1980 eruption of Mount St. Helens

• 1. Introduction

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  Mount St. Helens, in Skamania County, Washington, erupted at 8:32 on the morning of the 18th of May 1980. The eruption rated a 5 on the volcanic explosivity index, a scale that measures the size of volcanic events. No volcano in the contiguous United States had erupted since Lassen Peak in California in 1915, and that eruption was far smaller. Many people have since called the St. Helens event the most disastrous volcanic episode in American history. How does a mountain go from quiet to ruin in a single morning? What did the scientists watching it see coming, and what did they miss? And who was standing in its path when it let go?

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• 2. A Mountain Wakes

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  For 123 years, Mount St. Helens had been silent, its last period of activity dating to the 1840s and 1850s. Small earthquakes began on the 15th of March 1980, hinting that magma might be moving underground. Five days later, at 3:45 in the afternoon, a shallow quake of magnitude 4.2 shook the north flank and ended the long hibernation.

  A swarm of tremors then built steadily and began to peak around noon on the 25th of March. Seismographs in the area were saturated. Over the next two days the swarm produced 174 shocks of magnitude 2.6 or greater, among them one registering 5.1 on the Richter scale.

  At 12:36 in the afternoon of the 27th of March, steam explosions tore through the old summit crater. These phreatic eruptions happen when rising magma suddenly heats groundwater. They smashed rock apart, dug a fresh crater 250 ft wide, and sent an ash column about 7,000 ft into the sky. A fracture system 16,000 ft long had also opened across the summit. Later steam blasts lofted ash 10,000 to 11,000 ft above the vent. Some of it drifted 150 mi south to Bend, Oregon, and some travelled 285 mi east to Spokane, Washington.

  On the 29th of March, observers saw a second new crater and a blue flame, probably burning gas, flickering from both vents. Ash clouds rolling down the mountain generated static electricity, and lightning bolts up to 2 mi long flashed from them. The next day, 93 separate outbursts were reported. By the 7th of April the two craters had merged into one measuring 1,700 by 1,200 ft and 500 ft deep.

  Harmonic tremors, first detected on the 1st of April, alarmed the geologists. Governor Dixy Lee Ray declared a state of emergency on the 3rd of April. Her executive order of the 30th of April created a red zone around the volcano. Anyone caught inside without a pass faced a $500 fine or six months in jail, which kept many cabin owners away from their property.

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• 3. The Bulge

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  On the mountain's north face, the swelling was visible. In the last week of April, a USGS team found that a 1.5 mi section of the face had been pushed outward by at least 270 ft. Through the rest of April and into early May, the bulge crept out 5 to 6 ft every day. Behind it the summit sank, forming a down-dropped block called a graben. By the time of the climactic eruption, the north flank had been forced out nearly 500 ft.

  The cause was magma that had pushed into the mountain without breaking the surface. Because it stayed hidden, it was called a cryptodome, in contrast to a true lava dome exposed to the open air. By mid-May it had swollen the whole volcano by 0.03 mi3. On the 30th of April, geologists announced that a slide of the bulge was the greatest immediate danger, and that such a slide might set off an eruption.

  Rocky Crandell, a USGS employee in the Vancouver office near the mountain, had sought out volcanologist Barry Voight for his expertise in landslides. Voight watched the mountain from the 11th to the 19th of April. He warned that the bulge could fail and bring down the entire north sector, and that the collapse might trigger an eruption. He urged the team to track how fast the bulge was moving. He also advised hiring a local surveyor, which offended several of the geologists.

  Voight then returned to teaching at Pennsylvania State University. On the 1st of May he sent the USGS his full report. It predicted the failure of the bulge, the collapse of the north side, and a violent eruption that would demand an extensive evacuation zone.

  Eruptions like those of March and April resumed on the 7th of May. About 10,000 earthquakes were recorded before the 18th, most of them in a small zone less than 1.6 mi below the bulge. Visible eruptions stopped on the 16th of May, which cooled public interest and thinned the crowds of spectators. Pressure on officials grew, and on Saturday the 17th of May, 50 carloads of property owners were allowed into the danger zone to collect what they could carry. A second trip was set for 10 the next morning, a Sunday, when more than three hundred loggers who normally worked the area would be absent.

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• 4. The Slide

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  On the morning of the 18th of May, nothing on the mountain looked different. USGS volcanologist David A. Johnston was on duty at an observation post about 6 mi north of the volcano. At 6:00 his measurements showed nothing unusual. Bulge movement, sulfur dioxide emissions and ground temperatures all followed the pattern of the previous month.

  Then an earthquake of magnitude 5.1 struck directly beneath the north slope. Between 7 and 20 seconds later, that whole section of the mountain began to slide, and the main volcanic blast followed a few seconds after. The sector collapse remains the largest subaerial landslide in recorded history.

  The slide swept across the west arm of Spirit Lake. Part of it struck a ridge 1,150 ft high about 6 mi to the north, and some debris spilled over the top. Most of it, though, travelled 13 mi down the North Fork Toutle River and filled the valley to depths of up to 600 ft. In all, it covered about 24 mi2 and totalled about 0.7 mi3.

  Photographer Gary Rosenquist was camping 11 mi from the mountain. His rapid series of photographs later allowed scientists to reconstruct how the landslide moved. He, his party and his film survived because local topography deflected the blast 1 mi short of his location.

  Spirit Lake took the shock. The slide shoved its water up onto the ridge to the north in a wave about 600 ft high. The water then rushed back, carrying a 295 ft avalanche of debris and thousands of uprooted trees and stumps. Most of the trees had been sheared off at the stump seconds earlier by the superheated blast. All of that returning material raised the lake's surface by about 200 ft.

  Four decades later, mats of floating logs still drift on Spirit Lake and nearby St. Helens Lake, shifting with the wind. Trees that kept some of their roots turned upright under their own weight, became waterlogged, and sank into the mud. There, in mineral-rich water with little oxygen, they are slowly turning to stone.

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• 5. The Lateral Blast

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  The landslide pulled the lid off the mountain's neck. The dacite magma inside suddenly faced far lower pressure, and the gas-charged, partly molten rock and the steam above it exploded. Within seconds, explosions burst through the back of the slide and hurled debris northward. This pyroclastic flow was a mix of very hot gas, ash, fresh pumice and pulverized old rock, and it hugged the ground. It began at about 220 mph, accelerated to around 670 mph, and may briefly have broken the speed of sound.

  The flow overtook the landslide and devastated a fan-shaped area 23 mi across and 19 mi long. About 230 mi2 of forest was knocked flat, and heat killed trees miles beyond. At the vent the blast probably lasted no more than thirty seconds. The expanding cloud kept spreading for about another minute.

  Scientists divide the damage into roughly concentric zones. The innermost, about 8 mi in radius, is the direct blast zone, also called the tree-removal zone. Virtually everything natural or built there was obliterated or carried away, and the flow ignored the terrain.

  Beyond it lay the channelized blast zone, reaching as far as 19 mi from the volcano. It is also known as the tree-down zone. Large trees lay toppled in parallel rows, snapped at the base as if mown by a scythe. Topography channelled the flow, and the effects varied sharply from place to place. Where the blast struck open ground directly, it scoured away vegetation and even topsoil, and regrowth was delayed for years. Where it passed several metres overhead, the topsoil and its seeds survived, and scrub, herbs and later saplings returned faster. Sheltered stands nearby recovered comparatively quickly.

  The outermost fringe was the seared zone, also called the standing dead zone. Trees there stayed upright but were singed brown by the hot gases.

  The flow also flashed the water of Spirit Lake and the North Fork Toutle River to steam, setting off a larger secondary explosion. People heard it as far away as British Columbia, Montana, Idaho and Northern California. Yet Portland, Oregon, much closer, heard nothing. A so-called quiet zone extended a few tens of miles around the volcano. It formed because sound waves reacted to differences in temperature and air motion in the atmospheric layers, and to a lesser extent to local terrain.

  Later studies showed that only one-third of the 0.045 mi3 of material in the flow was new lava. The rest was fragmented older rock.

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• 6. Lives Lost

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  By the time the flow reached its first human victims, it was still as hot as 360 C and thick with suffocating gas and flying debris. Most of the 57 people known to have died that day were asphyxiated. Several others died of burns.

  Harry R. Truman, an innkeeper and World War I veteran, was buried under hundreds of feet of avalanche material. David A. Johnston was killed at the Coldwater II observation post, just six miles north of the mountain. Reid Blackburn, a photographer for the Vancouver Columbian and National Geographic, died near Coldwater Creek, 8 mi from the volcano.

  Robert Landsburg, another photographer, was within a few miles of the summit when the ash cloud killed him. He shielded his film with his body, and the surviving photographs gave geologists valuable documentation of the eruption.

  Amateur radio operator Gerry Martin was near the Coldwater peak, farther north than Johnston. He reported the blast engulfing the Coldwater II post. Then he described what he could see around him, saying: "Gentlemen, the camper and car that's sitting over to the south of me is covered. It's going to hit me, too." His radio went silent.

  The figure of 57 hides some doubt. Paul Hiatt and Dale Thayer are officially listed as victims after being reported missing. Investigators later found living people with those names. They could not confirm these were the same men, though. They could not learn who had reported Hiatt missing, and the woman listed as reporting Thayer missing said she had not done so. The names therefore stay on the list.

  Three other people, Robert Ruffle, Steven Whitsett and Mark Melanson, are not officially listed. Cowlitz County Emergency Services Management records them as possibly missing. In October 1983, county officials told Melanson's family that he was believed to be a victim. After years of searching, the family concluded that "he's buried in the ash."

  With these uncertainties, the direct death toll could be as low as 55 or as high as 60. Four more people died indirectly: two in accidents caused by poor visibility, and two from heart attacks while shoveling ash. Counting them, the total ranges from 59 to 64.

  A year and a half after the eruption, the bodies of two young women were found. Marsha Anne Weatter was 18 and Katherine Jean Allen was 20. They were believed to have been murdered about six weeks before the eruption, not killed by it. Their backpacks had been found in July 1980, and a layer of ash may have hidden the bodies. Each had been shot once, and the murders were later linked to serial killer Martin Lee Sanders.

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• 7. Ash and Mud

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  While the avalanche and first flow were still advancing, an ash column climbed 12 mi above the crater in under ten minutes. It fed material into the stratosphere for ten straight hours. Swirling ash produced lightning near the volcano, and the lightning started many forest fires. Parts of the mushroom-shaped column collapsed and fell back. Mixed with magma, mud and steam, that fallout sent more pyroclastic flows racing down the mountain's flanks.

  At least 17 separate pyroclastic flows occurred that day, totalling about 0.05 mi3. Two weeks later their deposits were still between 300 and 420 C. Steam blasts fed by that heat pitted the ground along the edge of the deposits, the south shore of Spirit Lake and the upper North Fork Toutle River. At least one such blast came a year later, on the 16th of May 1981.

  Strong high-altitude wind carried the ash east-northeast at an average of around 60 mph. It reached Yakima, Washington, 90 mi away, by 9:45 in the morning, and 4 to 5 in of ash fell there. By 11:45 it was over Spokane, and by noon that city was plunged into darkness, with visibility down to 10 ft and half an inch of ash on the ground. Ash reached the western part of Yellowstone National Park by 10:15 that night, and it lay on the ground in Denver the next day. Fall was eventually reported as far away as Minnesota and Oklahoma, and some ash circled the globe within about two weeks. During roughly nine hours of vigorous activity, about 540,000,000 tons of ash fell over more than 22,000 mi2.

  The hot, exploding material also melted nearly all of the mountain's glaciers, along with most of the snow above them. The result was lahars, or volcanic mudflows. They began moving as early as 8:50 in the morning. High on the volcano they ran as fast as 90 mph, slowing to about 3 mph on the flatter, wider stretches of the rivers.

  Mudflows from the southern and eastern flanks had the consistency of wet concrete. They raced down Muddy River, Pine Creek and Smith Creek to the Lewis River. Bridges were taken out at the mouth of Pine Creek and at the head of Swift Reservoir. The reservoir rose 2.6 ft by noon to absorb nearly 18,000,000 yd3 of extra water, mud and debris.

  Glacier and snowmelt on the northeast slope mixed with tephra to create much larger lahars. They ran down the north and south forks of the Toutle River and met the Cowlitz River near Castle Rock at 1:00 in the afternoon. Ninety minutes after the eruption, observers at Weyerhaeuser's Camp Baker watched a 12 ft wall of muddy water and debris pass. Near the confluence of the Toutle forks at Silver Lake, the flood reached a record stage of 23.5 ft.

  A slower flow with a mortar-like consistency followed in the early afternoon. By 2:30 it had destroyed Camp Baker, and over the following hours it carried away seven bridges. An estimated 3,900,000 yd3 of this material entered the Columbia River. It cut the river's depth by 25 ft along a 4 mi stretch, leaving 13 ft and closing the channel to ocean-going freighters. The closure cost Portland, Oregon, an estimated $5 million. In the end, more than 65,000,000 yd3 of sediment lay along the lower Cowlitz and Columbia Rivers.

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• 8. Aftermath

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  President Jimmy Carter surveyed the devastation and remarked that it looked more desolate than a moonscape. The eruption destroyed 200 houses, dozens of bridges, 15 mi of railway and 185 mi of highway. On the 23rd of May, a film crew dropped by helicopter onto the mountain found their compasses spinning in circles and quickly became lost. Another eruption came the next day. The crew survived and was rescued two days after that.

  The mountain itself was diminished. Losing its north side removed 13% of the cone's volume and about 1,300 ft of height. It left a crater 1 to 2 mi wide and 2,100 ft deep, open to the north in a huge breach. The eruption ejected more than 1 mi3 of material, a quarter of it fresh lava and the rest fragmented older rock. Its energy came to roughly 24 megatons of TNT, equivalent to 1,600 times the atomic bomb dropped on Hiroshima.

  More than 4,000,000,000 board feet of timber was damaged or destroyed, mostly by the lateral blast. At least a quarter of the destroyed timber was salvaged after September 1980. Where ash lay thick downwind, crops such as wheat, apples, potatoes and alfalfa were ruined. As many as 1,500 elk and 5,000 deer died. An estimated twelve million Chinook and Coho salmon fingerlings were killed when their hatcheries were destroyed. Another estimated 40,000 young salmon died in the turbine blades of hydroelectric generators on the Lewis River, after reservoirs were lowered to make room for floodwater.

  Ash also brought transport to a halt. Interstate 90 between Seattle and Spokane closed for a week and a half. Several airports in eastern Washington shut down for periods ranging from a few days to two weeks, and over a thousand commercial flights were cancelled. Fine, gritty ash contaminated oil systems, clogged air filters, scratched moving parts and short-circuited electrical transformers, causing power blackouts.

  State and federal agencies estimated that over 2,400,000 yd3 of ash, about 900,000 tons, was removed from Washington highways and airports. In Yakima the job took ten weeks and cost $2.2 million. Some cities dumped ash in old quarries and landfills. Others created dump sites wherever was fastest, and some covered them with topsoil and grass seed to keep the wind from stirring the ash up again. In Portland, the mayor eventually threatened businesses with fines if they did not clear ash from their parking lots.

  A study by the International Trade Commission, requested by Congress, set the cost at $1.1 billion. Congress voted a supplemental $951 million in disaster relief, with the largest shares going to the Small Business Administration, the U.S. Army Corps of Engineers and the Federal Emergency Management Agency. Unemployment near the mountain rose tenfold in the weeks after the eruption, then fell back toward normal once timber salvage and ash cleanup were underway. Several months later, some residents who had coped well during the crisis reported stress and emotional problems, and counties asked for funding for mental-health programs. Tourism took a nearly crippling blow, with conventions and gatherings cancelled even in cities untouched by the eruption. The damage proved temporary. The U.S. Forest Service and the State of Washington opened visitor centers so people could see the devastation.

  The volcano was not finished. It produced five more explosive eruptions between May and October 1980. On the 12th of June, one of them thinly coated Portland in ash in the middle of its annual Rose Festival. Between eruptions, dacite domes grew on the crater floor and were then blown apart. A third dome began forming within thirty minutes of the last explosion on the 18th of October, and a new glacier formed rapidly in the crater beside it. By 1987 that dome was more than 3,000 ft wide and 800 ft high. At least 21 periods of eruptive activity occurred through early 1990. A new lava dome grew from October 2004 to January 2008 without rising above the 1980 crater.

  At the time of the eruption, the summit belonged to the Burlington Northern Railroad. The U.S. Forest Service acquired the land afterward, and the area is now preserved in the Mount St. Helens National Volcanic Monument. The State of Washington recognizes May as Volcano Awareness Month, with events in the region to discuss safety and to commemorate the lives lost.

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