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92-457: The stratovolcano is 3,340 m (10,958 ft) high and is about 45 minutes from the Atlantic slope town of Turrialba . The summit has three craters, the largest of which has a diameter of 50 m (160 ft). Turrialba is adjacent to Irazú and both are among Costa Rica's largest volcanoes. Turrialba has had at least five large explosive eruptions in last 3500 years. The volcano

184-418: A lava spine nicknamed the "whaleback", which comprised long shafts of solidified magma being extruded by the pressure of magma beneath. These features were fragile and broke down soon after they were formed. On July 2, 2005, the tip of the whaleback broke off, causing a rockfall that sent ash and dust several hundred meters into the air. Mount St. Helens showed significant activity on March 8, 2005, when

276-407: A magnitude  5.1 earthquake, caused a lateral eruption that reduced the elevation of the mountain's summit from 9,677 to 8,363 ft (2,950 to 2,549 m), leaving a 1 mile (1.6 km) wide horseshoe-shaped crater. The debris avalanche was 0.6 cubic miles (2.5 km ) in volume. The 1980 eruption disrupted terrestrial ecosystems near the volcano. By contrast, aquatic ecosystems in

368-400: A 36,000-foot (11,000 m) plume of steam and ash emerged—visible from Seattle . This relatively minor eruption was a release of pressure consistent with ongoing dome building. The release was accompanied by a magnitude 2.5 earthquake. Another feature to emerge from the dome was called the "fin" or "slab". Approximately half the size of a football field, the large, cooled volcanic rock

460-747: A 4-inch thick ash layer can weigh 120-200 pounds and can get twice as heavy when wet. Wet ash also poses a risk to electronics due to its conductive nature. Dense clouds of hot volcanic ash can be expelled due to the collapse of an eruptive column , or laterally due to the partial collapse of a volcanic edifice or lava dome during explosive eruptions . These clouds are known as pyroclastic surges and in addition to ash , they contain hot lava , pumice , rock , and volcanic gas . Pyroclastic surges flow at speeds over 50 mph and are at temperatures between 200 °C – 700 °C. These surges can cause major damage to property and people in their path. Lava flows from stratovolcanoes are generally not

552-496: A crater 1.2 to 1.8 miles (2 to 3 km) wide and 2,084 feet (635 m) deep, with its north end open in a huge breach. The eruption killed 57 people, nearly 7,000 big-game animals ( deer , elk , and bear ), and an estimated 12 million fish from a hatchery. It destroyed or extensively damaged more than 200 homes, 185 miles (298 km) of highway , and 15 miles (24 km) of railways . Between 1980 and 1986, activity continued at Mount St. Helens, with

644-474: A fast moving mudflow . Lahars are typically about 60% sediment and 40% water. Depending on the abundance of volcanic debris the lahar can be fluid or thick like concrete. Lahars have the strength and speed to flatten structures and cause great bodily harm, gaining speeds up to dozens of kilometers per hour. In the 1985 eruption of Nevado del Ruiz in Colombia , Pyroclastic surges melted snow and ice atop

736-515: A final intermediate composition . When the magma nears the top surface, it pools in a magma chamber within the crust below the stratovolcano. The processes that trigger the final eruption remain a question for further research. Possible mechanisms include: These internal triggers may be modified by external triggers such as sector collapse , earthquakes , or interactions with groundwater . Some of these triggers operate only under limited conditions. For example, sector collapse (where part of

828-646: A friend of explorer George Vancouver who surveyed the area in the late 18th century. The volcano is part of the Cascade Volcanic Arc , a segment of the Pacific Ring of Fire . The Mount St. Helens major eruption of May 18, 1980 , remains the deadliest and most economically destructive volcanic event in U.S. history. Fifty-seven people were killed; 200 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed. A massive debris avalanche , triggered by

920-407: A gradual extrusion of lava forming a dome in the crater. On January 16, 2008, steam began seeping from a fracture on top of the lava dome. Associated seismic activity was the most noteworthy since 2004. Scientists suspended activities in the crater and the mountain flanks, but the risk of a major eruption was deemed low. By the end of January, the eruption paused; no more lava was being extruded from

1012-509: A new lava dome forming in the crater. Numerous small explosions and dome-building eruptions occurred. From December 7, 1989, to January 6, 1990, and from November 5, 1990, to February 14, 1991, the mountain erupted, sometimes huge clouds of ash. Magma reached the surface of the volcano about October 11, 2004, resulting in the building of a new lava dome on the existing dome's south side. This new dome continued to grow throughout 2005 and into 2006. Several transient features were observed, such as

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1104-456: A process known as subduction in geology. As the oceanic slab sinks deeper into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The supercritical water rises into the pliable mantle above the subducting plate, causing some of the mantle to melt. This newly formed magma ascends upward through

1196-739: A result of intraplate volcanism on oceanic islands far from plate boundaries. Examples are Teide in the Canary Islands , and Pico do Fogo in Cape Verde . Stratovolcanoes in the East African Rift include Ol Doinyo Lengai in Tanzania, and Longonot in Kenya. Subduction zone volcanoes form when hydrous minerals are pulled down into the mantle on the slab. These hydrous minerals, such as chlorite and serpentine , release their water into

1288-461: A significant threat to humans or animals because the highly viscous lava moves slowly enough for everyone to evacuate. Most deaths attributed to lava are due to related causes such as explosions and asphyxiation from toxic gas . Lava flows can bury homes and farms in thick volcanic rock which greatly reduces property value. However, not all stratovolcanoes erupt viscous and sticky lava . Nyiragongo , near Lake Kivu in central Africa ,

1380-402: A slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe. Due to the advance, two lobes of the glacier joined in late May 2008 and thus the glacier completely surrounds the lava domes. In addition, since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice onto its surface below; there are two rock glaciers to

1472-566: A small hypersthene-homblende dacite dome on the east slope of the volcano, was likely formed around the Sugar Bowl period. Formation of East Dome was preceded by an explosive eruption. Roughly 700 years of dormancy were broken in about 1480, when large amounts of pale gray dacite pumice and ash started to erupt, beginning the Kalama period. The 1480 eruption was several times larger than that of May 18, 1980. In 1482, another large eruption rivaling

1564-543: Is 140 inches (360 cm), and the snowpack on the mountain's upper slopes can reach 16 feet (4.9 m). The Lewis River is impounded by three dams for hydroelectric power generation. The southern and eastern sides of the volcano drain into an upstream impoundment, the Swift Reservoir , which is directly south of the volcano's peak. Although Mount St. Helens is in Skamania County, Washington, access routes to

1656-527: Is a passive release of gas during periods of dormancy. As per the above examples, while eruptions like Mount Unzen have caused deaths and local damage, the impact of the June 1991 eruption of Mount Pinatubo was seen globally. The eruptive columns reached heights of 40 km and dumped 17 megatons of SO 2 into the lower stratosphere . The aerosols that formed from the sulfur dioxide (SO 2 ), carbon dioxide (CO 2 ), and other gases dispersed around

1748-528: Is a popular hiking spot and it is climbed year-round. In 1982, the Mount St. Helens National Volcanic Monument was established by President Ronald Reagan and the U.S. Congress . Mount St. Helens is 34 miles (55 km) west of Mount Adams , in the western part of the Cascade Range. Considered "brother and sister" mountains, the two volcanoes are approximately 50 miles (80 km) from Mount Rainier ,

1840-575: Is at an elevation of 4,400 feet (1,300 m) on the northeastern side and 4,000 feet (1,200 m) elsewhere. At the pre-eruption tree line , the width of the cone was 4 miles (6.4 km). Streams that originate on the volcano enter three main river systems: The Toutle River on the north and northwest, the Kalama River on the west, and the Lewis River on the south and east. The streams are fed by abundant rain and snow. The average annual rainfall

1932-418: Is called the "Spirit Lake Stage". Collectively, the pre–Spirit Lake stages are known as the "ancestral stages". The ancestral and modern stages differ primarily in the composition of the erupted lavas; ancestral lavas consisted of a characteristic mixture of dacite and andesite , while modern lava is very diverse (ranging from olivine basalt to andesite and dacite). St. Helens started its growth in

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2024-595: Is considered the most active in the Cascades within the Holocene epoch, which encompasses roughly the last 10,000 years. Prior to the 1980 eruption, Mount St. Helens was the fifth-highest peak in Washington. It stood out prominently from surrounding hills because of the symmetry and extensive snow and ice cover of the pre-1980 summit cone, earning it the nickname, by some, " Fuji-san of America". Its ice cover just prior to

2116-716: Is likely on branches of the Toutle River , possibly causing destruction in inhabited areas along the I-5 corridor. In its undisturbed state, the slopes of Mount St. Helens lie in the Western Cascades Montane Highlands ecoregion. This ecoregion has abundant precipitation; an average of 93.4 inches (2,373 mm) of precipitation falls each year at Spirit Lake . This precipitation supported dense forest up to 5,200 feet (1,600 m), with western hemlock , Douglas fir , and western redcedar . Above this, this forest

2208-602: Is monitored by the Deep Earth Carbon Degassing Project . On clear days both the Pacific Ocean and Caribbean Sea can be seen from the summit. Below the summit is a mountain range and montane forest , with ferns , bromeliads , lichens and mosses . Most of the forest is either primary or secondary forest . The volcano is named after its canton , Turrialba , in Costa Rica's Cartago Province . There

2300-500: Is no clear consensus on the origin of the name Turrialba, but historians disagree with attempts to attribute the name to the patronym Torrealba (from Aragon in Spain ) or from the Latin Turris alba (white tower). The general consensus is that Turrialba derives from the local Indian ( Huetar language ), but there is no agreement on its actual roots. An eruption occurred on May 21, 2016. It

2392-476: Is often felsic , having high to intermediate levels of silica (as in rhyolite , dacite , or andesite ), with lesser amounts of less viscous mafic magma . Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi). The term composite volcano is used because the strata are usually mixed and uneven instead of neat layers. They are among the most common types of volcanoes; more than 700 stratovolcanoes have erupted lava during

2484-451: Is the most famous example of a hazardous stratovolcano eruption. It completely smothered the nearby ancient cities of Pompeii and Herculaneum with thick deposits of pyroclastic surges and pumice ranging from 6–7 meters deep. Pompeii had 10,000-20,000 inhabitants at the time of eruption. Mount Vesuvius is recognized as one of the most dangerous of the world's volcanoes, due to its capacity for powerful explosive eruptions coupled with

2576-450: Is typically between 700 and 1,200 °C (1,300-2,200 °F). Volcanic bombs are masses of unconsolidated rock and lava that are ejected during an eruption. Volcanic bombs are classified as larger than 64mm (2.5 inches). Anything below 64mm is classified as a volcanic block . When erupted Bombs are still molten and partially cool and solidify on their descent. They can form ribbon or oval shapes that can also flatten on impact with

2668-403: Is very dangerous because its magma has an unusually low silica content , making it much less viscous than other stratovolcanoes. Low viscosity lava can generate massive lava fountains , while lava of thicker viscosity can solidify within the vent, creating a volcanic plug . Volcanic plugs can trap gas and create pressure in the magma chamber, resulting in violent eruptions. Lava

2760-527: The Columbia River from the Far North in search for a suitable area to settle. They came upon an area that is now called The Dalles and thought they had never seen a land so beautiful. The sons quarreled over the land, so to solve the dispute their father shot two arrows from his mighty bow – one to the north and the other to the south. Pahto followed the arrow to the north and settled there while Wy'east did

2852-800: The Holocene Epoch (the last 11,700 years), and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times. Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives) and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people). In modern times, Mount St. Helens (1980) in Washington State , US, and Mount Pinatubo (1991) in

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2944-573: The Philippines have erupted catastrophically, but with fewer deaths. Stratovolcanoes are common at subduction zones , forming chains and clusters along plate tectonic boundaries where an oceanic crust plate is drawn under a continental crust plate (continental arc volcanism, e.g. Cascade Range , Andes , Campania ) or another oceanic crust plate ( island arc volcanism, e.g. Japan , Philippines , Aleutian Islands ). Stratovolcanoes also occur in some other geological settings, for example as

3036-623: The Pleistocene 37,600 years ago, during the Ape Canyon stage, with dacite and andesite eruptions of hot pumice and ash. Thirty-six thousand years ago a large mudflow cascaded down the volcano; mudflows were significant forces in all of St. Helens' eruptive cycles. The Ape Canyon eruptive period ended around 35,000 years ago and was followed by 17,000 years of relative quiet. Parts of this ancestral cone were fragmented and transported by glaciers 14,000–18,000 years ago during

3128-526: The Vancouver, Washington – Portland, Oregon metropolitan area less than 50 miles (80 km) to the southwest. The community nearest the volcano is Cougar , Washington, in the Lewis River valley 11 miles (18 km) south-southwest of the peak. Gifford Pinchot National Forest surrounds Mount St. Helens. During the winter of 1980–1981, a new glacier appeared. Now officially named Crater Glacier , it

3220-751: The Yn tephra . This eruptive period lasted until about 1600 BC and left 18 inches (46 cm) deep deposits of material 50 miles (80 km) distant in what is now Mount Rainier National Park . Trace deposits have been found as far northeast as Banff National Park in Alberta , and as far southeast as eastern Oregon . All told there may have been up to 2.5 cubic miles (10 km ) of material ejected in this cycle. Some 400 years of dormancy followed. St. Helens came alive again around 1200 BC—the Pine Creek eruptive period. This lasted until about 800 BC and

3312-891: The magma is too viscous to allow easy escape of volcanic gases . As a consequence, the tremendous internal pressures of the trapped volcanic gases remain and intermingle in the pasty magma . Following the breaching of the vent and the opening of the crater, the magma degasses explosively. The magma and gases blast out with high speed and full force. Since 1600 CE , nearly 300,000 people have been killed by volcanic eruptions . Most deaths were caused by pyroclastic flows and lahars , deadly hazards that often accompany explosive eruptions of subduction-zone stratovolcanoes. Pyroclastic flows are swift, avalanche-like, ground-sweeping, incandescent mixtures of hot volcanic debris, fine ash , fragmented lava , and superheated gases that can travel at speeds over 150 km/h (90 mph). Around 30,000 people were killed by pyroclastic flows during

3404-443: The mantle which decreases its melting point by 60 to 100 °C. The release of water from hydrated minerals is termed " dewatering ", and occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths. This allows the mantle to partially melt and generate magma . This is called flux melting . The magma then rises through the crust , incorporating silica-rich crustal rock, leading to

3496-607: The 1902 eruption of Mount Pelée on the island of Martinique in the Caribbean . During March and April 1982, El Chichón in the State of Chiapas in southeastern Mexico , erupted 3 times, causing the worst volcanic disaster in that country's history and killied more than 2,000 people in pyroclastic flows . Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards. On 15 June, Mount Pinatubo erupted and caused an ash cloud to shoot 40 km (25 mi) into

3588-493: The 1980 eruption in volume is known to have occurred. Ash and pumice piled 6 miles (9.7 km) northeast of the volcano to a thickness of 3 feet (0.9 m); 50 miles (80 km) away, the ash was 2 inches (5 cm) deep. Large pyroclastic flows and mudflows subsequently rushed down St. Helens' west flanks and into the Kalama River drainage system. This 150-year period next saw the eruption of less silica -rich lava in

3680-463: The 1980 eruption included eleven named glaciers: Wishbone, Loowit, Leschi, Forsyth, Nelson, Ape, Shoestring, Swift, Dryer, Toutle, and Talus. Of these eleven, only the Shoestring Glacier revived somewhat post-eruption. The peak rose more than 5,000 feet (1,500 m) above its base, where the lower flanks merge with adjacent ridges. The mountain is 6 miles (9.7 km) across at its base, which

3772-481: The 1982 eruption of Galunggung in Java , British Airways Flight 9 flew into the ash cloud, causing it to sustain temporary engine failure and structural damage. Although no crashes have happened due to ash, more than 60, mostly commercial aircraft , have been damaged. Some of these incidents resulted in emergency landings. Ashfalls are a threat to health when inhaled and are also a threat to property. A square yard of

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3864-585: The 5,321 m (17,457 ft) high Andean volcano. The ensuing lahar killed 25,000 people and flooded the city of Armero and nearby settlements. As a volcano forms, several different gases mix with magma in the volcanic chamber. During an eruption the gases are then released into the atmosphere which can lead to toxic human exposure. The most abundant of these gases is H 2 O ( water ) followed by CO 2 ( carbon dioxide ), SO 2 ( sulfur dioxide ), H 2 S ( hydrogen sulfide ), and HF ( hydrogen fluoride ). If at concentrations of more than 3% in

3956-782: The Klickitats as Louwala-Clough, which means "smoking or fire mountain" in their language (the Sahaptin call the mountain Loowit). The mountain is also of sacred importance to the Cowlitz and Yakama tribes that also live in the area. They find the area above its tree line to be of exceptional spiritual significance, and the mountain (which they call "Lawetlat'la", roughly translated as "the smoker") features prominently in their creation story, and in some of their songs and rituals. In recognition of its cultural significance, over 12,000 acres (4,900 ha) of

4048-534: The United States' largest slave rebellion . ) The vent was apparently at or near Goat Rocks on the northeast flank. Goat Rocks dome was near the site of the bulge in the 1980 eruption, and it was obliterated in the major eruption event on May 18, 1980, that destroyed the entire north face and top 1,300 feet (400 m) of the mountain. On March 20, 1980, Mount St. Helens experienced a magnitude  4.2 earthquake , and on March 27, steam venting started. By

4140-816: The air, when breathed in CO 2 can cause dizziness and difficulty breathing. At more than 15% concentration CO 2 causes death. CO 2 can settle into depressions in the land, leading to deadly, odorless pockets of gas. SO 2 classified as a respiratory, skin, and eye irritant if come into contact with. It is known for its pungent egg smell and role in ozone depletion and has the potential to cause acid rain downwind of an eruption. H 2 S has an even stronger odor than SO 2 as well as being even more toxic. Exposure for less than an hour at concentrations of over 500 ppm causes death. HF and similar species can coat ash particles and once deposited can poison soil and water. Gases are also emitted during volcanic degassing, which

4232-741: The air. It produced large pyroclastic surges and lahar floods that caused a lot of damage to the surrounding area. Pinatubo , located in Central Luzon just 90 km (56 mi) west-northwest of Manila , had been dormant for six centuries before the 1991 eruption. This eruption was one of the 2nd largest in the 20th century. It produced a large volcanic ash cloud that affected global temperatures, lowering them in areas as much as .5 °C. The volcanic ash cloud consisted of 22 million tons of SO 2 which combined with water droplets to create sulfuric acid . In 1991 Japan's Unzen Volcano also erupted, after 200 years of inactivity. It's located on

4324-436: The area greatly benefited from the amounts of ash, allowing life to multiply rapidly. Six years after the eruption, most lakes in the area had returned to their normal state. After its 1980 eruption, the volcano experienced continuous volcanic activity until 2008 . Geologists predict that future eruptions will be more destructive, as the configuration of the lava domes requires more pressure to erupt. However, Mount St. Helens

4416-545: The atmosphere. On the Volcanic Explosivity Index scale, the eruption was rated a 5, and categorized as a Plinian eruption . The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create lahars (volcanic mudflows). The lahars flowed many miles down the Toutle and Cowlitz Rivers , destroying bridges and lumber camps . A total of 3,900,000 cubic yards (3,000,000 m ) of material

4508-458: The composition of St. Helens' lava, with the addition of olivine and basalt . The pre-1980 summit cone started to form during the Castle Creek period. Significant lava flows in addition to the previously much more common fragmented and pulverized lavas and rocks ( tephra ) distinguished this period. Large lava flows of andesite and basalt covered parts of the mountain, including one around

4600-477: The cone. The ash drifted northeast over central and eastern Washington , northern Idaho , and western Montana . There were at least a dozen reported small eruptions of ash from 1831 to 1857, including a fairly large one in 1842. (The 1831 eruption is likely what tinted the sun bluish-green in Southampton County, Virginia on the afternoon of August 13—which Nat Turner interpreted as a final signal to launch

4692-468: The countryside with tephra . Swift Creek ended 8,000 years ago. A dormancy of about 4,000 years was broken around 2500 BC with the start of the Smith Creek eruptive period, when eruptions of large amounts of ash and yellowish-brown pumice covered thousands of square miles. An eruption in 1900 BC was the largest known eruption from St. Helens during the Holocene epoch, depositing

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4784-434: The crust along a path of least resistance, both by way of fractures and faults as well as by melting wall rocks. The addition of melted crust changes the geochemical composition. Some of the melt rises toward the Earth's surface to erupt, forming the Cascade Volcanic Arc above the subduction zone. The magma from the mantle has accumulated in two chambers below the volcano: one approximately 3–7 miles (5–12 km) below

4876-433: The disturbance. These biological legacies highly influence the reestablishment of the post-disturbance ecology. Some species from each trophic level survived the 1980 eruption, which allowed for relatively quick re-establishment of food webs . Larger species saw greater mortality rates, with each of the area's large mammals — mountain goats, elk, deer, black bear and cougars — completely decimated. Eventually, each of

4968-544: The end of April, the north side of the mountain had started to bulge. On May 18, a second earthquake, of magnitude 5.1, triggered a massive collapse of the north face of the mountain. It was the largest known debris avalanche in recorded history. The magma in St. Helens burst forth into a large-scale pyroclastic flow that flattened vegetation and buildings over an area of 230 square miles (600 km ). More than 1.5 million metric tons of sulfur dioxide were released into

5060-534: The eruption and because the eruption did not sterilize the immediate area. More than half of the papers on ecological response to volcanic eruption originated from studies of Mount St. Helens. Perhaps the most important ecological concept originating from the study of Mount St. Helens is the biological legacy . Biological legacies are the survivors of catastrophic disturbance; they can either be alive (e.g., plants that survive ashfall or pyroclastic flow), organic debris, or biotic patterns remaining from before

5152-540: The flank of a volcano collapses in a massive landslide) can only trigger the eruption of a very shallow magma chamber . Magma differentiation and thermal expansion also are ineffective as triggers for eruptions from deep magma chambers . In recorded history , explosive eruptions at subduction zone ( convergent-boundary ) volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, such as Mount St. Helens , Mount Etna and Mount Pinatubo , typically erupt with explosive force because

5244-434: The forest, as the treeline was thought to be moving up the slopes before the eruption. Alpine meadows were uncommon at Mount St. Helens. Mountain goats inhabited higher elevations of the peak, although their population was eliminated by the 1980 eruption. The eruption of Mount St. Helens has been subject to more ecological study than has any other eruption, because research into disturbance commenced immediately after

5336-471: The form of andesitic ash that formed at least eight alternating light- and dark-colored layers. Blocky andesite lava then flowed from St. Helens' summit crater down the volcano's southeast flank. Later, pyroclastic flows raced down over the andesite lava and into the Kalama River valley. It ended with the emplacement of a dacite dome several hundred feet (~200 m) high at the volcano's summit, which filled and overtopped an explosion crater already at

5428-478: The ground. Volcanic Bombs are associated with Strombolian and Vulcanian eruptions and basaltic lava . Ejection velocities ranging from 200 to 400 m/s have been recorded causing volcanic bombs to be destructive. Lahars (from a Javanese term for volcanic mudflows) are a mixture of volcanic debris and water. Lahars can result from heavy rainfall during or before the eruption or interaction with ice and snow. Meltwater mixes with volcanic debris causing

5520-458: The growth of new volcanic domes. The surface of the glacier, once mostly without crevasses, turned into a chaotic jumble of icefalls heavily criss-crossed with crevasses and seracs caused by movement of the crater floor. The new domes have almost separated the Crater Glacier into an eastern and western lobe. Despite the volcanic activity, the termini of the glacier have still advanced, with

5612-458: The high population density of the surrounding Metropolitan Naples area (totaling about 3.6 million inhabitants). In addition to potentially affecting the climate, volcanic ash clouds from explosive eruptions pose a serious hazard to aviation . Volcanic ash clouds consist of ash which is made of silt or sand sized pieces of rock, mineral, volcanic glass . Ash grains are jagged, abrasive, and don't dissolve in water. For example, during

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5704-503: The highest of the Cascade volcanoes. Mount Hood , the nearest major volcanic peak in Oregon , is 60 miles (100 km) southeast of Mount St. Helens. Mount St. Helens is geologically young compared with the other major Cascade volcanoes. It formed only within the past 40,000 years, and the summit cone present before its 1980 eruption began rising about 2,200 years ago. The volcano

5796-513: The huge bridge fell into the river, creating the cascades of the Columbia River Gorge . For punishment, the chief of the gods struck down each of the lovers and transformed them into great mountains where they fell. Wy'east, with his head lifted in pride, became the volcano known today as Mount Hood . Pahto, with his head bent toward his fallen love, was turned into Mount Adams . The beautiful Loowit became Mount St. Helens, known to

5888-423: The ice had an average thickness of 300 feet (100 m) and a maximum of 650 feet (200 m), nearly as deep as the much older and larger Carbon Glacier of Mount Rainier. The ice is all post-1980, making the glacier very young geologically. However, the volume of the new glacier is about the same as all the pre-1980 glaciers combined. From 2004, volcanic activity pushed aside the glacier lobes and upward by

5980-500: The island of Kyushu about 40 km (25 mi) east of Nagasaki . Beginning in June, a newly formed lava dome repeatedly collapsed. This generated a pyroclastic flow that flowed down the mountain's slopes at speeds as high as 200 km/h (120 mph). The 1991 eruption of Mount Unzen was one of the worst volcanic disasters in Japan's history, once killing more than 15,000 people in 1792. The eruption of Mount Vesuvius in 79 AD

6072-460: The larger mammals migrated back into the area. Without access to adequate forage, many elk starved to death in the winters in the following decades. By 2014, the mountain goat population had grown back to 65 members. In 2015, there were 152. Mountain goats are culturally significant to the Cowlitz Tribe, whose members historically harvested shed tufts of goat wool left behind on the mountain, and

6164-547: The last glacial period of the current ice age . The second eruptive period, the Cougar Stage, started 20,000 years ago and lasted for 2,000 years. Pyroclastic flows of hot pumice and ash along with dome growth occurred during this period. Another 5,000 years of dormancy followed, only to be upset by the beginning of the Swift Creek eruptive period, typified by pyroclastic flows, dome growth and blanketing of

6256-604: The lava dome sent an ash plume 2,000 feet (600 m) over the western rim of the crater; the ash plume then rapidly dissipated. On December 19, 2006, a large white plume of condensing steam was observed, leading some media people to assume there had been a small eruption. However, the Cascades Volcano Observatory of the USGS did not mention any significant ash plume. The volcano was in continuous eruption from October 2004, but this eruption consisted in large part of

6348-532: The lava dome. On July 10, 2008, it was determined that the eruption had ended, after more than six months of no volcanic activity. Future eruptions of Mount St. Helens will likely be even larger than the 1980 eruption. The current configuration of lava domes in the crater means that much more pressure will be required for the next eruption, and hence the level of destruction will be higher. Significant ashfall may spread over 40,000 square miles (100,000 km ), disrupting transportation. A large lahar flow

6440-660: The local Cowlitz people , and Loowit or Louwala-Clough to the Klickitat ) is an active stratovolcano located in Skamania County, Washington , in the Pacific Northwest region of the United States. It lies 52 miles (83 km) northeast of Portland, Oregon , and 98 miles (158 km) south of Seattle . Mount St. Helens takes its English name from that of the British diplomat Alleyne Fitzherbert, 1st Baron St Helens ,

6532-632: The metropolitan area were closed. [REDACTED] Media related to Turrialba volcano at Wikimedia Commons Stratovolcano A stratovolcano , also known as a composite volcano , is a conical volcano built up by many alternating layers ( strata ) of hardened lava and tephra . Unlike shield volcanoes , stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas . The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity . The magma forming this lava

6624-686: The mountain (roughly bounded by the Loowit Trail) have been listed on the National Register of Historic Places . Other area tribal names for the mountain include "nšh'ák'w" ("water coming out") from the Upper Chehalis , and "aka akn" ("snow mountain"), a Kiksht term. Royal Navy Commander George Vancouver and the officers of HMS Discovery made the Europeans' first recorded sighting of Mount St. Helens on 19 May 1792, while surveying

6716-528: The mountain run through Cowlitz County to the west, and Lewis County to the north. State Route 504 , locally known as the Spirit Lake Memorial Highway , connects with Interstate 5 at Exit 49, 34 miles (55 km) to the west of the mountain. That north–south highway skirts the low-lying cities of Castle Rock , Longview and Kelso along the Cowlitz River , and passes through

6808-663: The north of the eastern lobe of Crater Glacier. Mount St. Helens has an alpine tundra climate ( ET ). Mount St. Helens is part of the Cascades Volcanic Province , an arc-shaped band extending from southwestern British Columbia to Northern California , roughly parallel to the Pacific coastline. Beneath the Cascade Volcanic Province, a dense oceanic plate sinks beneath the North American Plate ;

6900-546: The northern Pacific Ocean coast. Vancouver named the mountain for British diplomat Alleyne Fitzherbert, 1st Baron St Helens on 20 October 1792, as it came into view when the Discovery passed into the mouth of the Columbia River. Years later, explorers, traders, and missionaries heard reports of an erupting volcano in the area. Geologists and historians determined much later that the eruption took place in 1800, marking

6992-506: The same for the arrow to the south. The chief of the gods then built the Bridge of the Gods, so his family could meet periodically. When the two sons of the chief of the gods fell in love with a beautiful maiden named Loowit, she could not choose between them. The two young chiefs fought over her, burying villages and forests in the process. The area was devastated and the earth shook so violently that

7084-460: The size of Mount Pinatubo affected the weather for a few years; with warmer winters and cooler summers observed. A similar phenomenon occurred in the April 1815, the eruption of Mount Tambora on Sumbawa island in Indonesia . The Mount Tambora eruption is recognized as the most powerful eruption in recorded history. Its eruption cloud lowered global temperatures as much as 0.4 to 0.7 °C. In

7176-431: The summit. Large parts of the dome's sides broke away and mantled parts of the volcano's cone with talus . Lateral explosions excavated a notch in the southeast crater wall. St. Helens reached its greatest height and achieved its highly symmetrical form by the time the Kalama eruptive cycle ended, in about 1647. The volcano remained quiet for the next 150 years. The 57-year eruptive period that started in 1800

7268-495: The surface, the other about 7–25 miles (12–40 km). The lower chamber may be shared with Mount Adams and the Indian Heaven volcanic field. The early eruptive stages of Mount St. Helens are known as the "Ape Canyon Stage" (around 40,000–35,000 years ago), the "Cougar Stage" (ca. 20,000–18,000 years ago), and the "Swift Creek Stage" (roughly 13,000–8,000 years ago). The modern period, since about 2500 BC,

7360-498: The tribe has played a role in monitoring the population, which continues to recover without human intervention. Native American lore contains numerous stories to explain the eruptions of Mount St. Helens and other Cascade volcanoes. The best known of these is the Bridge of the Gods story told by the Klickitat people . In the story, the chief of all the gods and his two sons, Pahto (also called Klickitat) and Wy'east, traveled down

7452-405: The vertical ash column declined in stature, and less-severe outbursts continued through the night and for the next several days. The St. Helens May 18 eruption released 24 megatons of thermal energy and ejected more than 0.67 cubic miles (2.79 km ) of material. The removal of the north side of the mountain reduced St. Helens' height by about 1,300 feet (400 m) and left

7544-412: The world. The SO 2 in this cloud combined with water (both of volcanic and atmospheric origin) and formed sulfuric acid , blocking a portion of the sunlight from reaching the troposphere . This caused the global temperature to decrease by about 0.4 °C (0.72 °F) from 1992 to 1993. These aerosols caused the ozone layer to reach the lowest concentrations recorded at that time. An eruption

7636-533: The year 100 BC that traveled all the way into the Lewis and Kalama river valleys. Others, such as Cave Basalt (known for its system of lava tubes ), flowed up to 9 miles (14 km) from their vents. During the first century, mudflows moved 30 miles (50 km) down the Toutle and Kalama river valleys and may have reached the Columbia River . Another 400 years of dormancy ensued. The Sugar Bowl eruptive period

7728-480: The year following the eruption, most of the Northern Hemisphere experienced cooler temperatures during the summer. In the northern hemisphere , 1816 was known as the " Year Without a Summer ". The eruption caused crop failures, food shortages, and floods that killed over 100,000 people across Europe , Asia , and North America . Mount St. Helens Mount St. Helens (known as Lawetlat'la to

7820-480: Was being forced upward as quickly as 6 ft (2 m) per day. In mid-June 2006, the slab was crumbling in frequent rockfalls, although it was still being extruded. The height of the dome was 7,550 feet (2,300 m), still below the height reached in July 2005 when the whaleback collapsed. On October 22, 2006, at 3:13 p.m. PST, a magnitude 3.5 earthquake broke loose Spine 7. The collapse and avalanche of

7912-547: Was characterized by one resident as the largest since 2010. Ash fell as far away as the capital, San Jose, and at least 500 people went to hospitals complaining of breathing problems. Flights into San Jose were cancelled due to concerns about ash. On September 19, at 02:54 an eruption lasting around fifteen minutes was the first event of many through the day that eventually covered the metropolitan area with ash. There were events at 11:30, 14:40, 15:34. The events continued through September 20 with an eruption at 06:20. Airports in

8004-404: Was characterized by smaller-volume eruptions. Numerous dense, nearly red hot pyroclastic flows sped down St. Helens' flanks and came to rest in nearby valleys. A large mudflow partly filled 40 miles (64 km) of the Lewis River valley sometime between 1000 BC and 500 BC. The next eruptive period, the Castle Creek period, began about 400 BC, and is characterized by a change in

8096-432: Was dominated by Pacific silver fir up to 4,300 feet (1,300 m). Finally, below treeline , the forest consisted of mountain hemlock , Pacific silver fir and Alaska yellow cedar . Large mammals included Roosevelt elk , black-tailed deer , American black bear , and mountain lion . The treeline at Mount St. Helens was unusually low, at about 4,400 feet (1,340 m), the result of prior volcanic disturbance of

8188-493: Was formerly known as the Tulutson Glacier. Shadowed by the crater walls and fed by heavy snowfall and repeated snow avalanches, it grew rapidly (14 feet (4.3 m) per year in thickness). By 2004, it covered about 0.36 square miles (0.93 km ), and was divided by the dome into a western and eastern lobe. Typically, by late summer, the glacier looks dark from rockfall from the crater walls and ash from eruptions. As of 2006,

8280-462: Was named after the Goat Rocks dome and is the first period for which both oral and written records exist. As with the Kalama period, the Goat Rocks period started with an explosion of dacite tephra , followed by an andesite lava flow, and culminated with the emplacement of a dacite dome. The 1800 eruption probably rivaled the 1980 eruption in size, although it did not result in massive destruction of

8372-474: Was short and markedly different from other periods in Mount St. Helens history. It produced the only unequivocal laterally directed blast known from Mount St. Helens before the 1980 eruptions. During Sugar Bowl time, the volcano first erupted quietly to produce a dome, then erupted violently at least twice producing a small volume of tephra, directed-blast deposits, pyroclastic flows, and lahars. East Dome,

8464-496: Was transported 17 miles (27 km) south into the Columbia River by the mudflows. For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 16 miles (19 to 26 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (100 km/h) with ash reaching Idaho by noon. Ashes from the eruption were found on top of cars and roofs the next morning as far away as Edmonton , Alberta, Canada. By about 5:30 p.m. on May 18,

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