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Mount St. Helens

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                              Mount St. Helens
   3,000 ft (1 km) steam plume on May 19, 1982
   Elevation     8,364 ft (2,550 m)
   Location      Washington, USA
   Range         Cascades
   Coordinates   46°11′28″N, 122°11′39″W
   Topo map      USGS Mount St. Helens
   Type          Active stratovolcano, otherwise known as composite volcano
   Age of rock   < 40,000 yrs
   Last eruption 2004-2006 (ongoing)
   First ascent  1853 by Thomas J. Dryer
   Easiest 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 and 53 miles
   (85 km) northeast of Portland, Oregon. The mountain, part of the
   Cascade Range, takes its English name from the British diplomat Lord St
   Helens, who was a friend of George Vancouver, an explorer who made a
   survey of the area in the late 18th century. Mount St. Helens is a part
   of the Pacific Ring of Fire that includes over 160 active volcanoes.
   This volcano is well known for its ash explosions and pyroclastic
   flows.

   Mount St. Helens is most famous for its catastrophic eruption on May
   18, 1980 at 08:32 Pacific Standard Time. The eruption was the most
   deadly and 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.) Fifty-seven people were
   killed; 250 homes, 47 bridges, 15 miles (24 km) of railways and 185
   miles (300 km) of highway were destroyed. The eruption caused a massive
   debris avalanche, reducing the elevation of the mountain's summit from
   9,677 feet (2,950 m) to 8,364 feet (2,550 m), and replacing it with a
   mile-wide (1.5 km-wide) horseshoe-shaped crater. The debris avalanche
   was up to 0.7 cubic miles (2.3 km³) in volume, making it the largest in
   recorded history. However, the scale of the blast pales in comparison
   with debris avalanches that have occurred in the geological past
   elsewhere on Earth.

   Like most other volcanoes in the Cascade Range, Mount St. Helens is a
   great cone of rubble consisting of lava rock interlayered with ash,
   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; another formed
   Goat Rocks dome on the northern flank. These were destroyed in the
   eruption of 1980.
   Mount St. Helens the day before the 1980 eruption, which removed much
   of the top of the mountain, leaving a large crater.
   Enlarge
   Mount St. Helens the day before the 1980 eruption, which removed much
   of the top of the mountain, leaving a large crater.
   The view in 2002 from Climbers Biviouc
   Enlarge
   The view in 2002 from Climbers Biviouc

Geographic setting and description

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

   Mount St. Helens is geologically young compared to the other major
   Cascade volcanoes. It was formed only within the last 40,000 years, and
   the pre-1980 summit cone started to grow only about 2,200 years ago.
   The volcano has also been the most active in the Cascades during the
   Holocene (the last 10,000 or so years).
   A view of St. Helens and the nearby area from space.
   Enlarge
   A view of St. Helens and the nearby area from space.

   Even before its loss of height, Mount St. Helens was not one of the
   highest peaks in the Cascade Range; its summit altitude made it only
   the fifth-highest peak in Washington. It stood out prominently,
   however, from surrounding hills because of the symmetry and extensive
   snow- and ice-cover of the pre-1980 summit cone, earning it the
   nickname, "Fujiyama 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 about 6 miles
   (9.5 km) across at its base, which is at an altitude of about
   4,400 feet (1,340 m) on the northeastern side and about 4,000 feet
   (1,220 m) elsewhere. At the pre-eruption tree-line the width of the
   cone was about 4 miles (6.4 km).

   Streams that 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 on
   the west. Washington State Route 504, locally known as the Spirit Lake
   Memorial Highway, connects with the heavily traveled Interstate 5 at
   Exit 49, about 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 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 about 11 miles (18 km)
   south-southwest of the peak. Gifford Pinchot National Forest surrounds
   Mount St. Helens.

Human history

Importance to Native Americans

   Traces of ancient campsites have been found in the Gifford Pinchot
   National Forest that surrounds the monument. These show 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. This caused the people to abandon their
   mountain territory for nearly 2000 years. In more recent times, Native
   Americans of the Cowlitz, Taidnapam, Klickitat, Upper Chinook, and
   Yakama tribes moved over the land in a seasonal pattern. They harvested
   huckleberries, salmon, elk, and deer.
   The symmetrical and aesthetic shape of the volcano inspired legends.
   Enlarge
   The symmetrical and aesthetic shape of the volcano inspired legends.

   Native American lore contain numerous legends to explain the eruptions
   of Mount St. Helens and other Cascade volcanoes. Perhaps 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 Wiyest, traveled
   down the Columbia River from the Far North in search for a suitable
   area to settle.

   They came upon an area that the white men now call The Dalles and
   thought they had never seen a land so beautiful. The sons quarreled
   over the land and 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 Wyest did the
   same for the arrow to the south. Saghalie then built Tanmahawis, the
   Bridge of the Gods, so his family could meet periodically.

   When two sons of the Saghalie 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 the huge bridge
   fell into the river, creating the cascades of the Columbia River Gorge.

   For punishment, Sahale struck down each of the lovers and transformed
   them into great mountains where they fell. Wyeast, 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).

Exploration by Whites

   Royal Navy Commander George Vancouver and the officers of HMS Discovery
   made the Europeans' first recorded sighting of Mount St. Helens, on May
   19, 1792, while they were 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 spent a great deal of time in prayer and dance instead of
   collecting food, and therefore suffered a hard winter.

   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 an
   ongoing eruption, or recent evidence of one. They did report the
   presence of quicksand and clogged channel conditions at the mouth of
   the Sandy River near Portland, suggesting an eruption by Mount Hood
   sometime in the previous decades.

White settlement and use of the area

   19th century photo of a fur trapper working in the Mount St. Helens
   area.
   Enlarge
   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 quantities large
   enough to be profitable. Much effort was spent in attempting to get a
   road or railroad built into the district. None ever came. By 1911, it
   was clear that there were no veins of precious minerals rich enough to
   offset the high transportation costs.
   James Dwight Dana was among the first geologists to view the volcano.
   Enlarge
   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 witness66 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 ( 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.
   Enlarge
   Mount St. Helens erupting at night. Painting by Paul Kane after his
   1847 visit to the area.

   In October 1843, future California governor Peter H. Burnett recounted
   a story of a Native American man who badly burned his foot and leg in
   lava or hot ash while hunting for deer. The likely apocryphal story
   went that the injured man sought treatment at Fort Vancouver but the
   contemporary fort commissary steward, Napolean McGilvery, disclaimed
   knowledge of the incident. 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.
   Boats in Spirit Lake sometime before the 1980 eruption.
   Enlarge
   Boats in Spirit Lake sometime before the 1980 eruption.

   Before the 1980 eruption, Spirit Lake offered year-round recreational
   activities. In the summer there was boating, swimming, and camping,
   while in the winter there was skiing.

Human impact from 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.
   Enlarge
   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 May 18, 1980. After many months
   of lead-up activity which included the growth of a huge bulge on the
   north part of the mountain, a moderate earthquake caused the entire
   north flank of the mountain to slide away in the largest landslide in
   recorded history. 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.)

   During the lead-up to the 1980 eruption of Mount St. Helens,
   84-year-old innkeeper 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, which left a
   huge crater open to the north. Fifty-seven people were killed or never
   found. Had the eruption occurred one day later, when loggers would have
   been at work, rather than on a Sunday, the death toll would almost
   certainly have been much higher.
   David A. Johnston hours before he was killed by the eruption.
   Enlarge
   David A. Johnston hours before he was killed by 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.

   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. A second eruption occurred on May 25,
   but the crew survived and was rescued two days later by National Guard
   helicopter pilots. Their film, St Helens, was released in 1981.

Protection and later history

   A steam plume rises from the mountain in December 2004.
   Enlarge
   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.

   Renewed activity started in 2004, causing the closure of parts of the
   monument to hikers and tourists. 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.

Geologic history

Ancestral stages of eruptive activity

   Plate tectonics of the Cascade Range.
   Enlarge
   Plate tectonics of the Cascade Range.

   The early eruptive stages of Mount St. Helens are known as the "Ape
   Canyon Stage" (around 40–35,000 years ago), the "Cougar Stage" (ca.
   20–18,000 years ago), and the "Swift Creek Stage" (roughly 13–8,000
   years ago). The modern period, since about 2500 BC, 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 the Pleistocene 37,600 years ago,
   during the Ape Canyon stage, with dacite and andesite eruptions of hot
   pumice and ash. 36,000 years ago a large mudflow cascaded down the
   volcano; mudflows were very 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
   to 18,000 years ago during the last glacial period of the current ice
   age.

   The second eruptive period, the Cougar Stage, started 20,000 years ago
   and lasted for about 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 the countryside with tephra. Swift Creek ended 8,000
   years ago.

Smith Creek and Pine Creek eruptive periods

   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, judged by the volume of one of the
   tephra layers from that period. This eruptive period lasted until about
   1600 BC and left 18-inch (46-cm)-deep deposits of material 50 miles (80
   km) distant in what is now Mt. 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 km³) 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 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 (65 km) of the Lewis River
   valley sometime between 1000 BC and 500 BC.

Castle Creek and Sugar Bowl eruptive periods

   The next eruptive period, the Castle Creek period, began about 400 BC,
   and is characterized by a change in 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 the year 100 AD 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 (15 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 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.

Kalama and Goat Rocks eruptive periods

   The symmetrical appearance of St. Helens prior to the 1980 eruption
   earned it the nickname "Mount Fuji of America". The once-familiar shape
   was formed out of the Kalama and Goat Rocks eruptive periods.
   Enlarge
   The symmetrical appearance of St. Helens prior to the 1980 eruption
   earned it the nickname " Mount Fuji of America". The once-familiar
   shape was formed out of the Kalama and Goat Rocks eruptive periods.

   Roughly 700 years of dormancy were broken about 1480, when large
   amounts of pale gray dacite pumice and ash started to erupt, beginning
   the Kalama period. The eruption in 1480 was several times larger than
   the May 18, 1980 eruption. In 1482, another large eruption rivaling the
   1980 eruption in volume is known to have occurred. Ash and pumice piled
   six miles (9.5 km) northeast of the volcano to a thickness of three
   feet (1 m); 50 miles (80 km) away, the ash was two 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
   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 high at the volcano's summit, which filled and overtopped
   an explosion crater already at 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, about 1647. 150 years
   of quiet returned to the volcano.

   The 57-year Goat Rocks eruptive period started in 1800, and is the
   first time that both oral and written records exist. Like 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 rivalled the
   1980 eruption in size, although it did not result in massive
   destruction of 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 vent was apparently at or
   near Goat Rocks on the northeast flank.

Modern eruptive period

1980 to 2001 activity

   Mount St. Helens erupted on May 18, 1980, at 08:32 a.m. Pacific
   Daylight Time.
   Enlarge
   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 magnitude 5.1
   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 the same magnitude on May 18 triggered a massive
   collapse of the north face of the mountain. It was the largest known
   debris avalanche in recorded history. 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).

   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.

   For more than nine hours, a vigorous plume of 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 dynamite; or 27,000 atomic blasts over Hiroshima; or
   seven times more than the strongest atomic bomb ever built and tested,
   the Tsar Bomba. It 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. 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 over 200
   homes, 185 miles (300 km) of highway and 15 miles of railways.
   Lava dome growth profile from 1980-1986.
   Enlarge
   Lava dome growth profile from 1980-1986.

   Between 1980 and 1986, activity continued at Mount St. Helens, with a
   new lava dome forming in the crater. Numerous small explosions and
   dome-building eruptions occurred. With the winter snow of 1980-1981, a
   still-unnamed horse-shoe-shaped glacier began to evolve in the shadow
   of the crater. As of 2004, it covered about 0.36 square mile (0.93
   km²). Until 2004's volcanic activity, it was considered the only
   growing glacier in the lower 48 United States. From December 7, 1989 to
   January 6, 1990, and from November 5, 1990 to February 14, 1991, the
   mountain erupted with sometimes huge clouds of ash.

2004 to present activity

   Mount St. Helens became active again in the autumn of 2004, indicated
   initially by hundreds and then thousands of localized earthquakes, and
   followed by several significant emissions of steam and ash.
   Appearance of the "Whaleback" in February 2005.
   Enlarge
   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 Spine 7. There was a collapse and avalanche
   of the lava dome that sent an ash plume 2,000 feet over the western rim
   of the crater; the ash plume then rapidly dissipated.
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