1980 eruption of Mount St. Helens 673671 move=:edit= 225460733 2008-07-13T20:31:17Z Plasma Twa 2 1031581 /* Ash column grows */ [[Image:sthelens1.jpg|thumb|right|150px|Mount St. Helens, [[May 17]] [[1980]].]] The '''1980 eruption of [[Mount St. Helens]]''', a volcano located in [[Washington]] state, in the United States, was a major [[plinian eruption|volcanic eruption]]. The eruption was the most significant to occur in the contiguous 48 [[U.S. state]]s ([[Volcanic Explosivity Index|VEI]] = 5, 0.3&nbsp;cu&nbsp;mi, 1.2&nbsp;km<sup>3</sup> of material erupted), in terms of power and volume of material released, since the 1915 eruption of [[California]]'s [[Lassen Peak]]. The eruption was preceded by a two-month series of [[earthquake]]s and [[steam]]-venting episodes, caused by an injection of [[magma]] at shallow depth below the mountain that created a huge bulge and a fracture system on [[Mount St. Helens]]' north slope. An earthquake at 8:32&nbsp;a.m. on [[May 18]], [[1980]], caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas- and [[steam]]-rich [[rock (geology)|rock]] in the volcano to lower pressure. The rock responded by exploding into a very hot mix of pulverized [[lava]] and older rock that sped toward [[Spirit Lake (Washington)|Spirit Lake]] so fast that it quickly passed the avalanching north face. == Impact == A [[volcanic ash]] column rose high into the [[Earth's atmosphere|atmosphere]] and deposited ash in 11 U.S. states.{{Fact|date=March 2008}} At the same time, snow, ice, and several entire [[glacier]]s on the mountain melted, forming a series of large [[lahar]]s (volcanic [[mudslide]]s) that reached as far as the [[Columbia River]], nearly fifty miles (eighty kilometers) to the south. Less severe outbursts continued into the next day only to be followed by other large but not as destructive eruptions later in 1980. By the time the ash settled, 57 people (including innkeeper [[Harry Truman (volcano victim)|Harry Truman]] and geologist [[David A. Johnston]]; a full list is available here: [http://www.kgw.com/news/pdf/helens_deathlist.pdf]) and thousands of animals were dead. Hundreds of square miles were reduced to wasteland, over a billion [[U.S. dollar]]s in damage had occurred ($2.74 billion in 2007 dollars<ref>As given by {{cite web|url=http://www.minneapolisfed.org/research/data/us/calc/|publisher=Federal Reserve Bank of Minneapolis|title=What is a dollar worth?|accessdate=2007-09-25}}</ref>), and the face of Mount St. Helens was scarred with a huge 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]].<ref name="TillingPastClimactic"/> The area was later preserved, as it was, in the [[Mount St. Helens National Volcanic Monument]]. [[Image:St Helens from Monitor Ridge feather.jpg|thumb|450px|Mount St. Helens from Monitor Ridge showing the cone of devastation, the huge crater open to the north, the post-eruption lava dome inside and [[Crater Glacier]] surrounding the lava dome. The small photo on the left was taken from Spirit Lake before the eruption and the small photo on the right was taken after the eruption from approximately the same place. Spirit Lake can also be seen in the larger image, as well as two other Cascade volcanoes.]] == Buildup to the eruption == Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s, until March 1980.<ref>{{cite news |title=The Volcano: Full Theater, Stuck Curtain; Hall Packed for Volcano, But the Curtain Is Stuck |publisher=The Washington Post |date=[[March 30]] [[1980]] |author=Gorney, Cynthia}}</ref> Several small earthquakes beginning as early as [[March 15]], [[1980]], indicated that magma may have been moving below the volcano.<ref name="PrecursorMar15-21">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/31521/31521.htm |year=2001|title=Mount St. Helens Precursory Activity: March 15–21, 1980 |accessdate=2007-05-26 |publisher=United States Geological Survey }}</ref> Then on [[March 18]] at 3:45&nbsp;p.m. [[Pacific Standard Time]] (all times will be in PST), a shallow [[Richter magnitude]]&nbsp;4.2 [[earthquake]] (the initial reading was 4.1), centered below the mountain's north flank,<ref name="PrecursorMar15-21"/> signaled the [[volcano]]'s violent return from 123&nbsp;years of hibernation.<ref name="FMW88-202">Harris, ''Fire Mountains of the West'' (1988), page 202</ref><!-- Harris text gives 3:47 --> A gradually building [[earthquake swarm]] saturated area [[seismograph]]s and started to climax at about noon on [[March 25]], reaching peak levels in the next two days, including an earthquake registering 4.5 on the Richter scale.<ref>{{cite news |title=Oregon volcano may be warming up for an eruption |publisher=Christian Science Monitor |date=[[March 27]] [[1980]] |author=Ray, Dewey}}</ref> A total of 174 shocks of magnitude&nbsp;2.6 or greater were recorded during those two days.<ref name="PrecursorMar22-28">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/31521/31521.htm |title=Mount St. Helens Precursory Activity: March 22–28, 1980 |accessdate=2007-05-26 |publisher=United States Geological Survey |Year=2001}}</ref> Shocks of magnitude&nbsp;3.2 or greater occurred at a slightly increasing rate during April and May with five earthquakes of magnitude&nbsp;4 or above per day in early April, and 8&nbsp;per&nbsp;day the week before [[May 18]].<ref name="FMW88-202"/> Initially there was no direct sign of eruption, but small earthquake-induced [[avalanche]]s of snow and ice were reported from aerial observations. At 12:36&nbsp;p.m. on [[March 27]], at least one but possibly two nearly simultaneous [[phreatic eruption]]s (exploding [[groundwater]]-derived [[steam]]) ejected smashed rock from within the old summit [[volcanic crater|crater]], excavating a new crater 250&nbsp;feet (76&nbsp;m) wide<ref name="FMW88-202"/> and sending an ash column about 7,000&nbsp;feet (2,100&nbsp;m) into the air.<ref name="PrecursorMar22-28"/> By this date, a {{convert|16000|ft|m|sing=on}} long, east-trending fracture system had also developed across the summit area.<ref name="FMW88-204">Harris, ''Fire Mountains of the West'' (1988), page 204</ref> This was followed by more earthquake storms and a series of steam explosions that sent ash 10,000 to 11,000&nbsp;feet (3,000 to 3,400&nbsp;m) above their vent.<ref name="FMW88-202"/> Most of this ash fell within 3 to 12&nbsp;miles (5 to 20&nbsp;km) from its vent, but some was carried as far as 150&nbsp;miles (240&nbsp;km) south to [[Bend, Oregon]], and 285&nbsp;miles (460&nbsp;km) east to [[Spokane, Washington]].<ref name="FMW88-203">Harris, ''Fire Mountains of the West'' (1988), page 203</ref> A second, new crater and a blue flame was observed on [[March 29]].<ref name="PrecursorMar29-Apr">[http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/32944/32944.htm Cascades Volcano Observatory] [[USGS]] Mount St. Helens Precursory Activity</ref><ref name="FMW88-203"/> The flame was visibly emitted from both craters and was probably created by burning gases. [[Static electricity]] generated from ash clouds rolling down the mountain sent out [[lightning]] bolts that were up to two miles (3&nbsp;km) long.<ref name="FMW88-203"/> Ninety-three separate outbursts were reported on [[March 30]],<ref name="FMW88-203"/> and increasingly strong [[harmonic tremor]]s 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">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/32944/32944.htm |year=2001|title=Mount St. Helens Precursory Activity: March 29–April 4, 1980 |accessdate=2007-05-26 |publisher=United States Geological Survey }}</ref> [[Image:MSH80 early eruption st helens from NE 04-10-80.jpg|thumb|left|150px|USGS photo showing a pre-avalanche eruption on [[April 10]].]] By [[April 7]] the combined crater was 1,700&nbsp;feet (520&nbsp;m) long, 1,200&nbsp;feet (365&nbsp;m) wide and 500&nbsp;feet (150&nbsp;m) deep.<ref name="PrecursorApr5-11">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/45411/45411.htm |year=2001|title=Mount St. Helens Precursory Activity: April 5–11, 1980 |accessdate=2007-05-26 |publisher=United States Geological Survey }}</ref> A [[USGS]] team determined in the last week of April that a {{convert|1.5|mi|km|sing=on}} diameter section of St. Helens' north face was displaced out at least 270&nbsp;feet (82&nbsp;m).<ref name="FMW88-204"/> For the rest of April and early May this bulge grew 5 to 6 ft (1.5 to 1.8&nbsp;m) per day, and by mid-May it extended more than 400&nbsp;feet (120&nbsp;m) north.<ref name="FMW88-204"/> 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. These changes in the volcano's shape were related to the overall deformation that increased the volume of the mountain by 0.03&nbsp;cubic miles (0.1&nbsp;km³) by mid-May.<ref name="Reawakening">{{cite web |url=http://pubs.usgs.gov/gip/msh//reawakening.html |year=1997 |title=Reawakening and Initial Activity |accessdate=2007-05-31 |publisher=United States Geological Survey }}</ref> This volume increase presumably corresponded to the volume of magma that pushed into the volcano and deformed its surface. Because the intruded 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. [[Image:MSH80 bulge on north side 04-27-80.jpg|thumb|right|150px|Photo showing the bulge on [[April 27]].]] On [[May 7]], eruptions similar to those in March and April resumed, and over the next days the bulge approached its maximum size.<ref name="PrecursorMay3-9">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/5359/5359.htm |year=2001|title=Mount St. Helens Precursory Activity: May 3–9, 1980 |accessdate=2007-05-26 |publisher=United States Geological Survey }}</ref> All activity had been confined to the 350-year-old summit dome and did not involve any new [[magma]]. A total of about 10,000 earthquakes were recorded prior to the [[May 18]] event, with most concentrated in a small zone less than 1.6&nbsp;miles (2.6&nbsp;km) 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">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/510517/510517.htm |year=2001|title=Mount St. Helens Precursory Activity: May 10–17, 1980 |accessdate=2007-05-26 |publisher=United States Geological Survey }}</ref> Mounting public pressure then forced officials to allow 50 carloads of property owners to enter the danger zone on [[May 17]] to gather whatever property they could carry.<ref name="PrecursorMay10-17"/> Another trip was scheduled for 10&nbsp;a.m. the next morning.<ref name="PrecursorMay10-17"/> Since that was Sunday, more than 300 loggers would not be working in the area. By the time of the climactic eruption, [[dacite]] magma intruding into the volcano had forced the north flank outward nearly 500&nbsp;feet (150&nbsp;m) and heated the volcano's [[groundwater]] system, causing many steam-driven explosions (phreatic eruptions). == North face slides away == [[Image:Msh may18 sequence.gif|thumb|right|350px|Sequence of events on [[May 18]].]] At 7&nbsp;a.m. on [[May 18]], USGS [[volcanology|volcanologist]] David A. Johnston, who had Saturday night duty at an observation post about 6&nbsp;miles (10&nbsp;km) north of the mountain, radioed in the results of some [[laser]]-beam measurements he had made moments earlier.<ref name="TillingPastClimactic"/> Mount St. Helens' activity that day did not show any change from the pattern of the preceding month. The rate of bulge movement, [[sulfur dioxide]] emission, and ground temperature readings did not reveal any unusual changes that might have indicated a catastrophic eruption. [[Image:North Fork Toutle River valley in November 1983.jpg|thumb|left|North Fork Toutle River valley filled with landslide deposits.]] Suddenly, at 8:32&nbsp;a.m., a magnitude&nbsp;5.1 earthquake centred directly below the north slope triggered that part of the mountain to slide,<ref name="FMW88-205">Harris, ''Fire Mountains of the West'' (1988), page 205</ref> approximately 7–20&nbsp;seconds (about 10&nbsp;seconds seems most reasonable) after the shock.<ref name="TillingPastClimactic"/> One of the largest landslides in recorded history, the slide traveled at 110 to 155&nbsp;miles per hour (175 to 250&nbsp;km/h) and moved across Spirit Lake's west arm; part of it hit a {{convert|1150|ft|m|sing=on}} high ridge about 6&nbsp;miles (9.5&nbsp;km) north.<ref name="TillingPastClimactic"/> Some of the slide spilled over the ridge, but most of it moved 13&nbsp;miles (21&nbsp;km) down the North Fork [[Toutle River]],<!-- FMW205 gives {{convert|17|mi|km}} --> filling its valley up to 600&nbsp;feet (180&nbsp;m) deep with avalanche debris.<ref name="FMW88-205"/> An area of about 24&nbsp;square miles (62&nbsp;km²) was covered, and the total volume of the deposit was about 0.7&nbsp;cubic miles (2.9&nbsp;km³).<ref name="TillingPastClimactic"/> Most of St. Helens' former north side became a rubble deposit 17&nbsp;miles (27&nbsp;km) long, averaging 150&nbsp;feet (46&nbsp;m) thick; the slide was thickest at one mile (1.6&nbsp;km) below Spirit Lake and thinnest at its western margin.<ref name="TillingPastClimactic"/> All the water in Spirit Lake was temporarily displaced by the landslide, sending {{convert|600|ft|m|sing=on}} high waves crashing into a ridge north of the lake,<ref name="FMW88-209"/> adding 295&nbsp;feet (90&nbsp;m) of new avalanche debris above the old lakebed, and raising its surface level by about 200&nbsp;feet (60&nbsp;m).<ref name="TillingPastClimactic"/> As the water moved back into its [[drainage basin|basin]], it pulled with it thousands of trees felled by a super-heated wall of volcanic gas and searing ash and rock that overtook the landslide seconds before. == Pyroclastic flows == === Initial lateral blast === [[Image:Computer animation showing May 18, 1980 St Helens landslide.png|thumb|left|Computer graphic showing the [[May 18]] landslide (green) being overtaken by the initial pyroclastic flow (red).]] The landslide suddenly exposed the [[dacite]] magma in 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 slide started. [[Explosion]]s burst through the trailing part of the landslide, blasting rock debris northward. The resulting blast laterally directed the [[pyroclastic flow]] of very hot volcanic gases, ash, and [[pumice]] from new lava, and pulverized old rock hugged the ground while initially moving at 220&nbsp;mph (350&nbsp;km/h) but quickly accelerating to 670&nbsp;mph (1080&nbsp;km/h) (it may have briefly passed the [[speed of sound]]).<ref name="TillingPastClimactic"/><ref name="FMW88-205"/> Pyroclastic flow material passed up the moving avalanche and spread outward, devastating a fan-shaped area 23&nbsp;miles (37&nbsp;km) across and 19&nbsp;miles (30&nbsp;km) long.<ref name="FMW88-205"/> In all, about 230&nbsp;square miles (600&nbsp;km²) of forest were knocked down<ref name="FMW88-205"/> within an 8-mile (13&nbsp;km) inner-fan area, and extreme heat killed trees miles beyond the blow-down zone. At its vent the lateral blast probably did not last longer than about 30&nbsp;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]],<ref name="FMW88-206">Harris, ''Fire Mountains of the West'' (1988), page 206</ref> [[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"/> === Lateral blast result === Everyone in the quiet zone could see the huge ash cloud that was sent skyward from St. Helens' northern foot. The near-supersonic lateral blast, loaded with volcanic debris, caused devastation as far as 19&nbsp;miles (30&nbsp;km) from the volcano. The area affected by the blast can be subdivided into three roughly concentric zones:<ref name="TillingPastClimactic"/> [[Image:St helens felled trees.jpg|thumb|right|150px|Felled trees at Johnston Ridge, 2004]] #''Direct blast zone'', the innermost zone, averaged about 8&nbsp;miles (13&nbsp;km) 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. #''Channelized blast zone'', an intermediate zone, extended out to distances as far as 19&nbsp;miles (30&nbsp;km) 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 force 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." #''Seared zone'', also called the "standing dead" zone, the outermost fringe of the impacted area, a zone in which trees remained standing but were singed brown by the hot [[gas]]es of the blast.<ref name="TillingPastClimactic"/> Later studies indicated that one-third of the 0.045&nbsp;cubic miles (188,000,000&nbsp;m³) of material in the flow was new lava, and the rest was fragmented, older rock.<ref name="FMW88-206"/> [[Image:Reid Blackburn's car after May 18, 1980 St. Helens eruption.jpg|thumb|Photographer Reid Blackburn's car after the eruption.]] By the time this pyroclastic flow hit its first human victims, it was still as hot as 360 °C (680 °F) and filled with suffocating gas and flying angular material.<ref name="FMW88-206">Harris, ''Fire Mountains of the West'' (1988), page 206</ref> 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 Truman (volcano victim)|Harry Truman]] was buried under hundreds of feet (tens of meters) of avalanche material. Volcanologist [[David A. Johnston]] was one of those killed, as was [[Reid Blackburn]], a ''[[National Geographic]]'' photographer. === Later flows === Subsequent outpourings of pyroclastic material from the breach left by the landslide consisted mainly of new magmatic debris rather than fragments of preexisting 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&nbsp;0.05 cubic miles (208,000,000&nbsp;m³).<ref name="TillingPastClimactic"/> The flow deposits were still at about 300 °C to 420 °C (570 °F to 785 °F) 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 about a year later, on [[May 16]], [[1981]].<ref name="TillingPastClimactic"/> == Ash column grows == [[Image:MSH80 eruption mount st helens plume 05-18-80.jpg|thumb|left|Photo of the lower part of the [[May 18]] ash column.]] As the avalanche and initial pyroclastic flow were still advancing, a huge ash column grew to a height of 12&nbsp;miles (19&nbsp;km) above the expanding crater in less than 10&nbsp;minutes and spewed [[tephra]] into the [[stratosphere]] for 10 straight hours.<ref name="FMW88-206"/> Near the volcano, the swirling ash particles in the atmosphere generated [[lightning]], which in turn started many [[forest fire]]s. During this time, parts of the [[Mushroom cloud|mushroom]]-shaped ash-cloud column collapsed, sending 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 65&nbsp;feet (20&nbsp;m) in diameter and sending ash as much as 6,500&nbsp;feet (1980&nbsp;m) into the air.<ref name="FMW88-208">Harris, ''Fire Mountains of the West'' (1988), page 208</ref> [[Image:1980 Mount st helens ash distribution.svg|thumb|Map of ash distribution over the United States.]] Strong high-[[altitude]] wind carried much of this material east-northeasterly from the volcano at an average speed of about 60&nbsp;mph (100&nbsp;km/h). By 9:45&nbsp;a.m. it had reached [[Yakima, Washington]], 90&nbsp;miles (145&nbsp;km) away, and by 11:45&nbsp;a.m. it was over [[Spokane, Washington]].<ref name="TillingPastClimactic"/><!-- FMW206 gives 10:10am and and 2pm --> A total of 4 to 5&nbsp;inches (100 to 130&nbsp;mm) of ash fell on Yakima, and areas as far east as Spokane were plunged into darkness by noon where visibility was reduced to 10&nbsp;feet (3&nbsp;m) and half an inch (13&nbsp;mm) of ash fell.<ref name="FMW88-206"/> Continuing east, St. Helens' ash fell in the western part of [[Yellowstone National Park]] by 10:15&nbsp;p.m. and was seen on the ground in [[Denver, Colorado]], the next day.<ref name="FMW88-206"/> 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 2&nbsp;weeks. During the nine hours of vigorous eruptive activity, about 540&nbsp;million&nbsp;tons of ash fell over an area of more than 22,000&nbsp;square miles (60,000&nbsp;km²).<ref name="TillingPastClimactic"/> The total volume of the ash before its compaction by [[rain]]fall was about 0.3&nbsp;cubic miles (1.3&nbsp;km³).<ref name="TillingPastClimactic"/> The volume of the uncompacted ash is equivalent to about 0.05&nbsp;mile³ (208,000,000&nbsp;m³) of solid rock, or about 7% of the amount of material that slid off in the debris avalanche.<ref name="TillingPastClimactic"/> By around 5:30&nbsp;p.m. on [[May 18]], the vertical ash column declined in stature, but less severe outbursts continued through the night and for several days.<ref name="FMW88-210"/> == Mudslides flow downstream == [[Image:Mudline from 1980 St Helens lahars next to Muddy River.jpg|thumb|left|Mudline next to Muddy River from the 1980 [[lahar]]s.]] The hot, exploding material also broke apart and melted nearly all of the mountain's [[glacier]]s along with most of the overlying snow. As in many previous St. Helens' eruptions, this created huge [[lahar]]s (volcanic [[mudflow]]s) and muddy floods that affected three of the four stream drainage systems on the mountain,<ref name="FMW88-208"/> and which started to move as early as 8:50 a.m.<ref name="FMW88-209">Harris, ''Fire Mountains of the West'' (1988), page 209</ref> Lahars traveled as fast as 90&nbsp;mph (145&nbsp;km/h) while still high on the volcano but progressively slowed to about 3&nbsp;mph (5&nbsp;km/h) 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 (Washington)|Lewis River]]. Bridges were taken out at the mouth of Pine Creek and the head of Swift Reservoir, which rose 2.6&nbsp;feet (0.8&nbsp;m)<ref name="FMW88-208"/> by noon to accommodate the nearly 18&nbsp;million&nbsp;cubic yards (13&nbsp;million&nbsp;m³) of additional water, mud, and debris.<ref name="TillingPastClimactic"/> Glacier and snow melt 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 1:00&nbsp;p.m. Ninety minutes after the eruption, the first mudflow had moved 27&nbsp;river miles (43&nbsp;km) upstream where observers at [[Weyerhaeuser]]'s Camp Baker saw a {{convert|12|ft|m|sing=on}} high wall of muddy water and debris pass.<ref name="FMW88-209"/> Near the confluence of the Toutle's north and south forks at Silver Lake, a record [[flood stage]] of 23.5&nbsp;feet (7.2&nbsp;m) was recorded.<ref name="FMW88-209"/> 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 2:30&nbsp;p.m. the massive mudflow had destroyed Camp Baker,<ref name="FMW88-209"/> and in the following hours seven bridges were carried away. Part of the flow backed up for 2.5&nbsp;miles (4&nbsp;km) soon after entering the Cowlitz River, but most continued downstream. After traveling 17&nbsp;miles (27&nbsp;km) further, an estimated 3.9&nbsp;million&nbsp;cubic yards (3.0&nbsp;million&nbsp;m³) of material were injected into the [[Columbia River]], reducing the river's depth by 25&nbsp;feet (7.6&nbsp;m) for a four-mile (6&nbsp;km) stretch.<ref name="FMW88-209"/> The resulting 13-foot (4&nbsp;m) river depth temporarily closed the busy channel to [[ocean]]-going [[freighter]]s, costing [[Portland, Oregon]] an estimated five million [[US dollar]]s.<ref name="FMW88-210">Harris, ''Fire Mountains of the West'' (1988), page 210</ref> Ultimately more than 65&nbsp;million&nbsp;cubic yards (50&nbsp;million&nbsp;m³) of sediment were dumped along the lower Cowlitz and Columbia Rivers.<ref name="TillingPastClimactic"/> == Aftermath == [[Image:St helens map showing 1980 eruption deposits.png|thumb|left|Map showing 1980 eruption deposits.]] === Direct results === The [[May 18]], [[1980]], event was the most deadly and economically destructive volcanic eruption in the [[history of the United States]].<ref name="TillingPastClimactic">{{cite web |author=Tilling, Robert I., Topinka, Lyn and Swanson, Donald A. |year=1990 |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/MSHPPF/MSH_past_present_future.html |title=Eruptions of Mount St. Helens: Past, Present, and Future |publisher=U.S. Geological Survey (Special Interest Publication)|accessdate=2007-06-03|work=The Climactic Eruption of May 18, 1980}}</ref> Fifty-seven people were killed and 200 homes, 47 bridges, 15&nbsp;miles (24&nbsp;km) of railways and 185&nbsp;miles (300&nbsp;km) of highway were destroyed. U.S. President [[Jimmy Carter]] surveyed the damage and stated it looked more desolate than a [[moon]]scape.{{Fact|date=March 2008}} A film crew was dropped by helicopter on St. Helens on [[May 23]] to document the destruction. Their [[compass]]es, however, spun in circles and they quickly became lost.{{Fact|date=May 2008}} A second eruption occurred the next day (see below), but the crew survived and were rescued two days after that. In all, St. Helens released an amount of [[energy]] equivalent to 27,000&nbsp;[[Little Boy|Hiroshima]]-sized [[nuclear weapon]]s and ejected more than 1&nbsp;[[cubic mile]] (4&nbsp;km³) of material.<ref name="FMW88-211">Harris, ''Fire Mountains of the West'' (1988), page 211</ref> A quarter of that volume was fresh lava in the form of ash, pumice, and volcanic bombs while the rest was fragmented, older [[rock (geology)|rock]].<ref name="FMW88-211"/> The removal of the north side of the mountain (13% of the cone's volume) reduced St. Helens' height by about 1,313&nbsp;feet (400&nbsp;m) and left a crater 1 to 2&nbsp;miles (2 to 3&nbsp;km) wide and 2,100&nbsp;feet (640&nbsp;m) deep with its north end open in a huge breach.<ref name="FMW88-211"/> [[Image:St Helens in September 1980.jpg|thumb|right|St. Helens in September 1980.]] More than 4&nbsp;billion&nbsp;[[board feet]] (14.6&nbsp;km³) of [[timber]] was damaged or destroyed, mainly by the lateral blast.<ref name="TillingPastClimactic"/><!-- FMW206 gives "about a billion" --> 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 12 million<ref name="TillingPastClimactic"/> [[Chinook salmon|Chinook]] and [[Coho salmon|Coho]] [[salmon]] fingerlings died when their hatcheries were destroyed. Another estimated 40,000 young [[salmon]] were lost when they swam through [[turbine]] blades of [[hydroelectric]] generators when [[lake|reservoir]] levels were lowered along the Lewis River to accommodate possible mudflows and [[flood]] waters.<ref name="TillingPastClimactic"/> === Digging out === The ash fall created some temporary but 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, Washington|Seattle]] to [[Spokane, Washington|Spokane]] was closed for a week and a half.<ref name="TillingPastClimactic"/> Air travel was disrupted for a few days to 2&nbsp;weeks as several airports in eastern Washington shut down because of ash accumulation and poor visibility. Over a thousand commercial flights were canceled following airport closures.<ref name="TillingPastClimactic"/> Fine-grained, gritty ash caused substantial problems for [[internal-combustion engine]]s and other mechanical and electrical equipment. The ash contaminated oil systems and clogged air filters, and scratched moving surfaces. Fine ash caused [[short circuit]]s in electrical transformers, which in turn caused [[power blackout]]s. Removing and disposing of the ash was a monumental task for some eastern Washington communities. State and federal agencies estimated that over 2.4&nbsp;million&nbsp;cubic yards (1.8&nbsp;million&nbsp;m³) of ash&nbsp;&mdash; equivalent to about 900,000&nbsp;tons in weight&nbsp;&mdash; were removed from highways and airports in Washington.<ref name="TillingPastClimactic"/> Ash removal cost $2.2&nbsp;million and took 10&nbsp;weeks in Yakima.<ref name="TillingPastClimactic"/> The need to remove ash quickly from transport routes and civil works dictated the selection of some disposal sites. Some cities used old quarries and existing sanitary [[landfill]]s; others created dumpsites wherever expedient. To minimize wind reworking of ash dumps, the surfaces of some disposal sites were covered with topsoil and seeded with grass. In Portland, the mayor eventually threatened businesses with fines if they failed to remove the ash from their parking lots.<ref>Painter, John Jr. The 1980s. ''[[The Oregonian]]'', [[December 31]] [[1989]].</ref> === Cost === [[Image:Home destroyed by 1980 St Helens eruption1.jpg|thumb|One of the 200 homes destroyed by the eruption.]] Early estimates of the cost of the eruption ranged from [[U.S. dollar|US$]]2–3&nbsp;[[1000000000 (number)|billion]].<ref name="TillingPastClimactic"/> A refined estimate of $1.1&nbsp;billion ($2.74 billion in 2007 dollars[http://www.minneapolisfed.org/research/data/us/calc/]) was determined in a study by the [[International Trade Commission]] at the request of the [[United States Congress]].<ref name="TillingPastClimactic"/> A supplemental appropriation of $951&nbsp;million for disaster relief was voted by Congress, of which the largest share went to the [[Small Business Administration]], [[U.S. Army Corps of Engineers]], and the [[Federal Emergency Management Agency]].<ref name="TillingPastClimactic"/> There were also indirect and intangible costs of the eruption. [[Unemployment]] in the immediate region of Mount St. Helens rose tenfold in the weeks immediately following the eruption, and then returned to nearly normal 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.<ref name="TillingPastClimactic"/> Several months after [[May 18]], a few residents reported suffering [[Stress (medicine)|stress]] and [[emotion]]al problems, even though they had coped successfully during the crisis. Counties in the region requested funding for mental health programs to assist such people.{{Fact|date=March 2008}} Initial public reaction to the [[May 18]] eruption nearly dealt a 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 canceled 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 [[United States 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 == {{Further|[[2004 and later volcanic activity of Mount St. Helens]]}} St. Helens produced five more explosive eruptions between May and October 1980. Through early 1990, a total of at least 21 periods of eruptive activity had occurred. The volcano remains active, with smaller, dome-building eruptions continuing into 2008. [[Image:MSH80 st helens eruption plume 07-22-80.jpg|thumb|Eruption on [[July 22]] [[1980]].]] An eruption occurred on [[May 25]] [[1980]] at 2:30&nbsp;a.m. that sent an ash column 9&nbsp;miles (14&nbsp;km) into the atmosphere.<ref name="FMW88-211"/> The eruption was preceded by a sudden increase in earthquake activity and occurred during a rain storm. 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.<ref name="FMW88-211"/> At 7:05&nbsp;p.m. on [[June 12]], a plume of ash billowed 2.5&nbsp;miles (4&nbsp;km) above the volcano. At 9:09&nbsp;p.m. a much stronger explosion sent an ash column about 10&nbsp;miles (16&nbsp;km) skyward.<ref name="FMW88-212">Harris, ''Fire Mountains of the West'' (1988), page 212</ref> 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> {{cite web |url=http://blog.oregonlive.com/rosefestivalstories/2007/05/he_remembers_the_year_the_moun/print.html |title=He Remembers the Year the Mountain Blew (1980) |accessdate=2008-01-28 |last= |first= |coauthors= |date= |work= |publisher=}}</ref> A [[dacite]] dome then oozed into existence on the crater floor, growing to a height of 200&nbsp;feet (60&nbsp;m) and a width of 1,200&nbsp;feet (370&nbsp;m) within a week.<ref name="FMW88-212"/> 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 5:14&nbsp;p.m. as an ash column shot 10&nbsp;miles (16&nbsp;km) and was followed by a faster blast at 6:25&nbsp;p.m. that pushed the ash column above its previous maximum height in just 7.5&nbsp;minutes.<ref name="FMW88-212"/> The final explosion started at 7:01&nbsp;p.m. and continued for over two hours.<ref name="FMW88-212"/> When the relatively small amount of ash settled over eastern Washington, the dome built in June was gone.<ref name="FMW88-213">Harris, ''Fire Mountains of the West'' (1988), page 213</ref> [[Image:St Helens dome on October 24, 1980.jpg|thumb|left|The growing third dome on [[October 24]] [[1980]].]] Seismic activity and gas emission steadily increased in early August, and on [[August 7]] at 4:26&nbsp;p.m., an ash cloud slowly expanded 8 miles (13&nbsp;km) into the sky.<ref name="FMW88-213"/> Small pyroclastic flows were sent through the northern breach and weaker outpouring of ash rose from the crater. This continued until 10:32&nbsp;p.m. when a second large blast sent ash high into the air.<ref name="FMW88-213"/> 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 [[October 18]]. This event obliterated the second dome, sent ash 10&nbsp;miles (16&nbsp;km) in the air and created small, red-hot [[pyroclastic]] flows.<ref name="FMW88-213"/> A third dome began to form within 30&nbsp;minutes after the final explosion on [[October 18]], and within a few days, it was about 900&nbsp;feet (270&nbsp;m) wide and 130&nbsp;feet (40&nbsp;m) high. In spite of the dome growth next to it, [[Crater Glacier|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 3,000&nbsp;feet (900&nbsp;m) wide and 800&nbsp;feet (240&nbsp;m) high.<ref name="FMW88-213"/> At that rate, assuming additional destructive eruptions do not occur, St. Helens' summit would be restored to its previous height sometime in the mid to late 22nd century. Further eruptions occurred over a few months during 1989–1991, and the mountain became active again in late 2004. ==Summary table== {| class="wikitable" |- ! colspan=3 | Eruption Summary<br /> May 18, 1980 Eruption of Mount St. Helens |- ! rowspan=3 | <big>Volcano</big> ! Elevation of Summit: | Before eruption: {{Convert|9677|ft|m|0}}<br/>After eruption: {{Convert|8363|ft|m|0}}<br/>Total removed: {{Convert|1314|ft|m|0}} |- ! Crater dimensions: | East-West: {{Convert|1.2|mi|km|1}}<br/> North-South: {{Convert|1.8|mi|km|1}}<br/> Depth: {{Convert|2084|ft|m|0}} |- ! Crater floor elevation: | {{Convert|6279|ft|m|0}} |- | colspan="3"| |- ! rowspan=3 | <big>Eruption</big> ! Date: | [[May 18]], [[1980]] |- ! Time of initial blast: | 8:32 a.m. Pacific Daylight Time (UTC-7) |- ! Eruption trigger: | A magnitude 5.1 earthquake about {{Convert|1|mi|km|1}} beneath the volcano |- | colspan="3" | |- ! rowspan=4 | <big>Landslide / <br /> Debris Avalanche</big> ! Area covered: | {{Convert|23|sqmi|km2|0}} |- ! Volume:<br/><small> (uncompacted deposits)</small> | 0.67&nbsp;mi³ (2.8&nbsp;km³) |- ! Depth of deposit: | Buried North Fork Toutle River to average depth of {{Convert|150|ft|m|0}} with a maximum depth of {{Convert|600|ft|m|0}} |- ! Velocity: | {{Convert|70|mph|km/h|0}} to {{Convert|150|mph|km/h|0}} |- | colspan="3" | |- ! rowspan=8 | <big>Lateral Blast</big> ! Area covered: | {{Convert|230|sqmi|km2|0}}; reached {{Convert|17|mi|km|0}} northwest of the crater |- ! Volume of deposit: <br/><small> (uncompacted deposits)</small> | 0.046&nbsp;mi³ (0.19&nbsp;km³) |- ! Depth of deposit: | From about {{Convert|3|ft|m|0}} at volcano to less than {{Convert|1|in|cm|1}} at blast edge |- ! Velocity: | At least {{Convert|300|mph|km/h|0}} |- ! Temperature: | As high as {{Convert|660|F|C|0}} |- ! Energy release: | 24 megatons thermal energy (7 by blast, rest through release of heat) |- ! Trees blown down: | 4&nbsp;billion&nbsp;board&nbsp;feet (9.4&nbsp;million&nbsp;m³) of timber (enough to build about 300,000 two-bedroom homes) |- ! Human fatalities: | 57 |- | colspan="3" | |- ! rowspan=4 | <big>Lahars</big> ! Velocity: | About {{Convert|10|mph|km/h|0}} to {{Convert|25|mph|km/h|0}} and over {{Convert|50|mph|km/h|0}} on steep flanks of volcano |- ! Damaged: | 27 bridges, nearly 200 homes. Blast and lahars destroyed more than {{Convert|185|mi|km|0}} of highways and roads and {{Convert|15|mi|km|0}} of railways. |- ! Effects on Cowlitz River: | Reduced carrying capacity at flood stage at Castle Rock from 76,000&nbsp;ft³/s (2,150&nbsp;m³/s) to less than 15,000&nbsp;ft³/s (225&nbsp;m³/s) |- ! Effects on Columbia River: | Reduced channel depth from {{Convert|40|ft|m|0}} to {{Convert|14|ft|m|0}}; stranded 31 ships in upstream ports |- | colspan="3" | |- ! rowspan=5 | <big>Eruption Column<br />And Cloud</big> ! Height: | Reached about {{Convert|80000|ft|m|-2}} in less than 15 minutes |- ! Downwind extent: | Spread across U.S. in 3 days; circled Earth in 15 days |- ! Volume of ash: <br/><small>(based on uncompacted deposits</small> | 0.26&nbsp;mi³ (1&nbsp;km³) |- ! Ash fall area: | Detectable amounts of ash covered {{Convert|22000|sqmi|km2|-3}} |- ! Ash fall depth: | {{Convert|10|in|cm|0}} at {{Convert|10|mi|km|0}} downwind (ash and pumice)<br /> {{Convert|1|in|cm|1}} at {{Convert|60|mi|km|0}} downwind<br /> {{Convert|0.5|in|cm|1}} at {{Convert|300|mi|km|1}} downwind |- | colspan="3" | |- ! rowspan=4 | <big>Pyroclastic Flows</big> ! Area covered: | {{Convert|6|sqmi|km2|0}}; reached as far as {{Convert|5|mi|km|0}} north of crater |- ! Volume and depth: <br/><small>(volume based on uncompacted deposits)</small> | 0.029&nbsp;mi³ (0.12&nbsp;km³); multiple flows {{Convert|3|ft|m|0}} to {{Convert|30|ft|m|0}} thick; cumulative depth of deposits reached {{Convert|120|ft|m|0}} in places |- ! Velocity: | Estimated at {{Convert|50|mph|km/h|-1}} to {{Convert|80|mph|km/h|-1}} |- ! Temperature: | At least {{Convert|1300|F|C|-2}} |- | colspan="3" | |- ! rowspan=2 | <big>Other</big> ! 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 12 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. |- | colspan=3 | Brantley and Myers, 1997, [http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/FS070-97/framework.html Mount St. Helens -- From the 1980 Eruption to 1996]: USGS Fact Sheet 070–97, accessed [[2007-06-05]]; and Tilling, Topinka, and Swanson, 1990, [http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/MSHPPF/MSH_past_present_future.html Eruption of Mount St. Helens - Past, Present, and Future]: USGS General Interest Publication, accessed [[2007-06-05]]. |- | colspan=3 | Table compiled by Lyn Topinka, USGS/CVO, 1997 |} == See also == *[[Cascade Range#High Cascades|High Cascades]] *[[Geology of the Pacific Northwest]] *[[Seconds_From_Disaster#Episodes|National Geographic ''Seconds From Disaster'' episodes]] ==Notes== {{reflist|2}} == References == *Harris, Stephen L. (1988). ''Fire Mountains of the West: The Cascade and Mono Lake Volcanoes''. Missoula: Mountain Press Publishing Company, Missoula. ISBN 0-87842-220-X *{{cite web |author=Tilling, Robert I., Topinka, Lyn and Swanson, Donald A. |year=1990 |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/MSHPPF/MSH_past_present_future.html |title=Eruptions of Mount St. Helens: Past, Present, and Future |publisher=U.S. Geological Survey|work=The Climactic Eruption of May 18, 1980}} (adapted public domain text) *{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/MSHThisWeek/intro.htm| date = [[2001-05-01]] | author = Klimasauskas, Ed |title=Mount St. Helens Precursory Activity|publisher=United States Geological Survey | accessdate = 2007-06-05}} *Topinka, Lyn. [http://vulcan.wr.usgs.gov/Volcanoes/MSH/SlideSet/ljt_slideset_old.html Mount St. Helens: A General Slide Set], Cascades Volcano Observatory, U.S. Geological Survey. Retrieved on [[2007-05-19]] == External links == *[http://web.archive.org/web/20070527160122/http://www.idreamof.com/disaster/vic_msh_fm.html List of victims] *[http://www.tdn.com/helens/noFlash/mainpage.php?p=1116268618&w=P List of victims with biographical details] *[http://www.destination360.com/us/washington/st-helens-summit.htm Mount St. Helens&nbsp;&mdash; a virtual tour] *[http://vulcan.wr.usgs.gov/Volcanoes/MSH/DebrisAval/description_msh_debris_aval.html USGS: Mount St. Helens 1980 Debris Avalanche Deposit] *[http://www.fs.fed.us/gpnf/volcanocams/msh USDA Forest Service: Mount St. Helens VolcanoCam] *[http://pubs.usgs.gov/fs/2005/3045/ Pre-1980 Eruptive History of Mount St. Helens, Washington] *[http://www.youtube.com/watch?v=bgRnVhbfIKQ Video approximation of the first seconds of the May 18th eruption from Gary Rosenquist's photos] {{featured article}} {{coor title dms|46|12|01|N|122|11|12|W|source:dewiki}} {{Cascade volcanoes}} [[Category:1980 natural disasters|Mount St. Helens]] [[Category:1980 in the United States|Mount St. Helens]] [[Category:History of Montana|Mount St. Helens 1980]] [[Category:History of Oregon|Mount St. Helens 1980]] [[Category:History of Washington|Mount St. Helens 1980]] [[Category:Volcanic events|Mount St. Helens 1980]] [[Category:Natural disasters in Washington|Mount St. Helens 1980]] [[Category:History of the United States (1980–1991)|Mount St. Helens]] [[Category:Cascade Volcanoes]] {{link FA|fr}} [[de:Ausbruch des Mount St. Helens 1980]] [[es:Erupción del Monte Saint Helens en 1980]] [[fr:Éruption du mont Saint Helens en 1980]]