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79-707: The North Fork Toutle River is a tributary of the Toutle River in southwestern Washington in the United States. The river has its headwaters near Spirit Lake , on the north side of Mount St. Helens , and flows 39 miles (63 km) to the Toutle River, about 17 miles (27 km) upstream of its confluence with the Cowlitz River . The largest tributary is the Green River , which joins near

158-475: A 12 ft-high (4 m) wall of muddy water and debris pass. Near the confluence of the Toutle's north and south forks at Silver Lake, a record flood stage of 23.5 ft (7.2 m) was recorded. A large but slower-moving mudflow with a mortar-like consistency was mobilized in early afternoon at the head of the Toutle River north fork. By 2:30 pm, the massive mudflow had destroyed Camp Baker, and in

237-503: A Vancouver Columbian and National Geographic photographer who was situated near Coldwater Creek 46°17′55.8″N 122°17′22.9″W  /  46.298833°N 122.289694°W  / 46.298833; -122.289694 , 8 miles (13 km) from the volcano, on the day of the eruption. Robert Landsburg , another photographer, who was within a few miles of the summit 46°12′46.3″N 122°16′03.3″W  /  46.212861°N 122.267583°W  / 46.212861; -122.267583 ,

316-422: A complex, down-dropped block called a graben . Geologists announced on April 30 that sliding of the bulge area was the greatest immediate danger and that such a landslide might spark an eruption. These changes in the volcano's shape were related to the overall deformation that increased the volume of the volcano by 0.03 cu mi (0.13 km ) by mid-May. This volume increase presumably corresponded to

395-461: A fan-like pattern of overlapping sheets, tongues, and lobes. At least 17 separate pyroclastic flows occurred during the May 18 eruption, and their aggregate volume was about 0.05 cu mi (0.21 km ). The flow deposits were still at about 570 to 790 °F (300 to 420 °C) two weeks after they erupted. Secondary steam-blast eruptions fed by this heat created pits on the northern margin of

474-479: A half after the eruption, the bodies of two young women, Marsha Anne Weatter and Katherine Jean Allen, 18 and 20 years old respectively, were discovered. They were believed to have been murdered six weeks before the eruption, rather than being killed by the events. Backpacks belonging to them had been found in July 1980, but a layer of ash deposited by the eruption may have hid the bodies, also preventing animals disturbing

553-453: A measure used in physics to describe how light propagates through a particular substance, is an important property of volcanic ash. This number is complex , having both real and imaginary parts, the real part indicating how light disperses and the imaginary part indicating how light is absorbed by the substance. The silicate particles are known to have a real index of refraction ranging between 1.5 and 1.6 for visible light. However,

632-459: A slightly increasing rate during April and May, with five earthquakes of magnitude 4 or above per day in early April, and eight per day the week before May 18. Initially, no direct sign of eruption was seen, but small earthquake-induced avalanches of snow and ice were reported from aerial observations. At 12:36 pm on March 27, phreatic eruptions (explosions of steam caused by magma suddenly heating groundwater ) ejected and smashed rock from within

711-423: A spectrum of colors is associated with samples of volcanic ash, from very light to dark gray. This makes for variations in the measured imaginary refractive index under visible light. In the case of Mount St. Helens, the ash settled in three main layers on the ground: For example, when comparing the imaginary part of the refractive index k of stratospheric ash from 9.3 and 11.2 mi (15 and 18 km) from

790-455: A state of emergency on April 3. Governor Ray issued an executive order on April 30 creating a "red zone" around the volcano; anyone caught in this zone without a pass faced a $ 500 fine (equivalent to $ 1,800 in 2023) or six months in jail. This precluded many cabin owners from visiting their property. By April 7, the combined crater was 1,700 by 1,200 ft (520 by 370 m) and 500 ft (150 m) deep. A USGS team determined in

869-422: A thousand commercial flights were cancelled following airport closures. Fine-grained, gritty ash caused substantial problems for internal combustion engines and other mechanical and electrical equipment. The ash contaminated oil systems, clogged air filters, and scratched moving surfaces. Fine ash caused short circuits in electrical transformers, which in turn caused power blackouts . Removing and disposing of

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948-430: A two-month series of earthquakes and steam-venting episodes caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain's north slope. An earthquake at 8:32:11 am PDT ( UTC −7) on May 18, 1980, caused the entire weakened north face to slide away, a sector collapse which was the largest subaerial landslide in recorded history. This allowed

1027-468: A victim of the May 18, 1980, eruption" and that after years of searching, the family eventually decided "he's buried in the ash". Taking these two points of uncertainty into consideration, the direct death toll could be as low as 55 or as high as 60. When combined with the four indirect victims (two dying from vehicle accidents due to poor visibility, and two dying from heart attacks triggered by shovelling ash) those numbers range from 59 to 64. A year and

1106-420: Is 2,095 cubic feet per second (59.3 m /s). This is from a drainage area of 416 square miles (1,080 km ), about 81 percent of the total Toutle River watershed. The maximum flow recorded there was 61,800 cubic feet per second (1,750 m /s) on Feb. 8, 1996, and the minimum flow was 243 cubic feet per second (6.88 m /s) on Oct. 14, 1987. This data covers a 30-year period that began in 1981, after

1185-581: Is the source of much of the excess sediment. Toutle River The river was altered by the 1980 eruption of Mount St. Helens , a nearby volcano, and subsequent flows of ash and other debris. It was further altered by dredging to remove sediment, and by construction of the Toutle River Sediment Retention Structure on the North Fork Toutle River . The Toutle River begins at the confluence of

1264-438: The speed of sound . Pyroclastic flow material passed over the moving avalanche and spread outward, devastating a fan-shaped area 23 miles across by 19 miles long (37 km × 31 km). In total, about 230 sq mi (600 km ) of forest were knocked down, and extreme heat killed trees miles beyond the blow-down zone. At its vent, the lateral blast probably did not last longer than about 30 seconds, but

1343-683: The $ 65 million Toutle River Sediment Retention Structure on the North Fork Toutle River to prevent debris from continuing downstream. Part of the same engineering works is a tunnel to drain Spirit Lake , on the north side of the volcano, after the eruption blocked the lake's natural outlet. 1980 eruption of Mount St. Helens On March   27, 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County , Washington, United States. A series of phreatic blasts occurred from

1422-442: The 350-year-old summit dome and did not involve any new magma. About 10,000 earthquakes were recorded before the May 18 event, with most concentrated in a small zone less than 1.6 mi (2.6 km) directly below the bulge. Visible eruptions ceased on May 16, reducing public interest and consequently the number of spectators in the area. Mounting public pressure then forced officials to allow 50 carloads of property owners to enter

1501-652: The Cowlitz River about 2 miles (3 km) upstream from the city of Castle Rock. Below the confluence, the Cowlitz continues for 20 miles (32 km), entering the Columbia River about 68 miles (109 km) from its mouth on the Pacific Ocean. The United States Geological Survey monitors the flow of the Toutle River at a stream gauge at RM 6.5 (RK 10.5). The average flow of the river

1580-539: The Lewis River to accommodate possible mudflows and flood waters. In total, Mount St. Helens released 24 megatons TNT of thermal energy, seven of which were a direct result of the blast. This is equivalent to 1,600 times the size of the atomic bomb dropped on Hiroshima . The death toll most commonly cited is 57, but two points of uncertainty remain. The first point regards two officially listed victims, Paul Hiatt and Dale Thayer. They were reported missing after

1659-643: The North Fork Toutle River and the South Fork Toutle River near the community of Toutle. The forks originate on Mount St. Helens in Mount St. Helens National Volcanic Monument , and flow generally west to form the main stem , which continues generally west, with significant north–south deviations. The town of Toutle lies to the left of the river at river mile (RM) 17.2 or river kilometer (RK) 27.7. At first

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1738-400: The Toutle River flows north for about 1 mile (2 km) along the base of Beigle Mountain, which is on its right . The river continues generally north until, at about RM 13 (RK 21), it begins a sweeping turn to the southwest. For the next several miles, Tower Road runs along the right bank of the river, and at about RM 10 (RK 16) Tower Cemetery is on the right. Downstream of

1817-446: The ash before its compaction by rainfall was about 0.3 cu mi (1.3 km ). The volume of the uncompacted ash is equivalent to about 0.05 cu mi (0.21 km ) of solid rock, or about 7% of the amount of material that slid off in the debris avalanche. By around 5:30 pm on May 18, the vertical ash column declined in stature, but less severe outbursts continued through the next several days. Generally, given that

1896-529: The ash was a monumental task for some Eastern Washington communities. State and federal agencies estimated that over 2,400,000 cu yd (1,800,000 m ) of ash, equivalent to about 900,000 tons in weight, were removed from highways and airports in Washington. The ash removal cost $ 2.2 million and took 10 weeks in Yakima. The need to remove ash quickly from transport routes and civil works dictated

1975-416: The blast was deflected by local topography 1 mi (1.6 km) short of his location. Most of St. Helens's former north side became a rubble deposit 17 mi (27 km) long, averaging 150 ft (46 m) thick; the slide was thickest at 1 mi (1.6 km) below Spirit Lake and thinnest at its western margin. The landslide temporarily displaced the waters of Spirit Lake to the ridge north of

2054-406: The blast. This so-called "quiet zone" extended radially a few tens of miles from the volcano and was created by the complex response of the eruption's sound waves to differences in temperature and air motion of the atmospheric layers, and to a lesser extent, local topography. Later studies indicated that one-third of the 0.045 cu mi (0.19 km ) of material in the flow was new lava, and

2133-412: The busy channel to ocean-going freighters , costing Portland, Oregon, an estimated $ 5 million (equivalent to $ 15.5 million 2023). Ultimately, more than 65 × 10 ^  cu yd (50 × 10 ^  m ; 1.8 × 10 ^  cu ft) of sediment were dumped along the lower Cowlitz and Columbia Rivers. The May 18, 1980, event was the most deadly and economically destructive volcanic eruption in

2212-544: The cemetery, the river passes through Hollywood Gorge, where Rock Creek enters from the right. The river continues southwest through RM 7 (RK 11), where it receives Stankey Creek from the left. The Toutle River then turns west, passing under Tower Road and receiving Cline Creek from the right. Over the next stretch, Burma Road is on the right. Over its final 4 miles (6 km), the Toutle meanders generally southwest through large deposits of sand. The stream passes under Barnes Drive and then Interstate 5 before entering

2291-545: The crisis. Counties in the region requested funding for mental-health programs to assist such people. Initial public reaction to the May 18 eruption dealt a nearly crippling blow to tourism, an important industry in Washington. Not only was tourism down in the Mount St. Helens– Gifford Pinchot National Forest area, but conventions, meetings and social gatherings also were cancelled or postponed at cities and resorts elsewhere in Washington and neighboring Oregon not affected by

2370-448: The damage, and said it looked more desolate than a moonscape. A film crew was dropped by helicopter on Mount St. Helens on May 23 to document the destruction, but their compasses spun in circles and they quickly became lost. A second eruption occurred the next day (see below), but the crew survived and was rescued two days after that. The eruption ejected more than 1 cu mi (4.2 km ) of material. A quarter of that volume

2449-410: The danger zone on Saturday, May 17, to gather whatever property they could carry. Another trip was scheduled for 10 am the next day, and because that was Sunday, more than 300 loggers who would normally be working in the area were not there. By the time of the climactic eruption, dacite magma intruding into the volcano had forced the north flank outward nearly 500 ft (150 m) and heated

North Fork Toutle River - Misplaced Pages Continue

2528-548: The eruption enveloping the Coldwater ;II observation post. As the blast overwhelmed Johnston's post, Martin declared solemnly: "Gentlemen, the camper and car that's sitting over to the south of me is covered. It's going to hit me, too." before his radio went silent. Subsequent outpourings of pyroclastic material from the breach left by the landslide consisted mainly of new magmatic debris rather than fragments of pre-existing volcanic rocks. The resulting deposits formed

2607-488: The eruption were incurred. Unemployment in the immediate region of Mount St. Helens rose 10-fold in the weeks immediately following the eruption, and then returned to near-normal levels once timber-salvaging and ash-cleanup operations were underway. Only a small percentage of residents left the region because of lost jobs owing to the eruption. Several months after May 18, a few residents reported suffering stress and emotional problems, though they had coped successfully during

2686-509: The expanding crater in less than 10 minutes and spread tephra into the stratosphere for 10 straight hours. Near the volcano, the swirling ash particles in the atmosphere generated lightning , which in turn started many forest fires . During this time, parts of the mushroom -shaped ash-cloud column collapsed, and fell back upon the earth. This fallout, mixed with magma, mud, and steam, sent additional pyroclastic flows speeding down St. Helens's flanks. Later, slower flows came directly from

2765-420: The explosion. In the aftermath, investigators were able to locate individuals named Paul Hiatt and Dale Thayer who were alive and well. However, they were unable to determine who reported Hiatt missing, and the person who was listed as reporting Thayer missing claimed she was not the one who had done so. Since the investigators could not thus verify that they were the same Hiatt and Thayer who were reported missing,

2844-568: The flatter and wider parts of rivers. Mudflows from the southern and eastern flanks had the consistency of wet concrete as they raced down Muddy River, Pine Creek, and Smith Creek to their confluence at the Lewis River . Bridges were taken out at the mouth of Pine Creek and the head of Swift Reservoir, which rose 2.6 ft (0.79 m) by noon to accommodate the nearly 18,000,000 cu yd (14,000,000 m ) of additional water, mud, and debris. Glacier and snowmelt mixed with tephra on

2923-498: The following hours, seven bridges were carried away. Part of the flow backed up for 2.5 mi (4.0 km) soon after entering the Cowlitz River, but most continued downstream. After traveling 17 mi (27 km) further, an estimated 3,900,000 cu yd (3,000,000 m ) of material were injected into the Columbia River, reducing the river's depth by 25 ft (8 m) for a 4 mi (6 km) stretch. The resulting 13 ft (4.0 m) river depth temporarily closed

3002-405: The history of the contiguous United States. About 57 people were killed directly from the blast, and 200 houses, 47 bridges, 15 mi (24 km) of railways, and 185 mi (298 km) of highway were destroyed; two people were killed indirectly in accidents that resulted from poor visibility, and two more suffered fatal heart attacks from shoveling ash. U.S. President Jimmy Carter surveyed

3081-483: The initial landslide. The debris was transported along with the water as it returned to its basin , raising the surface level of Spirit Lake by about 200 ft (61 m). Four decades after the eruption, floating log mats persist on Spirit Lake and nearby St. Helens Lake, changing position with the wind. The rest of the trees, especially those that were not completely detached from their roots, were turned upright by their own weight and became waterlogged, sinking into

3160-405: The lake, in a giant wave about 600 ft (180 m) high. This, in turn, created a 295 ft (90 m) avalanche of debris consisting of the returning waters and thousands of uprooted trees and stumps. Some of these remained intact with roots, but most had been sheared off at the stump seconds earlier by the blast of superheated volcanic gas and ash that had immediately followed and overtaken

3239-567: The largest subaerial landslide in recorded history, traveled at 110 to 155 mph (177 to 249 km/h) and moved across Spirit Lake's west arm. Part of it hit a 1,150 ft-high (350 m) ridge about 6 mi (10 km) north. Some of the slide spilled over the ridge, but most of it moved 13 mi (21 km) down the North Fork Toutle River , filling its valley up to 600 feet (180 m) deep with avalanche debris. An area of about 24 sq mi (62 km )

North Fork Toutle River - Misplaced Pages Continue

3318-414: The last week of April that a 1.5 mi-diameter (2.4 km) section of St. Helens's north face was displaced outward by at least 270 ft (82 m). For the rest of April and early May, this bulge grew by 5 to 6 ft (1.5 to 1.8 m) per day, and by mid-May, it extended more than 400 ft (120 m) north. As the bulge moved northward, the summit area behind it progressively sank, forming

3397-573: The lateral blast. At least 25% of the destroyed timber was salvaged after September 1980. Downwind of the volcano, in areas of thick ash accumulation, many agricultural crops, such as wheat, apples, potatoes, and alfalfa , were destroyed. As many as 1,500 elk and 5,000 deer were killed, and an estimated 12 million Chinook and Coho salmon fingerlings died when their hatcheries were destroyed. Another estimated 40,000 young salmon were killed when they swam through turbine blades of hydroelectric generators after reservoir levels were lowered along

3476-496: The muddy sediments at the bottom where they are in the process of becoming petrified in the anaerobic and mineral-rich waters. This provides insight into other sites with a similar fossil record. The landslide exposed the dacite magma in St. Helens's neck to much lower pressure, causing the gas-charged, partially molten rock and high-pressure steam above it to explode a few seconds after the landslide started. Explosions burst through

3555-480: The names remain listed among the presumed dead. The second point regards three missing people who are not officially listed as victims: Robert Ruffle, Steven Whitsett, and Mark Melanson. Cowlitz County Emergency Services Management lists them as "Possibly Missing — Not on [the official] List". According to Melanson's brother, in October 1983, Cowlitz County officials told his family that Melanson "is believed [...]

3634-559: The new north-facing crater and consisted of glowing pumice bombs and very hot pumiceous ash. Some of these hot flows covered ice or water, which flashed to steam, creating craters up to 65 ft (20 m) in diameter and sending ash as much as 6,500 ft (2,000 m) into the air. Strong, high-altitude wind carried much of this material east-northeasterly from the volcano at an average speed around 60 miles per hour (100 km/h). By 9:45 am, it had reached Yakima, Washington , 90 mi (140 km) away, and by 11:45 am, it

3713-410: The next day. In time, ash fall from this eruption was reported as far away as Minnesota and Oklahoma , and some of the ash drifted around the globe within about 2 weeks. During the nine hours of vigorous eruptive activity, about 540,000,000 tons (540 × 10 ^ short tons or 490 × 10 ^  t) of ash fell over an area of more than 22,000 sq mi (57,000 km ). The total volume of

3792-462: The northward-radiating and expanding blast cloud continued for about another minute. Superheated flow material flashed water in Spirit Lake and North Fork Toutle River to steam, creating a larger, secondary explosion that was heard as far away as British Columbia , Montana , Idaho , and Northern California , yet many areas closer to the eruption ( Portland, Oregon , for example) did not hear

3871-524: The old summit crater , excavating a new crater 250 feet (75 m) wide, and sending an ash column about 7,000 feet (2.1 km) into the air. By this date, a 16,000-foot-long (4.9 km) eastward-trending fracture system had also developed across the summit area. This was followed by more earthquake swarms and a series of steam explosions that sent ash 10,000 to 11,000 feet (3,000 to 3,400 m) above their vent. Most of this ash fell between 3 and 12 mi (5 and 19 km) from its vent, but some

3950-407: The overlying snow. As in many previous St. Helens eruptions, this created huge lahars (volcanic mudflows ) and muddy floods that affected three of the four stream drainage systems on the mountain, and which started to move as early as 8:50 am. Lahars travelled as fast as 90 mph (140 km/h) while still high on the volcano, but progressively slowed to about 3 mph (4.8 km/h) on

4029-402: The partly molten rock, rich in high-pressure gas and steam, to suddenly explode northward toward Spirit Lake in a hot mix of lava and pulverized older rock, overtaking the landslide. An eruption column rose 80,000 feet (24 km; 15 mi) into the atmosphere and deposited ash in 11 U.S. states and various Canadian provinces. At the same time, snow, ice, and several entire glaciers on

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4108-434: The pyroclastic-flow deposits, at the south shore of Spirit Lake, and along the upper part of the North Fork Toutle River. These steam-blast explosions continued sporadically for weeks or months after the emplacement of pyroclastic flows, and at least one occurred a year later, on May 16, 1981. As the avalanche and initial pyroclastic flow were still advancing, a huge ash column grew to a height of 12 mi (19 km) above

4187-448: The region, to discuss the eruption, safety concerns, and to commemorate lives lost during the natural disaster. Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980. Several small earthquakes, beginning on March 15, indicated that magma might have begun moving below the volcano . On March 20, at 3:45 pm Pacific Standard Time , a shallow, magnitude-4.2 earthquake centered below

4266-515: The remains. An autopsy showed they had each been shot once. The ash fall created some temporary major problems with transportation, sewage disposal, and water treatment systems. Visibility was greatly decreased during the ash fall, closing many highways and roads. Interstate 90 from Seattle to Spokane was closed for a week and a half. Air travel was disrupted for between a few days and two weeks, as several airports in eastern Washington shut down because of ash accumulation and poor visibility. Over

4345-434: The rest was fragmented, older rock. The huge ensuing ash cloud sent skyward from St. Helens's northern foot was visible throughout the quiet zone. The near-supersonic lateral blast, loaded with volcanic debris, caused devastation as far as 19 mi (31 km) from the volcano. The area affected by the blast can be subdivided into roughly concentric zones: By the time this pyroclastic flow hit its first human victims, it

4424-465: The selection of some disposal sites. Some cities used old quarries and existing sanitary landfills ; others created dump sites wherever expedient. To minimize wind reworking of ash dumps, the surfaces of some disposal sites were covered with topsoil and seeded with grass. In Portland, the mayor eventually threatened businesses with fines if they failed to remove the ash from their parking lots. A refined estimate of $ 1.1 billion ($ 3.4 billion in 2023)

4503-473: The summit and escalated until a major explosive eruption took place on May   18, 1980, at 8:32   am. The eruption, which had a volcanic explosivity index of 5, was the first to occur in the contiguous United States since the much smaller 1915 eruption of Lassen Peak in California. It has often been considered the most disastrous volcanic eruption in U.S. history. The eruption was preceded by

4582-424: The trailing part of the landslide, blasting rock debris northward. The resulting blast directed the pyroclastic flow laterally. It consisted of very hot volcanic gases, ash, and pumice formed from new lava, as well as pulverized old rock, which hugged the ground. Initially moving about 220 mph (350 km/h), the blast quickly accelerated to around 670 mph (1,080 km/h), and it may have briefly passed

4661-471: The unincorporated town of Toutle . The North Fork's watershed was severely affected by the 1980 eruption of Mount St. Helens , which coated the valley with ash and filled it with successive mudflows. The result of the eruption was that many hillsides were stripped of forest, and as a result erosion has increased dramatically and the North Fork is now extremely laden with sediment. Previously, Spirit Lake

4740-471: The volcanic eruption. Extremes outside the period of record include two large floods on May 18, 1980, related to volcanic mud flows that came down the South Fork and then the North Fork, spaced nine hours apart. The eruption of Mount St. Helens and subsequent lahars poured vast amounts of sediment into the Toutle. The United States Army Corps of Engineers dredged sediment from the river and built

4819-827: The volcano melted, forming a series of large lahars (volcanic mudslides ) that reached as far as the Columbia River , nearly 50 miles (80 km) to the southwest. Less severe outbursts continued into the next day, only to be followed by other large, but not as destructive, eruptions later that year. The thermal energy released during the eruption was equal to 26 megatons of TNT . About 57 people were killed, including innkeeper and World War I veteran Harry R. Truman , photographers Reid Blackburn and Robert Landsburg , and volcanologist David A. Johnston . Hundreds of square miles were reduced to wasteland, causing over $ 1 billion in damage (equivalent to $ 3.4 billion in 2023), thousands of animals were killed, and Mount St. Helens

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4898-399: The volcano's groundwater system, causing many steam-driven explosions (phreatic eruptions). As May 18 dawned, Mount St. Helens's activity did not show any change from the pattern of the preceding month. The rates of bulge movement and sulfur dioxide emission, and ground temperature readings did not reveal any changes indicating a catastrophic eruption. USGS volcanologist David A. Johnston

4977-516: The volcano's north flank, signaled the volcano's return from 123 years of hibernation. A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale . A total of 174 shocks of magnitude 2.6 or greater was recorded during those two days. Shocks of magnitude 3.2 or greater occurred at

5056-404: The volcano's northeast slope to create much larger lahars. These mudflows traveled down the north and south forks of the Toutle River and joined at the confluence of the Toutle forks and the Cowlitz River near Castle Rock, Washington , at 1:00 pm. Ninety minutes after the eruption, the first mudflow had moved 27 mi (43 km) upstream, where observers at Weyerhaeuser 's Camp Baker saw

5135-420: The volcano, they have similar values around 700 nm (around 0.009), while they differ significantly around 300 nm. Here, the 11.2 mi (18 km) sample ( k was found to be around 0.009) was much more absorbent than the 9.3 mi (15 km) sample ( k was found to be around 0.002). The hot, exploding material also broke apart and melted nearly all of the mountain's glaciers, along with most of

5214-464: The volume of magma that pushed into the volcano and deformed its surface. Because the intruding magma remained below ground and was not directly visible, it was called a cryptodome , in contrast to a true lava dome exposed at the surface. On May 7, eruptions similar to those in March and April resumed, and over the following days, the bulge approached its maximum size. All activity had been confined to

5293-695: The way airborne ash is deposited after an eruption is strongly influenced by the meteorological conditions, a certain variation of the ash type will occur, as a function of distance to the volcano or time elapsed from eruption. The ash from Mount St. Helens is no exception, hence the ash properties have large variations. The bulk chemical composition of the ash has been found to be about 65% silicon dioxide , 18% aluminum oxide , 5% ferric oxide , 4% each calcium oxide and sodium oxide , and 2% magnesium oxide . Trace elements were also detected, their concentrations varying as 0.05–0.09% chlorine , 0.02–0.03% fluorine , and 0.09–0.3% sulfur . The index of refraction ,

5372-428: Was built by the U.S. Army Corps of Engineers on the river in 1989 to prevent this sediment from traveling downstream and clogging the shipping channel of the Columbia River. The upper part of the North Fork Toutle River watershed was redirected to the crater of Mount St. Helens itself until 1982. The river's headstreams begin on a volcanic ash deposit roughly 3 miles (5 km) long and 200 feet (61 m) deep, which

5451-631: Was carried 150 mi (240 km) south to Bend, Oregon , or 285 mi (460 km) east to Spokane, Washington . A second, new crater and a blue flame were observed on March 29. The flame was visibly emitted from both craters and was probably created by burning gases. Static electricity generated from ash clouds rolling down the volcano sent out lightning bolts that were up to 2 mi (3 km) long. Ninety-three separate outbursts were reported on March 30, and increasingly strong harmonic tremors were first detected on April 1, alarming geologists and prompting Governor Dixy Lee Ray to declare

5530-455: Was covered, and the total volume of the deposit was about 0.7 cu mi (2.9 km ). Scientists were able to reconstruct the motion of the landslide from a series of rapid photographs by Gary Rosenquist, who was camping 11 mi (18 km) away from the blast 46°18′49″N 122°02′12″W  /  46.31361°N 122.03667°W  / 46.31361; -122.03667 . Rosenquist, his party, and his photographs survived because

5609-731: Was determined in a study by the International Trade Commission at the request of the United States Congress . A supplemental appropriation of $ 951 million for disaster relief was voted by Congress, of which the largest share went to the Small Business Administration , U.S. Army Corps of Engineers , and the Federal Emergency Management Agency . Also, indirect and intangible costs of

5688-493: Was fresh lava in the form of ash, pumice, and volcanic bombs , while the rest was fragmented, older rock. The removal of the north side of the mountain (13% of the cone's volume) reduced Mount St. Helens's height by about 1,300 ft (400 m) and left a crater 1 to 2 mi (1.6 to 3.2 km) wide and 2,100 ft (640 m) deep with its north end open in a huge breach. More than 4,000,000,000 board feet (9,400,000 m ) of timber were damaged or destroyed, mainly by

5767-515: Was killed by the ash cloud. He was able to protect his film with his body, and the surviving photos provided geologists with valuable documentation of the historic eruption. Another eruption victim, amateur radio operator Gerry Martin, located near the Coldwater peak and farther north of Johnston's position 46°17′59.7″N 122°12′55″W  /  46.299917°N 122.21528°W  / 46.299917; -122.21528 , reporting his sighting of

5846-618: Was left with a crater on its north side. At the time of the eruption, the summit of the volcano was owned by the Burlington Northern Railroad , but afterward, the railroad donated the land to the United States Forest Service . The area was later preserved in the Mount St. Helens National Volcanic Monument and due to the eruption, the state recognized the month of May as "Volcano Awareness Month" and events are held at Mt. St. Helens, or within

5925-426: Was on duty at an observation post around 6 mi (10 km) north of the volcano: as of 6:00 am, Johnston's measurements did not indicate any unusual activity. At 8:32 am, a magnitude-5.1 earthquake centered directly below the north slope triggered that part of the volcano to slide, approximately 7–20 seconds after the shock, followed a few seconds later by the main volcanic blast . The landslide,

6004-471: Was over Spokane, Washington . A total of 4 to 5 in (100 to 130 mm) of ash fell on Yakima, and areas as far east as Spokane were plunged into darkness by noon, where visibility was reduced to 10 ft (3 m) and 0.5 in (13 mm) of ash fell. Continuing eastward, St. Helens's ash fell in the western part of Yellowstone National Park by 10:15 pm, and was seen on the ground in Denver

6083-520: Was stationed at Observation post Coldwater II 46°16′37.5″N 122°13′28.0″W  /  46.277083°N 122.224444°W  / 46.277083; -122.224444 , located just 6 miles (10 km) north of the mountain, was one of those killed 46°17′37″N 122°13′27.1″W  /  46.29361°N 122.224194°W  / 46.29361; -122.224194 , as was Reid Blackburn 46°17′53.1″N 122°17′23.5″W  /  46.298083°N 122.289861°W  / 46.298083; -122.289861 ,

6162-469: Was still as hot as 680 °F (360 °C) and filled with suffocating gas and flying debris. Most of the 57 people known to have died in that day's eruption succumbed to asphyxiation , while several died from burns. Lodge owner Harry R. Truman was buried under hundreds of feet of avalanche material 46°15′59.6″N 122°09′33.3″W  /  46.266556°N 122.159250°W  / 46.266556; -122.159250 . Volcanologist David A. Johnston, who

6241-447: Was the source of the river, but eruptions blocked the outlet and Spirit Lake no longer drains directly into the North Fork; instead, a tunnel was excavated in 1985 to connect the lake with South Coldwater Creek, a tributary of the North Fork. Once a mature river, the North Fork has transformed into a braided stream of relatively young origin, and its valley floor is less than three decades old. The Toutle River Sediment Retention Structure

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