:Mount St. Helens

File:Mount St. Helens, one day before the devastating eruption.jpg]]

Mount St. Helens is {{convert|34|mi|km}} west of Mount Adams, in the western part of the Cascade Range. Considered "brother and sister" mountains, the two volcanoes are approximately {{convert|50|mi|km|-1}} from Mount Rainier, the highest of the Cascade volcanoes. Mount Hood, the nearest major volcanic peak in Oregon, is {{convert|60|mi|km|-1}} 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.{{cite report |last1=Mullineaux |first1=D. R. |last2=Crandell |first2=D. R. |year=1981 |title=The 1980 eruptions of Mount St. Helens, Washington |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/PP1250/MullineauxCrandell/eruptive_history.html |id=Professional Paper 1250 |page=3 |publisher=United States Geological Survey |access-date=2006-10-28 |archive-date=1 January 2007 |archive-url=https://web.archive.org/web/20070101023724/http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/PP1250/MullineauxCrandell/eruptive_history.html |url-status=dead }} The volcano is considered the most active in the Cascades within the Holocene epoch, which encompasses roughly the last 10,000 years.{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/description_msh.html |title=Description of Mount St. Helens |publisher=USGS |access-date=2006-11-15}}

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".{{cite book |last=Harris |first=Stephen L. |chapter=Mount St. Helens: A living fire mountain |pages=201–228 |title=Fire Mountains of the West: The Cascade and Mono Lake volcanoes |year=1988 |edition=1st |publisher=Mountain Press Publishing Company |location=Missoula, Montana |isbn=0-87842-220-X |chapter-url=https://archive.org/details/firemountainsofw00harr/page/201 |chapter-url-access=registration}}{{rp|page=201}} Its ice cover just prior to the 1980 eruption included eleven named glaciers: Wishbone, Loowit, Leschi, Forsyth, Nelson, Ape,

Shoestring, Swift, Dryer, Toutle, and Talus. Of these eleven, only the Shoestring Glacier revived somewhat post-eruption.{{cite journal|last=Phillips|first=William M.|title=Geologic Guide to the Monitor Ridge Climbing Route, Mount St. Helens, Washington |journal=Washington Geologic Newsletter|date=October 1987|volume=15|issue=4|pages=3–13|url=https://www.dnr.wa.gov/Publications/ger_washington_geology_1987_v15_no4.pdf}} The peak rose more than {{convert|5000|ft|m|-2}} above its base, where the lower flanks merge with adjacent ridges. The mountain is {{convert|6|mi|km}} across at its base, which is at an elevation of {{convert|4400|ft|m|-2}} on the northeastern side and {{convert|4000|ft|m|-2}} elsewhere. At the pre-eruption tree line, the width of the cone was {{convert|4|mi|km}}.

Streams that originate on the volcano enter three main river systems: The Toutle River on the north and northwest, the Kalama River on the west, and the Lewis River on the south and east. The streams are fed by abundant rain and snow. The average annual rainfall is {{convert|140|in|cm|}}, and the snowpack on the mountain's upper slopes can reach {{convert|16|ft|m|1}}. The Lewis River is impounded by three dams for hydroelectric power generation. The southern and eastern sides of the volcano drain into an upstream impoundment, the Swift Reservoir, which is directly south of the volcano's peak.

Although Mount St. Helens is in Skamania County, Washington, access routes to the mountain run through Cowlitz County to the west, and Lewis County to the north. State Route 504, locally known as the Spirit Lake Memorial Highway, connects with Interstate 5 at Exit 49, {{convert|34|mi|km}} to the west of the mountain.{{cite book |last=Harris |first=Stephen L. |chapter=Mount St. Helens: A living fire mountain |pages=201–228 |title=Fire Mountains of the West: The Cascade and Mono Lake volcanoes |year=2005 |edition=3rd |publisher=Mountain Press Publishing Company |location=Missoula, Montana |isbn=0-87842-511-X}}{{rp|page=297}} That north–south highway skirts the low-lying cities of Castle Rock, Longview and Kelso along the Cowlitz River, and passes through the Vancouver, Washington–Portland, Oregon metropolitan area less than {{convert|50|mi|km|-1}} to the southwest. The community nearest the volcano is Cougar, Washington, in the Lewis River valley {{convert|11|mi|km}} south-southwest of the peak. Gifford Pinchot National Forest surrounds Mount St. Helens.

{{Main|Crater Glacier}}

During the winter of 1980–1981, a new glacier appeared. Now officially named Crater Glacier, it was formerly known as the Tulutson Glacier. Shadowed by the crater walls and fed by heavy snowfall and repeated snow avalanches, it grew rapidly ({{convert|14|ft|m}} per year in thickness). By 2004, it covered about {{convert|0.36|sqmi|km2|2}}, and was divided by the dome into a western and eastern lobe. Typically, by late summer, the glacier looks dark from rockfall from the crater walls and ash from eruptions. As of 2006, the ice had an average thickness of {{convert|300|ft|m|-2}} and a maximum of {{convert|650|ft|m|-2}}, 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.{{cite report |last1=Brugman |first1=Melinda M. |first2=Austin |last2=Post |author2-link=Austin Post (photographer) |id=USGS Circular 850-D |title=Effects of volcanism on the glaciers of Mount St. Helens |website=United States Geological Survey |url=https://pubs.er.usgs.gov/publication/cir850D |year=1981 |page=22 |access-date=2007-03-07}}{{cite journal |last1=Wiggins |first1=Tracy B. |last2=Hansen |first2=Jon D. |last3=Clark |first3=Douglas H. |title=Growth and flow of a new glacier in Mount St. Helens Crater |journal=Abstracts with Programs |publisher=Geological Society of America |volume=34 |issue=5 |page=91 |year=2002}}{{cite journal |author1=Schilling, Steve P. |author2=Carrara, Paul E. |author3=Thompson, Ren A. |author4=Iwatsubo, Eugene Y. |title=Posteruption glacier development within the crater of Mount St. Helens, Washington, USA |journal=Quaternary Research |volume=61 |issue=3 |pages=325–329 |publisher=Elsevier Science (USA) |year=2004 |doi=10.1016/j.yqres.2003.11.002 |bibcode=2004QuRes..61..325S|s2cid=128528280 }}{{cite journal |last1=McCandless |first1=Melanie |last2=Plummer |first2=Mitchell |last3=Clark |first3=Douglas |title=Predictions of the growth and steady-state form of the Mount St. Helens Crater Glacier using a 2-D glacier model |journal=Abstracts with Programs |publisher=Geological Society of America |volume=37 |issue=7 |page=354 |year=2005}}{{cite web |author1=Schilling, Steve P. |author2=Ramsey, David W. |author3=Messerich, James A. |author4=Thompson, Ren A. |id=USGS Scientific Investigations Map 2928 |title=Rebuilding Mount St. Helens |url=http://pubs.usgs.gov/sim/2006/2928/ |date=2006-08-08 |access-date=2007-03-07 }}

From 2004, volcanic activity pushed aside the glacier lobes and upward by the growth of new volcanic domes. The surface of the glacier, once mostly without crevasses, turned into a chaotic jumble of icefalls heavily criss-crossed with crevasses and seracs caused by movement of the crater floor.{{cite report |url=http://www.fs.fed.us/gpnf/mshnvm/volcano-review/documents/Volcano_Review_2008_Final_lowrez-201.pdf |title=Volcano Review |archive-url=https://web.archive.org/web/20080626134702/http://www.fs.fed.us/gpnf/mshnvm/volcano-review/documents/Volcano_Review_2008_Final_lowrez-201.pdf |archive-date=2008-06-26 |publisher=US Forest Service}} The new domes have almost separated the Crater Glacier into an eastern and western lobe. Despite the volcanic activity, the termini of the glacier have still advanced, with a slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe. Due to the advance, two lobes of the glacier joined in late May 2008 and thus the glacier completely surrounds the lava domes.{{cite AV media |medium=photo |title=MSH08 aerial: New dome from north 30 May 2008 |url=http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_aerial_new_dome_from_north_05-30-08_med.jpg |archive-url=https://web.archive.org/web/20080626134704/http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_aerial_new_dome_from_north_05-30-08_med.jpg |archive-date=2008-06-26 |publisher=United States Geological Survey |first=Steve |last=Schilling |date=2008-05-30 |access-date=2008-06-07}} – Glacier is still connected south of the lava dome.{{cite AV media |medium=photo |title=MSH08 aerial: St. Helens crater from north 30 May 2008 |url=http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_crater_glacier_arms_touching_05-30-08_med.jpg |archive-url=https://web.archive.org/web/20080626134705/http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH08/MSH08_crater_glacier_arms_touching_05-30-08_med.jpg |archive-date=2008-06-26 |publisher=United States Geological Survey |first=Steve |last=Schilling |date=2008-05-30 |access-date=2008-06-07}} – Glacier arms touch on North end of glacier. In addition, since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice onto its surface below; there are two rock glaciers to the north of the eastern lobe of Crater Glacier.{{cite conference |author1=Haugerud, R. A. |author2=Harding, D. J. |author3=Mark, L. E. |author4=Zeigler, J. |author5=Queija, V. |author6=Johnson, S. Y. |title=Lidar measurement of topographic change during the 2004 eruption of Mount St. Helens, WA |date=December 2004 |bibcode=2004AGUFM.V53D..01H |volume=53 |page=1 |conference=American Geophysical Union, Fall Meeting}}

Mount St. Helens has an alpine tundra climate (ET).

{{Weather box

| single line = Y

| location = Mount St. Helens Summit. 1991–2020

| Jan high F = 30.0

| Feb high F = 29.4

| Mar high F = 30.1

| Apr high F = 33.7

| May high F = 42.3

| Jun high F = 48.8

| Jul high F = 59.7

| Aug high F = 60.2

| Sep high F = 55.1

| Oct high F = 44.5

| Nov high F = 33.0

| Dec high F = 28.6

| year high F = 41.3

| Jan mean F = 25.1

| Feb mean F = 23.2

| Mar mean F = 22.9

| Apr mean F = 25.4

| May mean F = 32.9

| Jun mean F = 38.7

| Jul mean F = 48.1

| Aug mean F = 48.6

| Sep mean F = 44.3

| Oct mean F = 35.8

| Nov mean F = 27.6

| Dec mean F = 23.9

| year mean F = 33.0

| Jan low F = 20.2

| Feb low F = 17.0

| Mar low F = 15.7

| Apr low F = 17.2

| May low F = 23.4

| Jun low F = 28.6

| Jul low F = 36.5

| Aug low F = 37.1

| Sep low F = 33.4

| Oct low F = 27.2

| Nov low F = 22.2

| Dec low F = 19.1

| year low F = 24.8

| precipitation colour = green

| Jan precipitation inch = 27.00

| Feb precipitation inch = 21.01

| Mar precipitation inch = 24.17

| Apr precipitation inch = 16.61

| May precipitation inch = 9.23

| Jun precipitation inch = 7.52

| Jul precipitation inch = 2.07

| Aug precipitation inch = 3.55

| Sep precipitation inch = 7.81

| Oct precipitation inch = 20.68

| Nov precipitation inch = 30.88

| Dec precipitation inch = 29.99

| year precipitation inch = 200.52

| Jan dew point F = 18.7

| Feb dew point F = 16.0

| Mar dew point F = 15.3

| Apr dew point F = 16.2

| May dew point F = 22.2

| Jun dew point F = 27.4

| Jul dew point F = 33.3

| Aug dew point F = 33.3

| Sep dew point F = 29.4

| Oct dew point F = 25.4

| Nov dew point F = 20.8

| Dec dew point F = 18.2

| year dew point F = 23.0

|source 1 = PRISM Climate Group{{cite web|url=http://prism.oregonstate.edu/explorer/|title=PRISM Climate Group, Oregon State University|website=www.prism.oregonstate.edu|access-date=January 12, 2022}}}}

{{see also|Geology of the Pacific Northwest}}

File:Cascade Range plate tectonics-en.svg of the Cascade Range]]

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.{{cite web|url=http://geomaps.wr.usgs.gov/parks/province/cascade1.html|title=Pacific – Cascades Volcanic Province|archive-url=https://web.archive.org/web/20060923012715/http://geomaps.wr.usgs.gov/parks/province/cascade1.html|archive-date=2006-09-23|access-date=2021-03-13}} {{PD-notice}} Beneath the Cascade Volcanic Province, a dense oceanic plate sinks beneath the North American Plate; a process known as subduction in geology. As the oceanic slab sinks deeper into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The supercritical water rises into the pliable mantle above the subducting plate, causing some of the mantle to melt. This newly formed magma ascends upward through the crust along a path of least resistance, both by way of fractures and faults as well as by melting wall rocks. The addition of melted crust changes the geochemical composition. Some of the melt rises toward the Earth's surface to erupt, forming the Cascade Volcanic Arc above the subduction zone.{{cite web|url=http://geomaps.wr.usgs.gov/parks/province/cascade2.html|title=Pacific – Cascades Volcanic Province|archive-url=https://web.archive.org/web/20060924090635/http://geomaps.wr.usgs.gov/parks/province/cascade2.html|archive-date=2006-09-24}} {{PD-notice}}

The magma from the mantle has accumulated in two chambers below the volcano: one approximately {{convert|5|-|12|km|mi|0|order=flip}} below the surface, the other about {{convert|12|-|40|km|mi|0|order=flip}}.{{cite journal|title=Deep magma chambers seen beneath Mount St. Helens|first=Eric|last=Hand|date=2015-11-04|journal=Science|doi=10.1126/science.aad7392|url=https://www.science.org/content/article/deep-magma-chambers-seen-beneath-mount-st-helens}} The lower chamber may be shared with Mount Adams and the Indian Heaven volcanic field.{{cite web|url=https://gizmodo.com/mount-saint-helens-may-share-magma-with-an-entire-field-1741775204|title=Mount Saint Helens May Share Magma with an Entire Field of Volcanoes|first=Mika|last=McKinnon|date=2015-11-10|website=Gizmodo}}

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).{{cite web|url=http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/volcanic-history-summary.shtml|publisher=USDA Forest Service |archive-url=https://web.archive.org/web/20081011012508/http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/volcanic-history-summary.shtml |archive-date=2008-10-11 |title=Mount St. Helens – Summary of Volcanic History}} The modern period, since about 2500 BC, is called the "Spirit Lake Stage". Collectively, the pre–Spirit Lake stages are known as the "ancestral stages". The ancestral and modern stages differ primarily in the composition of the erupted lavas; ancestral lavas consisted of a characteristic mixture of dacite and andesite, while modern lava is very diverse (ranging from olivine basalt to andesite and dacite).{{rp|page=214}}

St. Helens started its growth in the Pleistocene 37,600 years ago, during the Ape Canyon stage, with dacite and andesite eruptions of hot pumice and ash.{{rp|page=214}} Thirty-six thousand years ago a large mudflow cascaded down the volcano;{{rp|page=214}} 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 the last glacial period of the current ice age.{{rp|page=214}}

The second eruptive period, the Cougar Stage, started 20,000 years ago and lasted for 2,000 years.{{rp|page=214}} Pyroclastic flows of hot pumice and ash along with dome growth occurred during this period. Another 5,000 years of dormancy followed, only to be upset by the beginning of the Swift Creek eruptive period, typified by pyroclastic flows, dome growth and blanketing of the countryside with tephra. Swift Creek ended 8,000 years ago.

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.{{rp|page=215}} An eruption in 1900 BC was the largest known eruption from St. Helens during the Holocene epoch, depositing the Yn tephra.{{rp|page=215}}{{cite journal |last1=Pallister |first1=John S. |last2=Clynne |first2=Michael A. |last3=Wright|first3=Heather M. |last4=Van Eaton |first4=Alexa R. |last5=Vallance |first5=James W. |last6=Sherrod |first6=David R. |last7=Kokelaar |first7=B. Peter |title=Field-Trip Guide to Mount St. Helens, Washington: An overview of the eruptive history and petrology, tephra deposits, 1980 proclastic density current deposits, and the crater / Eruptive history |journal=Scientific Investigations Report |page=11 |publisher=United States Department of the Interior |year=2017 |issn=2328-0328}} This eruptive period lasted until about 1600 BC and left {{convert|18|in|cm}} deep deposits of material {{convert|50|mi|km|-1}} 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.{{rp|page=215}} All told there may have been up to {{convert|2.5|mi3|km3}} of material ejected in this cycle.{{rp|page=215}} Some 400 years of dormancy followed.

St. Helens came alive again around 1200 BC—the Pine Creek eruptive period.{{rp|page=215}} This lasted until about 800 BC and was characterized by smaller-volume eruptions. Numerous dense, nearly red hot pyroclastic flows sped down St. Helens' flanks and came to rest in nearby valleys. A large mudflow partly filled {{convert|40|mi|km}} of the Lewis River valley sometime between 1000 BC and 500 BC.

File:East Dome Mount St. Helens.jpg

The next eruptive period, the Castle Creek period, began about 400 BC, and is characterized by a change in the composition of St. Helens' lava, with the addition of olivine and basalt.{{rp|page=216}} The pre-1980 summit cone started to form during the Castle Creek period. Significant lava flows in addition to the previously much more common fragmented and pulverized lavas and rocks (tephra) distinguished this period. Large lava flows of andesite and basalt covered parts of the mountain, including one around the year 100 BC that traveled all the way into the Lewis and Kalama river valleys.{{rp|page=216}} Others, such as Cave Basalt (known for its system of lava tubes), flowed up to {{convert|9|mi|km}} from their vents.{{rp|page=216}} During the first century, mudflows moved {{convert|30|mi|km|-1}} down the Toutle and Kalama river valleys and may have reached the Columbia River. Another 400 years of dormancy ensued.

The Sugar Bowl eruptive period was short and markedly different from other periods in Mount St. Helens history. It produced the only unequivocal laterally directed blast known from Mount St. Helens before the 1980 eruptions. During Sugar Bowl time, the volcano first erupted quietly to produce a dome, then erupted violently at least twice producing a small volume of tephra, directed-blast deposits, pyroclastic flows, and lahars. East Dome, a small hypersthene-homblende dacite dome on the east slope of the volcano, was likely formed around the Sugar Bowl period.{{Cite web |date=2017-06-02 |title=The Eruptive History of Mount St. Helens |url=https://volcano.oregonstate.edu/eruptive-history-mount-st-helens |access-date=2023-03-02 |website=Volcano World |language=en}} Formation of East Dome was preceded by an explosive eruption.{{Cite web |title=Global Volcanism Program {{!}} Image GVP-02835 |url=https://volcano.si.edu/gallery/ShowImage.cfm?photo=GVP-02835 |access-date=2023-03-02 |website=volcano.si.edu |language=en}}

File:1890 Clohessy and Strengele engraving of Mount St Helens (cropped).jpg of America". The once-familiar shape was formed out of the Kalama and Goat Rocks eruptive periods.]]

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.{{cite report |url=https://pubs.er.usgs.gov/publication/pp1563 |title=Pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington |website=United States Geological Survey |id=Professional Paper 1563|first=Donal R.|last=Mullineaux|year=1996 |access-date=2006-11-15}} In 1482, another large eruption rivaling the 1980 eruption in volume is known to have occurred. Ash and pumice piled {{convert|6|mi|km}} northeast of the volcano to a thickness of {{convert|3|ft|m|1}}; {{convert|50|mi|km|-1}} away, the ash was {{convert|2|in|cm|0}} deep. Large pyroclastic flows and mudflows subsequently rushed down St. Helens' west flanks and into the Kalama River drainage system.

This 150-year period next saw the eruption of less silica-rich lava in the form of andesitic ash that formed at least eight alternating light- and dark-colored layers.{{rp|page=216}} Blocky andesite lava then flowed from St. Helens' summit crater down the volcano's southeast flank.{{rp|page=216}} 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 the summit.{{rp|page=217}} 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.{{rp|page=217}} The volcano remained quiet for the next 150 years.

The 57-year eruptive period that started in 1800 was named after the Goat Rocks dome and is the first period for which both oral and written records exist.{{rp|page=217}} 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 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 the United States' largest slave rebellion.{{cite book |last1=Breen |first1=Patrick H. |title=Nat Turner's revolt: rebellion and response in Southampton County, Virginia |date=2005 |url=https://esploro.libs.uga.edu/esploro/outputs/doctoral/Nat-Turners-revolt-rebellion-and-response-in-Southampton-County-Virginia/9949332806802959 |access-date=21 November 2021}}) The vent was apparently at or near Goat Rocks on the northeast flank.{{rp|page=217}} 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 {{convert|1300|ft|m}} of the mountain.

File:MSH-10B Mount St. Helens Erupts, Portland View, May 18, 1980 (22636191326).jpg as viewed from Portland, Oregon. The Fremont Bridge is visible in the bottom left corner.]]

File:MSH80 eruption mount st helens 05-18-80.jpg.]]

{{Main|1980 eruption of Mount St. Helens}}

On March 20, 1980, Mount St. Helens experienced a magnitude 4.2 earthquake, and on March 27, steam venting started.{{cite web|url=http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/pre-eruption-0322.shtml|publisher=USDA Forest Service |archive-url=https://web.archive.org/web/20071113092736/http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/pre-eruption-0322.shtml |archive-date=2007-11-13 |title=Summary of Events Leading Up to the May 18, 1980, eruption of Mount St. Helens: March 22–28}} By the end of April, the north side of the mountain had started to bulge.{{cite web |url=http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/pre-eruption-0426.shtml |publisher=USDA Forest Service |archive-url=https://web.archive.org/web/20071113092741/http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/pre-eruption-0426.shtml |archive-date=2007-11-13 |title=Summary of Events Leading Up to the May 18, 1980 Eruption of Mount St. Helens: April 26–May 2}}

On May 18, at 8:32 am, 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 {{convert|230|sqmi|km2|-1}}. More than 1.5 million metric tons of sulfur dioxide were released into the atmosphere.{{cite web |url=http://volcanoes.usgs.gov/activity/methods/gas/msh1980-88.php |title=Emission of sulfur dioxide gas from Mount St. Helens, 1980–1988 |publisher=United States Geological Survey |date=2008-09-25 |access-date=2009-03-25 |archive-date=13 April 2009 |archive-url=https://web.archive.org/web/20090413190247/http://volcanoes.usgs.gov/activity/methods/gas/msh1980-88.php |url-status=dead }} 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 {{convert|3900000|yd3|m3|-5}} of material was transported {{convert|17|mi|km}} south into the Columbia River by the mudflows.{{rp|page=209}}

For more than nine hours, a vigorous plume of ash erupted, eventually reaching {{convert|12|to|16|mi|km}} above sea level.{{cite book|title=Geology of U.S. parklands|first1=Eugene P.|last1=Kiver|first2=David V.|last2=Harris|year=1999|edition=5th|page=149|isbn=978-0-471-33218-3|publisher=Wiley}} The plume moved eastward at an average speed of {{convert|60|mph|km/h|-1}} with ash reaching Idaho by noon. Ashes from the eruption were found on top of cars and roofs the next morning as far away as Edmonton, Alberta, Canada.

By about 5:30 p.m. on May 18, the vertical ash column declined in stature, and less-severe outbursts continued through the night and for the next several days. The St. Helens May 18 eruption released 24 megatons of thermal energy{{cite web |url=http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/volcanic-eruption-summary.shtml |archive-url=https://web.archive.org/web/20090529034823/http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/volcanic-eruption-summary.shtml |archive-date=2009-05-29 |title=Mount St. Helens National Volcanic Monument |publisher=United States Forest Service |quote=24 megatons thermal energy}} and ejected more than {{convert|0.67|mi3|km3|2}} of material.{{cite web |url=http://pubs.usgs.gov/fs/2000/fs036-00/ |title=Mount St. Helens – From the 1980 eruption to 2000 |id=Fact Sheet 036-00 |publisher=United States Geological Survey |access-date=2006-11-12|year=2000}} The removal of the north side of the mountain reduced St. Helens' height by about {{convert|1300|ft|m|-2}} and left a crater {{convert|1.2 to 1.8|mi|km|0}} wide and {{convert|2,084|ft|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, {{convert|185|mi|km}} of highway, and {{convert|15|mi|km|0}} of railways.

Between 1980 and 1986, activity continued at Mount St. Helens, with a new lava dome forming in the crater. Numerous small explosions and dome-building eruptions occurred. 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.{{cite journal |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/EV23/small_expl.html |first=Bobbie |last=Myers |year=1992 |title=Small explosions interrupt 3 year quiescence at Mount St. Helens, Washington |journal=Earthquakes and Volcanoes |volume=23 |issue=2 |pages=58–73 |bibcode=1992EVUSG..23...58M |access-date=2006-11-26 |via=vulcan.wr.usgs.gov |archive-url=https://web.archive.org/web/20061230141620/http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/EV23/small_expl.html |archive-date=2006-12-30}}

{{Main|2004–2008 volcanic activity of Mount St. Helens}}

File:Whaleback, Mount St Helens volcanic crater (February 22 2005).jpg

Magma reached the surface of the volcano about October 11, 2004, resulting in the building of a new lava dome on the existing dome's south side. This new dome continued to grow throughout 2005 and into 2006. Several transient features were observed, such as a lava spine nicknamed the "whaleback", which comprised long shafts of solidified magma being extruded by the pressure of magma beneath. These features were fragile and broke down soon after they were formed. On July 2, 2005, the tip of the whaleback broke off, causing a rockfall that sent ash and dust several hundred meters into the air.{{cite web |title=Before and after images |publisher=USGS |url=http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH05/MSH05_dome_from_sugarbowl_tip_spine_collapse_July2005_med.jpg |archive-url=https://web.archive.org/web/20050903224652/http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH05/MSH05_dome_from_sugarbowl_tip_spine_collapse_July2005_med.jpg |archive-date=2005-09-03}}

Mount St. Helens showed significant activity on March 8, 2005, when a {{convert|36000|ft|m|adj=on}} plume of steam and ash emerged—visible from Seattle.{{cite web |archive-url=https://web.archive.org/web/20050311015440/http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/Monitoring/plume_in_the_evening_8march05.html |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/Monitoring/plume_in_the_evening_8march05.html |archive-date=2005-03-11 |title=Mount St. Helens, Washington – 'Plume in the Evening' |date=March 8, 2005 |publisher=USGS |access-date=2006-11-15}} This relatively minor eruption was a release of pressure consistent with ongoing dome building. The release was accompanied by a magnitude 2.5 earthquake.

Another feature to emerge from the dome was called the "fin" or "slab". Approximately half the size of a football field, the large, cooled volcanic rock was being forced upward as quickly as {{convert|6|ft|m|0|abbr=on}} per day.{{cite news |title=New slab growing in Mount St. Helens dome |url=http://www.foxnews.com/story/0,2933,194342,00.html |access-date=2010-12-06 |newspaper=Fox News |archive-url=https://web.archive.org/web/20121026095220/http://www.foxnews.com/story/0,2933,194342,00.html |archive-date=2012-10-26 }}{{cite web |title=Rock Slab Growing at Mt. St. Helens Volcano |date=May 9, 2006 |url=http://apod.nasa.gov/apod/ap060509.html |website=Astronomy Picture of the Day}} In mid-June 2006, the slab was crumbling in frequent rockfalls, although it was still being extruded. The height of the dome was {{convert|7550|ft|m}}, still below the height reached in July 2005 when the whaleback collapsed.

On October 22, 2006, at 3:13 p.m. PST, a magnitude 3.5 earthquake broke loose Spine 7. The collapse and avalanche of the lava dome sent an ash plume {{convert|2000|ft|m|-2}} 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.{{cite web |url=http://vulcan.wr.usgs.gov/ |title=In the News |website=Cascades Volcano Observatory |archive-url=https://web.archive.org/web/20070107023839/http://vulcan.wr.usgs.gov/ |archive-date=2007-01-07 |access-date=2007-01-04}} The volcano was in continuous eruption from October 2004, but this eruption consisted in large part of a gradual extrusion of lava forming a dome in the crater.

On January 16, 2008, steam began seeping from a fracture on top of the lava dome. Associated seismic activity was the most noteworthy since 2004. Scientists suspended activities in the crater and the mountain flanks, but the risk of a major eruption was deemed low.{{cite news |url=https://www.usatoday.com/tech/science/2008-01-17-3582451403_x.htm |title=Small quake reported at Mount St. Helens |newspaper=USA Today |access-date=2010-12-06 |date=January 17, 2008}} By the end of January, the eruption paused; no more lava was being extruded from the lava dome. On July 10, 2008, it was determined that the eruption had ended, after more than six months of no volcanic activity.{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/framework.html |title=Mount St. Helens, Washington – Eruption 2004 to current |publisher=USGS |access-date=2008-10-06 |archive-url=https://web.archive.org/web/20081006111613/http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/framework.html |archive-date=2008-10-06}}

File:Mount Saint Helens from the air, with Mount Adams in background 02.jpg in background]]

Future eruptions of Mount St. Helens will likely be even larger than the 1980 eruption.{{rp|296}} A large lahar flow is likely on branches of the Toutle River, possibly causing destruction in inhabited areas along the I-5 corridor.{{cite web | url=https://www.usgs.gov/volcanoes/mount-st-helens/volcanic-hazards-mount-st-helens | archive-url=https://web.archive.org/web/20210128124052/https://www.usgs.gov/volcanoes/mount-st-helens/volcanic-hazards-mount-st-helens | archive-date=28 January 2021 | title=Volcanic Hazards at Mount St. Helens }}

The volcano is considered "very high threat" by the United States Geological Survey and is closely monitored by the Cascades Volcano Observatory.{{Cite web |date=2023-11-08 |title=Hazards {{!}} U.S. Geological Survey |url=https://www.usgs.gov/volcanoes/mount-st.-helens/science/hazards |access-date=2025-02-16 |website=www.usgs.gov |language=en}}

File:Tree snags at Mount St. Helens.jpg

In its undisturbed state, the slopes of Mount St. Helens lie in the Western Cascades Montane Highlands ecoregion.{{cite web|last1=Pater|first1=D.|last2=Bryce|first2=S. A.|last3=Kagan|first3=J.|display-authors=et al|title=Ecoregions of Western Washington and Oregon|website=Environmental Protection Agency|url=ftp://newftp.epa.gov/EPADataCommons/ORD/Ecoregions/reg10/ORWAFront90.pdf|access-date=2021-03-26}}{{Dead link|date=March 2025 |bot=InternetArchiveBot |fix-attempted=yes }} Color poster with map, descriptive text, summary tables, and photographs; with a [ftp://newftp.epa.gov/EPADataCommons/ORD/Ecoregions/reg10/ORWABack.pdf Reverse side] This ecoregion has abundant precipitation; an average of {{convert|2373|mm|in|order=flip}} of precipitation falls each year at Spirit Lake.{{cite book|url=https://link.springer.com/content/pdf/10.1007%2F0-387-28150-9.pdf|title=Ecological Responses to the 1980 Eruption of Mount St. Helens|editor-first1=V. H.|editor-last1=Dale|editor-first2=F. J.|editor-last2=Swanson|editor-first3=C. M.|editor-last3=Crisafulli|chapter=Geological and Ecological Settings of MountSt. Helens Before May 18, 1980|first1=F. J.|last1=Swanson|first2=C. M.|last2=Crisafulli|first3=D. K.|last3=Yamaguchi|publisher=Springer|year=2005|doi=10.1007/0-387-28150-9|isbn=978-0-387-23868-5|s2cid=129738611 }} This precipitation supported dense forest up to {{convert|1600|m|ft|order=flip}}, with western hemlock, Douglas fir, and western redcedar. Above this, this forest was dominated by Pacific silver fir up to {{convert|1300|m|ft|order=flip}}. 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 {{convert|1340|m|ft|order=flip}}, the result of prior volcanic disturbance of 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.{{cite news|url=https://www.opb.org/artsandlife/article/mount-st-helens-washington-mountain-goats/|title=Counting Mountain Goats On Mount St. Helens|first=Jule|last=Gilfillan|publisher=Oregon Public Broadcasting|date=2017-06-30}}

The eruption of Mount St. Helens has been subject to more ecological study than has any other eruption, because research into disturbance commenced immediately after the eruption and because the eruption did not sterilize the immediate area. More than half of the papers on ecological response to volcanic eruption originated from studies of Mount St. Helens.{{cite book|chapter=Disturbance, Survival, and Succession: Understanding Ecological Responses to the 1980 Eruption of Mount St. Helens|first1=V. H.|last1=Dale|first2=F. J.|last2=Swanson|first3=C. M.|last3=Crisafulli|url=https://link.springer.com/content/pdf/10.1007%2F0-387-28150-9.pdf|title=Ecological Responses to the 1980 Eruption of Mount St. Helens|year=2005|editor-first1=V. H.|editor-last1=Dale|editor-first2=F. J.|editor-last2=Swanson|editor-first3=C. M.|editor-last3=Crisafulli|pages=3–11|doi=10.1007/0-387-28150-9|isbn=978-0-387-23868-5|s2cid=129738611 }}

Perhaps the most important ecological concept originating from the study of Mount St. Helens is the biological legacy.{{cite book|chapter=Reconfiguring Disturbance, Succession, and Forest Management: The Science of Mount St. Helens|first=J. F.|last=Franklin|url=https://link.springer.com/content/pdf/10.1007%2F0-387-28150-9.pdf|title=Ecological Responses to the 1980 Eruption of Mount St. Helens|year=2005|editor-first1=V. H.|editor-last1=Dale|editor-first2=F. J.|editor-last2=Swanson|editor-first3=C. M.|editor-last3=Crisafulli|pages=3–11|doi=10.1007/0-387-28150-9|isbn=978-0-387-23868-5|s2cid=129738611 }} Biological legacies are the survivors of catastrophic disturbance; they can either be alive (e.g., plants that survive ashfall or pyroclastic flow), organic debris, or biotic patterns remaining from before the disturbance.{{cite journal|title=Biological Legacies: A Critical Management Concept from Mount St. Helens|first=J. F.|last=Franklin|journal=Trans. 55' N. A. Wildl. & Nat. Res. Conf.|year=1990|pages=216–219|url=https://andrewsforest.oregonstate.edu/sites/default/files/lter/pubs/pdf/pub1231.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://andrewsforest.oregonstate.edu/sites/default/files/lter/pubs/pdf/pub1231.pdf |archive-date=2022-10-09 |url-status=live}} These biological legacies highly influence the reestablishment of the post-disturbance ecology.{{cite journal|title=Biological legacies: Direct early ecosystem recovery and food web reorganization after a volcanic eruption in Alaska|journal=Écoscience|first1=L. R.|last1=Walker|first2=D. S.|last2=Sikes|first3=A. R.|last3=DeGange|first4=S. C.|last4=Jewett|first5=G.|last5=Michaelson|first6=S. L.|last6=Talbot|first7=S. S.|last7=Talbot|first8=B.|last8=Wang|first9=J. C.|last9=Williams|display-authors=4|doi=10.2980/20-3-3603|volume=20|issue=3|pages=240–251|year=2013|bibcode=2013Ecosc..20..240W |s2cid=86156161}}

Some species from each trophic level survived the 1980 eruption, which allowed for relatively quick re-establishment of food webs.{{Cite web |title=Ecology of Mount St. Helen's National Monument {{!}} U.S. Geological Survey |url=https://www.usgs.gov/geology-and-ecology-of-national-parks/ecology-mount-st-helens-national-monument |access-date=2024-02-21 |website=www.usgs.gov}} Larger species saw greater mortality rates, with each of the area's large mammals — mountain goats, elk, deer, black bear and cougars — completely decimated.{{Cite news |last=McDonald |first=Bob |date=May 29, 2020 |title=40 years ago, Mount St. Helens blew its top. Here's how it got green again |url=https://www.cbc.ca/radio/quirks/may-30-swearing-makes-pain-more-tolerable-mt-st-helens-40-years-later-and-more-1.5589125/40-years-ago-mount-st-helens-blew-its-top-here-s-how-it-got-green-again-1.5589135 |access-date=February 21, 2024 |work=CBC Radio}} Eventually, each of the larger mammals migrated back into the area.{{Cite web |date=2013-10-20 |title=Life Reclaims Mount St. Helens |url=https://earthobservatory.nasa.gov/images/82151/life-reclaims-mount-st-helens |access-date=2024-02-21 |website=earthobservatory.nasa.gov |language=en}} Without access to adequate forage, many elk starved to death in the winters in the following decades.{{Cite web |title=Mount St. Helens elk starving to death {{!}} The Spokesman-Review |url=https://www.spokesman.com/stories/2006/may/14/mount-st-helens-elk-starving-to-death/ |access-date=2024-02-21 |website=www.spokesman.com}} By 2014, the mountain goat population had grown back to 65 members. In 2015, there were 152.{{Cite web |title=Counting Mountain Goats On Mount St. Helens |url=https://www.opb.org/artsandlife/article/mount-st-helens-washington-mountain-goats/ |access-date=2024-02-21 |website=opb |language=en}} Mountain goats are culturally significant to the Cowlitz Tribe, whose members historically harvested shed tufts of goat wool left behind on the mountain, and the tribe has played a role in monitoring the population, which continues to recover without human intervention.{{Cite web |date=2016-05-19 |title=Cowlitz Tribe Documents Return of Goats to Mount St. Helens |url=https://www.chronline.com/stories/cowlitz-tribe-documents-return-of-goats-to-mount-st-helens,52215 |access-date=2024-02-21 |website=The Daily Chronicle |language=en}}

File:St Helens before 1980 eruption horizon fixed.jpg legends were inspired by the volcano's beauty.]]

Native American lore contains numerous stories to explain the eruptions of Mount St. Helens and other Cascade volcanoes. The best known of these is the Bridge of the Gods story told by the Klickitat people.

In the story, the chief of all the gods and his two sons, Pahto (also called Klickitat) and Wy'east, traveled down the Columbia River from the Far North in search for a suitable area to settle.{{cite book |author-link=Archie Satterfield |last=Satterfield |first=Archie |title=Country Roads of Washington |publisher=iUniverse |year=2003 |isbn=0-595-26863-3 |page=82}}

They came upon an area that is now called The Dalles and thought they had never seen a land so beautiful. The sons quarreled over the land, so to solve the dispute their father shot two arrows from his mighty bow – one to the north and the other to the south. Pahto followed the arrow to the north and settled there while Wy'east did the same for the arrow to the south. The chief of the gods then built the Bridge of the Gods, so his family could meet periodically.

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 the huge bridge fell into the river, creating the cascades of the Columbia River Gorge.{{cite web |url=http://www.theoutlaws.com/indians4.htm |title=The Bridge of the Gods |website=theoutlaws.com |access-date=2006-11-26 |url-status=usurped |archive-url=https://web.archive.org/web/20060720204304/http://www.theoutlaws.com/indians4.htm |archive-date=2006-07-20}}

For punishment, the chief of the gods struck down each of the lovers and transformed them into great mountains where they fell. Wy'east, with his head lifted in pride, became the volcano known today as Mount Hood. Pahto, with his head bent toward his fallen love, was turned into Mount Adams. The beautiful Loowit became Mount St. Helens, known to the Klickitats as Louwala-Clough, which means "smoking or fire mountain" in their language (the Sahaptin call the mountain Loowit).{{cite web |title=Volcanoes and history: Cascade Range volcano names |url=http://vulcan.wr.usgs.gov/LivingWith/Historical/volcano_names.html |url-status=live |archive-url=https://web.archive.org/web/20061028220658/http://vulcan.wr.usgs.gov/LivingWith/Historical/volcano_names.html |archive-date=2006-10-28 |publisher=USGS |access-date=2006-10-20}}

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.{{cite web |title=Lawetlat'la |url=https://www.nps.gov/nr/feature/places/13000748.htm |website=www.nps.gov |access-date=16 July 2021}} In recognition of its cultural significance, over {{convert|12000|acre|ha}} of the mountain (roughly bounded by the Loowit Trail) have been listed on the National Register of Historic Places.{{cite web |url=http://www.nps.gov/history/nr/feature/places/pdfs/13000748.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.nps.gov/history/nr/feature/places/pdfs/13000748.pdf |archive-date=2022-10-09 |url-status=live |title=NRHP nomination form and supplementary listing record for Lawetlat'la [Mount St. Helens] |publisher=National Park Service |access-date=2013-10-30}}

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.

File:Fur trapper in Mount St Helen area.jpg working in the Mount St. Helens area]]

File:The Town Crier, v.12, no.33, Aug. 18, 1917 - DPLA - de44e160705c9a8bd082814fa232922c (page 1).jpg article from 1917 showing the northeast face of Mount Saint Helens. Although the newspaper is from 1917, the actual photograph was taken in 1899.]]

Royal Navy Commander George Vancouver and the officers of HMS Discovery made the Europeans' first recorded sighting of Mount St. Helens on May 19, 1792, while surveying the northern Pacific Ocean coast. Vancouver named the mountain for British diplomat Alleyne FitzHerbert, 1st Baron St Helens, on October 20, 1792,{{cite book |last1=Vancouver |first1=George |author-link=George Vancouver |title=A Voyage of Discovery to the North Pacific Ocean, and Round the World |date=1798 |location=London, UK |pages=421–422 |url=https://archive.org/stream/voyageofdiscover01vanc#page/420/mode/2up |oclc=54529835 |ol=24592146M}} as it came into view when the Discovery passed into the mouth of the Columbia River.

Years later, explorers, traders, and missionaries heard reports of an erupting volcano in the area. Geologists and historians determined much later that the eruption took place in 1800, marking the beginning of the 57 year-long Goat Rocks Eruptive Period (see geology section).{{rp|page=217}} 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.{{rp|page=217}}

In late 1805 and early 1806, members of the Lewis and Clark Expedition spotted Mount St. Helens from the Columbia River but did not report either an ongoing eruption or recent evidence of one.{{sfn|Pringle|1993}} They did however report the presence of quicksand and clogged channel conditions at the mouth of the Sandy River near Portland, suggesting an eruption by Mount Hood sometime in the previous decades.

In 1829, Hall J. Kelley led a campaign to rename the Cascade Range as the President's Range and also to rename each major Cascade mountain after a former President of the United States. In his scheme Mount St. Helens was to be renamed Mount Washington.{{cite journal |last=Meany |first=Edmond S. |author-link=Edmond S. Meany |year=1920 |title=Origin of Washington Geographic Names |journal=The Washington Historical Quarterly |volume=XI |pages= 211–212 |publisher=Washington University State Historical Society |url= https://books.google.com/books?id=dbsUAAAAYAAJ |access-date=2009-06-11}}

File:Mount St Helens erupting at night by Paul Kane.jpg Mount St. Helens erupting at night after his 1847 visit to the area]]

The first authenticated non-Indigenous eyewitness report of a volcanic eruption was made in March 1835 by Meredith Gairdner, while working for the Hudson's Bay Company stationed at Fort Vancouver.{{rp|page=219}} He sent an account to the Edinburgh New Philosophical Journal, which published his letter in January 1836. James Dwight Dana of Yale University, while sailing with the United States Exploring Expedition, saw the quiescent peak from off the mouth of the Columbia River in 1841. Another member of the expedition later described "cellular basaltic lavas" at the mountain's base.{{cite web |url=http://vulcan.wr.usgs.gov/LivingWith/Historical/LewisClark/Info/summary_mount_st_helens.html |title=The Volcanoes of Lewis and Clark |publisher=USGS |access-date=2006-11-15}}

In the late fall or early winter of 1842, nearby European settlers and missionaries witnessed the so-called Great Eruption. This small-volume outburst created large ash clouds, and mild explosions followed for 15 years.{{rp|pages=220–221}} The eruptions of this period were likely phreatic (steam explosions). Josiah Parrish in Champoeg, Oregon witnessed Mount St. Helens in eruption on November 22, 1842. Ash from this eruption may have reached The Dalles, Oregon, {{convert|48|mi|km}} southeast of the volcano.

In October 1843, future California governor Peter H. Burnett recounted a very likely apocryphal story of an Indigenous man who badly burned his foot and leg in lava or hot ash while hunting for deer. The story went that the injured man sought treatment at Fort Vancouver, but the contemporary fort commissary steward, Napoleon McGilvery, disclaimed knowledge of the incident.{{rp|page=224}} British lieutenant Henry J. Warre sketched the eruption in 1845, and two years later Canadian painter Paul Kane created watercolors of the gently smoking mountain. Warre's work showed erupting material from a vent about a third of the way down from the summit on the mountain's west or northwest side (possibly at Goat Rocks), and one of Kane's field sketches shows smoke emanating from about the same location.{{rp|pages=225, 227}}

On April 17, 1857, the Republican, a Steilacoom, Washington, newspaper, reported that "Mount St. Helens, or some other mount to the southward, is seen ... to be in a state of eruption".{{rp|page=228}} The lack of a significant ash layer associated with this event indicates that it was a small eruption. This was the first reported volcanic activity since 1854.{{rp|page=228}}

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

File:MSH80 david johnston at camp 05-17-80 med.jpg hours before he was killed by the eruption]]

Fifty-seven people were killed during the eruption.{{cite web|author=Grisham|first=Lori|date=May 17, 2015|title='I'm going to stay right here.' Lives lost in Mount St. Helens eruption|url=https://www.usatoday.com/story/news/nation-now/2015/05/17/mount-st-helens-people-stayed/27311467/|url-status=live|archive-url=https://web.archive.org/web/20210603020125/https://www.usatoday.com/story/news/nation-now/2015/05/17/mount-st-helens-people-stayed/27311467/|archive-date=June 3, 2021|access-date=2021-06-20|website=USA Today}} Had the eruption occurred one day later, when loggers would have been at work, rather than on a Sunday, the death toll could have been much higher.

Eighty-three-year-old Harry R. Truman, who ran the Spirit Lake Lodge and had lived near the mountain since 1929, gained much media attention when he decided not to evacuate before the impending eruption, despite repeated pleas by local authorities.{{cite web|last=Kean|first=Sam|date=December 12, 2018|title=Harry versus the volcano|url=https://www.sciencehistory.org/distillations/harry-versus-the-volcano|access-date=May 29, 2021|website=Science History Institute|publisher=Sam Kean}} His body was never found after the eruption.{{cite news |url=https://news.google.com/newspapers?id=M9MvAAAAIBAJ&pg=5277,988696&dq= |title=Sister, friend say Harry probably dead |agency=Associated Press |date=May 20, 1980 |newspaper=Spokane Daily Chronicle}}

Another victim of the eruption was 30-year-old volcanologist David A. Johnston, who was stationed on the nearby Coldwater Ridge. Moments before his position was hit by the pyroclastic flow, Johnston radioed his last words: "Vancouver! Vancouver! This is it!"{{cite news|last=Cartier|first=Kimberly|date=June 27, 2019|title=Perish the thought: A life in science sometimes becomes a death, too|newspaper=Eos|url=https://eos.org/features/honoring-volcanologist-david-johnston-as-a-hero-and-a-human|url-status=live|access-date=2021-06-20|archive-url=https://web.archive.org/web/20210610062416/https://eos.org/features/honoring-volcanologist-david-johnston-as-a-hero-and-a-human|archive-date=2021-06-10}} Johnston's body was never found.{{cite news |url=https://news.google.com/newspapers?id=zgwkAAAAIBAJ&pg=3835%2C2980629|title=Workers may have found body of man buried by volcanic ash|newspaper=Moscow-Pullman Daily News|date=1993-06-29}} Robert Landsburg was another victim, a photographer who took pictures of the approaching ash cloud. He placed his camera in his backpack and laid on top of it to protect the film.{{cite news |date=June 5, 1980 |title=Searchers Find Body of Another Volcano Victim |url=https://www.newspapers.com/article/the-republic-searchers-find-body-of-anot/153496385/ |access-date=August 17, 2024 |newspaper=The Republic |location=Columbus, Indiana |page=A2 |via=newspapers.com |agency=UPI}} His body and the camera were found on June 4, 1980. The photos survived and provided geologists with valuable documentation of the eruption.Robert Coenraads (2006). Natural Disasters and How We Cope, p. 50. Millennium House, {{ISBN|978-1-921209-11-6}}.

U.S. President Jimmy Carter surveyed the damage and said, "Someone said this area looked like a moonscape. But the moon looks more like a golf course compared to what's up there."{{cite web |url=http://murray.senate.gov/public/index.cfm?p=NewsReleases&ContentRecord_id=b7074254-a8dc-4b7a-9547-cb6dfcaacd28&ContentType_id=0b98dc1b-dd08-4df2-adac-21f6ae03beed&Group_id=97a054dd-8a74-4cd0-8771-fbc3be733874&MonthDisplay=5&YearDisplay=2005 |title=Mount St. Helens: Senator Murray Speaks on the 25th Anniversary of the May 18, 1980 Eruption |publisher=U.S. Senate |access-date=2006-11-12}} A film crew, led by Seattle filmmaker Otto Seiber, was dropped by helicopter on St. Helens on May 23 to document the destruction. Their compasses, however, spun in circles and they quickly became lost. A second eruption occurred on May 25, but the crew survived and was rescued two days later by National Guard helicopter pilots. Their film, The Eruption of Mount St. Helens!, later became a popular documentary.

The eruption had negative effects beyond the immediate area of the volcano. Ashfall caused approximately $100 million of damage to agriculture downwind in Eastern Washington, equivalent to ${{formatprice|{{inflation|US|100,000,000|1980}}}} in {{inflation/year|US}}.{{inflation/fn|US}}{{cite journal|title=Impact on Agriculture of the Mount St. Helens Eruptions|first1=R. J.|last1=Cook|first2=J. C.|last2=Barron|first3=R. I.|last3=Papendick|first4=G. J.|last4=Williams III|journal=Science|date=1981-01-02|volume=211|issue=4477|pages=16–22|doi=10.1126/science.211.4477.16|pmid=17731222|bibcode=1981Sci...211...16C}}

The eruption also had positive impacts on society. Apple and wheat production were higher in the 1980 growing season, possibly due to ash helping to retain moisture in the soil.{{cite web|url=https://pubs.usgs.gov/gip/msh/impact.html|title=Impact and aftermath|publisher=USGS|date=1997-06-25}} The ash was also a source of income: it was the raw material for the artificial gemstone helenite,{{cite web|url=https://sciencing.com/helenite-7966283.html|title=What is Helenite?|website=Sciencing}} or for ceramic glazes,{{cite news|url=https://www.spokesman.com/stories/2015/jun/12/potter-turns-ash-into-beauty/|title=Potter turns ash into beauty|newspaper=Spokane Spokesman-Review|date=June 12, 2015|first=Cindy|last=Hval}} or sold as a tourist curio.{{cite web|url=http://www.mt-st-helens.com/giftshop.html|title=Mount St. Helens Gift Shop|access-date=2021-03-13}}

File:Mount-St-Helens-Johnston-Ridge-36-years-later.JPG ), 16 July 2016, 36 years after the eruption, showing recovering plant growth]]

In 1982, President Ronald Reagan and the U.S. Congress established the Mount St. Helens National Volcanic Monument, a {{convert|110000|acre|ha|-3}} area around the mountain and within the Gifford Pinchot National Forest.{{cite web |archive-url=https://web.archive.org/web/20041121011430/http://www.fs.fed.us/gpnf/04mshnvm/general/index.shtml |url=http://www.fs.fed.us/gpnf/04mshnvm/general/index.shtml |archive-date=2004-11-21 |title=Mount St. Helens National Volcanic Monument: General visitor information |publisher=USDA Forest Service |access-date=2006-11-12}}

Following the 1980 eruption, the area was left to gradually return to its natural state. In 1987, the U.S. Forest Service reopened the mountain to climbing. It remained open until 2004 when renewed activity caused the closure of the area around the mountain (see Geological history section above for more details). The Monitor Ridge trail, which previously let up to 100 permitted hikers per day climb to the summit, ceased operation. On July 21, 2006, the mountain was again opened to climbers.{{cite web |archive-url=https://web.archive.org/web/20041019030041/http://www.fs.fed.us/gpnf/recreation/current-conditions/special.shtml |url=http://www.fs.fed.us/gpnf/recreation/current-conditions/special.shtml |archive-date=2004-10-19 |title=Climbing Mount St. Helens |publisher=USDA Forest Service |access-date=2006-11-12}} In February 2010, a climber died after falling from the rim into the crater.{{cite news |url=http://mynorthwest.com/?nid=11&sid=285165 |title=Climber dies after rescue attempts fail on Mount St. Helens |date=February 17, 2010 |website=MyNorthwest.com |archive-url=https://web.archive.org/web/20110721130446/http://mynorthwest.com/?nid=11&sid=285165 |archive-date=2011-07-21}}

Due to the eruption, the state recognizes the month of May as "Volcano Awareness Month" and events are held at Mt. St. Helens, or within the region, to discuss the eruption, safety concerns, and to commemorate lives lost during the natural disaster.{{cite news |last1=Barker |first1=Cade |title=Volcano Awareness Month: Numerous activities available in person, social media |url=https://www.thereflector.com/stories/volcano-awareness-month-numerous-activities-available-in-person-social-media,340241 |access-date=May 21, 2024 |work=The Reflector (Battle Ground, Washington) |date=May 13, 2024}}

On May 14, 2023, a mudslide and debris flow given the moniker, South Coldwater Slide by the U.S. Forest Service, destroyed the {{convert|85|ft|m|adj=mid}} Spirit Lake Outlet Bridge on Washington State Route 504 and cut off access to the Johnston Ridge Observatory. Closures and access to Coldwater Lake and hiking trails would vary in the month after the slide.{{cite news |author1=The Chronicle staff |title=Forest Service Hopes to Provide 'Alternative' Recreation at Mount St. Helens as Surveys of South Coldwater Slide Continue |url=https://www.chronline.com/stories/forest-service-hopes-to-provide-alternative-recreation-at-mount-st-helens-as-surveys-of,319780 |access-date=June 20, 2023 |work=The Chronicle |date=May 23, 2023}}{{cite news |author1=The Chronicle staff |title=Cause, Timeline Undetermined After 'Catastrophic' Slide on Road to Mount St. Helens |url=https://www.chronline.com/stories/cause-timeline-undetermined-after-catastrophic-slide-on-road-to-mount-st-helens,319418 |access-date=June 20, 2023 |work=The Chronicle |date=May 16, 2023}}{{cite news |author1=KOMO News staff |title=Coldwater Lake Recreation Area at Mount St. Helens reopens following SR 504 landslide |url=https://komonews.com/news/local/coldwater-lake-recreation-area-reopens-closure-landslide-mount-st-helens-national-volcanic-monument-trail-highway-sr-504-clean-up-repairs# |access-date=June 20, 2023 |work=KOMO News (Seattle, Washington) |date=June 19, 2023}}

Mount St. Helens is a common climbing destination for both beginning and experienced mountaineers. The peak is climbed year-round, although it is more often climbed from late spring through early fall. All routes include sections of steep, rugged terrain.

{{cite web

| url = http://www.fs.usda.gov/detail/mountsthelens/home/?cid=stelprdb5144806

| title = Climbing Mount St. Helens

| publisher = U.S. Forest Service

| access-date = 2014-02-28}} A permit system has been in place for climbers since 1987. A climbing permit is required year-round for anyone who will be above {{convert|4800|ft}} on the slopes of Mount St. Helens.

{{cite web

| url = http://www.fs.usda.gov/detail/mountsthelens/home/?cid=stelprdb5145230

| title = Mount St Helens Climbing Permit System

| publisher = U.S. Forest Service

| access-date = 2014-02-28}}

The standard hiking/mountaineering route in the warmer months is the Monitor Ridge Route, which starts at the Climbers Bivouac. This is the most crowded route to the summit in the summer and gains about {{convert|4600|ft}} in approximately {{convert|5|mi||sigfig=1}} to reach the crater rim.

{{cite web

| url = http://www.summitpost.org/monitor-ridge/155892

| title = Monitor Ridge

| publisher = SummitPost.org

| access-date = 2014-02-28}} Although strenuous, it is considered a non-technical climb that involves some scrambling. Most climbers complete the round trip in 7 to 12 hours.

{{cite web

| url = http://www.fs.usda.gov/recarea/mountsthelens/recreation/climbing/recarea/?recid=31604&actid=38

| title = Monitor Ridge Climbing Route

| publisher = U.S. Forest Service

| access-date = 2014-02-28}}

The Worm Flows Route is considered the standard winter route on Mount St. Helens, as it is the most direct route to the summit. The route gains about {{convert|5700|ft}} in elevation over about {{convert|6|mi||round=5}} from trailhead to summit but does not demand the technical climbing that some other Cascade peaks like Mount Rainier do. The route name refers to the rocky lava flows that surround the route.

{{cite web

| url = http://thepeakseeker.com/routes/worm-flows-route-mount-st-helens/

| title = Worm Flows Route, Mount St. Helens

| date = 7 January 2014

| publisher = The Peak Seeker

| access-date = 2016-02-17}} This route can be accessed via the Marble Mountain Sno-Park and the Swift Ski Trail.{{cite web

| url = http://www.fs.usda.gov/recarea/mountsthelens/recreation/climbing/recarea/?recid=71937&actid=38

| title = The Worm Flows, Winter Climbing Route

| publisher = U.S. Forest Service

| access-date = 2014-02-28}}

The mountain is now circled by the Loowit Trail at elevations of {{convert|4000|–|4900|ft|m}}. The northern segment of the trail from the South Fork Toutle River on the west to Windy Pass on the east is a restricted zone where camping, biking, pets, fires, and off-trail excursions are all prohibited.{{cite summitpost |id=742347 |name=Loowit Trail |access-date=2011-09-03}}{{cite web |url=http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5160314.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5160314.pdf |archive-date=2022-10-09 |url-status=live |title=Mount St. Helens Volcanic National Monument: Restricted Area |publisher=USDA Forest Service |access-date=2011-09-03}}

On April 14, 2008, John Slemp, a snowmobiler from Damascus, Oregon, fell 1,500 feet into the crater after a snow cornice gave way beneath him on a trip to the volcano with his son. Despite his long fall, Slemp survived with minor injuries, and was able to walk after coming to a stop at the foot of the crater wall, where he was rescued by a mountain rescue helicopter.{{cite web|last=Hwa Song|first=Jung|date=16 April 2008|title=Man Survives 1,500-Ft. Drop Down Mt. St. Helens|url=https://abcnews.go.com/WN/story?id=4651579&page=1|access-date=2021-03-15|website=ABC News|language=en}}

A visitor center run by the Washington State Parks is in Silver Lake, Washington, about {{convert|30|mi|km}} west of Mount St. Helens.{{cite web|title=Mount St. Helens Visitor Center|url=http://parks.state.wa.us/245/Mount-St-Helens|publisher=Washington State Parks|access-date=2016-01-19}} Exhibits include a large model of the volcano, a seismograph, a theater program, and an outdoor natural trail.

{{clear}}

{{wide image|Image:Mount St Helens Summit Pano II.jpg|x260px|Panoramic view from the summit of Mount St. Helens as seen in October 2009. Climbers stand on the crater rim and are visible along the Monitor Ridge climbing route.|90%}}

• List of volcanic eruptions by death toll
• List of volcanoes in the United States

Notes

{{reflist|25em}}

Bibliography

• {{cite book |last=Harris |first=Stephen L. |chapter=Mount St. Helens: A Living Fire Mountain |pages=[https://archive.org/details/firemountainsofw00harr/page/201 201–228] |title=Fire Mountains of the West: The Cascade and Mono Lake Volcanoes |year=1988 |edition=1st |publisher=Mountain Press Publishing Company |location=Missoula, Montana |isbn=0-87842-220-X |chapter-url-access=registration |chapter-url=https://archive.org/details/firemountainsofw00harr/page/201}}
• {{cite book |last1=Mullineaux |first1=D. R. |last2=Crandell |first2=D. R. |year=1981 |title=The 1980 eruptions of Mount St. Helens, Washington |chapter=The 1980 eruptions of Mount St. Helens, Washington |series=Professional Paper |chapter-url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/PP1250/MullineauxCrandell/eruptive_history.html |id=Professional Paper 1250 |publisher=United States Geological Survey |doi=10.3133/pp1250 |access-date=2006-10-28 |archive-date=1 January 2007 |archive-url=https://web.archive.org/web/20070101023724/http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/PP1250/MullineauxCrandell/eruptive_history.html |url-status=dead }}
• {{cite report |last=Mullineaux |first=D. R. |year=1996 |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/PP1563/eruptive_history.html |title=Pre-1980 tephra-fall deposits erupted from Mount St. Helens |id=Professional Paper 1563 |publisher=United States Geological Survey |access-date=2006-10-28 |archive-date=27 October 2006 |archive-url=https://web.archive.org/web/20061027104744/http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/PP1563/eruptive_history.html |url-status=dead }}
• {{cite report |last=Pringle |first=P. T. |year=1993 |title=Roadside Geology of Mount St. Helens National Volcanic Monument and Vicinity |url=http://campus.albion.edu/geol210/files/2011/03/MSH1.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://campus.albion.edu/geol210/files/2011/03/MSH1.pdf |archive-date=2022-10-09 |url-status=live |publisher=Washington State Department of Natural Resources |department=Division of Geology and Earth Resources Information |work=Circular 88 }}
• {{cite web |publisher=USGS |department=Cascades Volcano Observatory |location=Vancouver, Washington |title=Description: Mount St. Helens Volcano, Washington |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/description_msh.html |access-date=2006-10-28}}

Further reading

• {{cite magazine |title=Eruption of Mount St. Helens |magazine=National Geographic |date=January 1981 |volume=159 |issue=1 |pages=3–65 |issn=0027-9358 |oclc=643483454}}

{{sister project links|auto=1}}

• {{cite web |url=http://www.fs.usda.gov/mountsthelens/ |title=Mount St. Helens National Volcanic Monument |publisher=US Forest Service}}
• {{cite gvp |vn=321050 |name=St. Helens |access-date=2008-12-18}}
• {{cite report |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/ |title=Mount St. Helens photographs and current conditions |publisher=United States Geological Survey |archive-date=2 January 2007 |access-date=18 May 2003 |archive-url=https://web.archive.org/web/20070102120520/http://vulcan.wr.usgs.gov/Volcanoes/MSH/ |url-status=dead }}
• {{cite report |archive-url=https://web.archive.org/web/20061030185028/http://vulcan.wr.usgs.gov/Volcanoes/MSH/EruptiveHistory/framework.html |publisher=USGS |title=Mount St. Helens eruptive history|url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/EruptiveHistory/framework.html|archive-date=2006-10-30}}
• University of Washington Libraries: Digital Collections:
• {{cite web |url=http://content.lib.washington.edu/mshchemweb/index.html |title=Mount St. Helens post-eruption chemistry database |publisher=University of Washington |department=U.W. Libraries Digital Collections |quote=This collection contains photographs of Mount St. Helens, post-eruption, taken over the span of three years to provide a look at both the human and the scientific sides of studying the eruption of a volcano.}}
• {{cite web |url=http://content.lib.washington.edu/mtsthelensweb/index.html |title=Mount St. Helens succession collection |publisher=University of Washington |department=U.W. Libraries Digital Collections |quote=This collection consists of 235 photographs in a study of plant habitats following the May 18, 1980 eruption of Mount St. Helens.}}
• {{cite AV media |url=http://www.freesound.org/samplesViewSingle.php?id=21432 |title=Audio recording of the May 18, 1980 eruption |medium=audio |quote=Recorded {{convert|140|mi|km|0}} southwest of the mountain. Believed to be the only audio recording of the eruption.}}
• The Royal Geography Society's Hidden Journeys project:
• {{cite web |url=http://www.hiddenjourneys.co.uk/Vancouver-Los-Angeles/Cascade%20Mountains.aspx#level_2 |title=The 1980 Mount St. Helens Eruption|archive-url=https://web.archive.org/web/20140714165827/http://www.hiddenjourneys.co.uk/Vancouver-Los-Angeles/Cascade%20Mountains.aspx#level_2|archive-date=14 July 2014}}
• {{cite AV media |url=http://www.hiddenjourneys.co.uk/Audio%20Slideshows.aspx#level_9 |archive-url=https://web.archive.org/web/20140714172521/http://www.hiddenjourneys.co.uk/Audio%20Slideshows.aspx#level_9 |archive-date=2014-07-14 |medium=audio slideshow |title=Mount St Helens |quote=Volcanologist Sarah Henton discusses the Cascade Mountains and explains the geology and impact of the 1980 Mount St Helens eruption.}} (duration 6:29 min)
• {{cite AV media |url=https://sketchfab.com/models/fe617eabeec14099b0c14450eadb57a2 |medium=3D model |title=Mount St. Helens}}
• {{cite AV media |url=https://sketchfab.com/models/bedcff4c9da847cea4458847090addb7 |medium=3D model |title=Mount St. Helens on 14 September 1975, before eruption}}

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Category:Gifford Pinchot National Forest

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