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{{Short description|Relatively rapidly-moving portion of a glacier with chaotic crevassed surface}}
{{refimprove|date=September 2015}} {{more citations needed|date=September 2015}}
], ], U.S.]] An '''icefall''' is a portion of certain ]s characterized by rapid flow and a chaotic ]ed surface. The term ''icefall'' is formed by analogy with the word ''waterfall'', a similar, but much higher speed, phenomenon. When ice movement is faster than elsewhere, because the glacier bed steepens or narrows, the flow cannot be accommodated by plastic deformation and the ice fractures, forming crevasses. Where two fractures meet, ]s (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. ], ], U.S.]] An '''icefall''' is a portion of certain ]s characterized by relatively rapid flow and chaotic ]ed surface, caused in part by gravity. The term ''icefall'' is formed by analogy with the word ''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, the ice fractures, forming crevasses. Where two fractures meet, ]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

⚫ ==Ice flow==
⚫ Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/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 of the ice. Instead, the ice fractures forming ]s. Intersecting fractures form ice columns or ]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 ] climbing in an icefall.

Below the icefall, the glacier bed flattens and/or widens and the ice flow slows. Crevasses close and the glacier surface becomes much smoother and easier to traverse.

⚫ ==Examples==
⚫ ], ].]]Icefalls vary greatly in height. The ] icefall, on the north face of ] (], U.S.), is about 730 metres (2,400&nbsp;ft) high (photograph at right). The ice cliff of the left side of the ice fall and above the debris covering the glacier is 20 to 40 metres (70 to 140&nbsp;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 ]s. The icefall feeding the ] in Antarctica (photograph at left) is 7 kilometres (4.4&nbsp;mi) wide and 14 kilometres (9&nbsp;mi) long, even though the elevation difference is only 400 metres (1,300&nbsp;ft), a little more than half that of the Roosevelt Glacier icefall.

⚫ Icefalls are ] 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 ] on the ]ese side of ], variously described as "treacherous" and "dangerous." It is about 5,500 metres (18,000&nbsp;ft) above ].
⚫ ] on ]]]

⚫ ] on ].]]

{{clear|left}}

⚫ ==References==
*{{cite book
| last = Post | last = Post
| first = Austin | first = Austin
| authorlink =
|author2=Edward R. LaChapelle |author2=Edward R. LaChapelle
| editor =
| others =
| title = Glacier Ice | title = Glacier Ice
| origyear = 1971 | orig-year = 1971
| month =
| url =
| format =
| accessdate =
| edition = Revised | edition = Revised
|date= May 2000 |date= May 2000
| publisher = University of Washington Press | publisher = University of Washington Press
| location = Seattle, Washington | location = Seattle, Washington
| language =
| isbn = 0-295-97910-0 | isbn = 0-295-97910-0
| pages = 18–21 | pages = 18–21
| chapter =
| chapterurl =
| quote =
}} }}
</ref>

⚫ ==Ice flow==
⚫ Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/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 ] of the ice. Instead, the ice fractures, forming ]s. Intersecting fractures form ice columns or ]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 ] 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 and/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 ] icefall, on the north face of ] (], 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 ]s. The icefall feeding the ] 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 ] 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 ] on the ]ese side of ], variously described as "treacherous" and "dangerous." It is about {{convert|5,500|m|ft|abbr=off}} above ].

<gallery>
File:Icefall hires 2.jpg|An icefall feeding into the ], ].
⚫ File:KhumbuIcefall.jpg|The ] on ]
⚫ File:MSH06 east arm crater glacier 10-22-06.jpg|A small icefall on east lobe of the new ] on ].
File:IcefallAthabascaGlacierColumbiaIcefieldAlberta1993.jpg|An icefall on Athabasca Glacier, Columbia Icefield, ], Alberta.
</gallery>

==See also==
*]

⚫ ==References==
{{Reflist|2}}


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


{{glaciers}} {{glaciers}}


] ]
] ]
] ]
]

Latest revision as of 13:07, 29 March 2024

Relatively rapidly-moving portion of a glacier with chaotic crevassed surface
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The 730 m (2,400 ft) icefall (center) in the Roosevelt Glacier, Mount Baker, Washington, U.S.

An icefall is a portion of certain glaciers characterized by relatively rapid flow and chaotic crevassed surface, caused in part by gravity. The term icefall is formed by analogy with the word 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, the ice fractures, forming crevasses. Where two fractures meet, seracs (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.

Ice flow

Perhaps the most conspicuous consequence of glacier flow, icefalls occur where the glacier bed steepens and/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 of the ice. Instead, the ice fractures, forming crevasses. Intersecting fractures form ice columns or seracs. 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 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 and/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 icefall, on the north face of Mount Baker (Cascade Range, U.S.), is about 730 metres (2,400 feet) high. The ice cliff of the left side of the ice fall and above the debris covering the glacier is 20 to 40 metres (66 to 131 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 sheets. The icefall feeding the Lambert Glacier in Antarctica is 7 kilometres (4.3 miles) wide and 14 kilometres (8.7 miles) long, even though the elevation difference is only 400 metres (1,300 feet), a little more than half that of the Roosevelt Glacier icefall.

Icefalls are climbed 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 on the Nepalese side of Mount Everest, variously described as "treacherous" and "dangerous." It is about 5,500 metres (18,000 feet) above sea level.

See also

References

  1. Post, Austin; Edward R. LaChapelle (May 2000) . Glacier Ice (Revised ed.). Seattle, Washington: University of Washington Press. pp. 18–21. ISBN 0-295-97910-0.

External links

  • Media related to Icefalls at Wikimedia Commons
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