Mount St. Helens or Louwala-Clough (known as Lawetlat'la for the native Cowlitz, and Loowit to Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Northwest Pacific region of the United States. It is 50 miles (80 km) northeast of Portland, Oregon and 96 miles (154 km) south of Seattle, Washington. Mt. Helens took his English name from British diplomat Lord StÃ, Helens, a friend of George Vancouver explorers who made a survey of the area at the end of the 18th century. The volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire that includes more than 160 active volcanoes. The volcano is famous for its ash explosion and pyroclastic flow.
Mt. Helens is best known for his 1980s major eruption, the most deadly and most destructive volcanic event in the history of the United States. Fifty-seven people were killed; 250 houses, 47 bridges, 15 miles (24 km) of railroads, and 185 miles (298 km) of destroyed highways. Large landslides triggered by an earthquake of magnitude 5.1 on the Richter scale caused an eruption that reduced the height of the mountain peak from 9,677 ft (2,950 m) to 8,363 feet (2,549 m), leaving 1 mile (1.6 m) Ã, km) horseshoe shaped width. Landslide damage reached 0.7 cubic miles (2.9 km 3 ) in volume. Mt. Helens National Volcanic Monument was created to preserve the volcano and allow it thereafter to be studied scientifically.
Like most other volcanoes in the Cascade Mountains, Mt. Helens is a large cone consisting of lava rocks mixed with ash, pumice, and other sediments. This mountain includes basal and andesite layers traversed by several dacit lava domes. The largest of the dacite domes form the previous peak, and from the north side sit the smaller Goat Rocks dome. Both were destroyed in 1980's eruption.
Video Mount St. Helens
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Umum Edit
Mt. Helens is 34 miles (55 km) west of Mount Adams, west of the Cascade Range. This volcano "brother and sister" volcano is about 50 miles (80 km) from Mount Rainier, the highest Cascade volcano. Mount Hood, the nearest major volcano in Oregon, is 60 miles (100 km) southeast of Mt. Helens.
Mt. Helens is geologically young compared to other large Cascade volcanoes. It was formed only in the last 40,000 years, and the pre-1980 peak cone started rising about 2,200 years ago. Volcanoes are considered the most active in the Cascades in the Holocene period (the last 10,000 years or so).
Before the 1980 eruption, Mt. Helens is the fifth highest peak in Washington. It stood out from the surrounding hills due to its extensive symmetry and snow and ice cover from the summit of the pre-1980 summit, earning it the nickname "Fuji-san of America". The peak rises more than 5,000 feet (1,500 m) above its base, where the lower side joins the adjacent back. The mountain is 6 miles (9.7 km) at its base, which is at 4,400 feet (1,300 m) on the northeast side and 4,000 feet (1,200 m) elsewhere. In the pre-eruption tree line, the conical width is 4 miles (6.4 km).
Flows from volcanoes enter three major river systems: the Toutle River in the north and northwest, the Kalama River to the west, and the Lewis River in the south and east. The rivers are filled with rain and abundant snow. Average annual rainfall is 140 inches (3,600 mm), and snow packets on the top slopes of the mountain can reach 16 feet (4.9 m). The Lewis River is confiscated by three dams for hydroelectric power. The southern and eastern sides of the volcano flows into a upstream shelter, the Swift Reservoir, which is to the south of the volcano's peak.
Although Mt. Helens is in Skamania County, Washington, access routes to the mountain run through Cowlitz County to the west. State Route 504, known as the Spirit Lake Memorial Highway, connects with Interstate 5 at Exit Gate 49, 34 miles (55 km) to the west of the mountain. The north-south highway runs through Castle Rock, Longview and Kelso towns along the Cowlitz River, and crosses the Vancouver, Washington-Portland, Oregon metropolitan area less than 50 miles (80 km) to the southwest. The closest community of the volcano is Cougar, Washington, in the Lewis River valley 11 miles (18 km) south-southwest of the peak. Gifford Pinchot National Forest Surround Mt. Helens.
Crater Glaciers and other new stone glaciers Edit
During the winter of 1980-1981, a new glacier appeared. Now officially named Glacier Crater, it was formerly known as Glacier Tulutson. Overshadowed by the crater wall and fed by heavy snowfall and repetitive snowfall, it grows rapidly (14 feet (4.3 m) per year in thickness). In 2004, it covers about 0.36 square miles (0.93 km 2 ), and is divided by a dome to the west and east lobes. Usually, at the end of summer, glaciers appear dark from the cliffs from the crater wall and ash from the eruption. In 2006, ice had an average thickness of 300 feet (100 m) and a maximum of 650 feet (200 m), almost as deep as the much older and larger Mt. Rainier Glacier. The ice is all post-1980, making the geological glaciers very young. However, the new glacier volume is almost the same as all pre-1980 glaciers combined.
With recent volcanic activity initiated in 2004, the glacier lobes are pushed aside and upward by the growth of new volcano dome. The glacier's surface, which was once largely gapless, turned into a chaotic pile of ice clumps punctuated by niches and seracs caused by the crater floor movement. The new dome almost separates Crater Glaciers into the east and west lobes. Despite volcanic activity, the terminology of glaciers still continues, with little progress on the western lobe and greater advancement in the more shaded eastern lobes. Due to the face, two glacier lobes joined together at the end of May 2008 and thus the glacier completely surrounded the lava dome. In addition, since 2004, a new glacier has formed on the crater wall above the crater of Glacier feeding rock and ice to its surface below; there are two stone glaciers to the north of the eastern lobes of Crater Glacier. Crater Glacier is the only known advanced glacier in the United States adjacent.
Maps Mount St. Helens
Geological history Edit
Ancestral stage of eruption activity Edit
The earliest stages of Mount Helens eruption were known as the "Ape Canyon Stage" (about 40,000-35,000 years ago), "Cougar Stage" (about 20,000-18,000 years ago), and "Swift Creek Stage" (about 13,000-8,000 years ago). The modern period, since about 2500 BC, is called "Spirit Lake Stage". Collectively, the Pre-Spirit Lake stage is known as the "ancestral stage". The ancestral and modern stages differ mainly in the composition of the erupted lava; The ancestral lavas consist of a mixture of dacite and andesite characteristics, while modern lavas vary greatly (from basal olivine to andesite and dacite).
St. Helens started its growth in the Pleistocene 37,600 years ago, during the Ape Canyon stage, with dacit and andesite eruptions from hot pumice and ash. Thirty-six thousand years ago a huge mudflow was flowing beneath the volcano; mud is a significant force in all eruption cycles. Helens. The Ape Canyon eruption period ended about 35,000 years ago and was followed by a relatively quiet 17,000 years. Parts of this ancestral cone are fragmented and transported by glaciers 14,000 to 18,000 years ago during the last glacial period of the current ice age.
The second eruption period, Cougar Stage, began 20,000 years ago and lasted for 2,000 years. The pyroclastic flow of hot and ash pumice along with the growth of the dome occurred during this period. Over 5,000 years of dormancy followed, only to become angry at the start of the Swift Creek eruption period, characterized by pyroclastic flows, dome growth and rural blankets with tephra. Swift Creek ended 8,000 years ago. Smith Creek and the Pine Creek eruption period Edit
A dormancy of about 4,000 years was damaged around 2500 BC with the start of the Smith Creek eruption period, when eruptions from large amounts of pale brown ash and pumice covered thousands of square miles. The eruption in 1900 BC is the largest known eruption of St. Helens during the Holocene epoch, judged by the volume of one of the tephra layers of that period. This eruption period lasts until about 1600 BC and leaves 18 inches (46 cm) of deposits in material 50 miles (80 km) deep in what is now Mt. Rainier National Park. Trace deposits have been found as far north as Banff National Park in Alberta, and as far east as southeast of Oregon. All say there may be up to 2.5 cubic miles (10 km 3 ) of the material ejected in this cycle. About 400 years of dormancy followed.
St. Helens came back to life around 1200 BC - the eruption period of Pine Creek. This lasted until about 800 BC and was characterized by a smaller volume eruption. Many hot, red pyroclastic heat flows radiate beneath the flanks of St. Helens and stop at the nearest valleys. A large mud eruption partially fills 40 miles (64 km) of the Lewis River valley roughly between 1000 BC and 500 BC.
Castle Creek and Sugar Bowl eruption period Edit
The next eruption period, the Castle Creek period, begins around 400 BC, and is characterized by changes in St. lava composition Helens, with the addition of olivine and basalt. The summit of the pre-1980 summit began to form during the Castle Creek period. Significant lava flows in addition to lavas and previously more commonly fragmented and destroyed stones (tephra) distinguish this period. The large lava flows from andesite and basalt cover parts of the mountain, including one around 100 BC that travels along the road to the valleys of the Lewis and Kalama rivers. Others, such as Cave Basalt (known as the lava tube system), flow up to 9 miles (14 km) from their vents. During the first century, mudflows moved 30 miles (50 km) down the valleys of the Toutle and Kalama rivers and may have reached the Columbia River. Over 400 years of dormancy ensued.
The Sugar Bowl eruption period is short and very different from other periods in the history of Mt. Helens. This produces the only laterally-directed explosion known from Mt. Helens before the 1980 eruption. During the Sugar Bowl time, the volcano first erupted silently to produce the dome, then erupted violently at least twice resulting in a small volume of tephra, directed sediment, pyroclastic flows, and lava.
Kalama and Goat Rocks eruption period Edit
About 700 years of dormancy was damaged around 1480, when large amounts of pale gray pumice and ash began to erupt, beginning the Kalama period. The eruption in 1480 was several times larger than May 18, 1980, the eruption. In 1482, another major eruption that rivaled the 1980 eruption in known volumes had occurred. Ash and pumice stack 6 miles (9.7 km) northeast of the volcano to a thickness of 3 feet (0.9 m); 50 miles (80 km) away, ash is 2 inches (5 cm) deep. The large pyroclastic flows and mud flow then rush down to the western side of Helens and into the Kalama River drainage system.
The 150-year period then sees a less silica-rich lava eruption in the form of andesite ashes that form at least eight colored and dark layers back and forth. The rocky andesite lava then flows from the top of St. Helens to the southeast side of the volcano. Then, pyroclastic flows ran over the andesite lava and into the valley of the Kalama River. It ends with the placement of a dome of several hundred feet (~ 200 m) high dome at the top of the volcano, which fills and exceeds the already existing crater on the summit. Most of the side of the dome separates and coats the volcanic cones with the talus. The lateral explosion digs a notch on the southeast crater wall. St. Helens reached its greatest peak and achieved a very symmetrical shape as the Kalama eruption cycle ended, around 1647. The volcano remained calm for the next 150 years.
The 57-year eruption period started in 1800 was named after the Goat Rocks dome, and is the first time that both oral and written notes exist. Like the Kalama period, the Stone Goat period begins with the explosion of the dacite tephra, followed by the andesite lava flow, and culminates with the emptiness of the dacite dome. The 1800 eruption might rival the size of the 1980 eruption, although it did not result in massive loss. Ash drifts in the northeast in central and eastern Washington, northern Idaho, and western Montana. There are at least a dozen reported small ash eruptions from 1831-1857, including a fairly large one in 1842. The hole was apparently at or near Goat Rocks on the northeast side. The Goat Rocks Dome is a bulge site on the 1980 eruption, and it was obliterated in a major eruption on May 18, 1980 which destroyed the entire north face and over 1,300 feet (400 m) of mountains.
Modern eruption period Edit
1980 to 2001 activity Edit
On March 20, 1980, Mt. Helens suffered a magnitude 4.2 earthquake; and, on March 27, the steam vent started. At the end of April, the north side of the mountain began to swell. On May 18, a second earthquake, measuring 5.1, triggered a massive collapse of the north face of the mountain. It is the largest avalanche of debris known in recorded history. Magma in St. Petersburg Helens exploded into a large-scale pyroclastic flow that flattened vegetation and buildings above 230 square miles (600 km 2 ). More than 1.5 million metric tons of sulfur dioxide are released into the atmosphere. At the scale of the Volcanic Explosion Index, the eruption was rated five, and categorized as a Plinian eruption.
The collapse of the north side of St. Helens mixed with ice, snow, and water to create lava (volcano). The lava people flowed for miles to the Toutle and Cowlitz Rivers, destroying bridges and wooden camps. A total of 3.900.000 cubic meters (3,000,000 m 3 ) material transported 17 miles (27 km) south to the Columbia River by mud.
For more than nine hours, a lump of strong ash erupts, eventually reaching 12 to 16 miles (20 to 27 km) above sea level. The plains move eastward at an average speed of 60 miles per hour (100 km/h) with ash reaching Idaho during the day. Ash from the eruption was found collecting on the car and roof the next morning, as far as the city of Edmonton in Alberta, Canada.
At about 5:30 am on May 18, the vertical ash column declined in stature, and a less severe explosion continued through the night and for the next several days. The St. Helens May 18 eruption released 24 megatons of thermal energy; it spilled over 0.67 cubic miles (2.79 km 3 ) material. Removal of the northern side of the mountain reduces the height of St. Helens about 1,300 feet (400 m) and leaves the crater 1 mile (1.6 km) to 2 miles (3.2 km) wide and 0.5 miles (800 m) deep, with the north end open in big offense. The eruption killed 57 people, nearly 7,000 large animals (deer, deer, and bear), and about 12 million fish from hatcheries. It destroys or extensively damages more than 200 homes, 185 miles (298 km) of highways and 15 miles (24 km) from trains.
Between 1980 and 1986, activity continued on Mount St. Helens, with a new lava dome formed in the crater. Many small explosions and dome eruptions occur. From December 7, 1989, to January 6, 1990, and from November 5, 1990, to February 14, 1991, the mountain erupted with a sometimes large ash cloud.
2004 to 2008 activity Edit
Magma reached the surface of the volcano around October 11, 2004, producing a new lava dome building on the south side of the existing dome. This new dome continued to grow throughout 2005 and into 2006. Some temporary features were observed, such as the lava spine dubbed "whaleback", which consisted of a compact magma-length shaft that was extruded by the magma pressure underneath. These features are fragile and damaged as soon as they are formed. On July 2, 2005, the end of the whaleback was cut off, causing rocks to send ash and dust several hundred meters into the air.
Mount St. Helens showed significant activity on March 8, 2005, when 36,000 feet of steam and ash (11,000 m) emerged - visible from Seattle. This relatively small eruption is the release of pressure that is consistent with the building's ongoing dome. The release was accompanied by a 2.5-magnitude earthquake.
Another feature that emerges from the dome is called "fins" or "slabs." About half the size of a soccer field, large, cooled volcanic rocks are forced to rise upward as fast as 6 feet (2 m) per day. In mid-June 2006, the plates collapsed on a frequent cliff, though still extruded. The height of the dome is 7,550 feet (2,300 m), still below the heights reached in July 2005 when the whaleback collapsed.
On October 22, 2006, 3:13 pm PST, a magnitude 3.5 quake ruptured Spine 7. The collapse and lava dome avalanche sent a 2,000ft (600m) ash cloud over the western edge of the crater; the ash feathers then disappear quickly.
On December 19, 2006, a large clump of condensate vapor was observed, causing some media people to consider a small eruption. However, the Cascades Volcano Observatory from the USGS does not mention significant ash fur. The volcano has been continuously erupting since October 2004, but this eruption consists mainly of lava extrusion gradually forming a dome in the crater.
On January 16, 2008, the steam began seeping from the fracture above the lava dome. The related seismic activity is the most important since 2004. Scientists suspend activity in craters and mountain slopes, but the risk of large eruptions is considered low. At the end of January, the eruption stopped; no more lava extruded from the lava dome. On July 10, 2008, it was determined that the eruption had ended, after more than six months of no volcanic activity.
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Human history Edit
Interests for Native Americans Edit
American Indian knowledge contains many legends to explain the eruption of Mt. Helens and other Cascade volcanoes. The most famous of these is the legend of the Bridge of the Gods told by the Klickitat people. In their story, the heads of all the gods and his two sons, Pahto (also called Klickitat) and Wy'east, travel down the Columbia River from the Far North to find a suitable place to settle.
They arrived in what is now called The Dalles and thought they had never seen such a beautiful land. His sons quarreled over the land, so to settle their father's dispute fired two arrows from his powerful 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 the same for the arrow in the south. The heads of the gods then built the Bridge of the Gods, so that his family could meet periodically.
When the two sons of the godhead fall in love with a beautiful girl named Loowit, he can not choose between them. The two young leaders are fighting over themselves, burying villages and forests in the process. The area was shattered and the earth shook so great that the big bridge fell into the river, creating the Columbia River River rafting.
For punishment, the heads of the gods attack each lover and turn him into the great mountains where they fall. Wy'east, with his head raised in pride, became a volcano known today as Mount Hood. Pahto, with his head bent toward falling love, turned into Mount Adams. The Fair Loowit becomes Mt. Helens, known as Klickitats as Louwala-Clough, meaning "smoking or volcano" in their language (called Sahaptin mountain Loowit).
The mountain is also important for the Cowlitz and Yakama tribes who also historically live in the area. They found the area above the tree line to have extraordinary spiritual significance, and the mountain (which they call "Lawetlat'la", roughly translated as "smokers") stands out in the myth of their creation, and in some of their songs and rituals. In recognition of this cultural significance, more than 12,000 acres (4,900 ha) of mountains (roughly bounded by the Loowit Path) have been listed on the National Register of Historic Places.
Other tribal names for mountains include "n? HÃ,Â'ÃÆ'¡kÃ,Â'" ("water coming out") from Upper Chehalis, and "aka akn" ("snow mountain"), a Kiksht term.
European explorations Edit
Royal Navy commander George Vancouver and the HMS Discovery officers made the Europeans first see Mount Helens on May 19, 1792, while observing the northern Pacific coast. Vancouver named the mountain for British diplomat Alleyne Fitzherbert, 1st Baron St. Helens on October 20, 1792, when it was seen when Discovery passed through the mouth of the Columbia River.
Years later, explorers, merchants, and missionaries heard reports of volcanoes erupting in the area. Geologists and historians then decided that the eruption took place in 1800, marking the start of the 57-year-old Goat Lunar Period (see geology section). Worried about "dry snow", the Nespelem tribe in northeastern Washington danced and prayed instead of collecting food and suffering during the winter from starvation.
In late 1805 and early 1806, Lewis and Clark Expedition members found Mt. Helens from the Columbia River but did not report either ongoing eruptions or recent evidence from one. However they reported the existence of sand and suction conditions at the mouth of the Sandy River near Portland, indicating an eruption by Mount Hood sometimes in previous decades.
In 1829 Hall J. Kelley led a campaign to rename the Cascade Range as a Range of Presidents and also to rename every major Cascade mountain after the former President of the United States. In his plan, Mt. Helens will be renamed Mount Washington.
European settlement and use of Edit
The first eyewitness account of the volcano eruption was made in March 1835 by Meredith Gairdner, while working for the Hudson Bay Company stationed at Fort Vancouver. He sent an account to Edinburgh New Philosophical Journal, which published his letter in January 1836. James Dwight Dana of Yale University, while sailing with the United States Exploration Expedition, saw a silent peak from the mouth of the Columbia River in 1841. Members another of the expedition then explained the "cellular basal lava" at the base of the mountain.
In late autumn or early winter of 1842, settlers and missionaries nearby witnessed the so-called "Big Eruption". This small-volume explosion created a large ash cloud, and a mild explosion followed for 15 years. Eruptions from this period may be phreatic (steam explosion). Josiah Parrish in Champoeg, Oregon watched Mt. Helens in the eruption on November 22, 1842. Ash from this eruption may have reached The Dalles, Oregon, 48 miles (80 km) southeast of the volcano.
In October 1843, California's future governor Peter H. Burnett told the story of an American Aboriginal man who burned his feet and legs in lava or hot ashes while hunting deer. The possible apocryphal story is that the injured man sought treatment at Fort Vancouver, but the guardian of the contemporary comedy castle, Napoleon McGilvery, denied knowing the incident. English lieutenant Henry J. Warre sketched the eruption in 1845, and two years later Canadian painter Paul Kane invented watercolors from a smoky mountain. Warre's work shows material that erupts from a hole about a third of the way from a mountain peak on the west or northwest side (possibly on Goat Rocks), and one of Kane's field sketches shows smoke radiating from around the same location.
On April 17, 1857, the Republic of Steilacoom, Washington, reported that "Mount St. Helens, or some other mountain to the south, is seen... in a state of eruption." The lack of a significant ash layer associated with this event indicates that it was a small eruption. This is the first volcanic activity reported since 1854.
Prior to the 1980 eruption, Spirit Lake offers recreational activities throughout the year. In summer there is boating, swimming and camping, while in the winter there is skiing.
The human impact of the 1980 eruption Edit
Fifty-seven people died during the eruption. If the eruption happened one day later, when the loggers would work, rather than on Sunday, the death toll could be much higher.
Harry R. Truman, 83, who lived near the mountain for 54 years, became famous when he decided not to flee before the impending eruption, despite repeated requests by local authorities. His body was never found after the eruption.
Another victim of the eruption was a 30-year-old volcanologist, David A. Johnston, stationed at nearby Coldwater Ridge. Shortly before his position was exposed to pyroclastic flows, Johnston broadcast his famous last words: "Vancouver! Vancouver! Here it is!" Johnston's body was never found.
US President Jimmy Carter observed the damage and said, "Someone says this area looks like waves, but the moon is more like a golf course than what is there." A film crew, led by Seattle filmmaker Otto Seiber, was dropped by helicopter at St. Helens on May 23 to document the destruction. However, their compass circled and quickly disappeared. The second eruption occurred on May 25, but the crew survived and were rescued two days later by National Guard helicopter pilots. Their film, Mount St. Eruption Helens , then became a popular documentary.
Next protection and history Edit
In 1982, President Ronald Reagan and the US Congress established the National Volcanic Monument of Mt. Helens, an area of ​​110,000 hectares (45,000 ha) around the mountain and inside the Gifford Pinchot National Forest.
After the 1980 eruption, the area was left to gradually return to its natural state. In 1987, the US Forest Service reopened the mountain to climb. It remained open until 2004 when new activity led to the closure of the area around the mountain (see Geological history above for more details).
Most important is the closure of the Monitor Ridge trail, which previously allowed up to 100 climbers allowed per day to climb to the top. On July 21, 2006, the mountain was reopened for climbers. In February 2010, a climber died after falling from the rim to the crater.
The mountain is now circled by the Loowit Trail at an altitude of 4000-4900 feet (1,200-1,500 m). The northern segment of the trail from the South Fork Toutle River in the west to the Windy Pass to the east is a restricted zone where camping, cycling, pets, fires, and off-trail excursions are all forbidden.
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Climb and recreation Edit
Mt. Helens is a popular hiking destination for early and experienced mountain climbers. The peak rises throughout the year, though more often rises from late spring until early fall. All routes include steep sections, heavy terrain. The permit system has been available for climbers since 1987. Climbing permit is required throughout the year for anyone who will be above 4,800 feet (1,500 m) on the slopes of Mt. Helens.
The standard hiking/mountain route in the warmer months is the Monitor Ridge Route, which starts at Climbers Bivouac. It is the most popular and bustling route to the summit in summer and reaches about 4,600 feet (1,400 m) at about 5 miles (8 km) to reach the crater lips. Though heavy, it's considered a non-technical ascent involving some randomization. Most climbers complete round trips in 7 to 12 hours.
Source of the article : Wikipedia
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