# Icefall

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{{Short description|Relatively fast part of a glacier with chaotic crevassed surface}}
{{for|the 2025 film|Icefall (film)}}
{{more citations needed|date=September 2015}}
[[Image:Roosevelt Glacier 6940.JPG|thumb|right|The {{convert|730|m|ft|abbr=on}} icefall (center) in the Roosevelt Glacier, [Mount Baker](/source/Mount_Baker), [Washington](/source/Washington_(state)), U.S.]] An '''icefall''' is a portion of certain [glacier](/source/glacier)s characterized by relatively rapid flow and chaotic [crevass](/source/crevass)ed surface, caused in part by gravity. The term ''icefall'' is formed by analogy with the word ''[waterfall](/source/waterfall)'', which is a similar phenomenon of the liquid phase but at a more spectacular speed. When ice movement of a glacier is faster than elsewhere, because the glacier bed steepens or narrows, and the flow cannot be accommodated by [plastic deformation](/source/plastic_deformation), the ice fractures, forming crevasses. Where two fractures meet, [serac](/source/serac)s (or ice towers) can be formed. When the movement of the ice slows down, the crevasses can coalesce, resulting in the surface of the glacier becoming smoother.<ref>{{cite book
 | last = Post
 | first = Austin
 |author2=Edward R. LaChapelle
 | title = Glacier Ice
 | orig-year = 1971
 | edition = Revised
 |date= May 2000
 | publisher = University of Washington Press
 | location = Seattle, Washington
 | isbn = 0-295-97910-0
 | pages = 18–21
}}
</ref>

==Ice flow==
Perhaps the most conspicuous consequence of [glacier flow](/source/Glacier), icefalls occur where the glacier bed steepens or narrows. Most glacier ice flows at speeds of a few hundred metres per year or less. However, the flow of ice in an icefall may be measured in kilometres per year. Such rapid flow cannot be accommodated by [plastic deformation](/source/plastic_deformation) of the ice. Instead, the ice fractures, forming [crevasse](/source/crevasse)s. Intersecting fractures form ice columns or [serac](/source/serac)s. These processes are imperceptible for the most part; however, a serac may collapse or topple abruptly and without warning. This behavior often poses the biggest risk to [mountaineers](/source/mountaineering) climbing in an icefall.

As the glacier transitions below the icefall, the topography of the glacier bed plays a crucial role in modifying its dynamics, leading to a flatter or wider bed that significantly reduces the velocity of ice movement. This change in speed and pressure causes crevasses to close up, resulting in a smoother glacier surface that presents fewer challenges for navigation and traversal.

==Examples==
Icefalls vary greatly in height. The [Roosevelt Glacier](/source/Roosevelt_Glacier) icefall, on the north face of [Mount Baker](/source/Mount_Baker) ([Cascade Range](/source/Cascade_Range), U.S.), is about {{convert|730|m|ft|abbr=off}} high. The ice cliff of the left side of the ice fall and above the debris covering the glacier is {{convert|20|to|40|m|ft}} high. Typical of mountain glaciers, this icefall forms as the ice flows from a high elevation plateau or basin accumulation zone to a lower valley ablation zone. Much larger icefalls may be found in the outlet glaciers of continental [ice sheet](/source/ice_sheet)s. The icefall feeding the [Lambert Glacier](/source/Lambert_Glacier) in Antarctica is {{convert|7|km|mi|abbr=off}} wide and {{convert|14|km|mi|abbr=off}} long, even though the elevation difference is only {{convert|400|m|ft|abbr=off}}, a little more than half that of the Roosevelt Glacier icefall.

Icefalls are [climbed](/source/ice_climbing) because of their beauty and the challenge they pose. In some cases, an icefall may provide the only feasible or the easiest route up one face of a mountain. An example is the [Khumbu Icefall](/source/Khumbu_Icefall) on the [Nepal](/source/Nepal)ese side of [Mount Everest](/source/Mount_Everest), variously described as "treacherous" and "dangerous." It is about {{convert|5,500|m|ft|abbr=off}} above [sea level](/source/sea_level).

<gallery>
File:Icefall hires 2.jpg|An icefall feeding into the [Lambert Glacier](/source/Lambert_Glacier), [Antarctica](/source/Antarctica).
File:KhumbuIcefall.jpg|The [Khumbu Icefall](/source/Khumbu_Icefall) on [Mount Everest](/source/Mount_Everest)
File:MSH06 east arm crater glacier 10-22-06.jpg|A small icefall on east lobe of the new [Crater Glacier](/source/Crater_Glacier) on [Mount St. Helens](/source/Mount_St._Helens).
File:IcefallAthabascaGlacierColumbiaIcefieldAlberta1993.jpg|An icefall on Athabasca Glacier, Columbia Icefield, [Jasper National Park](/source/Jasper_National_Park), Alberta.
</gallery>

==See also==
*[Glacier morphology](/source/Glacier_morphology)

==References==
{{Reflist|2}}

==External links==
*{{commons category-inline|Icefalls}}

{{glaciers}}
{{Authority control}}

Category:Icefalls
Category:Ice climbing
Category:Bodies of ice
Category:Hazards of outdoor recreation
Category:Geographical terminology in mountaineering

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Adapted from the Wikipedia article [Icefall](https://en.wikipedia.org/wiki/Icefall) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Icefall?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.