Editing Crevasse

{{Short description|Deep crack, or fracture, in an ice sheet or glacier}}
{{Distinguish|Crevice (disambiguation){{!}}Crevice}}
{{Hatnote|Crevasse is also a traditional term for a [[levee breach]].}}

[[File:Parque estatal Chugach, Alaska, Estados Unidos, 2017-08-22, DD 94.jpg|thumb|right|upright=1.3|Transverse crevasses, [[Chugach State Park]], Alaska]]
A '''crevasse''' is a deep crack that forms in a [[glacier]] or ice sheet. Crevasses form as a result of the movement and resulting stress associated with the [[shear stress]] generated when two semi-rigid pieces above a plastic substrate have different rates of movement. The resulting intensity of the shear stress causes a breakage along the faces.

==Description==
[[File:Crevasse-Tangra-Mountains.jpg|thumb|right|A crevasse in [[Tangra Mountains]], Antarctica]]
Crevasses often have vertical or near-vertical walls, which can then melt and create [[serac]]s, [[arch]]es, and other [[Ice|ice formations]].<ref name="Crevasses on Glacier">{{cite journal | title=Crevasses on Glaciers | author=van der Veen, C | journal=[[Polar Geography]] | year=1990 | volume=23 | issue=3 | pages=213–245 | doi=10.1080/10889379909377677}}</ref> These walls sometimes expose layers that represent the glacier's [[stratigraphy]]. Crevasse size often depends upon the amount of liquid water present in the glacier. A crevasse may be as deep as {{convert|45|m|ft|-1}} and as wide as {{convert|20|m|ft|-1}}<ref name=natgeo/>

The presence of water in a crevasse can significantly increase its penetration. Water-filled crevasses may reach the bottom of glaciers or [[ice sheets]] and provide a direct hydrologic connection between the surface,<ref>{{cite journal|author1=Boon, S. |author2=M.J. Sharp |date= 2003|title= The role of hydrologically-driven ice fracture in drainage system evolution on an Arctic glacier|journal=Geophysical Research Letters|volume=30|issue= 18|pages=1916|doi=10.1029/2003gl018034|bibcode=2003GeoRL..30.1916B |s2cid= 133697259|doi-access=free}}</ref> where significant summer melting occurs, and the bed of the glacier, where additional water may moisten and lubricate the bed and accelerate ice flow.<ref>{{cite journal|author1=Zwally, H.J. |author2=Abdalati, W. |author3=Herring, T. |author4=Larson, K. |author5=Saba, J. |author6=Steffen, K. |date=2002|title= Surface melt-induced acceleration of Greenland ice-sheet flow|journal=[[Science (journal)|Science]]|volume=297|issue=5579|pages=218–222|doi=10.1126/science.1072708|pmid=12052902|bibcode=2002Sci...297..218Z |s2cid=37381126|doi-access=free}}</ref><ref name=Colgan>{{cite journal|author1=Colgan, W. |author2=Rajaram, H. |author3=Abdalati, W. |author4=McCutchan, C. |author5=Mottram, R. |author6=Moussavi, M.S. |author7=Grigsby, S. |date=2016|title= Glacier crevasses: Observations, models, and mass balance implications|journal= Rev. Geophys.|volume= 54|issue=1 | doi= 10.1002/2015RG000504|pages= 119–161|bibcode=2016RvGeo..54..119C |doi-access= free}}</ref> Direct drains of water from the top of a glacier, known as [[moulin (geomorphology)|moulin]]s, can also contribute the lubrication and acceleration of ice flow.<ref name=Colgan/>

==Types==
[[Image:Glaciereaston.jpg|thumb|200px|A man crosses a crevasse in [[Easton Glacier]], [[Mount Baker]], in the [[North Cascades]], [[Washington (state)|Washington]]]]
*Longitudinal crevasses form parallel to flow where the glacier width is expanding. They develop in areas of [[tensile stress]], such as where a valley widens or bends. They are typically concave down and form an angle greater than 45° with the margin.<ref name="transverse crevasses" />
*Splaying crevasses appear along the edges of a glacier and result from shear stress from the margin of the glacier and longitudinal compressing stress from lateral extension. They extend from the glacier's margin and are concave up with respect to glacier flow, making an angle less than 45° with the margin. 
*Transverse crevasses are the most common crevasse type. They form in a zone of longitudinal extension where the principal stresses are parallel to the direction of glacier flow, creating extensional tensile stress. These crevasses stretch across the glacier transverse to the flow direction, or cross-glacier.  They generally form where a valley becomes steeper.<ref name="transverse crevasses">{{cite journal | title=Primary Transverse Crevasses | author=Holdsworth, G | journal=Journal of Glaciology |date=October 1956 | volume=8 | issue=52 | pages=107–129| doi=10.1017/S0022143000020797 | doi-access=free }}</ref>

==Dangers==
[[Image:Wildspitze seen from Hinterer Brunnkogel, with marked ascent track of ski mountaineer.jpg|thumb|upright=1.15|The glacier Taschachferner below the [[Wildspitze]] (left, 3.768 m) in Tyrolia in [[Austria]] in April 2005. There are some zones with large open crevasses, e.g., the spot-shaped area below the middle of the image and most right. The line marks the ascent track of [[Ski touring|mountaineers on skis]] which intentionally avoided these dangerous areas.]]
Falling into glacial crevasses can be dangerous and life-threatening.<ref>{{cite journal|last1=Pasquier|first1=M|last2=Taffé|first2=P|last3=Kottmann|first3=A|last4=Mosimann|first4=U|last5=Reisten|first5=O|last6=Hugli|first6=O|title=Epidemiology and mortality of glacier crevasse accidents|journal=Injury|date=Nov 2014|volume=45|issue=11|pages=1700–3|doi=10.1016/j.injury.2014.07.001|pmid=25082349}}</ref> Some glacial crevasses (such as on the [[Khumbu Icefall]] at [[Mount Everest]]) can be {{convert|160|ft|m|-1|order=flip}} deep, which can cause fatal injuries upon falling.<ref>{{cite news|url=https://www.usatoday.com/story/news/nation/2023/04/13/mount-everest-climbers-missing/11655531002/|title=Mount Everest: 3 Sherpa climbers missing after falling into deep Khumbu Icefall crevasse|first=Binaj|last=Gurubacharya|publisher=Associated Press|date=2023-04-13}}</ref> [[Hypothermia]] is often a cause of death when falling into a crevasse.<ref name=natgeo>{{cite web|url=https://education.nationalgeographic.org/resource/crevasse/|title=Crevasse|publisher=National Geographic|access-date=2023-06-22}}</ref>

A crevasse may be covered, but not necessarily filled, by a [[snow bridge]] made of the previous years' accumulation and snow drifts. The result is that crevasses are rendered invisible, and thus potentially lethal to anyone attempting to navigate across a glacier.  Occasionally a snow bridge over an old crevasse may begin to sag, providing some landscape relief, but this cannot be relied upon.<ref name=mountaineers>{{cite book|title=[[Mountaineering: The Freedom of the Hills]]|publisher=The Mountaineers|edition=6th|year=1997|editor1-first=Don|editor1-last=Graydon|editor2-first=Kurt|editor2-last=Hanson|isbn=0-89886-427-5}}</ref>{{rp|343}}

The danger of falling into a crevasse can be minimized by roping together multiple climbers into a [[rope team]],<ref name=mountaineers/>{{rp|340}} and the use of [[List of friction hitch knots|friction knot]]s.<ref>{{cite web|url=https://blog.alpineclubofcanada.ca/blog/2021/11/29/mountain-safety-glacier-travel-and-crevasse-rescue-for-two-person-teams|title=MOUNTAIN SAFETY: GLACIER TRAVEL AND CREVASSE RESCUE FOR TWO-PERSON TEAMS|first=Doug|last=Latimer|date=2022-06-20|publisher=Alpine Club of Canada}}</ref>

==See also==
* {{annotated link|Bergschrund}}
* {{annotated link|Bowie Crevasse Field}}
* {{annotated link|Glaciology}}
* {{annotated link|Crevasse rescue}}

==References==
{{Reflist|30em}}

==Bibliography==
*{{cite journal|vauthors=Das SB, Joughin I, Behn MD, Howat IM, King MA, Lizarralde D, Bhatia MP| date=2008| title=Fracture propagation to the base of the Greenland Ice Sheet during supraglacial lake drainage| journal=Science| volume=320| issue=5877| pages=778–781| pmid=18420900| doi=10.1126/science.1153360| bibcode=2008Sci...320..778D| s2cid=41582882| hdl=1912/2506| hdl-access=free}}
*{{cite book|author=Paterson, W.S.B.|date= 1994|title=The Physics of Glaciers|edition=3rd |isbn=0-7506-4742-6}}
*{{cite journal|vauthors=van der Veen CJ|date=1998 |title=Fracture mechanics approach to penetration of surface crevasses on glaciers |journal=Cold Regions Science and Technology |volume=27 |issue=1 |pages=31–47 |doi=10.1016/s0165-232x(97)00022-0 |bibcode=1998CRST...27...31V}}

==External links==
*{{Commons and category inline}}

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[[Category:Glaciology]]
[[Category:Glacial landforms]]
[[Category:Geographical terminology in mountaineering]]
[[Category:Crevasse fields| ]]
[[Category:Hazards of outdoor recreation]]