Volcano Eruption Mount St. Helens May 18, 1980 USGS - YouTube Volcano Eruption Mount St. Helens May 18, 1980 USGS Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. Rating is available when the video has been rented. This feature is not available right now. Please try again later. Uploaded on Jan 26, 2011 Produced by Stephen M. Wessells. USGS scientists recount their experiences before, during and after the May 18, 1980 eruption of Mount St. Helens. Loss of their colleague David A. Johnston and 56 others in the eruption cast a pall over one of the most dramatic geologic moments in American history. Video Credit: U.S. Geological Survey Department of the Interior/USGS Category What happened when Mount St. Helens erupted on May 18, 1980? | Volcano World | Oregon State University What happened when Mount St. Helens erupted on May 18, 1980? , with a list of references.

Time The climatic eruption began at 08:32 PDT on May 18, 1980. Deaths 57 people were killed directly by the eruption. There was also a plane crash, a traffic accident, and shoveling ash which killed a total of 7 more. Height of Mount St. Helens The summit elevation was 9,760 feet (2,975 m) before the eruption. After the eruption the elevation of the new summit was about 8,525 feet (2,600 m). Volume About 0.25 cubic kilometers of new volcanic rock was erupted on May 18, 1980. This would make a cube about 600 meters (~2000 ft) on a side! But much more material was moved by the eruption: the entire northern side of the volcano collapsed and flowed down hill. The volume of this collapse was about 2.5 cubic kilometers – ten times bigger than the new . Ash The eruption began at 8:45 a.m. At noon, the ash plume (in the upper troposphere and lower stratosphere) had reached Moscow, Idaho.

By about 3 p.m. it was near Missoula, Montana and starting to spread south. By 6 pm it was eas! of Pocatello, Idaho. At the end of the day, about 16 hours after the eruption started, the ash plume was near central Colorado. A huge volume of ash was created by the various 1980 eruptions of Mount St. Helens. Every community affected had its own ways of dealing with the ash. Tons of ash was probably washed down storm drains and into sewer systems as people cleaned roofs and sidewalks. Local landfills received ash. Many tons of ash came down rivers and streams into the Columbia River. The river had to be dredged to allow shipping to pass, and the sand dredged from the bottom was deposited in large dikes along the Columbia. These dikes are now covered in grass and trees, but if a person was to dig down a few feet they would find the ash. Ash can still be found on the floor of forested areas all around the mountain, and the blast zone is still heavily covered by ash. Souvenir “ash” trays and mugs made from Mount St. Helens ash can be purchased at gift shops near the mountain.

Sources of Information: Christiansen, R.L., and Peterson, D.W., 1981, Chronology of the 1980 eruptive activity, in Lipman, P.W., and Mullineaux, D.R., eds., The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 17-30. Danielsen, E.F., 1981, Trajectories of the Mount St. Helens eruption plume: Science, v. 211, p. 819-821. McClelland, L., Simkin, T., Summers, M., Nielson, E., Stein, T.C., 1989, Global volcanism 1975-1985: Prentice Hall, Englewood Cliffs, New Jersey, and American Geophysical Union, Washington DC, 655 p.

Sarna-Wojcicki, A.M., Shipley, S., Waitt, Jr., R.B., Dzurisin, D., and Wood, S.H., 1981, Areal distribution, thickness, mass, volume, and grain size of air-fall from the six major eruptions of 1980, in Lipman, P.W. and Mullineaux, D.R., (eds.),The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 577-600. Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, P.O. Box 42948, Tucson, AZ 85733-2948) Contact Info VW is a higher education, k-12, and public outreach project of the Oregon Space Grant Consortium administered through the Department of Geosciences at Oregon State University. Mount St. Helens Eruption: Facts & Information Mount St.

Helens Eruption: Facts & Information By Mary Bagley, LiveScience Contributor | February 28, 2013 04:22pm ET MORE The May 18 eruption sent volcanic ash, steam, water, and debris to a height of 60,000 feet (18,288 meters), while the mountain lost 1,300 feet (396 meters) of altitude. Fifty-seven people were killed or are still missing. USGS Photograph taken on May 18, 1980, by Robert Krimmel. Credit: Robert Krimmel, USGS Mount St. Helens erupted on May 18, 1980. The volcano, located in southwestern Washington, used to be a beautiful symmetrical cone about 9,600 feet (3,000 meters) above sea level. The eruption, which removed the upper 1,300 feet (396 meters) of the summit, left a horseshoe-shaped crater and a barren wasteland. Today the land is healing, having recovered its natural beauty, but the landscape has been permanently altered.

Native Americans in the Pacific Northwest called the mountain "Louwala-Clough" or "Smoking Mountain." The modern name came from Capt. George Vancouver of the British Royal navy, who named it in honor of Alleyne Fitzherbert, the British Ambassador to Spain, who also held the title Baron St. Helens. The volcano was relatively active in the early 19th century, and may have had a major explosive eruption in 1800, according to the Mount St. Helens Forest Learning Center . There were minor eruptions in 1898, 1903 and 1932, but for most of the 20th century, the mountain was seen as a peaceful, beautiful mountain and recreation area. That serenity was shattered in 1980. On shaky ground On March 1, 1980, a new system of seismographs at the University of Washington went into operation to monitor earthquake activity in the Cascades. On March 20, it recorded a magnitude-4.2 earthquake deep beneath Mount St. Helens, inaugurating a round-the-clock watch that was to save many lives.

From March 25 to March 27, quakes of magnitude 4.0 rocked the mountain as many as three times a day, and smaller quakes occurred several times every hour. At 8 a.m. PST on March 27, the U.S. Geological Survey issued an official Hazard Watch for Mount St. Helens; around noon, the first eruption of steam from the summit sent a column of ash and steam 6,000 feet (1,829 meters) into the air. Twin fissures opened on the mountain’s north face. A "bulge" developed on the north side of Mount St. Helens as magma pushed up within the peak. Measurements suggested the bulge was growing at a rate of up to 5feet (1.5 meters) per day. By May 17, part of the volcano's north side had been pushed upward and outward more than 450 feet (135 meters). This image, a view is from the northeast, was taken on April 13, 1980 by Austin Post, USGS.

Credit: Austin Post, USGS Volcanologists set up reflective targets between the fissures and used lasers placed on a mountain ridge six miles away to record changes. On March 31, instruments began to record the rhythmic pulses known as “volcanic tremor.” Such pulses indicated that magma was on the move. In April, the laser equipment began to detect changes to the mountain’s profile; an ominous swelling bulge was forming between the fissures. By late April, the laser measurements showed that the bulge was growing at a rate of about five feet per day. 'This is it!' On the morning of May 18, USGS volcanologist David A. Johnston, camped on the ridge with his lasers, radioed in his regular 7 a.m. report. The changes to the bulging mountain were consistent with what had been reported several times daily since the watch began. At 8:32, a magnitude-5.1 earthquake registered on the seismographic equipment. His excited radio message, “This is it!” was followed by a stream of data. It was his last transmission; the ridge he camped on was within the direct blast zone. [Gallery: The Incredible Eruption of Mount St.

Helens ] Overhead, Keith and Dorothy Stoffel were making an aerial survey of the volcano when they noticed a landslide on the lip of the summit crater. Within 15 seconds, the whole north face of the mountain was on the move. Just as they passed around to the east side of the mountain, the north face collapsed, releasing superheated gases and trapped magma in a massive lateral explosion. Keith put the plane into a steep dive to gain the speed to outrun the cloud of incandescent gas; Dorothy continued to photograph the eruption through the rear windows of the plane as they made their escape. The abrupt release of pressure over the magma chamber created a “nuees ardentes,” a glowing cloud of superheated gas and rock debris blown out of the mountain face moving at nearly supersonic speeds. Everything within eight miles of the blast was wiped out almost instantly. The shockwave rolled over the forest for another 19 miles, leveling century-old trees; all the trunks neatly aligned to the north. Beyond this “tree down zone” the forest remained standing but was seared lifeless. The area devastated by the direct blast force covered an area of nearly 230 square miles (596 square kilometers).

Shortly after the lateral blast, a second, vertical explosion occurred at the summit of the volcano, sending a mushroom cloud of ash and gases more than 12 miles into the air. The cloud of ash darkened the skies, causing streetlights to come on as far away as Spokane, Wash., more than 300 miles (480 km) away. Ash continued to erupt for more than nine hours. Ultimately, an estimated 540 million tons (490,000 kilotons) of ash drifted up to 2,200 square miles (5,700 square km) settling over seven states. As the north face was blown apart, the heat instantly vaporized glacial ice and snow around the remaining parts of the mountain. By 8:50 a.m., massive mudflows were moving through the river systems to the west and southeast of Mount St. Helens. The hot mud moved in excess of 90 mph (145 kph), sweeping away everything in its path. Most destructive U.S. volcano In terms of economic impact, the Mount St. Helens eruption was the most destructive in U.S. history. Fifty-seven people are known to have died.

More than 200 homes were destroyed. More than 185 miles of roads and 15 miles of railways were damaged. Ash clogged sewage systems, damaged cars and buildings, and temporarily shut down air traffic over the Northwest. The International Trade Commission estimated damages to timber, civil works and agriculture to be $1.1 billion. In addition, Congress approved $950 million in emergency funds to the Army Corps of Engineers, FEMA, and the Small Business Administration to help recovery efforts. [Related: Why Was Mount St. Helens So Destructive? ] Today Mount St. Helens and other volcanoes in the Pacific Northwest are closely monitored by geologists at the David A. Johnston Cascades Volcano Observatory in Vancouver. In partnership with two other USGS installations located in Alaska and Hawaii, they are providing valuable information on volcanic activity to the United States and countries along the Pacific Ring of Fire. Latest on Mount St. Helens Eruption: Facts & Information How Volcanoes Work - the Mt. St. Helens eruption MT. ST. HELENS ERUPTION (1980) OVERVIEW The 1980 eruption of Mt. St.

Helens is the most studied volcanic eruption of the twentieth century. Although most people were unaware of the potential for such a violent display of volcanism in the contiguous U.S., volcanologists were keenly aware of the potential danger. Months before it erupted, the U.S. Geological Survey (USGS) established a base of operations at Vancouver, Washington to monitor the volcano. On May 18, survey volcanologist David Johnston was camping on Coldwater Ridge, only a few miles north of Mt. St. Helens. The eruption occurred that morning. At 8:32 a.m., Johnston radioed the USGS base and exclaimed "Vancouver, Vancouver, this is it!" The ensuing volcanic blast devastated the northern flank of the volcano, killing Johnston and 56 other victims. At the same time, geologists Keith and Dorothy Stoffel were flying in a light plane only 400 meters above the summit of Mt. St. Helens. From their vantage point, they witnessed one of the largest landslides ever recorded in historic times. Seconds later, a massive explosion shot out the north side of the volcano, toward Coldwater Ridge and Spirit Lake.

The explosion generated a billowing cloud with numerous lightning bolts thousands of meters high. The cloud began to expand rapidly toward their aircraft and appeared to be gaining on them, but by turning south they managed to outrun it and survive. PHYSIOGRAPHY Mt. St. Helen's was known as one of the most picturesque stratovolcanoes in the Cascade Range before its violent eruption on May 18, 1980. The eruption generated a massive lateral blast that devastated the northern flank of the volcano, flattening millions of mature Douglas fir trees over a fan-shaped area of 600 square kilometers. The blast zone was further subjected to a huge debris avalanche, followed by the deposition of numerous lahars and pyroclastic flows . The extent of the blast zone and related deposits from the 1980 eruption are shown in the map below. The major physiographic landmarks on the map include the westward-draining North- and South Forks of the Toutle River, Spirit Lake, and Johnston Ridge. Spirit Lake is located 5 kilometers from the summit, as is Johnston Ridge, immediately to the west of Spirit Lake.

Johnston Ridge, previously called Coldwater Ridge, was named in honor of David Johnston, the USGS volcanologist who died in the 1980 eruption. Mt. St. Helens was declared a National Volcanic Monument by an act of congress in 1982. Mt. St. Helens RECORD OF HISTORIC ERUPTIONS There are fifteen subduction-related volcanoes currently active along the Cascade chain. Before 1980, the last one to erupt was California's Mt. Lassen, from 1914 to 1917. In the mid-1970's scientists were concerned that Mt. Baker, in northern Washington, might be the site of the next volcanic eruption, based on increased fumarolic activity on the volcano. However, in 1978, Dwight Crandell and Don Millineaux of the USGS suggested that Mt. St. Helens was potentially the most likely volcano to erupt in the twentieth century. They based their evidence on the relatively young age of the volcano, and its frequent historic eruptions. Mt. St.

Helens is less than about 37,000 years old, but it has been especially active over the last 4000 years. Since about 1400 A.D., eruptions have occurred at a rate of about one per 100 years. Before the 1980 eruption, it had been 130 years since Mt. St. Helens last erupted. The style of historic eruptions at Mt. St. Helens was also worrisome. Mt. St. Helens typically generates explosive pyroclastic eruptions, in contrast to many other Cascade volcanoes, such as Mt. Rainier which typically generates relatively non-explosive eruptions of lava. PRECURSOR EVENTS In 1980, the University of Washington had just completed the establishment of a system of seismometers to help monitor the Cascade volcanoes. The computer feeds for the station went into operation on March 1. The first indications of a major problem came on March 20, when a 4.2 magnitude earthquake was recorded beneath Mt. St. Helens.

Three days later another 4.0 M was recorded, and that evening the earthquakes began occurring in swarms centered directly beneath the volcano, at a rate of about 15 per hour. By March 25, magnitude 4 events were shaking Mt. St. Helens at a rate of about 3 per hour. On the same day, several overflights revealed new fractures on the glacier surfaces and a number of avalanches and rockfalls. In early afternoon on March 27, a loud explosion was heard from the direction of Mt. St. Helens. Although the volcano was shrouded in clouds, a summit eruption was verified by a news team from the Vancouver Columbian. As they circled the summit in an airplane, they spotted a dense column of ash rising through the clouds to a height of about 2000 m. As the weather cleared later in the day, a new crater was visible, with a diameter of about 70 m, and snow on the summit area was covered by a thin veneer of dark ash. The summit eruption on March 27 was typical of several small eruptions that would occur through April and early May.

None of these eruptions were magmatic in character, but instead they were steam eruptions generated by the heating of groundwater above a rising plug of magma that had invaded the central conduit of the volcano. Steam eruption, April 1980 The north-flank bulge The March 27 eruption generated a huge east-trending fissure high on the north side of the summit. It extended down both sides of the volcano over a distance of about 1500 m. Another, less extensive fracture system had developed farther down the north flank of the volcano, parallel to the higher fracture. Measurements showed that the region between the two fractures had expanded outward to produce a huge north-flank bulge . The bulge was verified by a US Forest Service aerial spotter who reported seeing both fractures open and close as the north flank bulged upward during the hours immediately following the steam eruption. Several more steam eruptions occurred on March 28, many of which were only a few minutes or an hour in duration. Harmonic tremors and minor eruptions occurred through March and April, with the eruption rate declining from about one per hour in March to about one per day in April.

By mid-April, the eruptions had reamed out a new crater, with a diameter of about 400 m. Although the eruptions had declined somewhat in April, earthquake activity continued at impressive rates (>30/day above 3.0M). The epicenters were largely confined to a shallow area beneath the north-flank bulge. The bulge was continually monitored and it got larger and more conspicuous with time. A week before the climactic blast, it had expanded outward by over 100 m and the rate of expansion was about 2 m/day! THE CLIMACTIC ERUPTION The eruption began during a relatively quite period in which no steam explosions had occurred for four days. On May 18, at 8:32 a.m., a 5.0-M earthquake triggered a very rapid series of events. The entire northern slope above the bulge failed and the north flank of the volcano began to slide downward from almost the exact site of the east-west fracture at the summit. This gigantic landslide released a tremendous mass from above the hydrothermal system that had driven the precursor steam eruptions.

The abrupt loss of confining pressure above the heated groundwater caused a massive flashing to steam, which initiated a hydrothermal blast that was directed laterally through the landslide scarp. The lateral hydrothermal blast rapidly overtook the avalanche and devastated a fan-shaped area to the north, which was nearly 30 km wide over a distance of 20 kilometers. Trees were blown down like matchsticks. The debris avalanche partly filled Spirit Lake, raising the lake bed more than 60 m and doubling the size of the shoreline. However, the bulk of the avalanche entered the North Fork of the Toutle River and flowed 23 km westward to fill the valley with a craggy and hummocky deposit. The length of the avalanche makes it one of the world's largest ever recorded. The debris avalanche incorporated a significant amount of water, which resulted in voluminous lahars later in the day. These flowed down the North Fork of the Toutle River across the avalanche deposit, and continued downstream as far as the Cowlitz River. THE PLINIAN COLUMN. The avalanche and lateral blast unloaded a large volume of material sitting above the shallow magma source beneath the north-flank bulge.

Pressure-release caused the magma to de-gas violently, and within a few minutes a Plinian eruption column began to rise from the former summit. In 10 minutes it had risen to a height of 20 km, where it spread into a umbrella region driven by high-level winds to the east-northeast. Significant ashfall deposits were produced as far as the Great Plains and minor ash was found even much farther east. As the Plinian eruption grew, it continued to ream out the volcanic conduit. The combined destructive forces of the avalanche, the lateral blast, and the Plinian eruption, resulted in the development of a huge amphitheater (1.5 x 3 km) along the volcano's northern flank. The Plinian eruption lasted for 9 hours. In addition to airfall, the Plinian phase was associated with numerous pyroclastic flows from column collapse . Most of these were directed toward the north and deposited as pumiceous ignimbrites above the avalanche deposit. Some of these pyroclastic flows extended into Spirit Lake and down the North Fork of the Toutle River.

The heat provided by the flows resulted in secondary steam explosions that formed large craters (20m in diameter) with ash columns as high as 2000 m. Smaller magmatic eruptions followed the main Plinian blast on May 25, June 12, July 22, and October 16-18. Each of these subsequent events lasted several hours and produced eruptive columns more than 10 kilometers high. THE LAVA DOME Degassing of the source magma in the underlying magma reservoir resulted in the waning of Plinian-type eruptions. The pastey magma left in the central conduit , and in magma chamber below it, became increasingly less volatile. Shortly after the June 12 eruption, this residual viscous magma began to rise through the vent crater to form a lava dome . The dome was most likely rising into the central conduit even before the June 12 eruption, but was not yet visible. An indication of this is in the nature of the pyroclastic flows associated with the June 12 eruption. Previous flows (on May 18 and May 25) were pumice-rich ignimbrites produced by column collapse.

However, the June 12 flows were block-and-ash flows containing abundant non-vesiculated blocks of dense, gray dacite . These pyroclastic-flow types are typically deposited by nuée ardentes , which are generated by dome collapse. Mount St. Helens -- From the 1980 Eruption to 2000, Fact Sheet 036-00 THE VOLCANO AWAKENS March 16 - May 17, 1980 The first sign of activity at Mount St. Helens in the spring of 1980 was a series of small earthquakes that began on March 16. After hundreds of additional earthquakes, steam explosions on March 27 blasted a crater through the volcano's summit ice cap. Within a week the crater had grown to about 1,300 feet in diameter and two giant crack systems crossed the entire summit area. By May 17, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward at least 450 feet to form a noticeable bulge.

Such dramatic deformation of the volcano was strong evidence that molten rock (magma) had risen high into the volcano CATACLYSMIC ERUPTION May 18, 1980 Within 15 to 20 seconds of a magnitude 5.1 earthquake at 8:32 a.m., the volcano's bulge and summit slid away in a huge landslide - the largest on Earth in recorded history. The landslide depressurized the volcano's magma system, triggering powerful explosions that ripped through the sliding debris. Rocks, ash, volcanic gas, and steam were blasted upward and outward to the north. This lateral blast of hot material accelerated to at least 300 miles per hour, then slowed as the rocks and ash fell to the ground and spread away from the volcano; several people escaping the blast on its western edge were able to keep ahead of the advancing cloud by driving 65 to 100 miles an hour! The blast cloud traveled as far as 17 miles northward from the volcano and the landslide traveled about 14 miles west down the North Fork Toutle River.

The lateral blast produced a column of ash and gas (eruption column) that rose more than 15 miles into the atmosphere in only 15 minutes. Less than an hour later, a second eruption column formed as magma erupted explosively from the new crater. Then, beginning just after noon, swift avalanches of hot ash, pumice, and gas (pyroclastic flows) poured out of the crater at 50 to 80 miles per hour and spread as far as 5 miles to the north. Based on the eruption rate of these pyroclastic flows, scientists estimate that the eruption reached its peak between 3:00 and 5:00 p.m. Over the course of the day, prevailing winds blew 520 million tons of ash eastward across the United States and caused complete darkness in Spokane, Washington, 250 miles from the volcano. During the first few minutes of this eruption, parts of the blast cloud surged over the newly formed crater rim and down the west, south, and east sides of the volcano.

The hot rocks and gas quickly melted some of the snow and ice capping the volcano, creating surges of water that eroded and mixed with loose rock debris to form volcanic mudflows (lahars). Several lahars poured down the volcano into river valleys, ripping trees from their roots and destroying roads and bridges. The largest and most destructive lahar was formed by water seeping from inside the huge landslide deposit through most of the day. This sustained flow of water eroded material from both the landslide deposit and channel of the North Fork Toutle River. The lahar increased in size as it traveled downstream, destroying bridges and homes and eventually flowing into the Cowlitz River. It reached its maximum size at about midnight in the Cowlitz River about 50 miles downstream from the volcano. The cataclysmic eruption of Mount St. Helens, Washington, on May 18, 1980, formed a deep north-facing horseshoe-shaped crater. Small eruptions from 1980 to 1986 built a lava dome. The lava dome can be seen here steaming within the crater. (Photos by Austin Post and Lyn Topinka, USGS.) Mount St.

Helens: May 18, 1980 - YouTube Mount St. Helens: May 18, 1980 Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. The interactive transcript could not be loaded. Loading... Rating is available when the video has been rented. This feature is not available right now. Please try again later. Uploaded on May 11, 2010 For more information visit: USGS scientists recount their experiences before, during and after the May 18, 1980 eruption of Mount St. Helens. Loss of their colleague David A. Johnston and 56 others in the eruption cast a pall over one of the most dramatic geologic moments in American history. Category Pre-1980 Eruptive History of Mount St. Helens, Washington | USGS Fact Sheet 2005-3045 U.S. GEOLOGICAL SURVEY and the U.S. FOREST SERVICE-OUR VOLCANIC PUBLIC LANDS Pre-1980 Eruptive History of Mount St. Helens, Washington Mount St.

Helens, famous for its explosive 1980 eruption, has long been the most active volcano in the Pacific Northwest. U.S. Geological Survey (USGS) scientists have documented the volcano's 300,000- year geologic history, including powerful explosions of ash, outpourings of lava, and huge landslides and volcanic mudflows. Understanding this history helps USGS scientists evaluate current activity at Mount St. Helens so that timely warnings of hazards can be issued to the public. On May 18, 1980, Mount St. Helens, Washington, exploded in a spectacular and devastating eruption that brought the volcano to the attention of the world. Few people realized that Mount St. Helens had long been the most active volcano in the Cascade Range of the Pacific Northwest. It has a rich and complex 300,000-year history and has produced both violent explosive eruptions of volcanic ash and pumice and relatively quiet outpourings of lava. The volcano's edifice was mostly built by lava domes and flows from numerous eruptions. Using evidence in these lavas and other deposits, U.S.

Geological Survey (USGS) scientists have documented dozens of major individual eruptions of the volcano. An extensive apron of ash and fragmented volcanic rocks surrounds Mount St. Helens and mostly fills the valleys draining its slopes. This material was transported by pyroclastic flows (searingly hot flows of ash and volcanic gases), lahars (volcanic mudflows), and debris avalanches (landslides). Farther away from the volcano, pumice and ash that fell during explosive eruptions form layers that bury the landscape to depths of 10 feet or more. The pre-1980 eruptive history of Mount St. Helens is strongly episodic. Volcanologists have recognized and named four episodes of volcanic activity, called "stages"-- Ape Canyon, Cougar, Swift Creek, and Spirit Lake--separated by dormant intervals. The youngest stage, Spirit Lake, is further subdivided into six eruptive periods. Because the preservation of deposits and other geologic evidence is best for the youngest stages, the farther scientists look back in time the less detail they can infer for the history of volcanism at Mount St. Helens. Mount St.

Helens rises majestically above surrounding forests in this photo taken on May 17, 1980. In the devastating eruption the following day, 57 people were killed, most of the forest destroyed, and 1,300 feet of volcanic rock removed from the volcano's edifice, lowering its summit elevation to 8,364 feet (inset photo). During the volcano's 300,000-year history, dozens of eruptions have repeatedly changed its appearance. (USGS photos by Harry Glicken and Lyn Topinka.) Ape Canyon Stage (300 to 35 ka) The early history of Mount St. Helens is poorly known, and a long timespan is covered by the Ape Canyon Stage. During this stage, lava domes erupted west of the present edifice of the volcano in two distinct periods--one from 300 to 250 thousand years ago (ka) and a second from 125 to 35 ka.

A number of ash layers, called the "C" set, are clearly related to volcanism during the younger phase of the Ape Canyon Stage, and a few ashes found in central Washington older than the C set are also from Mount St. Helens. Although some Ape Canyon-age lava domes are exposed in the area of Goat Mountain and Butte Camp, the best record of early Mount St. Helens volcanism is preserved in the Cougar-age debris avalanche (see below) and in glacial deposits and lahars in the Lewis River Valley. Many Ape Canyon-age rocks were altered hydrothermally (by volcanically heated ground water), indicating that an extensive hydrothermal system existed during the latter part of the stage. Volcanism during the Ape Canyon Stage produced a small cluster of lava domes with maximum elevations of about 4,000 feet. [Dormant Interval 35 to 23 ka] Cougar Stage (23 to 17 ka) During the Cougar Stage, Mount St. Helens produced lava domes and flows, as well as explosive eruptions that ejected large volumes of ash and generated pyroclastic flows. A huge debris avalanche and subsequent lahars were also emplaced.

This avalanche (Cougar debris avalanche) is composed primarily of Ape Canyon-age rocks and was the most devastating event of the stage. The debris avalanche originated in the area of Butte Camp and emplaced a deposit 600 to 900 feet thick on the south flank of the volcano. This avalanche, which was at least twice as large as the huge debris avalanche that triggered Mount St. Helens' 1980 eruption, dammed the Lewis River. Downcutting of the dam caused flooding downstream as far as the Columbia River and filled the lower Lewis River Valley with volcanic debris (ash and broken rock) at least 200 feet thick. The Cougar debris avalanche was followed by a large explosive eruption producing pyroclastic flows that buried the avalanche deposits with a 300-foot-thick sheet of dacite pumice (the "2-pumice pf"). (Dacite is volcanic rock containing 63 to 68% silica [SiO2].) Continued explosive activity deposited ash sets "M" and "K" and more pyroclastic flows (the "white pumice"). The Cougar Stage culminated with the eruption of the largest lava flow in the history of Mount St.

Helens (Swift Creek flow). The vent for this andesite (53 to 63% SiO2) lava flow, at an elevation of 6,000 feet on the south flank of Mount St. Helens, marks the summit of the volcano at that time. [Dormant Interval 17 to 13 ka] Swift Creek Stage (13 to 11 ka) During the Swift Creek Stage, explosive eruptions produced two widespread ash layers, and three extensive fans of volcanic debris were emplaced from growing, unstable dacite lava domes. The Swift Creek fan, composed of pyroclastic flows and lahars, buried Cougar- age deposits on the south flank of Mount St. Helens. The Crescent fan consists of pyroclastic flows at least 600 feet thick on the west flank of the volcano that were derived from the Crescent lava dome. The Cedar Flats fan completely filled the ancestral valley of Pine Creek and spilled into the Lewis River at Cedar Flats. It was at least 300 feet thick in the Cedar Flats area. This fan is dominated by lahar deposits, but also contains pyroclastic material produced by collapses of lava domes.

All three fans are associated with the deposition of ash set "S" dated at 13 to 12.5 ka. The Swift Creek Stage culminated with deposition of ash set "J" at about 11.5 to 11 ka. At the end of Swift Creek time, Mount St. Helens consisted of a cluster of dacite domes with elevations as high as 7,000 feet. [Dormant Interval 11 to 3.9 ka] Spirit Lake Stage (3.9 ka to present) The bulk of the pre-1980 edifice of Mount St. Helens was constructed by eruptions during the Spirit Lake Stage. Excellent preservation of deposits, as well as numerous ages from radiocarbon and tree-ring dating, provide considerable detail for this stage. Volcanism was intermittent, with lulls on the order of a few to about 600 years. As in earlier stages, Spirit Lake volcanism erupted mostly dacite, but significant amounts of basalt (less than 53% SiO2) and andesite were also erupted.

The Spirit Lake Stage is subdivided into six eruptive periodsï¿½the Smith Creek, Pine Creek, Castle Creek, Sugar Bowl, Kalama, and Goat Rocks Eruptive Periods. This map, originally produced by the U.S. Geological Survey in 1919, shows the pre-1980 topography of Mount St. Helens. The gentle slopes on the flanks of the volcano are fans of volcanic debris and consist of ash, pumice, and volcanic rock fragments. Dashed lines show the extent of these fans. Smith Creek Eruptive Period (3.9 to 3.3 ka)--During this period, Mount St. Helens erupted mostly ash. Two periods of activity, about 3.90 to 3.85 ka and 3.5 to 3.3 ka, deposited set "Y" ashes. The second period was initiated with an eruption that produced "Yn" ash. This eruption, possibly the most voluminous in Mount St. Helens' history, was about four times larger than the 1980 eruption. During late Smith Creek time, huge lahars swept down the Toutle River, and some probably reached the Columbia River.

The primarily ash-producing eruptions of Mount St. Helens during Smith Creek time did not significantly change the volcano's shape. Pine Creek Eruptive Period (2.9 to 2.55 ka)--During the Pine Creek Eruptive Period, Mount St. Helens erupted ash and produced pyroclastic flows and dacite domes, and two small debris avalanches occurred on its north flank. Repeated collapse of hot, growing lava domes produced an extensive and broad fan of volcanic debris as much as 600 feet thick on the south flank of the volcano. Similar deposits on the north flank can still be found as far downstream as the town of Toutle. Pine Creek-age dacite domes exposed in the walls of the crater left by the 1980 eruption show that at the end of Pine Creek time, the volcano was a cluster of lava domes with a maximum elevation of about 7,000 feet. Castle Creek Eruptive Period (2.55 to 1.895 ka)--The Castle Creek Eruptive Period produced many lava flows and domes, pyroclastic flows, and ash.

Andesite lava flows and ash erupted from the summit were emplaced on all flanks of Mount St. Helens between 2.55 and about 2.50 ka. A lull of about 300 years followed, and volcanism resumed at about 2.2 ka with eruption of andesite lava flows on the volcano's north flank. Several thick dacite lava flows and domes, pyroclastic flows and ash, and lahars were produced at 2.0 ka. Castle Creek activity culminated with eruption of three groups of fluid basalt lava flows that poured down all flanks of the volcano as far as 8 miles. The Cave Basalt, erupted at 1.895 ka, was the most recent of these. Castle Creek lavas transformed the Pine Creek-age cluster of domes into a classic cone-shaped composite volcano, with a summit elevation of about 8,500 feet. CHRONOLOGY OF ERUPTIVE ACTIVITY AT MOUNT ST. HELENS This simplified chronology shows the volcanic history of Mount St.

Helens from its earliest beginnings about 300,000 years ago (300 ka) to its devastating and deadly eruption on May 18, 1980. The major volcanic deposits of each stage and period are listed to the right of the time columns. Lava and ash erupted by the volcano are mostly dacite (volcanic rock containing 63 to 68% silica [SiO2]), but also include andesite (53 to 63% SiO2) and basalt (less than 53% SiO2). Pyroclastic flows are searingly hot flows of ash and volcanic gases, and lahars are volcanic mudflows. "Dormant" intervals are time periods during which no volcanic activity is known. The diagram below shows how Mount St. Helens evolved from a small cluster of dacite lava domes to a moderate-size conical volcano. The Profile of Mount St. Helens Through Time THE HISTORY OF MOUNT ST. HELENS IS WRITTEN IN LAYERS OF ASH By examining layers of volcanic ash (tiny jagged particles of volcanic rock and glass) and pumice deposited by successive explosive eruptions, U.S.

Geological Survey scientists have deciphered the eruptive history of Mount St. Helens. Groups or "sets" of ash layers of similar age are designated with letters and signify explosive episodes in the volcano's history. Ages of ash layers less than 50,000 years old are determined by radiocarbon dating of wood or charcoal trapped in the ash. The 20-foot-high cliff at "Stratigraphy Viewpoint" along the Muddy River (photo above) exposes a series of deposits from the past 13,000 years of Mount St. Helens' history. The prominent yellow-brown layer in the middle is part of ash set "Y" from the Smith Creek Eruptive Period. The cliff is capped by deposits several feet thick from the volcano's devastating 1980 eruption. Major explosive eruptions not only leave deposits near the volcano but also inject fine ash (see inset photo) high into the atmosphere, where wind can carry it great distances. The map shows the known distribution of recognizable ash layers from three fairly typical explosive eruptions of Mount St. Helens in the past few thousand years.

The eruption that produced the "Yn" ash was about four times as large as that of 1980 and was probably the largest explosive eruption in the volcano's history. Sugar Bowl Eruptive Period (1.2 to 1.15 ka [A.D. 850 to 900, corrected radiocarbon dates])--During the Sugar Bowl Eruptive Period, three lava domes were built on the flanks of Mount St. Helens. Explosive eruptions associated with growth of the Sugar Bowl Dome produced two "lateral blasts" that affected an area about one-tenth as large as that of the lateral blast in the 1980 eruption. Ash layer "D" and lahars were also emplaced. The Sugar Bowl period was short lived, produced a small volume of volcanic materials, and did not significantly change the appearance of the volcano. Kalama Eruptive Period (A.D. 1479 to 1720)--Activity during this period produced large-volume dacite ashes, pyroclastic flows, domes, lahars, and andesite lava flows. Mount St.

Helens added about 1,000 feet of elevation and attained its pre-1980 form during the Kalama Period. The Kalama Eruptive Period is subdivided into three series of eventsï¿½the early, middle, and late Kalama phases. The early Kalama phase began in 1479 with a large pyroclastic eruption that deposited dacite ash layer "Wn." In 1482, a smaller eruption produced ash layer "We." Over the next 10 to 20 years, a number of lava domes grew in the volcano's crater and were disrupted by explosive eruptions. Lahars and pyroclastic flows associated with early Kalama eruptions are abundant on the volcano's west and south flanks. The middle Kalama phase began about 1510 with eruption of andesite as pyroclastic flows (which generated hot lahars), a few lava flows, and ash set "X." The middle phase peaked about 1535 with eruption of the many thick andesite lava flows prominent on all flanks of Mount St. Helens, including the Worm Complex flows, and ended by 1570.

The most significant event of the late Kalama phase was growth of a large dacite dome at the summit (Summit Dome). The Summit Dome took nearly 100 years to grow (1620 to 1720) and gave Mount St. Helens its pre-1980 form. During growth, it shed material as pyroclastic flows and lahars on all flanks of the volcano. Mount St. Helens acquired its pre- 1980 cover of glaciers as a result of growth of the Summit Dome. Goat Rocks Eruptive Period (A.D. 1800ï¿½ 1857)--The Goat Rocks Period was short and relatively small. An explosive eruption in 1800 produced ash layer "T" and was followed in 1801 by an andesite lava fl ow, called the "Floating Island," on Mount St. Helens' north fl ank. Eruptions observed intermittently from 1831 to 1857 produced ash and the Goat Rocks Dome, whose growth also resulted in a small fan of volcanic debris and lahars. The last significant eruption of Mount St.

Helens before 1980 is generally considered to have occurred in 1857. Minor explosions reported in 1898, 1903, and 1921 were probably steam-driven and not magmatic (molten rock) eruptions. Eruptions of the Goat Rocks Period did not significantly change the appearance of Mount St. Helens, but they added the final pieces to the edifice and set the stage for the 1980 eruption. Recent work by scientists with the USGS in cooperation with the U.S. Forest Service is shedding new light on the 300,000-year history of Mount St. Helens Volcano. The work of these USGS scientists is only part of the USGS Volcano Hazards Program's ongoing efforts to protect people's lives and property in all of the volcanic regions of the United States, including the Pacifi c Northwest, eastern California, Wyoming, Alaska, and Hawaii. Michael A. Clynne, David W. Ramsey, and Edward W. Wolfe Edited by James W. Hendley II and Peter H.

Stauffer Graphic design by Susan Mayfield and Sara Boore; Web design by Michael Diggles COOPERATING ORGANIZATION Volcanic Cones and Eruptions Lesson #8 | Volcano World | Oregon State University Volcanic Cones and Eruptions Lesson #8 The photo above is of Mt. St. Helens today. This once beautiful mountain was changed dramatically on May 18, 1980. The eruption, which is the most violent eruption classification. As you learned in the last lesson, different magmas have varying amounts of to either be thick and pasty or thin and runny. The thickness and thinness of the magma will determine how a volcano will erupt and what kind of a cone will form. Volcanoes will erupt for two reasons 1. The magma deep under the crust is less dense than the surrounding rock causing it to rise. 2. As the magma approaches the surface of the Earth the gas that is in the magma will come bubbling out because the pressure surrounding the magma will decrease nearer the surface. Have you ever had a can of soda pop explode all over the room? This "eruption" of pop is caused by the same scientific principle that causes a volcano to erupt violently.

When you open the pop can the pressure is released so quickly that the gas that is dissolved in the pop comes rushing out along with some of the pop. Volcanoes are classified by the eruption type and by the volcanic cone shape. There are three cone shapes and six eruption types. The three cone shapes are cinder cones, shield cones, and composite cones or stratovolcanoes. Notice how, as the eruptions become more violent, the cone shapes become more steeply constructed. You will read about these volcanic types in more depth later in the lesson. Icelandic, flood, or fissure eruptions are all terms for volcanic eruptions that flood the surface of the Earth with massive amounts of very hot, very thin, runny lava. The lava comes out of the ground through long cracks in the surface called fissures . Some of these fissures can be up to 15 miles long. The type of cone produced from icelandic eruptions is a shield cone. Shield cones are very low and very broad shaped volcanoes. These volcanoes erupt many times over the same area forming huge, and thick lava plateaus.

The Deccan Plateau of India was formed this way and covers 100,000 square miles (A little smaller than the state of Montana). The Columbia Plateau of the western United States is the largest lava plateau in the world. It covers almost 100,000 square miles and is almost a mile thick in places. The photo above is of Krafla Volcano on the island of Iceland. Hawaiian eruptions are similar to Icelandic eruptions because both eruption types have many fissures bringing the lava to the surface. Both types of eruptions are known for their beautiful fire fountains like the one shown above. The lava that flows from both types of eruptions is very hot, thin, and runny which allows for fast flowing lava flows. The main difference lies in the fact that most Hawaiian eruptions have the greatest quantity of lava pouring out of the main at the volcano's summit, not along side fissures. These summit eruptions build the cone steeper and higher. The volcano above was formed from Hawaiian eruptions. Shield cones were named by Icelandic people because the cone's shape reminded them of a warriors shield layed down.

Shield cones form from hot, runny lava that is erupted from the the volcano through its summit and the many side vents and fissures throughout the volcano's flanks (Sides). Shield cones are low, very broad, and gently sloping volcanoes. The volcano pictured above is Mauna Kea, which is located on the big island of Hawaii. Mauna Loa, which is also on the big island, is the largest volcano on Earth and the tallest mountain in the world if measured from the floor of the ocean where it was formed. Mauna Loa is 13,677 feet above sea level but over 17,000 feet of mountain lies under the water. This volcanic mountain is over 30,000 feet tall from sea floor to the summit. Maua Loa started to form above the Hawaiian about one million years ago and broke the surface of the ocean about 500,000 years ago. Strombolian and Vulcanian eruptions are more explosive than Icelandic and Hawaiian eruptions. Strombolian eruptions are named for the volcanic island off of the coast of Italy. Stromboli has erupted over many centuries almost constantly.

Stromboli has been named the "Lighthouse of the Mediterranean" because it erupts every 20 minutes or so. Strombolian eruptions are short lived explosive eruptions that shoot very thick and pasty lava into the air along with bursts of steam and gas. Strombolian eruptions usually produce little or no lava. Because of this the cones that are produced by this type of eruption is a very steep sided cone called a cinder cone. The photo shows a strombolian eruption taking place from a cinder cone. Cinder cones get their name from the material that forms them, cinders. Cinder cones are the simplest volcanic ash . These cinders and ash settle around the main vent and build a steep sided cone. Very little lava is erupted from a cinder cone. Cinder cones very rarely rise to more than 1,000 feet above the surrounding landscape. Cinder cones are known for their very violent, explosive, exciting eruptions. Paricutin in Mexico and Mt. Vesuvius in Italy are famous cinder cones. Vulcanian eruptions are more violent and explosive than strombolian eruptions.

Vulcanian eruptions are named after the island of Vulcano off the coast of Italy. This is the same island that gave us the name "Volcano". Vulcanian eruptions contain high dark clouds of steam, ash, and gas. The ash plume builds a cauliflower shaped head and a thinner more treetrunk-like base. When the volcano quits erupting ash and gases it then ejects thick pasty lava. Vulcanian eruptions usually build a steep sided cone that is more symetrical than a cinder cone. This more symetrical cone is called a strovolcano. Vulcanian eruptions will send an ash plume to a height of 2 -9 miles. The photo to the left is of Katla volcano in Iceland which erupted in 1918. Stratovolcanoes or composite cones are formed from a combination of eruptions. First the volcano will have an explosive eruption that ejects huge amounts of steam, gas and ash. This will be followed by the ejection of lava. A large stratovolcano will be built with many layers of ash and lava. Stratovolcanoes are the most common type of volcanic cone.

There are many famous stratovolcanoes in the world. Mt. St. Helens and Rainier in Washington, Mt. Fuji in Japan, Mt. Pinatubo in the Philippines, and Mt. Etna in Sicily are all examples of stratovolcanoes. The photo above is of the volcano Mayon, which is in the Philippines. Pelean and Plinian eruptions are the most dangerous and explosive of the eruption types. Pelean eruptions are named for the catastophic eruption on the island of Martinique in the Carribean Sea in 1902. The eruption and the pyroclastic flow that followed killed 29,000 people almost instantly. "Glowing clouds" of gas and ash flew down the mountain at over 70 miles per hour. The cloud was so full of ash that it was heavier than air and hugged the ground as it approached the coast. The temperatures were probably around 700 degress F. which would annihalate everything in its path. The only person to survive was a prisoner that was sentenced to death.

The only reason he survived was that he was imprisoned in a very thick walled cell and the only door faced away from the explosion. A Plinian eruption is the most explosive of the eruption types. Mt. St. Helens eruption was a plinian eruption. Plinian eruptions are characterized by a very high ash cloud that rise upwards to 50,000 feet (almost 10 miles) high. Very deadly pyroclastic flows are also part of plinian eruptions. Mt. Vesuvius, which erupted in 79 A.D. in Italy, was a classic Plinian eruption. Very hot ash falls killed thousands of people in the city of Pompei. Ash falls as high as 17 feet buried the city. Plinian eruptions were named for Pliny the Elder of Rome who died in one of the many eruptions of Vesuvius. The photo on the left side of this card shows Mt. St. Helens in its plinian eruption on May 18, 1980. The ash cloud rose to a height of over 50,000 feet. Write your answers to the questions on a sheet of paper.

When you finish the lesson click on the "Earth" icon so that the next pair of students will be transported to the start of this lesson. Click on the page titles located directly under the questions to maneuver your way through the lesson to find the answers for the following questions. 1. Name the six eruption types and the three cone shapes. 2. Describe how a: Shield cone form Cinder cone forms Stratovolcano forms 3. Draw diagrams to represent the six eruption types. USGS: Volcano Hazards Program CVO Mount St. Helens 1980 Cataclysmic Eruption Summary of Events Magma began intruding into the Mount St. Helens edifice in the late winter and early spring of 1980. By May 18, the cryptodome (bulge) on the north flank had likely reached the point of instability, and was creeping more rapidly toward failure. A magnitude-5+ earthquake was accompanied by a debris avalanche, which in turn unloaded the confining pressure at the top of the volcano by removing the cryptodome. This abrupt pressure release allowed hot water in the system to flash to steam, which expanded explosively , initiating a hydrothermal blast directed laterally through the landslide scar.

Because the upper portion of the volcano was removed, the pressure decreased on the system of magma beneath the volcano. A wave of decreasing pressure down the volcanic conduit to the subsurface magma reservoir , which then began to rise, form bubbles (degas), and erupt explosively, driving a 9-hour long Plinian eruption. Precursory Activity On March 16, 1980, the first sign of activity at Mount St. Helens occurred as a series of small earthquakes . On March 27, after hundreds of additional earthquakes, the volcano produced its first eruption in over 100 years. Steam explosions blasted a 60- to 75-m (200- to 250-ft) wide crater through the volcano's summit ice cap and covered the snow-clad southeast sector with dark ash . Within a week the crater had grown to about 400 m (1,300 ft) in diameter and two giant crack systems crossed the entire summit area. Eruptions occurred on average from about 1 per hour in March to about 1 per day by April 22 when the first period of activity ceased. Small eruptions resumed on May 7 and continued to May 17.

By that time, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward about 140 m (450 ft) to form a prominent bulge. From the start of the eruption, the bulge grew outward—nearly horizontally—at consistent rates of about 2 m (6.5 ft) per day. Such dramatic deformation of the volcano was strong evidence that molten rock ( magma ) had risen high into the volcano. In fact, beneath the surficial bulge was a cryptodome that had intruded into the volcano's edifice , but had yet to erupt on the surface. Debris Avalanche With no immediate precursors, a magnitude 5.1 earthquake occurred at 8:32 a.m. on May 18, 1980 and was accompanied by a rapid series of events. At the same time as the earthquake, the volcano's northern bulge and summit slid away as a huge landslide—the largest debris avalanche on Earth in recorded history.

A small, dark, ash -rich eruption plume rose directly from the base of the debris avalanche scarp, and another from the summit crater rose to about 200 m (650 ft) high. The debris avalanche swept around and up ridges to the north, but most of it turned westward as far as 23 km (14 mi) down the valley of the North Fork Toutle River and formed a hummocky deposit. The total avalanche volume is about 2.5 km3 (3.3 billion cubic yards), equivalent to 1 million Olympic swimming pools. Lateral Blast The landslide removed Mount St. Helens' northern flank, including part of the cryptodome that had grown inside the volcano. The cryptodome was a very hot and highly pressurized body of magma . Its removal resulted in immediate depressurization of the volcano's magmatic system and triggered powerful eruptions that blasted laterally through the sliding debris and removed the upper 300 m (nearly 1,000 ft) of the cone. As this lateral blast of hot material overtook the debris avalanche ; it accelerated to at least 480 km per hr (300 mi per hr).

Within a few minutes after onset, an eruption cloud of blast tephra began to rise from the former summit crater. Within less than 15 minutes it had reached a height of more than 24 km (15 mi or 80,000 ft). The lateral blast devastated an area nearly 30 km (19 mi) from west to east and more than 20 km (12.5 mi) northward from the former summit. In an inner zone extending nearly 10 km (6 mi) from the summit, virtually no trees remained of what was once dense forest. Just beyond this area, all standing trees were blown to the ground, and at the blast's outer limit, the remaining trees were thoroughly seared. The 600 km2 (230 mi2) devastated area was blanketed by a deposit of hot debris carried by the blast. Plinian Eruption Removal of the cryptodome and flank exposed the conduit of Mount St. Helens, resulting in a release of pressure on the top of the volcano's plumbing system.

This caused a depressurization wave to propagate down the conduit to the volcano's magma storage region, allowing the pent-up magma to expand upward toward the vent opening. Less than an hour after the start of the eruption, this loss of conduit pressure initiated a Plinian eruption that sent a massive tephra plume high into the atmosphere. Beginning just after noon, swift pyroclastic flows poured out of the crater at 80 - 130 km/hr (50 to 80 mi/hr) and spread as far as 8 km (5 mi) to the north creating the Pumice Plain. The Plinian phase continued for 9 hours producing a high eruption column , numerous pyroclastic flows, and ash fall downwind of the eruption. Scientists estimate that the eruption reached its peak between 3:00 and 5:00 p.m. When the Plinian phase was over, a new northward opening summit amphitheater 1.9 x 2.9 km (1.2 x 1.8 mi) across was revealed.

Over the course of the day, prevailing winds blew 520 million tons of ash eastward across the United States and caused complete darkness in Spokane, Washington, 400 km (250 mi) from the volcano. Major ash falls occurred as far away as central Montana, and ash fell visibly as far eastward as the Great Plains of the Central United States, more than 1,500 km (930 mi) away. The ash cloud spread across the U.S. in three days and circled the Earth in 15 days. Lahars During the first few minutes of this eruption, parts of the blast cloud surged over the newly formed crater rim and down the west, south, and east sides of the volcano. The turbulently flowing hot rocks and gas quickly eroded and melted some of the snow and ice capping the volcano, creating surges of water that eroded and mixed with loose rock debris to form lahars . Several lahars poured down the volcano into river valleys, ripping trees from their roots and destroying roads and bridges.

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

Question: What volcano famously erupted on May 18, 1980?
Answer: Mount St. Helens