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141-432: Kamaʻehuakanaloa began forming around 400,000 years ago and is expected to begin emerging above sea level about 10,000–100,000 years from now. At its summit, Kamaʻehuakanaloa Seamount stands more than 10,000 ft (3,000 m) above the seafloor, making it taller than Mount St. Helens was before its catastrophic 1980 eruption . A diverse microbial community resides around Kamaʻehuakanaloa many hydrothermal vents . In

282-503: A US Geological Survey research ship collected dredge samples and photographed Kamaʻehuakanaloa's summit with the goal of studying whether Kamaʻehuakanaloa is active. Analysis of the photos and testing of pillow lava rock samples appeared to show that the material was "fresh", yielding more evidence that Kamaʻehuakanaloa is still active. An expedition from October 1980 to January 1981 collected further dredge samples and photographs, providing additional confirmation. Studies indicated that

423-418: A lava spine nicknamed the "whaleback", which comprised long shafts of solidified magma being extruded by the pressure of magma beneath. These features were fragile and broke down soon after they were formed. On July 2, 2005, the tip of the whaleback broke off, causing a rockfall that sent ash and dust several hundred meters into the air. Mount St. Helens showed significant activity on March 8, 2005, when

564-407: A magnitude  5.1 earthquake, caused a lateral eruption that reduced the elevation of the mountain's summit from 9,677 to 8,363 ft (2,950 to 2,549 m), leaving a 1 mile (1.6 km) wide horseshoe-shaped crater. The debris avalanche was 0.6 cubic miles (2.5 km ) in volume. The 1980 eruption disrupted terrestrial ecosystems near the volcano. By contrast, aquatic ecosystems in

705-400: A 36,000-foot (11,000 m) plume of steam and ash emerged—visible from Seattle . This relatively minor eruption was a release of pressure consistent with ongoing dome building. The release was accompanied by a magnitude 2.5 earthquake. Another feature to emerge from the dome was called the "fin" or "slab". Approximately half the size of a football field, the large, cooled volcanic rock

846-460: A break, separating the older Emperor Seamount Chain from the younger Hawaiian Ridge; the V-shaped bend of the chain is easily noticeable on maps. The volcanoes are progressively younger to the southeast; the oldest dated volcano, located at the northern end, is 81 million years old. The break between the two subchains is 43 million years; in comparison, the oldest of the principal islands, Kauaʻi ,

987-403: A combination of pāhoehoe and ʻaʻā. It is during this stage, that the low-profile " shield " shape of Hawaiian volcanoes is formed, named for the shape of a warrior's shield. Eruption rates and frequencies peak, and about 95% of the volcano's eventual volume forms during a period of roughly 500,000 years. The lava erupted in this stage form flows of pāhoehoe or ʻaʻā. During this subaerial stage,

1128-516: A coral-capped seamount. These flat-topped seamounts are called guyots . Most, if not all, of the volcanoes west of Kure Atoll, as well as most, if not all, of the volcanoes in the Emperor Seamount chain, are guyots or seamounts . Eventually the guyot will be taken to a subduction plate were it will be destroyed like Meiji Seamount in a few million years. Not all Hawaiian volcanoes go through all of these stages of activity. An example

1269-496: A crater 1.2 to 1.8 miles (2 to 3 km) wide and 2,084 feet (635 m) deep, with its north end open in a huge breach. The eruption killed 57 people, nearly 7,000 big-game animals ( deer , elk , and bear ), and an estimated 12 million fish from a hatchery. It destroyed or extensively damaged more than 200 homes, 185 miles (298 km) of highway , and 15 miles (24 km) of railways . Between 1980 and 1986, activity continued at Mount St. Helens, with

1410-461: A few meters or feet at a time to form a broad and gently sloping shape. Hawaiian islands undergo a systematic pattern of submarine and subaerial growth that is followed by erosion. An island's stage of development reflects its distance from the Hawaii hotspot . The Hawaiian–Emperor seamount chain is remarkable for its length and its number of volcanoes. The chain is split into two subsections across

1551-661: A friend of explorer George Vancouver who surveyed the area in the late 18th century. The volcano is part of the Cascade Volcanic Arc , a segment of the Pacific Ring of Fire . The Mount St. Helens major eruption of May 18, 1980 , remains the deadliest and most economically destructive volcanic event in U.S. history. Fifty-seven people were killed; 200 homes, 47 bridges, 15 miles (24 km) of railways, and 185 miles (298 km) of highway were destroyed. A massive debris avalanche , triggered by

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1692-407: A gradual extrusion of lava forming a dome in the crater. On January 16, 2008, steam began seeping from a fracture on top of the lava dome. Associated seismic activity was the most noteworthy since 2004. Scientists suspended activities in the crater and the mountain flanks, but the risk of a major eruption was deemed low. By the end of January, the eruption paused; no more lava was being extruded from

1833-460: A large discharge of hydrothermal material. The presence of certain indicator minerals in the mixture suggested temperatures exceeded 250 °C (482 °F), a record for an underwater volcano. The composition of the materials was similar to that of black smokers , the hydrothermal vent plumes located along mid-ocean ridges . Samples from mounds built by discharges from the hydrothermal plumes resembled white smokers . The studies demonstrated that

1974-421: A lower level of activity, producing an alkali basalt lava. Continued volcanism is expected to eventually give birth to an island at Kamaʻehuakanaloa. It experiences frequent landslides ; the growth of the volcano has destabilized its slopes, and extensive areas of debris inhabit the steep southeastern face. Similar deposits from other Hawaiian volcanoes indicate that landslide debris is an important product of

2115-473: A magnitude greater than 3.0, including more than 40 greater than 4.0 and a 5.0 tremor. The final two weeks of the earthquake swarm were observed by a rapid response cruise launched in August 1996. The National Science Foundation funded an expedition by University of Hawaiʻi scientists, led by Frederick Duennebier, that began investigating the swarm and its origin in August 1996. The scientists' assessment laid

2256-509: A new lava dome forming in the crater. Numerous small explosions and dome-building eruptions occurred. From December 7, 1989, to January 6, 1990, and from November 5, 1990, to February 14, 1991, the mountain erupted, sometimes huge clouds of ash. Magma reached the surface of the volcano about October 11, 2004, resulting in the building of a new lava dome on the existing dome's south side. This new dome continued to grow throughout 2005 and into 2006. Several transient features were observed, such as

2397-621: A north–south trend. Rather, most of the earthquakes occur in the southwest portion of Kamaʻehuakanaloa. The largest recorded swarms took place on Kamaʻehuakanaloa in 1971, 1972, 1975, 1991–92 and 1996. The nearest seismic station is around 20 mi (30 km) from Kamaʻehuakanaloa, on the south coast of Hawaii. Seismic events that have a magnitude under 2 are recorded often, but their location cannot be determined as precisely as it can for larger events. In fact, HUGO (Hawaii Undersea Geological Observatory), positioned on Kamaʻehuakanaloa's flank, detected ten times as many earthquakes as were recorded by

2538-465: A period of about 250,000 years, eventually stopping altogether as the volcano becomes dormant . Mauna Kea , Hualālai , and Haleakalā volcanoes are in this stage of activity. After the volcano becomes dormant, the forces of erosion gain control of the mountain. The volcano subsides into the oceanic crust due to its immense weight and loses elevation. Meanwhile, rain also erodes the volcano, creating deeply incised valleys. Coral reefs grow along

2679-460: 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

2820-402: A slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe. Due to the advance, two lobes of the glacier joined in late May 2008 and thus the glacier completely surrounds the lava domes. In addition, since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice onto its surface below; there are two rock glaciers to

2961-576: A small hypersthene-homblende dacite dome on the east slope of the volcano, was likely formed around the Sugar Bowl period. Formation of East Dome was preceded by an explosive eruption. Roughly 700 years of dormancy were broken in about 1480, when large amounts of pale gray dacite pumice and ash started to erupt, beginning the Kalama period. The 1480 eruption was several times larger than that of May 18, 1980. In 1482, another large eruption rivaling

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3102-489: A volcano is created near the Hawaiian hotspot, it begins its growth in the submarine preshield stage, characterized by infrequent, typically low volume eruptions. The volcano is steep-sided, and it usually has a defined caldera and has two or more rift zones radiating from the summit. The type of lava erupted in this stage of activity is alkali basalt . Due to stretching forces, the development of two or more rift zones

3243-399: A year, Kamaʻehuakanaloa was 25 mi (40 km) southeast of its current position at the time of its initial eruption. Kamaʻehuakanaloa is a young and fairly active volcano, although less active than nearby Kīlauea . In the past few decades, several earthquake swarms have been attributed to Kamaʻehuakanaloa, the largest of which are summarized in the table below. The volcano's activity

3384-557: Is 140 inches (360 cm), and the snowpack on the mountain's upper slopes can reach 16 feet (4.9 m). The Lewis River is impounded by three dams for hydroelectric power generation. The southern and eastern sides of the volcano drain into an upstream impoundment, the Swift Reservoir , which is directly south of the volcano's peak. Although Mount St. Helens is in Skamania County, Washington, access routes to

3525-457: Is Koʻolau Range on Oʻahu , which was prehistorically devastated by a cataclysmic landslide , never underwent the postshield stage and went dormant for hundreds of thousands of years after the shield stage before coming back to life. Some volcanoes never made it above sea level; there is no evidence to suggest that West Molokai went through the rejuvenated stage, while its younger neighbors, East Molokai and West Maui , have evidently done so. It

3666-451: Is a seamount , or underwater volcano , on the flank of Mauna Loa , the Earth's tallest shield volcano . It is the newest volcano produced by the Hawaiʻi hotspot in the extensive Hawaiian–Emperor seamount chain . The distance between the summit of the older Mauna Loa and the summit of Kamaʻehuakanaloa is about 50 mi (80 km), which is, coincidentally, also the approximate diameter of

3807-540: Is a popular hiking spot and it is climbed year-round. In 1982, the Mount St. Helens National Volcanic Monument was established by President Ronald Reagan and the U.S. Congress . Mount St. Helens is 34 miles (55 km) west of Mount Adams , in the western part of the Cascade Range. Considered "brother and sister" mountains, the two volcanoes are approximately 50 miles (80 km) from Mount Rainier ,

3948-587: Is at an elevation of 4,400 feet (1,300 m) on the northeastern side and 4,000 feet (1,200 m) elsewhere. At the pre-eruption tree line , the width of the cone was 4 miles (6.4 km). Streams that originate on the volcano enter three main river systems: The Toutle River on the north and northwest, the Kalama River on the west, and the Lewis River on the south and east. The streams are fed by abundant rain and snow. The average annual rainfall

4089-418: Is called the "Spirit Lake Stage". Collectively, the pre–Spirit Lake stages are known as the "ancestral stages". The ancestral and modern stages differ primarily in the composition of the erupted lavas; ancestral lavas consisted of a characteristic mixture of dacite and andesite , while modern lava is very diverse (ranging from olivine basalt to andesite and dacite). St. Helens started its growth in

4230-487: Is characterized by a high concentration of CO 2 and iron , while being low in sulfide. These characteristics make a perfect environment for iron-oxidizing bacteria , called FeOB, to thrive in. In 1997, scientists from the University of Hawaiʻi installed an ocean bottom observatory on the summit of Kamaʻehuakanaloa Seamount. The submarine observatory was nicknamed HUGO (Hawaiʻi Undersea Geological Observatory). HUGO

4371-437: Is common. The lava accumulates in a shallow magma storage reservoir. Because the eruptions occur with the volcano underwater, the form of lava typically erupted is pillow lava . Pillow lava is rounded balls of lava that was given very little time to cool due to immediate exposure to water. Water pressure prevents the lava from exploding upon contact with the cold ocean water, forcing it to simmer and solidify quickly. This stage

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4512-611: 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

4653-739: Is likely on branches of the Toutle River , possibly causing destruction in inhabited areas along the I-5 corridor. In its undisturbed state, the slopes of Mount St. Helens lie in the Western Cascades Montane Highlands ecoregion. This ecoregion has abundant precipitation; an average of 93.4 inches (2,373 mm) of precipitation falls each year at Spirit Lake . This precipitation supported dense forest up to 5,200 feet (1,600 m), with western hemlock , Douglas fir , and western redcedar . Above this, this forest

4794-488: Is little more than 5 million years. The "assembly line" that forms the volcanoes is driven by a hotspot , a plume of magma deep within the Earth producing lava at the surface. As the Pacific Plate moves in a west-northwest direction, each volcano moves with it away from its place of origin above the hotspot. The age and location of the volcanoes are a record of the direction, rate of movement, and orientation of

4935-411: Is now known to predate scientific record keeping of its activity, which commenced in 1959. Most earthquake swarms at Kamaʻehuakanaloa have lasted less than two days; the two exceptions are the 1990-1991 earthquake, lasting several months, and the 1996 event, which was shorter but much more pronounced. The 1996 event was directly observed by an ocean bottom seismometer (OBS), allowing scientists to calculate

5076-596: Is still the primary factor controlling the volcano's development. After this stage the volcano becomes extinct and never erupts again. Eventually, erosion and subsidence break the volcano down to sea level. At this point, the volcano becomes an atoll, with a ring of coral and sand islands surrounding a lagoon . All the Hawaiian islands west of the Gardner Pinnacles in the Northwestern Hawaiian Islands are in this stage. Atolls are

5217-400: Is the breakup of Maui Nui , initially a seven-volcano island, which was transformed into five islands as a result of subsidence. High rainfall due to the trade wind effect impacts on the severity of erosion on many of the major volcanoes. Coastline collapses, a notable part of the history of many of the Hawaiian volcanoes, are often devastating and destroy large parts of the volcanoes. When

5358-411: Is thought to last about 200,000 years, but lavas erupted during this stage make up only a tiny fraction of the final volume of the volcano. As time progresses, eruptions become stronger and more frequent. The only example of a Hawaiian volcano in this stage is Kamaʻehuakanaloa Seamount (formerly Lōʻihi), which is thought to be transitioning from the submarine preshield stage into the submarine phase of

5499-539: 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

5640-548: The Hawaiian Volcano Observatory (HVO) seismic network. The largest amount of activity recorded for the Kamaʻehuakanaloa seamount was a swarm of 4,070 earthquakes between July 16 and August 9, 1996. This series of earthquakes was the largest recorded for any Hawaiian volcano to date in both amount and intensity. Most of the earthquakes had moment magnitudes of less than 3.0. "Several hundred" had

5781-659: The Pacific Plate . The pronounced 43-million-year-old break separating the Hawaiian Ridge from the Emperor Chain marks a dramatic change in direction of plate movement. Initial, deeper-water volcanic eruptions are characterized by pillow lava , so named for their shape, while shallow-water eruptions tend to be composed mainly of volcanic ash . Once the volcano is high enough so as to eliminate interference from water, its lava flows become those of ropey pāhoehoe and blocky ʻAʻā lava. Our current understanding of

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5922-635: The Pleistocene 37,600 years ago, during the Ape Canyon stage, with dacite and andesite eruptions of hot pumice and ash. Thirty-six thousand years ago a large mudflow cascaded down the volcano; mudflows were significant forces in all of St. Helens' eruptive cycles. The Ape Canyon eruptive period ended around 35,000 years ago and was followed by 17,000 years of relative quiet. Parts of this ancestral cone were fragmented and transported by glaciers 14,000–18,000 years ago during

6063-537: The Vancouver, Washington – Portland, Oregon metropolitan area less than 50 miles (80 km) to the southwest. The community nearest the volcano is Cougar , Washington, in the Lewis River valley 11 miles (18 km) south-southwest of the peak. Gifford Pinchot National Forest surrounds Mount St. Helens. During the winter of 1980–1981, a new glacier appeared. Now officially named Crater Glacier , it

6204-765: The Yn tephra . This eruptive period lasted until about 1600 BC and left 18 inches (46 cm) deep deposits of material 50 miles (80 km) distant in what is now Mount Rainier National Park . Trace deposits have been found as far northeast as Banff National Park in Alberta , and as far southeast as eastern Oregon . All told there may have been up to 2.5 cubic miles (10 km ) of material ejected in this cycle. Some 400 years of dormancy followed. St. Helens came alive again around 1200 BC—the Pine Creek eruptive period. This lasted until about 800 BC and

6345-411: The "shield" shape that shield volcanoes are named for. It is also the stage at which the volcano's eruptive frequency reaches its peak. As eruptions become more and more frequent at the end of the preshield stage, the composition of the lava erupted from the Hawaiian volcano changes from alkalic basalt to tholeiitic basalt and the volcano enters the submarine phase of the shield stage. In this phase,

6486-405: The 160 °C (320 °F) vents, and included a novel jelly -like organism. Samples were collected for study at NSF's Marine Bioproducts Engineering Center (MarBEC). In 2001, Pisces V collected samples of the organisms and brought them to the surface for study. NOAA's National Undersea Research Center and NSF's Marine Bioproducts Engineering Center are cooperating to sample and research

6627-499: The 1980 eruption in volume is known to have occurred. Ash and pumice piled 6 miles (9.7 km) northeast of the volcano to a thickness of 3 feet (0.9 m); 50 miles (80 km) away, the ash was 2 inches (5 cm) deep. Large pyroclastic flows and mudflows subsequently rushed down St. Helens' west flanks and into the Kalama River drainage system. This 150-year period next saw the eruption of less silica -rich lava in

6768-471: The 1980 eruption included eleven named glaciers: Wishbone, Loowit, Leschi, Forsyth, Nelson, Ape, Shoestring, Swift, Dryer, Toutle, and Talus. Of these eleven, only the Shoestring Glacier revived somewhat post-eruption. The peak rose more than 5,000 feet (1,500 m) above its base, where the lower flanks merge with adjacent ridges. The mountain is 6 miles (9.7 km) across at its base, which

6909-399: The 1996 event; no activity was recorded from 2002 to 2004. The seamount showed signs of unrest again in 2005 by generating an earthquake bigger than any previously recorded there. USGS-ANSS ( Advanced National Seismic System ) reported two earthquakes, magnitudes 5.1 and 5.4, on May 13 and July 17. Both originated from a depth of 27 mi (44 km). On April 23, a magnitude 4.3 earthquake

7050-504: The 1996 swarm and is monitored by the United States Geological Survey (USGS). The Hawaii Undersea Geological Observatory (HUGO) provided real-time data on Kamaʻehuakanaloa between 1997 and 1998. Kamaʻehuakanaloa's last known eruption was in 1996, before the earthquake swarm of that summer. The name Kamaʻehuakanaloa is a Hawaiian language word for "glowing child of Kanaloa ", the god of the ocean. This name

7191-647: The Fe-Oxidizing Microbial Observatory (FeMO), funded by the National Science Foundation and Microbial Observatory Program, has led cruises to Kamaʻehuakanaloa investigate its microbiology every October. The first cruise, on the ship R/V Melville and exploiting the submersible JASON2 , lasted from September 22 to October 9. These cruises study the large number of Fe-oxidizing bacteria that have colonized Kamaʻehuakanaloa. Kamaʻehuakanaloa's extensive vent system

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7332-531: The Hawaiian–Emperor seamount chain. Kamaʻehuakanaloa is built on the seafloor with a slope of about five degrees. Its northern base on the flank of Mauna Loa is 2,100 yd (1,900 m) below sea level, but its southern base is a more substantial 15,600 ft (4,755 m) below the surface. Thus, the summit is 3,054 ft (931 m) above the seafloor as measured from the base of its north flank, but 12,421 ft (3,786 m) high when measured from

7473-459: The Hawaiʻi hotspot . Kamaʻehuakanaloa consists of a summit area with three pit craters , a 7 mi (11 km) long rift zone extending north from the summit, and a 12 mi (19 km) long rift zone extending south-southeast from the summit. The summit's pit craters are named West Pit, East Pit, and Pele's Pit. Pele's Pit is the youngest of this group and is located at the southern part of

7614-802: The Klickitats as Louwala-Clough, which means "smoking or fire mountain" in their language (the Sahaptin call the mountain Loowit). The mountain is also of sacred importance to the Cowlitz and Yakama tribes that also live in the area. They find the area above its tree line to be of exceptional spiritual significance, and the mountain (which they call "Lawetlat'la", roughly translated as "the smoker") features prominently in their creation story, and in some of their songs and rituals. In recognition of its cultural significance, over 12,000 acres (4,900 ha) of

7755-541: The United States' largest slave rebellion . ) The vent was apparently at or near Goat Rocks on the northeast flank. Goat Rocks dome was near the site of the bulge in the 1980 eruption, and it was obliterated in the major eruption event on May 18, 1980, that destroyed the entire north face and top 1,300 feet (400 m) of the mountain. On March 20, 1980, Mount St. Helens experienced a magnitude  4.2 earthquake , and on March 27, steam venting started. By

7896-436: The area greatly benefited from the amounts of ash, allowing life to multiply rapidly. Six years after the eruption, most lakes in the area had returned to their normal state. After its 1980 eruption, the volcano experienced continuous volcanic activity until 2008 . Geologists predict that future eruptions will be more destructive, as the configuration of the lava domes requires more pressure to erupt. However, Mount St. Helens

8037-541: The area include two species endemic to the hydrothermal vents, a bresiliid shrimp ( Opaepele loihi ) of the family Alvinocarididae (described in 1995), and a tube or pogonophoran worm . Dives conducted after the 1996 earthquake swarms were unable to find either the shrimp or the worm, and it is not known if there are lasting effects on these species. From 1982 to 1992, researchers in Hawaiʻi Undersea Research Laboratory submersibles photographed

8178-560: The atmosphere. On the Volcanic Explosivity Index scale, the eruption was rated a 5, and categorized as a Plinian eruption . The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create lahars (volcanic mudflows). The lahars flowed many miles down the Toutle and Cowlitz Rivers , destroying bridges and lumber camps . A total of 3,900,000 cubic yards (3,000,000 m ) of material

8319-429: The base of its southern flank. Kamaʻehuakanaloa is following the pattern of development that is characteristic of all Hawaiian volcanoes. Geochemical evidence from Kamaʻehuakanaloa's lavas indicates that Kamaʻehuakanaloa is in transition between the preshield and shield volcano stage, providing valuable clues to the early development of Hawaiian volcanoes. In the preshield stage, Hawaiian volcanoes have steeper sides and

8460-493: 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 supposedly danced and prayed rather than collecting food and suffered during that winter from starvation. Evolution of Hawaiian volcanoes The evolution of Hawaiian volcanoes occurs in several stages of growth and decline. The fifteen volcanoes that make up

8601-464: The composition of St. Helens' lava, with the addition of olivine and basalt . The pre-1980 summit cone started to form during the Castle Creek period. Significant lava flows in addition to the previously much more common fragmented and pulverized lavas and rocks ( tephra ) distinguished this period. Large lava flows of andesite and basalt covered parts of the mountain, including one around

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8742-485: The cone. The ash drifted northeast over central and eastern Washington , northern Idaho , and western Montana . There were at least a dozen reported small eruptions of ash from 1831 to 1857, including a fairly large one in 1842. (The 1831 eruption is likely what tinted the sun bluish-green in Southampton County, Virginia on the afternoon of August 13—which Nat Turner interpreted as a final signal to launch

8883-474: The countryside with tephra . Swift Creek ended 8,000 years ago. A dormancy of about 4,000 years was broken around 2500 BC with the start of the Smith Creek eruptive period, when eruptions of large amounts of ash and yellowish-brown pumice covered thousands of square miles. An eruption in 1900 BC was the largest known eruption from St. Helens during the Holocene epoch, depositing

9024-492: The creation of Pele's Pit changed this, and initiated high temperature venting; exit temperatures were measured at 77 °C (171 °F) in 1996. The vents lie 1,100 to 1,325 m (3,609 to 4,347 ft) below the surface, and range in temperature from 10 to over 200 °C (392 °F). The vent fluids are characterized by a high concentration of CO 2 (up to 17 mM) and Fe ( Iron ), but low in sulfide . Low oxygen and pH levels are important factors in supporting

9165-434: The crust along a path of least resistance, both by way of fractures and faults as well as by melting wall rocks. The addition of melted crust changes the geochemical composition. Some of the melt rises toward the Earth's surface to erupt, forming the Cascade Volcanic Arc above the subduction zone. The magma from the mantle has accumulated in two chambers below the volcano: one approximately 3–7 miles (5–12 km) below

9306-408: The depth of the earthquakes as 4 mi (6 km) to 5 mi (8 km) below the summit, approximating to the position of Kamaʻehuakanaloa's extremely shallow magma chamber . This is evidence that Kamaʻehuakanaloa's seismicity is volcanic in origin. The low-level seismic activity documented on Kamaʻehuakanaloa since 1959 has shown that between two and ten earthquakes per month are traceable to

9447-433: The disturbance. These biological legacies highly influence the reestablishment of the post-disturbance ecology. Some species from each trophic level survived the 1980 eruption, which allowed for relatively quick re-establishment of food webs . Larger species saw greater mortality rates, with each of the area's large mammals — mountain goats, elk, deer, black bear and cougars — completely decimated. Eventually, each of

9588-423: The early development of Hawaiian volcanoes. Kamaʻehuakanaloa is predicted to rise above the surface in 10,000 to 100,000 years. Radiometric dating was used to determine the age of rock samples from Kamaʻehuakanaloa. The Hawaii Center for Volcanology tested samples recovered by various expeditions, notably the 1978 expedition, which provided 17 dredge samples. Most of the samples were found to be of recent origin;

9729-594: The eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch 5,800 kilometers (3,600 mi) across the North Pacific Ocean , called the Hawaiian–Emperor seamount chain . Hawaiʻi's volcanoes rise an average of 4,600 meters (15,000 ft) to reach sea level from their base. The largest, Mauna Loa , is 4,169 meters (13,678 ft) high. As shield volcanoes , they are built by accumulated lava flows, growing

9870-547: The end of April, the north side of the mountain had started to bulge. On May 18, a second earthquake, of magnitude 5.1, triggered a massive collapse of the north face of the mountain. It was the largest known debris avalanche in recorded history. The magma in St. Helens burst forth into a large-scale pyroclastic flow that flattened vegetation and buildings over an area of 230 square miles (600 km ). More than 1.5 million metric tons of sulfur dioxide were released into

10011-534: The eruption and because the eruption did not sterilize the immediate area. More than half of the papers on ecological response to volcanic eruption originated from studies of Mount St. Helens. Perhaps the most important ecological concept originating from the study of Mount St. Helens is the biological legacy . Biological legacies are the survivors of catastrophic disturbance; they can either be alive (e.g., plants that survive ashfall or pyroclastic flow), organic debris, or biotic patterns remaining from before

10152-420: The eruptions came from the southern part of the rift crater. This area is closest to the Hawaiʻi hotspot, which supplies Kamaʻehuakanaloa with magma . Following a 1986 seismic event, a network of five ocean bottom observatories (OBOs) were deployed on Kamaʻehuakanaloa for a month. Kamaʻehuakanaloa's frequent seismicity makes it an ideal candidate for seismic study through OBOs. In 1987, the submersible DSV Alvin

10293-592: The explosive reactions with lava that take place, begins when the volcano just breaches the surface. The pressure and instantaneous cooling of being underwater stops, replaced instead by contact with air. Lava and seawater make intermittent contact, resulting in a lot of steam. The change in environment also engenders a change in lava type, and the lava from this stage is mostly fragmented into volcanic ash. These explosive eruptions continue intermittently for several hundred thousand years. Calderas continually develop and fill, and rift zones remain prominent. The phase ends when

10434-468: The fish of Kamaʻehuakanaloa Seamount, Johnston Atoll , and Cross Seamount at depths between 40 and 2,000 m (130 and 6,560 ft). A small number of species identified at Kamaʻehuakanaloa were newly recorded sightings in Hawaiʻi, including the tasseled coffinfish ( Chaunax fimbriatus ), and the Celebes monkfish. Mount St. Helens Mount St. Helens (known as Lawetlat'la to

10575-413: The flanks of the growing volcanoes are unstable and as a result, large landslides may occur. At least 17 major landslides have occurred around the major Hawaiian islands. This stage is arguably the most well-studied, as all eruptions that occurred in the 20th century on the island of Hawaii were produced by volcanoes in this phase. Mauna Loa and Kīlauea volcanoes are in this phase of activity. As

10716-434: The forest, as the treeline was thought to be moving up the slopes before the eruption. Alpine meadows were uncommon at Mount St. Helens. Mountain goats inhabited higher elevations of the peak, although their population was eliminated by the 1980 eruption. The eruption of Mount St. Helens has been subject to more ecological study than has any other eruption, because research into disturbance commenced immediately after

10857-471: The form of andesitic ash that formed at least eight alternating light- and dark-colored layers. Blocky andesite lava then flowed from St. Helens' summit crater down the volcano's southeast flank. Later, pyroclastic flows raced down over the andesite lava and into the Kalama River valley. It ended with the emplacement of a dacite dome several hundred feet (~200 m) high at the volcano's summit, which filled and overtopped an explosion crater already at

10998-552: The groundwork for many of the expeditions that followed. Follow-up expeditions to Kamaʻehuakanaloa took place, including a series of crewed submersible dives in August and September. These were supplemented by a great deal of shore-based research. Fresh rock collected during the expedition revealed that an eruption occurred before the earthquake swarm. Submersible dives in August were followed by NOAA -funded research in September and October 1996. These more detailed studies showed

11139-465: 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

11280-448: The high amounts of Fe (iron), one of the hallmark features of Kamaʻehuakanaloa. These characteristics make a perfect environment for iron-oxidizing bacteria, called FeOB, to thrive in. An example of these species is Mariprofundus ferrooxydans , sole member of the class Zetaproteobacteria . The composition of the materials was similar to that of black smokers , that are a habitat of archaea extremophiles . Dissolution and oxidation of

11421-512: The highest of the Cascade volcanoes. Mount Hood , the nearest major volcanic peak in Oregon , is 60 miles (100 km) southeast of Mount St. Helens. Mount St. Helens is geologically young compared with the other major Cascade volcanoes. It formed only within the past 40,000 years, and the summit cone present before its 1980 eruption began rising about 2,200 years ago. The volcano

11562-522: The huge bridge fell into the river, creating the cascades of the Columbia River Gorge . For punishment, the chief of the gods struck down each of the lovers and transformed them into great mountains where they fell. Wy'east, with his head lifted in pride, became the volcano known today as Mount Hood . Pahto, with his head bent toward his fallen love, was turned into Mount Adams . The beautiful Loowit became Mount St. Helens, known to

11703-423: The ice had an average thickness of 300 feet (100 m) and a maximum of 650 feet (200 m), nearly as deep as the much older and larger Carbon Glacier of Mount Rainier. The ice is all post-1980, making the glacier very young geologically. However, the volume of the new glacier is about the same as all the pre-1980 glaciers combined. From 2004, volcanic activity pushed aside the glacier lobes and upward by

11844-467: The larger mammals migrated back into the area. Without access to adequate forage, many elk starved to death in the winters in the following decades. By 2014, the mountain goat population had grown back to 65 members. In 2015, there were 152. Mountain goats are culturally significant to the Cowlitz Tribe, whose members historically harvested shed tufts of goat wool left behind on the mountain, and

11985-559: The last glacial period of the current ice age . The second eruptive period, the Cougar Stage, started 20,000 years ago and lasted for 2,000 years. Pyroclastic flows of hot pumice and ash along with dome growth occurred during this period. Another 5,000 years of dormancy followed, only to be upset by the beginning of the Swift Creek eruptive period, typified by pyroclastic flows, dome growth and blanketing of

12126-475: The late 1980s. These vents are remarkably similar to those found at the mid-ocean ridges , with similar composition and thermal differences. The two most prominent vent fields are at the summit: Pele's Pit (formally Pele's Vents ) and Kapo's Vents . They are named after the Hawaiian deity Pele and her sister Kapo . These vents were considered "low temperature vents" because their waters were only about 30 °C (86 °F). The volcanic eruption of 1996 and

12267-620: The lava dome sent an ash plume 2,000 feet (600 m) over the western rim of the crater; the ash plume then rapidly dissipated. On December 19, 2006, a large white plume of condensing steam was observed, leading some media people to assume there had been a small eruption. However, the Cascades Volcano Observatory of the USGS did not mention any significant ash plume. The volcano was in continuous eruption from October 2004, but this eruption consisted in large part of

12408-532: The lava dome. On July 10, 2008, it was determined that the eruption had ended, after more than six months of no volcanic activity. Future eruptions of Mount St. Helens will likely be even larger than the 1980 eruption. The current configuration of lava domes in the crater means that much more pressure will be required for the next eruption, and hence the level of destruction will be higher. Significant ashfall may spread over 40,000 square miles (100,000 km ), disrupting transportation. A large lahar flow

12549-422: The lava is a sign of what stage the volcano is in, as over time the volcano's lavas shift from alkalic to tholeiitic lava, and then back to alkalic. Although volcanism and erosion are the chief factors in the growth and denudation of a volcano, other factors are also involved. Subsidence is known to occur. Changes in sea level, occurring mostly during the Pleistocene , have caused drastic changes; an example

12690-401: The lavas erupted in this stage is usually alkalic. The stage commonly occurs between 0.6 and 2 million years after it has entered the weathering cycle. The Koʻolau Range and West Maui volcanoes are examples of volcanoes in this stage of development. Note, however, that because in this stage eruptions are very infrequent (occurring thousands or even tens of thousands of years apart), erosion

12831-685: The local Cowlitz people , and Loowit or Louwala-Clough to the Klickitat ) is an active stratovolcano located in Skamania County, Washington , in the Pacific Northwest region of the United States. It lies 52 miles (83 km) northeast of Portland, Oregon , and 98 miles (158 km) south of Seattle . Mount St. Helens takes its English name from that of the British diplomat Alleyne Fitzherbert, 1st Baron St Helens ,

12972-443: The local bacteria and archaea extremophiles . The fourth FeMO (Fe-Oxidizing Microbial Observatory) cruise occurred during October 2009. Marine life inhabiting the waters around Kamaʻehuakanaloa is not as diverse as life at other, less active seamounts . Fish found living near Kamaʻehuakanaloa include the Celebes monkfish ( Sladenia remiger ), and members of the cutthroat eel family, Synaphobranchidae . Invertebrates identified in

13113-469: The mantle. New oceanic crust moves away from the spreading center. Over a period of 80–100 million years, the sea floor under Hawaii moved from the East Pacific Rise to its present location 3,700 mi (6,000 km) west, carrying ancient seamounts with it. When scientists investigated a series of earthquakes off Hawaii in 1970, they discovered that Kamaʻehuakanaloa was an active member of

13254-585: The mineral observed over the next two years suggests the sulfate is not easily preserved. A diverse community of microbial mats surround the vents and virtually cover Pele's Pit. The Hawaiʻi Undersea Research Laboratory (HURL), NOAA 's Research Center for Hawaiʻi and the Western Pacific, monitors and researches the hydrothermal systems and studies the local community. The National Science Foundation ( NSF ) funded an extremophile sampling expedition to Kamaʻehuakanaloa in 1999. Microbial mats surrounded

13395-403: The most volcanically and hydrothermally active area was along the southern rift. Dives on the less active northern rim indicated that the terrain was more stable there, and high lava columns were still standing upright. A new hydrothermal vent field (Naha Vents) was located in the upper-south rift zone, at a depth of 1,449 yd (1,325 m). Kamaʻehuakanaloa has remained largely quiet since

13536-712: The mountain (roughly bounded by the Loowit Trail) have been listed on the National Register of Historic Places . Other area tribal names for the mountain include "nšh'ák'w" ("water coming out") from the Upper Chehalis , and "aka akn" ("snow mountain"), a Kiksht term. Royal Navy Commander George Vancouver and the officers of HMS Discovery made the Europeans' first recorded sighting of Mount St. Helens on 19 May 1792, while surveying

13677-547: The mountain run through Cowlitz County to the west, and Lewis County to the north. State Route 504 , locally known as the Spirit Lake Memorial Highway , connects with Interstate 5 at Exit 49, 34 miles (55 km) to the west of the mountain. That north–south highway skirts the low-lying cities of Castle Rock , Longview and Kelso along the Cowlitz River , and passes through

13818-699: 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 ;

13959-487: The north rift zone contains three 200–260 ft (60–80 m) cone-shaped prominences. Until 1970, Kamaʻehuakanaloa was thought to be an inactive volcano that had been transported to its current location by sea-floor spreading . The seafloor under Hawaii is 80–100 million years old and was produced at the East Pacific Rise , an oceanic spreading center where new sea floor forms from magma that erupts from

14100-558: The northern Pacific Ocean coast. Vancouver named the mountain for British diplomat Alleyne Fitzherbert, 1st Baron St Helens on 20 October 1792, as it came into view when the Discovery passed into the mouth of the Columbia River. Years later, explorers, traders, and missionaries heard reports of an erupting volcano in the area. Geologists and historians determined much later that the eruption took place in 1800, marking

14241-466: The oldest dated rock is around 300,000 years old. Following the 1996 event, some young breccia was also collected. Based on the samples, scientists estimate Kamaʻehuakanaloa is about 400,000 years old. The rock accumulates at an average rate of 1 ⁄ 8  in (3.5 mm) per year near the base, and 1 ⁄ 4  in (7.8 mm) near the summit. If the data model from other volcanoes such as Kīlauea holds true for Kamaʻehuakanaloa, 40% of

14382-409: The past. Kamaʻehuakanaloa's north–south trending rift zones form a distinctive elongated shape, from which the volcano's earlier Hawaiian name "Lōʻihi," meaning "long", derives. The north rift zone consists of a longer western portion and a shorter eastern rift zone. Observations show that both the north and south rift zones lack sediment cover, indicating recent activity. A bulge in the western part of

14523-517: The process of evolution originates from the first half of the 20th century. The understanding of the process was advanced by frequent observation of volcanic eruptions, study of contrasting rock types, and reconnaissance mapping. More recently our understanding has been aided by geophysical studies, offshore submersible studies, the advent of radioactive dating, advances in petrology and geochemistry, advanced surveillance and monitoring, and detailed geological studies. The ratio of magnesium to silica in

14664-419: The product of the growth of tropical marine organisms , so this island type is only found in warm tropical waters . Eventually, the Pacific Plate carries the volcanic atoll into waters too cold for these marine organisms to maintain a coral reef by growth. Volcanic islands located beyond the warm water temperature requirements of reef-building organisms become seamounts as they subside and are eroded away at

14805-514: The same for the arrow to the south. The chief of the gods then built the Bridge of the Gods, so his family could meet periodically. When the two sons of the chief of the gods fell in love with a beautiful maiden named Loowit, she could not choose between them. The two young chiefs fought over her, burying villages and forests in the process. The area was devastated and the earth shook so violently that

14946-513: The seamount in 1955, describing the long and narrow shape of the volcano as Kamaʻehuakanaloa . In 1978, an expedition studied intense, repeated seismic activity known as earthquake swarms in and around the Kamaʻehuakanaloa area. Rather than finding an old, extinct seamount, data collected revealed Kamaʻehuakanaloa to be a young, possibly active volcano. Observations showed the volcano to be encrusted with young and old lava flows. Fluids erupting from active hydrothermal vents were also found. In 1978,

15087-440: The seamount was actually an active submarine shield volcano , similar to the two active Hawaiian volcanoes, Mauna Loa and Kīlauea . Macdonald's hypothesis placed the seamount as the newest volcano in the Hawaiian–Emperor seamount chain , created by the Hawaiʻi hotspot . However, because the earthquakes were oriented east–west (the direction of the volcanic fault ) and there was no volcanic tremor in seismometers distant from

15228-406: The seamount, Macdonald attributed the earthquake to faulting rather than a volcanic eruption . Geologists suspected the seamount could be an active undersea volcano, but without evidence the idea remained speculative. The volcano was largely ignored after the 1952 event, and was often mislabeled as an "older volcanic feature" in subsequent charts. Geologist Kenneth O. Emery is credited with naming

15369-410: The shield stage. All older volcanoes have had their preshield stage lavas buried by younger lavas, so everything that is known about this stage comes from research done on Kamaʻehuakanaloa Seamount . The shield stage of the volcano is subdivided into three phases: the submarine, explosive, and subaerial. During this stage of growth, the volcano accumulates about 95 percent of its mass and it takes on

15510-513: The shoreline. The volcano becomes a skeleton of its former self. Kohala , Māhukona , Lānaʻi , and Waiʻanae volcanoes are examples of volcanoes in this stage of development. After a long period of dormancy and erosion of the surface, the volcano may become active again, entering a final stage of activity called the rejuvenated stage. During this stage, the volcano erupts small volumes of lava very infrequently. These eruptions are often spread out over several millions of years. The composition of

15651-409: The southern portion of Kamaʻehuakanaloa's summit had collapsed, a result of a swarm of earthquakes and the rapid withdrawal of magma from the volcano. A crater 0.6 mi (1 km) across and 330 yd (300 m) deep formed out of the rubble. The event involved the movement of 100 million cubic meters of volcanic material . A region of 3.9 to 5.0 sq mi (10 to 13 km) of the summit

15792-403: The stage before it. Some Hawaiian volcanoes diverge from this, however. Lava is erupted as stocky, pasty ʻaʻā flows along with a lot of cinder . Caldera development stops, and the rift zones become less active. The new lava flows increase the slope grade, as the ʻaʻā never reaches the base of the volcano. These lavas commonly fill and overflow the caldera . Eruption rate gradually decreases over

15933-458: The summer of 1996, a swarm of 4,070 earthquakes was recorded at Kamaʻehuakanaloa. At the time this was the most energetic earthquake swarm in Hawaii recorded history . The swarm altered 4 to 5 sq mi (10 to 13 km) of the seamount's summit; one section, Pele's Vents , collapsed entirely upon itself and formed the renamed Pele's Pit . The volcano has remained relatively active since

16074-431: The summit. Large parts of the dome's sides broke away and mantled parts of the volcano's cone with talus . Lateral explosions excavated a notch in the southeast crater wall. St. Helens reached its greatest height and achieved its highly symmetrical form by the time the Kalama eruptive cycle ended, in about 1647. The volcano remained quiet for the next 150 years. The 57-year eruptive period that started in 1800

16215-419: The summit. Earthquake swarm data have been used to analyze how well Kamaʻehuakanaloa's rocks propagate seismic waves and to investigate the relationship between earthquakes and eruptions. This low level activity is periodically punctuated by large swarms of earthquakes, each swarm composed of up to hundreds of earthquakes. The majority of the earthquakes are not distributed close to the summit, though they follow

16356-476: The summit. The walls of Pele's Pit stand 700 ft (200 m) high and were formed in July 1996 when its predecessor, Pele's Vent, a hydrothermal field near Kamaʻehuakanaloa summit, collapsed into a large depression . The thick crater walls of Pele's Pit – averaging 70 ft (20 m) in width, unusually thick for Hawaiian volcanic craters – suggest its craters have filled with lava multiple times in

16497-502: The surface, the other about 7–25 miles (12–40 km). The lower chamber may be shared with Mount Adams and the Indian Heaven volcanic field. The early eruptive stages of Mount St. Helens are known as the "Ape Canyon Stage" (around 40,000–35,000 years ago), the "Cougar Stage" (ca. 20,000–18,000 years ago), and the "Swift Creek Stage" (roughly 13,000–8,000 years ago). The modern period, since about 2500 BC,

16638-486: The surface. An island that is located where the ocean water temperatures are just sufficiently warm for upward reef growth to keep pace with the rate of subsidence is said to be at the Darwin point . Islands in more northerly latitudes evolve towards seamounts or guyots; islands closer to the equator evolve towards atolls (see Kure Atoll ). After the reef dies, the volcano subsides or erodes below sea level and becomes

16779-502: The tribe has played a role in monitoring the population, which continues to recover without human intervention. Native American lore contains numerous stories to explain the eruptions of Mount St. Helens and other Cascade volcanoes. The best known of these is the Bridge of the Gods story told by the Klickitat people . In the story, the chief of all the gods and his two sons, Pahto (also called Klickitat) and Wy'east, traveled down

16920-405: The vertical ash column declined in stature, and less-severe outbursts continued through the night and for the next several days. The St. Helens May 18 eruption released 24 megatons of thermal energy and ejected more than 0.67 cubic miles (2.79 km ) of material. The removal of the north side of the mountain reduced St. Helens' height by about 1,300 feet (400 m) and left

17061-433: The volcano continues to erupt pillow lava. Calderas form, fill, and reform at the volcano's summit and the rift zones remain prominent. The volcano builds its way up to sea level. The submarine phase ends when the volcano is only shallowly submerged. The only example of a volcano in this stage is Kamaʻehuakanaloa Seamount, which is now transitioning into this phase from the preshield stage. This volcanic phase, so named for

17202-437: The volcano has sufficient mass and height (about 1,000 meters (3,000 ft) above sea level) that the interaction between sea water and erupting lava fades away. Once a volcano has added enough mass and height to end frequent contact with water, the subaerial substage begins. During this stage of activity, the explosive eruptions become much less frequent and the nature of the eruptions become much more gentle. Lava flows are

17343-400: The volcano reaches the end of the shield stage, the volcano goes through another series of changes as it enters the postshield stage. The type of lava erupted changes from tholeiitic basalt back to alkalic basalt and eruptions become slightly more explosive. Eruptions in the postshield stage cap the volcano with a carapace of lava, containing low silica and high alkali contents, the reverse of

17484-409: The volcano's mass formed within the last 100,000 years. Assuming a linear growth rate, Kamaʻehuakanaloa is 250,000 years old. However, as with all hotspot volcanoes, Kamaʻehuakanaloa's level of activity has increased with time; therefore, it would take at least 400,000 years for such a volcano to reach Kamaʻehuakanaloa's mass. As Hawaiian volcanoes drift northwest at a rate of about 4 in (10 cm)

17625-449: The water. The bacteria that feed on the dissolved nutrients had already begun colonizing the new hydrothermal vents at Pele's Pit (formed from the collapse of the old ones), and may be indicators of the kinds of material ejected from the newly formed vents. They were carefully sampled for further analysis in a laboratory. An OBO briefly sat on the summit before a more permanent probe could be installed. Repeated multibeam bathymetric mapping

17766-541: The year 100 BC that traveled all the way into the Lewis and Kalama river valleys. Others, such as Cave Basalt (known for its system of lava tubes ), flowed up to 9 miles (14 km) from their vents. During the first century, mudflows moved 30 miles (50 km) down the Toutle and Kalama river valleys and may have reached the Columbia River . Another 400 years of dormancy ensued. The Sugar Bowl eruptive period

17907-451: Was altered and populated by bus-sized pillow lava blocks , precariously perched along the outer rim of the newly formed crater. "Pele's Vents", an area on the southern side, previously considered stable, collapsed completely into a giant pit, renamed "Pele's Pit". Strong currents make submersible diving hazardous in the region. The researchers were continually met by clouds of sulfide and sulfate . The sudden collapse of Pele's Vents caused

18048-433: Was being forced upward as quickly as 6 ft (2 m) per day. In mid-June 2006, the slab was crumbling in frequent rockfalls, although it was still being extruded. The height of the dome was 7,550 feet (2,300 m), still below the height reached in July 2005 when the whaleback collapsed. On October 22, 2006, at 3:13 p.m. PST, a magnitude 3.5 earthquake broke loose Spine 7. The collapse and avalanche of

18189-404: Was characterized by smaller-volume eruptions. Numerous dense, nearly red hot pyroclastic flows sped down St. Helens' flanks and came to rest in nearby valleys. A large mudflow partly filled 40 miles (64 km) of the Lewis River valley sometime between 1000 BC and 500 BC. The next eruptive period, the Castle Creek period, began about 400 BC, and is characterized by a change in

18330-467: Was connected to the shore, 34 km (21 mi) away, by a fiber optic cable . It was designed to give scientists real-time seismic, chemical and visual data about the state of Kamaʻehuakanaloa, which had by then become an international laboratory for the study of undersea volcanism. The cable that provided HUGO with power and communications broke in April 1998, effectively shutting it down. The observatory

18471-432: Was dominated by Pacific silver fir up to 4,300 feet (1,300 m). Finally, below treeline , the forest consisted of mountain hemlock , Pacific silver fir and Alaska yellow cedar . Large mammals included Roosevelt elk , black-tailed deer , American black bear , and mountain lion . The treeline at Mount St. Helens was unusually low, at about 4,400 feet (1,340 m), the result of prior volcanic disturbance of

18612-501: Was formerly known as the Tulutson Glacier. Shadowed by the crater walls and fed by heavy snowfall and repeated snow avalanches, it grew rapidly (14 feet (4.3 m) per year in thickness). By 2004, it covered about 0.36 square miles (0.93 km ), and was divided by the dome into a western and eastern lobe. Typically, by late summer, the glacier looks dark from rockfall from the crater walls and ash from eruptions. As of 2006,

18753-599: Was found in two Hawaiian mele from the 19th and early twentieth centuries based on research at the Bishop Museum and was assigned by the Hawaiʻi Board on Geographic Names in 2021 and adopted by the U.S. Geological Survey. From 1955 to 2021 the seamount was called "Lōʻihi", the Hawaiian word for "long", describing its shape. The change to Kamaʻehuakanaloa was made in an effort to be more culturally appropriate given native Hawaiian traditions for naming. Kamaʻehuakanaloa

18894-468: Was named after the Goat Rocks dome and is the first period for which both oral and written records exist. As with the Kalama period, the Goat Rocks period started with an explosion of dacite tephra , followed by an andesite lava flow, and culminated with the emplacement of a dacite dome. The 1800 eruption probably rivaled the 1980 eruption in size, although it did not result in massive destruction of

19035-486: Was recorded at a depth of approximately 21 mi (33 km). Between December 7, 2005, and January 18, 2006, a swarm of around 100 earthquakes occurred, the largest measuring 4 on the Moment magnitude scale and 7 to 17 mi (12 to 28 km) deep. Another earthquake measuring 4.7 was later recorded approximately midway between Kamaʻehuakanaloa and Pāhala (on the south coast of the island of Hawaii ). Data collected

19176-407: Was recovered from the seafloor in 2002. Kamaʻehuakanaloa's mid-Pacific location and its well-sustained hydrothermal system contribute to a rich oasis for a microbial ecosystem . Areas of extensive hydrothermal venting are found on Kamaʻehuakanaloa's crater floor and north slope, and along the summit of Kamaʻehuakanaloa itself. Active hydrothermal vents were first discovered at Kamaʻehuakanaloa in

19317-479: Was short and markedly different from other periods in Mount St. Helens history. It produced the only unequivocal laterally directed blast known from Mount St. Helens before the 1980 eruptions. During Sugar Bowl time, the volcano first erupted quietly to produce a dome, then erupted violently at least twice producing a small volume of tephra, directed-blast deposits, pyroclastic flows, and lahars. East Dome,

19458-590: Was the first solid evidence of the volcano being active. Much is learned about Kamaʻehuakanaloa's microbial community. Kamaʻehuakanaloa Seamount's first depiction on a map was on Survey Chart 4115, a bathymetric rendering of part of Hawaiʻi compiled by the United States Coast and Geodetic Survey in 1940. At the time, the seamount was non-notable, being one of many in the region. A large earthquake swarm first brought attention to it in 1952. That same year, geologist Gordon A. Macdonald hypothesized that

19599-496: Was transported 17 miles (27 km) south into the Columbia River by the mudflows. For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 16 miles (19 to 26 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (100 km/h) with ash reaching Idaho by noon. Ashes from the eruption were found on top of cars and roofs the next morning as far away as Edmonton , Alberta, Canada. By about 5:30 p.m. on May 18,

19740-435: Was used to survey Kamaʻehuakanaloa Another autonomous observatory was positioned on Kamaʻehuakanaloa in 1991 to track earthquake swarms. The bulk of information about Kamaʻehuakanaloa comes from dives made in response to the 1996 eruption. In a dive conducted almost immediately after seismic activity was reported, visibility was greatly reduced by high concentrations of displaced minerals and large floating mats of bacteria in

19881-402: Was used to measure the changes in the summit following the 1996 collapse. Hydrothermal plume surveys confirmed changes in the energy, and dissolved minerals emanating from Kamaʻehuakanaloa. Hawaiʻi Undersea Research Laboratory , HURL's 2,000 m (6,562 ft) submersible Pisces V allowed scientists to sample the vent waters, microorganisms and hydrothermal mineral deposits. Since 2006,

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