – From the 1980 Eruption to 1996: USGS Fact Sheet 070–97, accessed 2007-06-05; and Tilling, Topinka, and Swanson, 1990, Eruption of Mount St. Helens – Past, Present, and Future: USGS General Interest Publication, accessed 2007-06-05. | ||
| Table compiled by Lyn Topinka, USGS/CVO, 1997 | ||
See also
- Cascade Volcanoes – High Cascades
- The Eruption of Mount St. Helens! (1980 film) – documentary movie about the eruption
- St. Helens (1981 film) - television movie about the eruption
- Geology of the Pacific Northwest
- Helenite – An artificial glass marketed as a gemstone, made by fusing the volcanic dust from Mount St. Helens' May 1980 eruption
- List of Cascade volcanoes
- List of volcanoes in the United States
- Pacific Ring of Fire
References
Citations
Sources
- Template:USGS
- Template:Cite book
- Template:Cite book
- Template:Cite web
- Template:Cite web (adapted public domain text)
- Template:Cite web
Further reading
External links
- Template:Cite web
- List of victims with biographical details
- USGS: Mount St. Helens 1980 Debris Avalanche Deposit
- USDA Forest Service: Mount St. Helens VolcanoCam
- Pre-1980 Eruptive History of Mount St. Helens, Washington
- USGS: Before, During, and After May 18, 1980
- Boston.com – The Big Picture – 30 years later
- Template:Internet Archive short film
- Template:Internet Archive short film
- Aerial pictures of the July 22nd, 1980, secondary eruption
- News reports Template:Webarchive at The Museum of Classic Chicago Television
- AI video construction of the eruption from photographs
Template:Cascade volcanoes Template:US state navigation box Template:Oregon Modern History Template:Natural disasters Template:Authority control
- Pages with broken file links
- 1980 in Idaho
- 1980 in Montana
- 1980 in Oregon
- 1980 in Washington (state)
- 1980 natural disasters in the United States
- 20th-century volcanic events
- Cascade Volcanoes
- Gifford Pinchot National Forest
- Mount St. Helens
- Natural disasters in Washington (state)
- Volcanism of Washington (state)
- 1980 natural disasters
- 1980s landslides
- May 1980 in the United States
- Megatsunamis
- VEI-5 eruptions
- Volcanic eruptions in the United States
- Phreatic eruptions
- Plinian eruptions
- Peléan eruptions
- Volcanic tsunamis