Вулкан Сент-Хеленс: История и современное состояние

Volcano in Washington, U. S.
the volcano in Washington state

Mount St. Helens (known as Lawetlat'la to the indigenous Cowlitz people, and Loowit or Louwala Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, and south of Seattle. Mount St. Helens takes its English name from that of the British diplomat Alleyne Fitzherbert, 1st Baron St Helens, a friend of explorer George Vancouver who surveyed the area in the late 18th century. Fifty seven people were killed; 200 homes, 47 bridges, 15 mile (24 km) of railways, and 185 mile (298 km) of highway were destroyed. A massive debris avalanche, triggered by a magnitude 5.1 earthquake, caused a lateral eruption The debris avalanche was in volume. The 1980 eruption disrupted terrestrial ecosystems near the volcano. By contrast, aquatic ecosystems in 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 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 mile (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 mile (80 km) from Mount Rainier, the highest of the Cascade volcanoes. Mount Hood, the nearest major volcanic peak in Oregon, is 60 mile (97 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 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 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 5000 feet (1524 m) above its base, where the lower flanks merge with adjacent ridges. The mountain is 6 mile (10 km) across at its base, which is at an elevation of 4400 feet (1341 m) on the northeastern side and 4000 feet (1219 m) elsewhere. At the pre eruption tree line, the width of the cone was 4 mile (6 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 is , and the snowpack on the mountain's upper slopes can reach 16 feet (5 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 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 mile (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 the Vancouver, Washington–Portland, Oregon metropolitan area less than 50 mile (80 km) to the southwest. The community nearest the volcano is Cougar, Washington, in the Lewis River valley 11 mile (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 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 m) per year in thickness). By 2004, it covered about 0.36 square miles (1 km2), 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, the ice had an average thickness of 300 feet (91 m) and a maximum of 650 feet (198 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 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 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 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; 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 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 below the surface, the other about 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, 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). This eruptive period lasted until about 1600 BC and left deep deposits of material 50 mile (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. 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 the 1980 eruption in volume is known to have occurred.) The vent was apparently at or near Goat Rocks on the northeast flank. By 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 (596 km2). More than 1.5 million metric tons of sulfur dioxide were released into 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 of material was transported 17 mile (27 km) south into the Columbia River by the mudflows. The plume moved eastward at an average speed of 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, 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 of material. The removal of the north side of the mountain reduced St. Helens' height by about 1300 feet (396 m) and left a crater 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.

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 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 a 36000 feet (10973 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 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 7550 feet (2301 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 the lava dome sent an ash plume 2000 feet (610 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 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 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.

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 of precipitation falls each year at Spirit Lake. This precipitation supported dense forest up to , with western hemlock, Douglas fir, and western redcedar. Above this, this forest was dominated by Pacific silver fir up to Finally, below treeline, the forest consisted of mountain hemlock, Pacific silver fir and Alaska yellow cedar.

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 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 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, Eventually, each of 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,

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 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 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. 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 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 of 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. 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).

The first authenticated non Indigenous eyewitness report of a volcanic eruption was made in March 1835 by Meredith Gairdner, while working for the Hudson's Bay Company stationed at Fort Vancouver. In the late fall or early winter of 1842, nearby European settlers and missionaries witnessed the so called Great Eruption. This small volume outburst created large ash clouds, and mild explosions followed for 15 years. Had the eruption occurred one day later, when loggers would have been at work, rather than on a Sunday, the death toll could have been much higher. Eighty three year old Harry R. Truman, who ran the Spirit Lake Lodge and had lived near the mountain since 1929, gained much media attention when he decided not to evacuate before the impending eruption, despite repeated pleas by local authorities. His body was never found after the eruption. Another victim of the eruption was 30 year old volcanologist David A. Johnston, who was stationed on the nearby Coldwater Ridge. Moments before his position was hit by the pyroclastic flow, Johnston radioed his 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. Their compasses, however, spun in circles and they quickly became lost. A second eruption occurred on May 25, but the crew survived and was rescued two days later by National Guard helicopter pilots. Their film, The Eruption of Mount St. Helens!, later became a popular documentary. The eruption had negative effects beyond the immediate area of the volcano. Ashfall caused approximately $100 million of damage to agriculture downwind in Eastern Washington, equivalent to $ in
The eruption also had positive impacts on society. Apple and wheat production were higher in the 1980 growing season, possibly due to ash helping to retain moisture in the soil. The ash was also a source of income: it was the raw material for the artificial gemstone helenite, or for ceramic glazes, or sold as a tourist curio.

In 1982, President Ronald Reagan and the U. S. Congress established the Mount St. Helens National Volcanic Monument, a 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. In 1987, the U. S. 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 Geological history section above for more details). The Monitor Ridge trail, which previously let up to 100 permitted hikers per day climb to the summit, ceased operation. On July 21, 2006, the mountain was again opened to climbers. In February 2010, a climber died after falling from the rim into the crater. On May 14, 2023, a mudslide and debris flow given the moniker, South Coldwater Slide by the U. S. Forest Service, destroyed the 85 feet (26 m) Spirit Lake Outlet Bridge on Washington State Route 504 and cut off access to the Johnston Ridge Observatory. Closures and access to Coldwater Lake and hiking trails would vary in the month after the slide.

Mount St. Helens is a common climbing destination for both beginning and experienced mountaineers. The peak is climbed year round, although it is more often climbed from late spring through early fall. All routes include sections of steep, rugged terrain. A permit system has been in place for climbers since 1987. A climbing permit is required year round for anyone who will be above 4800 feet (1463 m) on the slopes of Mount St. Helens. The standard hiking/mountaineering route in the warmer months is the Monitor Ridge Route, which starts at the Climbers Bivouac. This is the most crowded route to the summit in the summer and gains about 4600 feet (1402 m) in approximately 5 mile (8 km) to reach the crater rim. Although strenuous, it is considered a non technical climb that involves some scrambling. Most climbers complete the round trip in 7 to 12 hours. The Worm Flows Route is considered the standard winter route on Mount St. Helens, as it is the most direct route to the summit. The route gains about 5700 feet (1737 m) in elevation over about 6 mile (10 km) from trailhead to summit but does not demand the technical climbing that some other Cascade peaks like Mount Rainier do. The route name refers to the rocky lava flows that surround the route. This route can be accessed via the Marble Mountain Sno Park and the Swift Ski Trail. The mountain is now circled by the Loowit Trail at elevations of The northern segment of the trail from the South Fork Toutle River on the west to Windy Pass on the east is a restricted zone where camping, biking, pets, fires, and off trail excursions are all prohibited. On April 14, 2008, John Slemp, a snowmobiler from Damascus, Oregon, fell 1,500 feet into the crater after a snow cornice gave way beneath him on a trip to the volcano with his son. Despite his long fall, Slemp survived with minor injuries, and was able to walk after coming to a stop at the foot of the crater wall, where he was rescued by a mountain rescue helicopter. A visitor center run by the Washington State Parks is in Silver Lake, Washington, about 30 mile (48 km) west of Mount St. Helens. Exhibits include a large model of the volcano, a seismograph, a theater program, and an outdoor natural trail.