1980 eruption of Mount St. Helens
Overview
 
The 1980 eruption of Mount St. Helens
Mount St. Helens
Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...

, a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 located in Washington state, in the United States, was a major volcanic eruption
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

. The eruption (which was a VEI
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

 5 event) was the only significant one to occur in the contiguous 48 U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

s since the 1915 eruption of Lassen Peak
Lassen Peak
Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...

 in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. The eruption was preceded by a two-month series of earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

s and steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

-venting episodes, caused by an injection of magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 at shallow depth below the volcano that created a huge bulge and a fracture system on Mount St. Helens
Mount St. Helens
Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...

' north slope.

USGS scientists convinced the authorities to close Mount St.
Encyclopedia
The 1980 eruption of Mount St. Helens
Mount St. Helens
Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...

, a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 located in Washington state, in the United States, was a major volcanic eruption
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

. The eruption (which was a VEI
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

 5 event) was the only significant one to occur in the contiguous 48 U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

s since the 1915 eruption of Lassen Peak
Lassen Peak
Lassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...

 in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. The eruption was preceded by a two-month series of earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

s and steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

-venting episodes, caused by an injection of magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 at shallow depth below the volcano that created a huge bulge and a fracture system on Mount St. Helens
Mount St. Helens
Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...

' north slope.

USGS scientists convinced the authorities to close Mount St. Helens to the general public and to maintain the closure in spite of pressure to re-open it; their work saved thousands of lives. An earthquake at 8:32:17 a.m. PDT (UTC
Coordinated Universal Time
Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

−7) on Sunday, May 18, 1980, caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas- and steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

-rich rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 in the volcano to lower pressure. The rock responded by exploding a hot mix of lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 and pulverized older rock toward Spirit Lake
Spirit Lake (Washington)
Spirit Lake is a lake north of Mount St. Helens in Washington State. The lake was a popular tourist destination for many years until the 1980 eruption of Mount St. Helens. With the eruption and resulting megatsunami, thousands of trees were torn from the surrounding hillside after lake water was...

 so fast that it overtook the avalanching north face.

An eruption column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...

 rose 80000 feet (24,384 m) into the atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 and deposited ash in 11 U.S. states. At the same time, snow, ice and several entire glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

s on the volcano melted, forming a series of large lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...

s (volcanic mudslides) that reached as far as the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

, nearly fifty miles (eighty kilometers) to the southwest. Less severe outbursts continued into the next day only to be followed by other large but not as destructive eruptions later in 1980.

57 people (including innkeeper Harry R. Truman, photographer Reid Blackburn
Reid Blackburn
Reid Turner Blackburn was a photographer killed in the 1980 volcanic eruption of Mount St. Helens. Blackburn was a photojournalist covering the eruption for a local newspaper—the Vancouver, Washington Columbian—as well as National Geographic magazine and the United States Geological Survey when he...

 and geologist David A. Johnston
David A. Johnston
David Alexander Johnston was an American volcanologist with the United States Geological Survey who was killed by the 1980 eruption of Mount St. Helens in Washington. One of the principal scientists on the monitoring team, Johnston died while manning an observation post about 6 miles from the...

) and thousands of animals were killed. Hundreds of square miles were reduced to wasteland, causing over a billion U.S. dollars in damage ($2.74 billion in 2007 dollars), 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
Burlington Northern Railroad
The Burlington Northern Railroad was a United States-based railroad company formed from a merger of four major U.S. railroads. Burlington Northern operated between 1970 and 1996....

, but afterward the land passed to the United States Forest Service
United States Forest Service
The United States Forest Service is an agency of the United States Department of Agriculture that administers the nation's 155 national forests and 20 national grasslands, which encompass...

. The area was later preserved, as it was, in the Mount St. Helens National Volcanic Monument
Mount St. Helens National Volcanic Monument
Mount St. Helens National Volcanic Monument is a U.S. National Monument that includes the area around Mount St. Helens in Washington. It was established on August 27, 1982 by U.S. President Ronald Reagan following the 1980 eruption of Mount St. Helens. The 110,000 acre National Volcanic...

.

Buildup to the eruption

Mount. St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980. Several small earthquakes beginning as early as March 15, 1980, indicated that magma may have been moving below the volcano. Then on March 18 at 3:45 p.m. Pacific Standard Time (all times will be in PST or PDT), a shallow Richter magnitude 4.2 earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

 (the initial reading was 4.1), centered below the volcano's north flank, signaled the volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

's violent return from 123 years of hibernation. A gradually building earthquake swarm
Earthquake swarm
Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but the United States Geological Survey points out that an event may be on the order of days, weeks, or...

 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. A total of 174 shocks of magnitude 2.6 or greater were recorded during those two days.

Shocks of magnitude 3.2 or greater occurred at a slightly increasing rate during April and May with five earthquakes of magnitude 4 or above per day in early April, and 8 per day the week before May 18. Initially there was no direct sign of eruption, but small earthquake-induced avalanche
Avalanche
An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...

s of snow and ice were reported from aerial observations.

At 12:36 p.m. on March 27, at least one but possibly two nearly simultaneous phreatic eruption
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...

s (exploding groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

-derived steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

) ejected and smashed rock from within the old summit crater
Volcanic crater
A volcanic crater is a circular depression in the ground caused by volcanic activity. It is typically a basin, circular in form within which occurs a vent from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of great depth...

, excavating a new crater 250 feet (76 m) wide and sending an ash column about 7,000 feet (2,100 m) into the air. By this date, a 16000 feet (4,876.8 m) long, east-trending fracture system had also developed across the summit area. This was followed by more earthquake swarms and a series of steam explosions that sent ash 10,000 to 11,000 feet (3,000 to 3,400 m) above their vent. Most of this ash fell within 3 to 12 miles (5 to 20 km) from its vent, but some was carried as far as 150 miles (240 km) south to Bend, Oregon
Bend, Oregon
Bend is a city in and the county seat of Deschutes County, Oregon, United States, and the principal city of the Bend, Oregon Metropolitan Statistical Area. Bend is Central Oregon's largest city, and, despite its modest size, is the de facto metropolis of the region, owing to the low population...

, and 285 miles (460 km) east to Spokane, Washington
Spokane, Washington
Spokane is a city located in the Northwestern United States in the state of Washington. It is the largest city of Spokane County of which it is also the county seat, and the metropolitan center of the Inland Northwest region...

.

A second, new crater and a blue flame was observed on March 29. The flame was visibly emitted from both craters and was probably created by burning gases. Static electricity
Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...

 generated from ash clouds rolling down the volcano sent out lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

 bolts that were up to two miles (3 km) long. Ninety-three separate outbursts were reported on March 30, and increasingly strong harmonic tremor
Harmonic tremor
Harmonic tremor describes a long-duration release of seismic energy, with distinct spectral lines, that often precedes or accompanies a volcanic eruption...

s were first detected on April 1, alarming geologists and prompting Governor Dixy Lee Ray
Dixy Lee Ray
Dixy Lee Ray was the 17th Governor of the U.S. State of Washington. She was Washington's first female governor.-Early years:...

 to declare a state of emergency on April 3. 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 or six months in prison. This excluded many cabin owners from visiting their property.

By April 7 the combined crater was 1,700 feet (520 m) long, 1,200 feet (365 m) wide and 500 feet (150 m) deep. A USGS team determined in the last week of April that a 1.5 miles (2.4 km) diameter section of St. Helens' north face was displaced out at least 270 feet (82 m). For the rest of April and early May this bulge grew 5 to 6 ft (1.5 to 1.8 m) per day, and by mid-May it extended more than 400 feet (120 m) north. As the bulge moved northward, the summit area behind it progressively sank, forming a complex, down-dropped block called a graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....

. Geologists announced on April 30 that sliding of the bulge area was the greatest immediate danger and that such a landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...

 might spark an eruption. These changes in the volcano's shape were related to the overall deformation that increased the volume of the volcano by 0.03 cubic miles (0.1 km³) by mid-May. 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
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...

 exposed at the surface.

On May 7, eruptions similar to those in March and April resumed, and over the next days the bulge approached its maximum size. All activity had been confined to the 350-year-old summit dome and did not involve any new magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

. 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 miles (2.6 km) directly below the bulge. Visible eruptions ceased on May 16, reducing public interest and consequently the number of spectators in the area. 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. Another trip was scheduled for 10 a.m. the next day. Since that was Sunday, more than 300 loggers would not be working in the area. By the time of the climactic eruption, dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...

 magma intruding into the volcano had forced the north flank outward nearly 500 feet (150 m) and heated the volcano's groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 system, causing many steam-driven explosions (phreatic eruptions).

North face slides away

At 7 a.m. on May 18, USGS volcanologist
Volcanology
Volcanology is the study of volcanoes, lava, magma, and related geological, geophysical and geochemical phenomena. The term volcanology is derived from the Latin word vulcan. Vulcan was the ancient Roman god of fire....

 David A. Johnston
David A. Johnston
David Alexander Johnston was an American volcanologist with the United States Geological Survey who was killed by the 1980 eruption of Mount St. Helens in Washington. One of the principal scientists on the monitoring team, Johnston died while manning an observation post about 6 miles from the...

, who had Saturday night duty at an observation post about 6 miles (10 km) north of the volcano, radioed in the results of some laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

-beam measurements he had made moments earlier. 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
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 emission, and ground temperature readings did not reveal any unusual changes that might have indicated a catastrophic eruption.

Suddenly, at 8:32 a.m., a magnitude 5.1 earthquake centred directly below the north slope triggered that part of the volcano to slide, approximately 7–20 seconds (about 10 seconds seems most reasonable) after the shock. The landslide, one of the largest in recorded history, travelled at 110 to 155 miles per hour (175 to 250 km/h) and moved across Spirit Lake's west arm. Part of it hit a 1150 feet (350.5 m) high ridge about 6 miles (10 km) north. Some of the slide spilled over the ridge, but most of it moved 13 miles (21 km) down the North Fork Toutle River
Toutle River
The Toutle River is a river in southwestern Washington State, in the Pacific Northwest region of the United States. It rises in two forks on the flanks of Mount St. Helens and joins the Cowlitz River near Castle Rock.-Eruption of Mount St. Helens:...

, filling its valley up to 600 feet (180 m) deep with avalanche debris. An area of about 24 square miles (62 km²) was covered, and the total volume of the deposit was about 0.7 cubic miles (2.9 km³).

Scientists were able to reconstruct the landslide due to a series of rapid photographs by Gary Rosenquist, who was camping 11 miles (17.7 km) away from the blast. Rosenquist, his party, and his photographs survived because the blast was deflected by local topography 1 miles (1.6 km) short of his location.

Most of St. Helens' former north side became a rubble deposit 17 miles (27 km) long, averaging 150 feet (46 m) thick; the slide was thickest at one mile (1.6 km) below Spirit Lake and thinnest at its western margin. Thousands of trees were torn from the surrounding hillside after the lake was sloshed 800 ft (250 m) up the hillside. All the water in Spirit Lake was temporarily displaced by the landslide, sending 600 feet (182.9 m) high waves crashing into a ridge north of the lake, adding 295 feet (90 m) of new avalanche debris above the old lakebed, and raising its surface level by about 200 feet (60 m). As the water moved back into its basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

, 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.

Initial lateral blast

The landslide exposed the dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...

 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
Explosion
An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. An explosion creates a shock wave. If the shock wave is a supersonic detonation, then the source of the blast is called a "high explosive"...

s burst through the trailing part of the landslide, blasting rock debris northward. The resulting blast laterally directed the pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

 of very hot volcanic gases, ash and pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

 formed from new lava, while pulverized old rock hugged the ground, initially moving at 220 mph (350 km/h) but quickly accelerating to 670 mph (1080 km/h) (it may have briefly passed the speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

).

Pyroclastic flow material passed over the moving avalanche and spread outward, devastating a fan-shaped area 23 miles (37 km) across and 19 miles (30 km) long. In all, about 230 square miles (600 km²) of forest were knocked down, and extreme heat killed trees miles beyond the blow-down zone. At its vent the lateral blast
Lateral eruption
A lateral eruption, also called a flank eruption or lateral blast if explosive, is a volcanic eruption that takes place on the flanks of a volcano instead of at the summit. Lateral eruptions are typical at rift zones where a volcano is breaking apart...

 probably did not last longer than about 30 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
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

, and Northern California
Northern California
Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...

. Yet many areas closer to the eruption (Portland, Oregon
Portland, Oregon
Portland is a city located in the Pacific Northwest, near the confluence of the Willamette and Columbia rivers in the U.S. state of Oregon. As of the 2010 Census, it had a population of 583,776, making it the 29th most populous city in the United States...

, 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
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...

.

Later studies indicated that one-third of the 0.045 cubic miles (188,000,000 m³) of material in the flow was new lava, and the rest was fragmented, older rock.

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 miles (30 km) from the volcano. The area affected by the blast can be subdivided into three roughly concentric zones:
  1. Direct blast zone, the innermost zone, averaged about 8 miles (13 km) in radius, an area in which virtually everything, natural or artificial, was obliterated or carried away. 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.
  2. Channelized blast zone, an intermediate zone, extended out to distances as far as 19 miles (30 km) from the volcano, an area in which the flow flattened everything in its path and was channeled to some extent by topography. 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
    Scythe
    A scythe is an agricultural hand tool for mowing grass, or reaping crops. It was largely replaced by horse-drawn and then tractor machinery, but is still used in some areas of Europe and Asia. The Grim Reaper is often depicted carrying or wielding a scythe...

    . This zone was also known as the "tree-down zone."
  3. 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
    Gas
    Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

    es of the blast.


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. Most of the 57 people known to have died in that day's eruption succumbed to asphyxiation while several died from burns. Lodge owner Harry R. Truman was buried under hundreds of feet of avalanche material. Volcanologist David A. Johnston
David A. Johnston
David Alexander Johnston was an American volcanologist with the United States Geological Survey who was killed by the 1980 eruption of Mount St. Helens in Washington. One of the principal scientists on the monitoring team, Johnston died while manning an observation post about 6 miles from the...

 was one of those killed, as was Reid Blackburn
Reid Blackburn
Reid Turner Blackburn was a photographer killed in the 1980 volcanic eruption of Mount St. Helens. Blackburn was a photojournalist covering the eruption for a local newspaper—the Vancouver, Washington Columbian—as well as National Geographic magazine and the United States Geological Survey when he...

, 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 0.05 cubic miles (208,000,000 m³).

The flow deposits were still at about 300 °C to 420 °C (570 °F to 785 °F) two weeks after they erupted. 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.

Ash column grows

As the avalanche and initial pyroclastic flow were still advancing, a huge ash column grew to a height of 12 miles (19 km) above the expanding crater in less than 10 minutes and spread tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....

 into the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...

 for 10 straight hours. Near the volcano, the swirling ash particles in the atmosphere generated lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

, which in turn started many forest fires. During this time, parts of the mushroom
Mushroom cloud
A mushroom cloud is a distinctive pyrocumulus mushroom-shaped cloud of condensed water vapor or debris resulting from a very large explosion. They are most commonly associated with nuclear explosions, but any sufficiently large blast will produce the same sort of effect. They can be caused by...

-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 65 feet (20 m) in diameter and sending ash as much as 6,500 feet (1980 m) into the air.

Strong high-altitude wind carried much of this material east-northeasterly from the volcano at an average speed of about 60 mph (100 km/h). By 9:45 a.m. it had reached Yakima, Washington
Yakima, Washington
Yakima is an American city southeast of Mount Rainier National Park and the county seat of Yakima County, Washington, United States, and the eighth largest city by population in the state itself. As of the 2010 census, the city had a total population of 91,196 and a metropolitan population of...

, 90 miles (145 km) away, and by 11:45 a.m. it was over Spokane, Washington
Spokane, Washington
Spokane is a city located in the Northwestern United States in the state of Washington. It is the largest city of Spokane County of which it is also the county seat, and the metropolitan center of the Inland Northwest region...

. A total of 4 to 5 inches (100 to 130 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 feet (3 m) and half an inch (13 mm) of ash fell. Continuing east, St. Helens' ash fell in the western part of Yellowstone National Park
Yellowstone National Park
Yellowstone National Park, established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872, is a national park located primarily in the U.S. state of Wyoming, although it also extends into Montana and Idaho...

 by 10:15 p.m. and was seen on the ground in Denver, Colorado
Denver, Colorado
The City and County of Denver is the capital and the most populous city of the U.S. state of Colorado. Denver is a consolidated city-county, located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains...

, the next day. In time ash fall from this eruption was reported as far away as Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

 and Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...

, and some of the ash drifted around the globe within about 2 weeks.

During the nine hours of vigorous eruptive activity, about 540 million tons of ash fell over an area of more than 22,000 square miles (60,000 km²). The total volume of the ash before its compaction by rainfall was about 0.3 cubic miles (1.3 km³). The volume of the uncompacted ash is equivalent to about 0.05 mile³ (208,000,000 m³) of solid rock, or about 7% of the amount of material that slid off in the debris avalanche. By around 5:30 p.m. on May 18, the vertical ash column declined in stature, but less severe outbursts continued through the next several days.

Mudslides flow downstream

The hot, exploding material also broke apart and melted nearly all of the mountain's glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

s along with most of the overlying snow. As in many previous St. Helens' eruptions, this created huge lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...

s (volcanic mudflow
Mudflow
A mudslide is the most rapid and fluid type of downhill mass wasting. It is a rapid movement of a large mass of mud formed from loose soil and water. Similar terms are mudflow, mud stream, debris flow A mudslide is the most rapid (up to 80 km/h, or 50 mph) and fluid type of downhill mass...

s) and muddy floods that affected three of the four stream drainage systems on the mountain, and which started to move as early as 8:50 a.m. Lahars travelled as fast as 90 mph (145 km/h) while still high on the volcano but progressively slowed to about 3 mph (5 km/h) on the flatter and wider parts of rivers. 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
Lewis River (Washington)
The Lewis River is a tributary of the Columbia River, about long, in southwestern Washington in the United States. It drains part of the Cascade Range north of the Columbia River. The drainage basin of the Lewis River covers about . The river's mean annual discharge is about . Unlike nearby Lewis...

. Bridges were taken out at the mouth of Pine Creek and the head of Swift Reservoir, which rose 2.6 feet (0.8 m) by noon to accommodate the nearly 18 million cubic yards (13 million m³) of additional water, mud and debris.

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
Cowlitz River
The Cowlitz River is a river in the state of Washington in the United States, a tributary of the Columbia River. Its tributaries drain a large region including the slopes of Mount Rainier, Mount Adams, and Mount St. Helens....

 near Castle Rock, Washington
Castle Rock, Washington
Castle Rock is a city in Cowlitz County, Washington, United States. Nestled between the Willapa Hills and western base of Mount St. Helens, Castle Rock is at the heart of Washington timber country in the Pacific temperate rain forest...

, at 1:00 p.m. Ninety minutes after the eruption, the first mudflow had moved 27 river miles (43 km) upstream where observers at Weyerhaeuser
Weyerhaeuser
Weyerhaeuser is one of the largest pulp and paper companies in the world. It is the world's largest private sector owner of softwood timberland; and the second largest owner of United States timberland, behind Plum Creek Timber...

's Camp Baker saw a 12 feet (3.7 m) high wall of muddy water and debris pass. Near the confluence of the Toutle's north and south forks at Silver Lake, a record flood stage
Flood stage
Flood stage is the level at which the surface of a river, creek, or other body of water has risen to a sufficient level to cause damage or affects use of man-made structures...

 of 23.5 feet (7.2 m) was recorded.

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 p.m. the massive mudflow had destroyed Camp Baker, and in the following hours seven bridges were carried away. Part of the flow backed up for 2.5 miles (4 km) soon after entering the Cowlitz River, but most continued downstream. After traveling 17 miles (27 km) further, an estimated 3.9 million cubic yards (3.0 million m³) of material were injected into the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

, reducing the river's depth by 25 feet (7.6 m) for a four-mile (6 km) stretch. The resulting 13-foot (4 m) river depth temporarily closed the busy channel to ocean-going freighters
Cargo ship
A cargo ship or freighter is any sort of ship or vessel that carries cargo, goods, and materials from one port to another. Thousands of cargo carriers ply the world's seas and oceans each year; they handle the bulk of international trade...

, costing Portland, Oregon
Portland, Oregon
Portland is a city located in the Pacific Northwest, near the confluence of the Willamette and Columbia rivers in the U.S. state of Oregon. As of the 2010 Census, it had a population of 583,776, making it the 29th most populous city in the United States...

 an estimated five million US dollars. Ultimately more than 65 million cubic yards (50 million m³) of sediment were dumped along the lower Cowlitz and Columbia Rivers.

Direct results

The May 18, 1980, event was the most deadly and economically destructive volcanic eruption in the history of the United States
History of the United States
The history of the United States traditionally starts with the Declaration of Independence in the year 1776, although its territory was inhabited by Native Americans since prehistoric times and then by European colonists who followed the voyages of Christopher Columbus starting in 1492. The...

. 57 people were killed and 200 houses, 27 bridges, 15 miles (24 km) of railways and 185 miles (300 km) of highway were destroyed. U.S. President Jimmy Carter
Jimmy Carter
James Earl "Jimmy" Carter, Jr. is an American politician who served as the 39th President of the United States and was the recipient of the 2002 Nobel Peace Prize, the only U.S. President to have received the Prize after leaving office...

 surveyed the damage and said it looked more desolate than a moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

scape. A film crew was dropped by helicopter on St. Helens on May 23 to document the destruction. Their compass
Compass
A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

es, however, spun in circles and they quickly became lost. A second eruption occurred the next day (see below), but the crew survived and were rescued two days after that. The eruption ejected more than 1 cubic mile (4 km³) of material. A quarter of that volume was fresh lava in the form of ash, pumice and volcanic bomb
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...

s while the rest was fragmented, older rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

. The removal of the north side of the mountain (13% of the cone's volume) reduced St. Helens' height by about 1,313 feet (400 m) and left a crater 1 to 2 miles (2 to 3 km) wide and 2,100 feet (640 m) deep with its north end open in a huge breach.

More than 4 billion board feet (14.6 km³) of timber
Timber
Timber may refer to:* Timber, a term common in the United Kingdom and Australia for wood materials * Timber, Oregon, an unincorporated community in the U.S...

 was 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
Alfalfa
Alfalfa is a flowering plant in the pea family Fabaceae cultivated as an important forage crop in the US, Canada, Argentina, France, Australia, the Middle East, South Africa, and many other countries. It is known as lucerne in the UK, France, Australia, South Africa and New Zealand, and known as...

, were destroyed. As many as 1,500 elk
Elk
The Elk is the large deer, also called Cervus canadensis or wapiti, of North America and eastern Asia.Elk may also refer to:Other antlered mammals:...

 and 5,000 deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...

 were killed, and an estimated 12 million Chinook
Chinook salmon
The Chinook salmon, Oncorhynchus tshawytscha, is the largest species in the pacific salmon family. Other commonly used names for the species include King salmon, Quinnat salmon, Spring salmon and Tyee salmon...

 and Coho
Coho salmon
The Coho salmon, Oncorhynchus kisutch, is a species of anadromous fish in the salmon family. Coho salmon are also known as silver salmon or "silvers". It is the state animal of Chiba, Japan.-Description:...

 salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

 fingerlings died when their hatcheries were destroyed. Another estimated 40,000 young salmon were lost when they swam through turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

 blades of hydroelectric generators when reservoir
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 levels were lowered along the Lewis River to accommodate possible mudflows and flood waters.

In all, Mount St. Helens released 24 megatons of thermal energy, 7 of which was a direct result of the blast. This is equivalent to 1,600 times the size of the atomic bomb dropped on Hiroshima
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...

.

Digging out

The ash fall created some temporary but major problems with transportation, sewage
Sewage
Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

 disposal, and water treatment
Water treatment
Water treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the...

 systems. Visibility was greatly decreased during the ash fall, closing many highways and roads. Interstate 90
Interstate 90
Interstate 90 is the longest Interstate Highway in the United States at . It is the northernmost coast-to-coast interstate, and parallels US 20 for the most part. Its western terminus is in Seattle, at Edgar Martinez Drive S. near Safeco Field and CenturyLink Field, and its eastern terminus is in...

 from Seattle to Spokane
Spokane, Washington
Spokane is a city located in the Northwestern United States in the state of Washington. It is the largest city of Spokane County of which it is also the county seat, and the metropolitan center of the Inland Northwest region...

 was closed for a week and a half. Air travel was disrupted for a few days to 2 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 and clogged air filters, and scratched moving surfaces. Fine ash caused short circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....

s in electrical transformers, which in turn caused power blackouts.

Removing and disposing of the ash was a monumental task for some eastern Washington communities. State and federal agencies estimated that over 2.4 million cubic yards (1.8 million m³) of ash, equivalent to about 900,000 tons in weight, were removed from highways and airports in Washington. The ash removal cost $2.2 million and took 10 weeks in Yakima. 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
Landfill
A landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...

s; 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.

Cost

Early estimates of the cost of the eruption ranged from US$2–3 billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....

. A refined estimate of $1.1 billion ($2.74 billion in 2007 dollars) was determined in a study by the International Trade Commission at the request of the United States Congress
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

. A supplemental appropriation of $951 million for disaster relief was voted by Congress, of which the largest share went to the Small Business Administration
Small Business Administration
The Small Business Administration is a United States government agency that provides support to entrepreneurs and small businesses. The mission of the Small Business Administration is "to maintain and strengthen the nation's economy by enabling the establishment and viability of small businesses...

, U.S. Army Corps of Engineers and the Federal Emergency Management Agency
Federal Emergency Management Agency
The Federal Emergency Management Agency is an agency of the United States Department of Homeland Security, initially created by Presidential Reorganization Plan No. 1 of 1978 and implemented by two Executive Orders...

.

There were also indirect and intangible costs of the eruption. Unemployment
Unemployment
Unemployment , as defined by the International Labour Organization, occurs when people are without jobs and they have actively sought work within the past four weeks...

 in the immediate region of Mount St. Helens rose tenfold in the weeks immediately following the eruption, and then returned to nearly 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
Stress (medicine)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...

 and emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...

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.

Initial public reaction to the May 18 eruption dealt a nearly crippling blow to tourism
Tourism
Tourism is travel for recreational, leisure or business purposes. The World Tourism Organization defines tourists as people "traveling to and staying in places outside their usual environment for not more than one consecutive year for leisure, business and other purposes".Tourism has become a...

, an important industry in Washington. Not only was tourism down in the Mount St. Helens–Gifford Pinchot National Forest
Gifford Pinchot National Forest
Gifford Pinchot National Forest is a U.S. National Forest located in southern Washington, USA. With an area of 1.37 million acres , it extends 116 km along the western slopes of Cascade Range from Mount Rainier National Park to the Columbia River. It includes the 110,000 acre Mount St....

 area, but conventions, meetings and social gatherings also were cancelled or postponed at cities and resorts elsewhere in Washington and neighboring Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

 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
United States Forest Service
The United States Forest Service is an agency of the United States Department of Agriculture that administers the nation's 155 national forests and 20 national grasslands, which encompass...

 and the State of Washington opened visitor centers and provided access for people to view the volcano's devastation.

Photographic and video record

The eruption of Mount St. Helens on May 18, 1980 was also one of the most well documented volcanic eruptions in recorded history. It is also one of very few major volcanic eruptions ever to be recorded on film at the moment of eruption. Early that morning at around 3AM local time, KOMO-TV
KOMO-TV
KOMO-TV, virtual channel 4, is a television station in Seattle, Washington. It is an affiliate of ABC and broadcasts on digital channel 38. KOMO-TV is the flagship station of Fisher Communications, and its studios and offices are co-located with sister radio stations KOMO , KVI , and KPLZ-FM ...

 news photographer Dave Crockett had left Seattle in a KOMO-TV news car bound for a lookout on the South Fork of the Toutle River where news crews had been stationed previously. At a campground 10 miles (16.1 km) away to the northeast, amateur photographer Gary Rosenquist as well as University of Washington graduate student Keith Ronnholm had been waiting. In the air directly above the volcano, geologists Keith and Dorothy Stoffel had chartered a Cessna aircraft from Yakima to do some photographic documentation of the summit bulge. To the west near the South Fork Toutle River, ham radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...

 operators Ty and Mariana Kearney were stationed at a lookout point monitoring the activity for an emergency radio network.

At the moment of eruption, Gary Rosenquist was alerted to the volcano by a few members of his camping party and began firing off the first of a 24-frame sequence that clearly illustrated the landslide and beginning moments of the lateral blast and simultaneously doing so was Keith Ronnholm a few feet away. At the same time, Ty and Mariana Kearney were photographing it from the west side, as well as Keith and Dorothy Stoffel from the air. Arriving also at the moment of eruption was KOMO News photographer Dave Crockett. As the ash cloud loomed overhead and continued to spread out, a lahar coming down the South Fork Toutle River blocked his path of escape. He then got out of the car and began filming the eruption's ash column as well as the lightning and the lahars. As the cloud began darkening the sky he began a trek up a logging road and turned the camera on once again, this time narrating his video in what was recorded as a "death march." The video, of which 11 minutes is recorded in total darkness, was played out on newscasts worldwide. Crockett was later reprimanded for losing the station's news car.

Several other photographers perished during the blast. Reid Blackburn
Reid Blackburn
Reid Turner Blackburn was a photographer killed in the 1980 volcanic eruption of Mount St. Helens. Blackburn was a photojournalist covering the eruption for a local newspaper—the Vancouver, Washington Columbian—as well as National Geographic magazine and the United States Geological Survey when he...

, photographer for The Columbian
The Columbian
The Columbian is a daily newspaper for Vancouver, Washington and Clark County in Washington State in the United States. The paper was published for its first decade as a four page daily that was meant as a counterweight to the local Republican newspaper The Independent. Printer Tom Carolan began...

and monitor for the United States Geological Survey, was killed at his campsite, eight miles (13 km) from the volcano. He took several photos, but the film was destroyed by the pyroclastic flows. Robert Landsberg
Robert Landsberg
Robert Landsburg was a photographer from Portland, Oregon who was killed in the May 18, 1980 eruption of Mount St. Helens.In the weeks leading up to the eruption, Landsburg visited the area tens of times in order to photographically document the changing volcano. On the morning of May 18, he was...

 (spelled Landsburg in some accounts) succumbed to the eruption, but managed to secure his camera film; though damaged by the eruption, his photos—depicting the advancing pyroclastic surge—were processed and published in National Geographic magazine in 1981.

Later eruptions

St. Helens produced an additional five 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.

An eruption occurred on May 25, 1980 at 2:30 a.m. that sent an ash column 9 miles (14 km) into the atmosphere. 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.

At 7:05 p.m. on June 12, a plume of ash billowed 2.5 miles (4 km) above the volcano. At 9:09 p.m. a much stronger explosion sent an ash column about 10 miles (16 km) skyward. 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. A dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...

 dome then oozed into existence on the crater floor, growing to a height of 200 feet (60 m) and a width of 1,200 feet (370 m) within a week.

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
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

. The first hit at 5:14 p.m. as an ash column shot 10 miles (16 km) and was followed by a faster blast at 6:25 p.m. that pushed the ash column above its previous maximum height in just 7.5 minutes. The final explosion started at 7:01 p.m. and continued for over two hours. When the relatively small amount of ash settled over eastern Washington, the dome built in June was gone.

Seismic activity and gas emission steadily increased in early August, and on August 7 at 4:26 p.m., an ash cloud slowly expanded 8 miles (13 km) into the sky. Small pyroclastic flows were sent through the northern breach and weaker outpouring of ash rose from the crater. This continued until 10:32 p.m. when a second large blast sent ash high into the air. 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 miles (16 km) in the air and created small, red-hot pyroclastic flows. A third dome began to form within 30 minutes after the final explosion on October 18, and within a few days, it was about 900 feet (270 m) wide and 130 feet (40 m) high. In spite of the dome growth next to it, a new glacier
Crater Glacier
The Crater Glacier is a geologically young glacier that is located on Mount Saint Helens, in the U.S. state of Washington. The glacier formed after the 1980 Eruption and due to its location, the body of ice grew rapidly, unknown to the public for nearly 20 years...

 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 feet (900 m) wide and 800 feet (240 m) high.

Further eruptions occurred over a few months during 1989–1991, and the mountain became active again in late 2004 building a new dome. This activity lasted until January 2008.

Summary table

Eruption summary

May 18, 1980, eruption of Mount St. Helens
Volcano Elevation of summit: Before eruption: 9677 feet (2,950 m)
After eruption: 8363 feet (2,549 m)
Total removed: 1314 feet (401 m)
Crater dimensions: East-West: 1.2 miles (1.9 km)
North-South: 1.8 miles (2.9 km)
Depth: 2084 feet (635 m)
Crater floor elevation: 6279 feet (1,914 m)
Eruption 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 1 miles (1.6 km) beneath the volcano
Landslide and
debris avalanche
Area covered: 23 square miles (60 km²)
Volume:
(uncompacted deposits)
0.67 mi³ (2.8 km³)
Depth of deposit: Buried North Fork Toutle River to average depth of 150 feet (46 m) with a maximum depth of 600 feet (183 m)
Velocity: 70 miles per hour (113 km/h) to 150 miles per hour (241 km/h)
Lateral blast Area covered: 230 square miles (596 km²); reached 17 miles (27 km) northwest of the crater
Volume of deposit:
(uncompacted deposits)
0.046 mi³ (0.19 km³)
Depth of deposit: From about 3 foot (0.9144 m) at volcano to less than 1 inches (2.5 cm) at blast edge
Velocity: At least 300 miles per hour (483 km/h)
Temperature: As high as 660 °F (349 °C)
Energy release: 24 megatons thermal energy (7 by blast, rest through release of heat)
Trees blown down: 4 billion board feet (9.4 million m³) of timber (enough to build about 300,000 two-bedroom homes)
Human fatalities: 57
Lahars Velocity: About 10 miles per hour (16 km/h) to 25 miles per hour (40 km/h) and over 50 miles per hour (80 km/h) on steep flanks of volcano
Damaged: 27 bridges, nearly 200 homes. Blast and lahars destroyed more than 185 miles (298 km) of highways and roads and 15 miles (24 km) of railways.
Effects on Cowlitz River: Reduced carrying capacity at flood stage at Castle Rock from 76,000 ft³/s (2,150 m³/s) to less than 15,000 ft³/s (225 m³/s)
Effects on Columbia River: Reduced channel depth from 40 feet (12 m) to 14 feet (4 m); stranded 31 ships in upstream ports
Eruption column
and cloud
Height: Reached about 80000 feet (24,384 m) 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)
0.26 mi³ (1 km³)
Ash fall area: Detectable amounts of ash covered 22000 square miles (56,979.7 km²)
Ash fall depth: 10 inches (25 cm) at 10 miles (16 km) downwind (ash and pumice)
1 inches (2.5 cm) at 60 miles (97 km) downwind
0.5 inches (1.3 cm) at 300 miles (482.8 km) downwind
Pyroclastic flows Area covered: 6 square miles (16 km²); reached as far as 5 miles (8 km) north of crater
Volume and depth:
(volume based on uncompacted deposits)
0.029 mi³ (0.12 km³); multiple flows 3 foot (0.9144 m) to 30 feet (9 m) thick; cumulative depth of deposits reached 120 feet (37 m) in places
Velocity: Estimated at 50 miles per hour (80.5 km/h) to 80 miles per hour (128.7 km/h)
Temperature: At least 1300 °F (704.4 °C)
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 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.
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

  • High Cascades
  • Geology of the Pacific Northwest
    Geology of the Pacific Northwest
    The geology of the Pacific Northwest refers to the study of the composition , structure, physical properties and the processes that shape the Pacific Northwest region of the United States and Canada...

  • National Geographic Seconds From Disaster episodes
  • The Eruption of Mount St. Helens!
    The Eruption of Mount St. Helens!
    The Eruption of Mount St. Helens! is a 1980 short documentary film directed by George Casey. It was nominated for an Academy Award for Best Documentary Short....

    , a 1980 documentary film about the eruption
  • Pacific Ring of Fire
    Pacific Ring of Fire
    The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...


External links

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