Editing Mount St. Helens (section)

==Geographic setting and description==
===General===
[[File:Mount St. Helens, one day before the devastating eruption.jpg|thumb|alt=A large conical volcano.|Mount St.&nbsp;Helens pictured the day before the 1980 eruption, which removed much of the northern face of the mountain, leaving a large [[Volcanic crater|crater]]]]
Mount St.&nbsp;Helens is {{convert|34|mi|km}} west of [[Mount Adams (Washington)|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.&nbsp;Helens.

Mount St. Helens is geologically young compared with the other major Cascade volcanoes. It formed only within the past 40,000&nbsp;years, and the summit cone present before its 1980 eruption began rising about 2,200&nbsp;years ago.<ref name=Mullineaux_Crandell_1981>{{cite report |last1=Mullineaux |first1=D. R. |last2=Crandell |first2=D. R. |year=1981 |title=The 1980 eruptions of Mount St.&nbsp;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 }}</ref> The volcano is considered the most active in the Cascades within the [[Holocene]] epoch, which encompasses roughly the last 10,000 years.<ref name="USGS-Description">{{cite web |url=http://vulcan.wr.usgs.gov/Volcanoes/MSH/description_msh.html |title=Description of Mount St.&nbsp;Helens |publisher=USGS |access-date=2006-11-15}}</ref>

Prior to the 1980 eruption, Mount St.&nbsp;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, "[[Mount Fuji|Fuji-san]] of America".<ref name=Harris1988>{{cite book |last=Harris |first=Stephen L. |chapter=Mount St.&nbsp;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}}</ref>{{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.<ref name=phillips>{{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}}</ref> 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}}.

[[Stream]]s 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 (Washington)|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 [[dam]]s 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.&nbsp;Helens is in Skamania County, Washington, access routes to the mountain run through [[Cowlitz County, Washington|Cowlitz County]] to the west, and [[Lewis County, Washington|Lewis County]] to the north. [[Washington State Route 504|State Route 504]], locally known as the [[Spirit Lake Memorial Highway]], connects with [[Interstate 5 (Washington)|Interstate&nbsp;5]] at Exit&nbsp;49, {{convert|34|mi|km}} to the west of the mountain.<ref name=Harris2005>{{cite book |last=Harris |first=Stephen L. |chapter=Mount St.&nbsp;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}}</ref>{{rp|page=297}} That north–south highway skirts the low-lying cities of [[Castle Rock, Washington|Castle Rock]], [[Longview, Washington|Longview]] and [[Kelso, Washington|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|Cougar]], Washington, in the Lewis River valley {{convert|11|mi|km}} south-southwest of the peak. [[Gifford Pinchot National Forest]] surrounds Mount St.&nbsp;Helens.

===Crater Glacier and other new rock glaciers===
{{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.<ref name="Brugman81">{{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}}</ref><ref name="Wiggins02">{{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.&nbsp;Helens Crater |journal=Abstracts with Programs |publisher=Geological Society of America |volume=34 |issue=5 |page=91 |year=2002}}</ref><ref name="Schilling04">{{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.&nbsp;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 }}</ref><ref>{{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.&nbsp;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}}</ref><ref>{{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.&nbsp;Helens |url=http://pubs.usgs.gov/sim/2006/2928/ |date=2006-08-08 |access-date=2007-03-07 }}</ref>

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 [[icefall]]s heavily criss-crossed with [[crevasse]]s and [[serac]]s caused by movement of the crater floor.<ref name="VR">{{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]]}}</ref> 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&nbsp;2008 and thus the glacier completely surrounds the lava domes.<ref name="VR"/><ref name="SE">{{cite AV media |medium=photo |title=MSH08 aerial: New dome from north 30&nbsp;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.</ref><ref name="NT">{{cite AV media |medium=photo |title=MSH08 aerial: St.&nbsp;Helens crater from north 30&nbsp;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.</ref> 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.<ref>{{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.&nbsp;Helens, WA |date=December 2004 |bibcode=2004AGUFM.V53D..01H |volume=53 |page=1 |conference=American Geophysical Union, Fall Meeting}}</ref>

===Climate===
Mount St. Helens has an alpine [[Tundra|tundra climate]] ([[Köppen climate classification|ET]]).

{{Weather box	
| single line = Y
| location = Mount St. Helens Summit. 1991&ndash;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<ref name=prism>{{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}}</ref>}}