Mount Saint Helens

Mount St. Helens
3,000 ft (1 km) steam plume on May 19, 1982
Elevation	8,364 ft (2,550 m)
Location	Washington, USA
Mountain range	Cascades
Geographic coordinates	{{#invoke:Coordinates|coord}}{{#coordinates:46|11|28|N|122|11|39|W|type:mountain_region:US		name= }}
Topographic map	USGS Mount St. Helens
Type	Active Stratovolcano, otherwise known as Composite volcano
Geologic time scale	< 40,000 yrs
Last eruption	2004-2007 (ongoing)
First ascent	1853 by Thomas J. Dryer
Easiest Climbing route	Hike via south slope

Mount St. Helens is an active stratovolcano in Skamania County, Washington, in the Pacific Northwest region of the United States. It is located 96 miles (154 km) south of the city of Seattle, Washington and 53 miles (85 km) northeast of Portland, Oregon. The mountain is part of the Cascade Volcanic Belt of the Cascade Range and the larger Pacific Ring of Fire that includes over 500-600 active volcanoes. It takes its English name from the British diplomat Lord St Helens. Helens was a friend of George Vancouver, an explorer who made a survey of the area in the late 18th century.

This volcano is well known for its volcanic ash explosions and pyroclastic flows and is most famous for its catastrophic eruption on May 18, 1980. The 1980 eruption of Mount St. Helens was the deadliest and most economically destructive volcanic event in the history of the United States. (In 1912, Mount Katmai, Alaska, was the site of the largest volcanic eruption in U.S. history.) In the St. Helens eruption fifty-seven people were killed, the eruption caused a massive debris avalanche, reducing the elevation of the mountain's summit from 9,600 feet (2,950 m) to 8,000 feet (2,550 m), and replacing it with a mile-wide (1.5 km-wide) horseshoe-shaped crater. It destroyed, or extensively damaged, over 200 homes, 185 miles (300 km) of highway and 15 miles of railways. The debris avalanche was up to 0.7 cubic miles (2.3 km³) in volume, making it the largest in recorded history.

As with most other volcanoes in the Cascade Range, Mount St. Helens is a large eruptive cone consisting of lava rock interlayered with volcanic pumice, and other deposits. The mountain includes layers of basalt and andesite through which several domes of dacite lava have erupted. The largest of the dacite domes formed the previous summit; and off of its northern flank sat the smaller Goat Rocks dome. Both were destroyed in the 1980 eruption.

File:Sthelens1.jpg

Mount St. Helens the day before the 1980 eruption, which removed much of the northern face of the mountain, leaving a large crater (caldera).

File:Mt St Helens from climbers biviouc.JPG

The view in 2002 from Climbers Bivouac

Geographic setting and description

General

Mount St. Helens is located 34 miles (55 km) west of Mount Adams, in the eastern part of the Cascade Range. These "sister and brother" volcanic mountains are each approximately 50 miles (80 km) from Mount Rainier, the largest of Cascade volcanoes. Mount Hood, the nearest major volcanic peak in Oregon, is 60 miles (95 km) southeast of Mount St. Helens.

Mount St. Helens is geologically young compared to the other major Cascade volcanoes. It only formed within the last 40,000 years, and the pre-1980 summit cone began rising around 2,200 years ago. The volcano is considered the most active in the Cascades within the Holocene epoch (the last 10,000 or so years).

A view of St. Helens and the nearby area from space.

Even before the 1980 eruption, Mount St. Helens was not the highest peak in the Cascade Range; its summit altitude made it only the fifth-highest peak in Washington State. It stood out prominently, however, from surrounding hills due to the symmetry and extensive snow and ice cover of the pre-1980 summit cone, earning it the nickname, "Fuji-san of America" ("Mount Fuji of America"). 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 (9.5 km) across at its base, which is at an altitude of 4,400 feet (1,340 m) on the northeastern side and 4,000 feet (1,220 m) elsewhere. At the pre-eruption tree-line the width of the cone was 4 miles (6.4 km).

Streams which start on the volcano enter three main river systems: the Toutle River on the north and north-west, 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 is 140 inches (3.6 m), 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, the best access routes to the mountain run through Cowlitz County, Washington to the west. Washington State Route 504, locally known as the Spirit Lake Memorial Highway, connects with the heavily traveled Interstate 5 at Exit 49, 34 miles (55 km) to the west of the mountain. That major north-south highway skirts the low-lying cities of Castle Rock, Longview, and Kelso, Washington along the Cowlitz River, and passes through 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.

Human history

Importance to Native Americans

File:Archaeologists working in the Mount St Helens area.jpg

Archaeologists working in the Mount St. Helens area.

Traces of ancient campsites have been found in the Gifford Pinchot National Forest which surrounds the monument. Dating of these sites reveal that people have lived in this area for at least 6500 years. Throughout human history, Mount St. Helens eruptions have had a dramatic effect on the lives of local inhabitants. Work by archaeologists has shown that a massive eruption 3500 years ago buried Native American settlements with a thick layer of pumice. As a result, the people abandoned the area for nearly 2000 years. More recently, Native Americans of the Cowlitz, Taidnapam, Klickitat, Upper Chinook, and Yakama tribes moved seasonally over the land, harvesting huckleberries and hunting salmon, elk, and deer.

The symmetrical and aesthetic shape of the volcano inspired legends.

Native American lore contains numerous legends to explain the eruptions of Mount St. Helens and other Cascade volcanoes. The most famous of these is the Bridge of the Gods legend told by the Klickitats. In their tale, the chief of all the gods, Tyhee Saghalie and his two sons, Pahto (also called Klickitat) and Wy'east, traveled down the Columbia River from the Far North in search for a suitable area to settle. The sons fought over a maiden, Loowit, that as legend tells, resulted in huge destruction of the land. Wy'east, with his head lifted in pride, became the volcano known today as Mount Hood and Pahto, with his head bent toward his fallen love, was turned into Mount Adams. The fair Loowit became Mount St. Helens, known to the Klickitats as Louwala-Clough which means "smoking or fire mountain" in their language (the Sahaptin called the mountain Loowit).

Early explorations

Royal Navy Commander George Vancouver and the officers of HMS Discovery(1789) made the Europeans' first recorded sighting of Mount St. Helens, on May 19, 1792, while surveying the northern Pacific Ocean coast. Vancouver named the mountain for British diplomat Alleyne Fitzherbert, 1st Baron St Helens on October 20, 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 the beginning of the 57-year-long Goat Rocks Eruptive Period (see geology section). Alarmed by the "dry snow", the Nespelem tribe of northeastern Washington danced and prayed rather than collecting food, and suffered during that winter from starvation.

In late 1805 and early 1806, members of the Lewis and Clark Expedition spotted Mount St. Helens from the Columbia River but did not report either an ongoing eruption or recent evidence of one. They did however report the presence of quicksand and clogged channel conditions at the mouth of the Sandy River near Portland, Oregon, suggesting an eruption by Mount Hood sometime in the previous decades.

James Dwight Dana was among the first geologists to view the volcano.

The first authenticated eyewitness report of a volcanic eruption was made in March 1835 by Dr. Meredith Gairdner, while working for the Hudson's Bay Company stationed at Fort Vancouver. He sent an account to the Edinburgh New Philosophical Journal, which published his letter in January 1836. James Dwight Dana of Yale University, while sailing with the United States Exploring Expedition, saw the then-quiescent peak from off the mouth of the Columbia River in 1841. Another member of the expedition later described "cellular basaltic lavas" at the mountain's base.

In late fall or early winter of 1842, nearby settlers and missionaries were witness to the so-called "Great Eruption". This small-volume outburst created large ash clouds, and mild explosions followed for 15 years. The eruptions of this period were likely phreatic eruption (steam explosions). The Reverend Josiah Parrish in Champoeg, Oregon witnessed Mount St. Helens in eruption on November 22, 1842. Ash from this eruption may have reached The Dalles, Oregon, 48 miles (80 km) southeast of the volcano.

Mount St. Helens erupting at night. Painting by Paul Kane after his 1847 visit to the area.

British lieutenant Henry J. Warre sketched the eruption in 1845, and two years later Canadian painter Paul Kane created watercolors of the gently smoking mountain. Warre's work showed erupting material from a vent about a third of the way down from the summit on the mountain's west or northwest side (possibly at Goat Rocks), and one of Kane's field sketches shows smoke emanating from about the same location.

On April 17, 1857, the Republican, a Steilacoom, Washington newspaper, reported that "Mount St. Helens, or some other mount to the southward, is seen ... to be in a state of eruption". The lack of a significant ash layer associated with this event indicates that it was a small eruption. This was the first reported volcanic activity since 1854.

White settlement and use of the area

19th-century photo of a fur trapper working in the Mount St. Helens area.

The area's first non-Native American inhabitants were the fur traders and trappers. Most of these men worked for the fur trading enterprise of the British-owned Hudson's Bay Company. In the early 1890s, Ole' Peterson set up housekeeping at Cougar Flats, on the Upper Lewis River. He was a true hermit—preferring to keep to himself, and enjoying the quiet solitude of nature.

Also in the early 1890s, a 156 square mile mining district north of Spirit Lake was established. By 1911, over 400 mining claims had been filed. However, the minerals were never found in profitable quantities, and though much effort was spent in attempting to build a road or railroad into the district, by 1911, it was clear that there were no veins of precious minerals rich enough to offset the high transportation costs.

The 1980 Eruption

Ash from the eruption disrupted life for millions of people. Fifty-seven people died, and the economic cost was US$1 billion.

St. Helens catastrophically erupted on Sunday, May 18, 1980. Prior to the eruption, there were months of activity and build up.

File:Sthelens3.jpg

Mount St. Helens erupted on May 18, 1980, at 08:32 a.m. Pacific Daylight Time.

On March 20, 1980, Mount St. Helens experienced a 4.2 magnitude earthquake. Steam venting started on March 27. By the end of April, the north side of the mountain started to bulge. With little warning, a second earthquake of magnitude 5.1 on May 18, triggered a massive collapse of the north face of the mountain. The scale of the blast is considered minor when compared with past debris avalanches elsewhere on Earth; however, it created the largest landslide in recorded history. 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 3.9 million cubic yards (3.0 million m³) of material was transported 17 miles (27 km) south into the Columbia River by the mudflows.

The newly-exposed hot and pressurized rock in the volcano responded by producing the largest historic volcanic eruption in the 48 contiguous U.S. states. (See the Geology section for more detail.) The magma inside of St. Helens burst forth into a large-scale pyroclastic flow that flattened vegetation and buildings over 230 square miles (600 km²). On the Volcanic Explosivity Index scale, the eruption was rated a five (a Plinian eruption).

For more than nine hours, a vigorous plume of volcanic ash erupted, eventually reaching 12 to 16 miles (20 to 27 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (95 km/h), with ash reaching Idaho by noon.

By about 5:30 p.m. on May 18, the vertical ash column declined in stature, and less severe outbursts continued through the night and for the next several days. In all, St. Helens released energy equivalent to 350 megatons of TNT; or 27,000 Atomic bombings of Hiroshima and Nagasaki.; This was seven times more than Tsar Bomba, the strongest atomic bomb ever built and tested, which ejected more than 0.67 cubic miles (2.8 cubic 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 a crater one to two miles (1.6 to 3.2 km) wide and 0.5 mile (800 m) deep, with its north end open in a huge breach.

Human impact

The eruption killed 57 people, nearly 7,000 big game animals including deer, elk , and bear, and an estimated 12 million fish from a hatchery.

File:Mt st helens dome growth schematic 80-86.gif

Lava dome growth profile from 1980-1986.

It destroyed or extensively damaged over 200 homes, 185 miles (300 km) of highway and 15 miles of railways.

During the lead-up to the 1980 eruption of Mount St. Helens, 84-year-old Harry Truman, who had lived near the mountain for about 54 years, became nationally famous when he decided not to evacuate before the impending eruption, despite repeated pleas by local authorities. His body was never found after the eruption. Among the victims of the 1980 eruption was the 30-year-old vulcanologist David A. Johnston, who was stationed on the nearby Coldwater Ridge. Johnston, moments before his position was hit by the hot ash cloud, uttered his famous last words: "Vancouver! Vancouver! This is it!" Johnston's body was never found.

David A. Johnston hours before he was killed by the eruption.

U.S. President Jimmy Carter surveyed the damage and said "Someone said this area looked like a moonscape. But the moon looks more like a golf course compared to what's up there." A film crew, led by Seattle filmmaker Otto Seiber, was dropped by helicopter on St. Helens on May 23 to document the destruction. Their compasses, however, spun in circles and they quickly became lost. A second eruption occurred on May 25, but the crew survived and were rescued two days later by National Guard helicopter pilots. Their film, The Eruption of Mount St. Helens, later became a popular documentary.

Protection and later history

A steam plume rises from the mountain in December 2004.

In 1982, President Ronald Reagan and the U.S. Congress established the Mount St. Helens National Volcanic Monument, a 110,000-acre (445-km²) area around the mountain and within the Gifford Pinchot National Forest.

Following the 1980 eruption, the area was left to gradually return to its natural state preceding the devastation. In 1987, the National Forest Service reopened the mountain to climbing. It remained open until 2004 when renewed activity caused the closure of the area around the mountain (see Geology section for more detail).

Most notable was the closure of the Monitor Ridge trail, which previously let up to 100 permitted hikers per day summit the volcano. However, on July 21, 2006, the mountain was again opened to climbers.

2004 to present activity

Appearance of the "Whaleback" in February 2005.

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. A number of transient features were observed, such as the "whaleback", which comprised long shafts of solidified magma being exuded by the pressure of magma underneath it. These features are very fragile and break down soon after they are 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. (see USGS before and after images)

Mount St. Helens showed significant activity on March 8, 2005, when 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 grow from the dome is called the "fin" or "slab". Approximately half the size of a football field, the large, cooled volcanic rock was being forced upward as quickly as 6 feet (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 (2,301 m), still below the height reached in July 2005 when the whaleback collapsed.

On October 22, 2006, at 3:13 p.m. PST, there was a magnitude 3.5 earthquake that broke loose a portion of the mountain named Spine 7. There was a collapse and an avalanche of the lava dome. This sent an ash plume 2,000 feet 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 to some media assuming that there had been a small eruption. However, the Cascades Volcano Observatory of the USGS does not mention any significant ash plume. The volcano has been in continuous eruption since October 2004 but this eruption has in large part consisted of a gradual extrusion of lava forming a dome in the crater.

Tulutson Glacier and other new rock glaciers

During the winter of 1980-1981, a glacier, formally named Tulutson Glacier (although the USGS still calls it informally Crater Glacier), began to grow very rapidly (14 m/year thickness) in the shadow of the crater. It is formed from the annual winter snowfall. By 2004, it covered about 0.36 square mile (0.93 km²) and there was a western and eastern lobe flowing around the 1980's dome. The glacier looks dark and dirty in appearance in summer due to the numerous rockfalls on the steep, unstable crater walls and ash from eruptions. The ice is very thick, with an average thickness of 100 meters and a maximum thickness of around 200 meters, nearly as deep as Rainier's Carbon Glacier. None of the ice is older than the year 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. With the recent volcanic activity starting in 2004, the glacier lobes were pushed aside and higher by the growth of new volcanic domes. The surface of the glacier, once mostly uncrevassed, turned into a chaotic jumble of icefalls heavily criss-crossed with crevasses and seracs due to movement of the crater floor. The appearance of the glacier changes rapidly due to constant uplift of the crater and heavy snowfall. The new domes have almost separated the Tulutson Glacier into an eastern and western lobe. Despite the ongoing volcanic activity, the termini of the glacier have still advanced, with a slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe. Since 2004, new glaciers have formed on the crater wall above Tulutson Glacier feeding rock and ice to the Tulutson Glacier below. In addition, there are two rock glaciers to the north of the eastern lobe of Tulutson Glacier including several patches of permanent snow. These rapidly forming glaciers play a part in the build up of pressure and debris, adding to the instabliliy within the crater.

Sources and Further Reading

View of the hillside at the Johnston Ridge Observatory, 25 years after the eruption.

• Harris, Stephen L, Fire mountains of the west : the Cascade and Mono Lake volcanoes, Montana, Mountain Press Publisher Corporation, 1988, ISBN 087842220X
• Pringle, Patrick T, Roadside Geology of Mount St. Helens National Volcanic Monument and Vicinity, Washington, Washington State Department of Natural Resources, 1993, OCLC 28399127
• Satterfield, Archie , Country roads of Washington, Nebraska, IUniverse Inc., 1989, ISBN 0595268633

External links

Wikimedia Commons has media related to:

Mount St. Helens

• Mount St. Helens Washington, United States Geological Survey, Accessed March 19, 2007
• Mount St. Helens, Washington Eruptive History, United States Geological Survey, Accessed March 19, 2007
• [http://pubs.usgs.gov/fs/2000/fs036-00/ Mount St. Helens –

From the 1980 Eruption to 2000 ], United States Geological Survey, Accessed March 19, 2007

• Mount St. Helens, Washington Crater, Dome, and Eruption Images, United States Geological Survey, Accessed March 19, 2007
• [http://vulcan.wr.usgs.gov/Volcanoes/MSH/description_msh.htmlDESCRIPTION:

Mount St. Helens Volcano, Washington], United States Geological Survey, Accessed March 19, 2007

• Eruptive History of Mount St. Helens], United States Geological Survey, Accessed March 19, 2007
• Mount St. Helens Eruptive History, United States Geological Survey, Accessed March 19, 2007
• Mount St. Helens, Darryl Luscombe, Accessed March 19, 2007
• Mount St. Helens Post-Eruption Chemistry Database, University of Washington Libraries, Accessed March 19, 2007
• Mount St. Helens Succession Collection, University of Washington Libraries, Accessed March 19, 2007

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

• Mount Saint Helens  ^history

The history of this article since it was imported to New World Encyclopedia:

• History of "Mount Saint Helens"

Note: Some restrictions may apply to use of individual images which are separately licensed.