Ice calving

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A mass of ice calves from the Perito Moreno glacier in Lago Argentino SantaCruz-Spegazzini-CaidaAnimation.gif
A mass of ice calves from the Perito Moreno glacier in Lago Argentino

Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier. [1] It is a form of ice ablation or ice disruption. It is the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, ice shelf, or crevasse. The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway. [2]

Contents

Calving of glaciers is often accompanied by a loud cracking or booming sound [3] before blocks of ice up to 60 metres (200 ft) high break loose and crash into the water. The entry of the ice into the water causes large, and often hazardous waves. [4] The waves formed in locations like Johns Hopkins Glacier can be so large that boats cannot approach closer than three kilometres (1+1⁄2 nautical miles). These events have become major tourist attractions in locations such as Alaska.

Many glaciers terminate at oceans or freshwater lakes which results naturally [5] with the calving of large numbers of icebergs. Calving of Greenland's glaciers produce 12,000 to 15,000 icebergs each year alone. [6]

Calving of ice shelves is often preceded by a rift. [7] An ice shelf in steady state calves at roughly the same rate as the influx of new ice, [8] [9] and calving events may occur on sub-annual to decadal timescales to maintain an overall average mean position of the ice shelf front. When calving rates exceed the influx of new ice, ice front retreat occurs, and ice shelves may grow smaller and weaker. [10]

Causes

Video of iceberg calving in Greenland, 2007
A calving glacier and the resulting ice field Alaskan glacier and ice field.jpeg
A calving glacier and the resulting ice field
Glacier Bay, glacier calving Glacier Bay - Johns Hopkins glacier calving.jpg
Glacier Bay, glacier calving

It is useful to classify causes of calving into first, second, and third order processes. [11] First order processes are responsible for the overall rate of calving at the glacier scale. The first order cause of calving is longitudinal stretching, which controls the formation of crevasses. When crevasses penetrate the full thickness of the ice, calving will occur. [12] Longitudinal stretching is controlled by friction at the base and edges of the glacier, glacier geometry and water pressure at the bed. These factors, therefore, exert the primary control on calving rate.

Second and third order calving processes can be considered to be superimposed on the first order process above, and control the occurrence of individual calving events, rather than the overall rate. Melting at the waterline is an important second order calving process as it undercuts the subaerial ice, leading to collapse. Other second order processes include tidal and seismic events, buoyant forces and melt water wedging.

When calving occurs due to waterline melting, only the subaerial part of the glacier will calve, leaving a submerged 'foot'. Thus, a third order process is defined, whereby upward buoyant forces cause this ice foot to break off and emerge at the surface. This process is extremely dangerous, as it has been known to occur, without warning, up to 300 m (980 ft) from the glacier terminus. [13]

Calving law

Though many factors that contribute to calving have been identified, a reliable predictive mathematical formula is still under development. Data is currently being assembled from ice shelves in Antarctica and Greenland to help establish a 'calving law'. Variables used in models include properties of the ice such as thickness, density, temperature, c-axis fabric, and impurity loading. A property known as 'ice front normal spreading stress' may be of key importance, despite it not normally being measured. [ citation needed ]

There are currently several concepts upon which to base a predictive law. One theory states that the calving rate is primarily a function of the ratio of tensile stress to vertical compressive stress, i.e., the calving rate is a function of the ratio of the largest to smallest principle stress. [14] Another theory, based on preliminary research, shows that the calving rate increases as a power of the spreading rate near the calving front.[ citation needed ]

Major calving events

Filchner-Ronne Ice Shelf

In October, 1988, the A-38 iceberg broke away from the Filchner-Ronne Ice Shelf. It was about 150 km x 50 km. A second calving occurred in May 2000 and created an iceberg 167 km x 32 km.

Amery Ice Shelf

A major calving event occurred in 1962 to 1963. Currently, there is a section at the front of the shelf referred to as the 'loose tooth'. This section, about 30 km by 30 km is moving at about 12 metres (39 ft) per day and is expected to eventually calve away. [15]

Ward Hunt Ice Shelf

The largest observed calving of an ice island happened at Ward Hunt Ice Shelf. Sometime between August 1961 and April 1962 almost 600 km2 (230 sq mi) of ice broke away. [16]

Ayles Ice Shelf

In 2005, nearly the entire shelf calved from the northern edge of Ellesmere Island. Since 1900, about 90% of Ellesmere Island's ice shelves have calved and floated away. This event was the biggest of its kind for at least the past 25 years. A total of 87.1 km2 (33+5⁄8 sq mi) of ice was lost in this event. The largest piece was 66.4 km2 (25+5⁄8 sq mi) in area, which is slightly larger than the City of Manhattan. [17]

Landsat image of Jakobshavn Isbrae. The lines show the position of the calving front of the Jakobshavn Isbrae since 1851. The date of this image is 2001, and the calving front of the glacier can be seen at the 2001 line. The area stretching from the calving front to the sea (towards the bottom left corner) is the Ilulissat icefjord. Courtesy of NASA Space Observatory. Jakobshavn retreat-1851-2006.jpg
Landsat image of Jakobshavn Isbræ. The lines show the position of the calving front of the Jakobshavn Isbræ since 1851. The date of this image is 2001, and the calving front of the glacier can be seen at the 2001 line. The area stretching from the calving front to the sea (towards the bottom left corner) is the Ilulissat icefjord. Courtesy of NASA Space Observatory.

Larsen Ice Shelf

This large ice shelf, located in the Weddell Sea, extending along the east coast of Antarctic Peninsula, consists of three segments, two of which have calved. In January 1995, the Larsen A Ice Shelf containing 3,250 km2 (1,250 sq mi) of ice 200 m (660 ft) thick calved and disintegrated. Then the Larsen B Ice Shelf calved and disintegrated in February 2002.

Jakobshavn Isbrae Glacier

Also known as the Ilulissat Glacier or Sermeq Kujalleq in western Greenland, in an ongoing event, 35 billion tonnes of icebergs calve off and pass out of the fjord every year.

Photographer James Balog and his team were examining this glacier in 2008 when their cameras caught a piece of glacier the size of Lower Manhattan fall into the ocean. [18] The calving event lasted for 75 minutes, during which time the glacier retreated a full mile across a calving face three miles (five kilometers) wide. Adam LeWinter and Jeff Orlowski captured this footage, which is featured in the film Chasing Ice .

Glacier surfing

First conceived in 1995 by Ryan Casey while filming for IMAX, this sport involves a surfer being towed into range by a jet ski and waiting for a mass of ice to calve from a glacier. [19] Surfers can wait for several hours in the icy water for an event. When a glacier calves, the mass of ice can produce 8 metres (26 ft) waves. Rides of 300 metres (980 ft) lasting for one minute can be achieved. [20]

See also

Related Research Articles

<span class="mw-page-title-main">Ellesmere Island</span> Island of the Arctic Archipelago in Nunavut, Canada

Ellesmere Island is Canada's northernmost and third largest island, and the tenth largest in the world. It comprises an area of 196,236 km2 (75,767 sq mi), slightly smaller than Great Britain, and the total length of the island is 830 km (520 mi).

<span class="mw-page-title-main">Iceberg</span> Large piece of freshwater ice broken off a glacier or ice shelf and floating in open water

An iceberg is a piece of freshwater ice more than 15 meters long that has broken off a glacier or an ice shelf and is floating freely in open water. Smaller chunks of floating glacially derived ice are called "growlers" or "bergy bits". Much of an iceberg is below the water's surface, which led to the expression "tip of the iceberg" to illustrate a small part of a larger unseen issue. Icebergs are considered a serious maritime hazard.

<span class="mw-page-title-main">Ross Ice Shelf</span> Ice shelf in Antarctica

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<span class="mw-page-title-main">Ice shelf</span> Antarctic ice shelf in the Amundsen Sea

An ice shelf is a large platform of glacial ice floating on the ocean, fed by one or multiple tributary glaciers. Ice shelves form along coastlines where the ice thickness is insufficient to displace the more dense surrounding ocean water. The boundary between the ice shelf (floating) and grounded ice is referred to as the grounding line; the boundary between the ice shelf and the open ocean is the ice front or calving front.

<span class="mw-page-title-main">Larsen Ice Shelf</span> Ice shelf in Antarctica

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<span class="mw-page-title-main">Drygalski Ice Tongue</span> Glacier in Antarctica

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<span class="mw-page-title-main">Ward Hunt Ice Shelf</span>

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<span class="mw-page-title-main">Ayles Ice Shelf</span>

The Ayles Ice Shelf was one of six major ice shelves in Canada, all on the north coast of Ellesmere Island, Nunavut. The ice shelf broke off from the coast on August 13, 2005, forming a giant ice island 37 m (121 ft) thick and measuring around 14 by 5 km in size. The oldest ice in the ice shelf is believed to be over 3,000 years old. The ice shelf was at, approximately 800 km (500 mi) south of the North Pole.

<span class="mw-page-title-main">Erebus Glacier Tongue</span>

The Erebus Glacier Tongue is a mountain outlet glacier and the seaward extension of Erebus Glacier from Ross Island. It projects 11 kilometres (6.8 mi) into McMurdo Sound from the Ross Island coastline near Cape Evans, Antarctica. The glacier tongue varies in thickness from 50 metres (160 ft) at the snout to 300 metres (980 ft) at the point where it is grounded on the shoreline. Explorers from Robert F. Scott's Discovery Expedition (1901–1904) named and charted the glacier tongue.

<span class="mw-page-title-main">Ward Hunt Island</span> Island in Nunavut, Canada

Ward Hunt Island is a small, uninhabited island in the Arctic Ocean, located off the north coast of Ellesmere Island near the Ward Hunt Ice Shelf. The island is located just 750 km (470 mi) from the geographical North Pole. The northern cape of Ward Hunt Island is one of the northernmost elements of land in Canada. Only a 17 km (11 mi) stretch of northern coast of Ellesmere Island around Cape Columbia is more northerly. The island is 5.0 km (3.1 mi) long, east to west, and 3.0 km (1.9 mi) wide. The first known sighting was in 1876 by Pelham Aldrich, a lieutenant with the George Nares expedition, and named for George Ward Hunt, who was First Lord of the Admiralty at the time (1874–1877). Today, the Island is part of the Quttinirpaaq National Park.

The Ellesmere Ice Shelf was the largest ice shelf in the Arctic, encompassing about 9,100 square kilometres of the north coast of Ellesmere Island, Nunavut, Canada. The ice shelf was first documented by the British Arctic Expedition of 1875–76, in which Lieutenant Pelham Aldrich's party went from Cape Sheridan to Cape Alert. The continuous mass of the Ellesmere Ice Shelf had been in place for at least 3,000 years.

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<span class="mw-page-title-main">Alfred Ernest Ice Shelf</span>

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<span class="mw-page-title-main">Ice mélange</span> Mixture of sea ice types, icebergs, and snow without a clearly defined floe

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<span class="mw-page-title-main">Liu Yan (scientist)</span> Chinese Antarctic researcher

Liu Yan is a Chinese Antarctic researcher best known for her work on iceberg calving. She is an associate professor of geography in the College of Global Change and Earth System Science (GCESS) and Polar Research Institute, Beijing Normal University.

An ice shelf basal channel is a type of subglacial meltwater channel that forms on the underside of floating ice shelves connected to ice sheets. Basal channels are generally rounded cavities which form parallel to ice sheet flow. These channels are found mainly around the Greenland and Antarctic ice sheets in places with relatively warm ocean water. West Antarctica in particular has the highest density of basal channels in the world. Basal channels can be tens of kilometers long, kilometers wide, and incise hundreds of meters up into an ice shelf. These channels can evolve and grow just as rapidly as ice shelves can, with some channels having incision rates approaching 22 meters per year. Basal channels are categorized based on what mechanisms created them and where they formed.

References

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  2. ↑ Glossary of Glacier Terms, Ellin Beltz, 2006. Retrieved July 2009.
  3. ↑ Glacier Bay, National Park Service. Retrieved July 2009.
  4. ↑ Glacier Calving photos Archived 2010-01-25 at the Wayback Machine . Retrieved July 2009.
  5. ↑ ARCTIC, Vol. 39, No. 1 (March 1986) P. 15-19, Ice Island Calvings and Ice Shelf Changes, Milne Ice Shelf and Ayles Ice Shelf, Ellesmere Island, N.W.T. Archived 2019-09-28 at the Wayback Machine , Martin O. Jeffries, 1985, University of Calgary. Retrieved 18 July 2009.
  6. ↑ Oceans, Oxfam. Retrieved June 2009.
  7. ↑ Promotions/Public Relations (2006-12-08). "The loose tooth: rifting and calving of the Amery Ice Shelf - Australian Antarctic Division". Aad.gov.au. Archived from the original on October 2, 2009. Retrieved 2010-07-30.
  8. ↑ Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B. (19 July 2013). "Ice-Shelf Melting Around Antarctica". Science. 341 (6143): 266–270. doi: 10.1126/science.1235798 . PMID   23765278. S2CID   206548095.
  9. ↑ Depoorter, M. A.; Bamber, J. L.; Griggs, J. A.; Lenaerts, J. T. M.; Ligtenberg, S. R. M.; van den Broeke, M. R.; Moholdt, G. (3 October 2013). "Calving fluxes and basal melt rates of Antarctic ice shelves". Nature. 502 (7469): 89–92. doi:10.1038/nature12567. PMID   24037377. S2CID   4462940.
  10. ↑ Greene, Chad A.; Gardner, Alex S.; Schlegel, Nicole-Jeanne; Fraser, Alexander D. (10 August 2022). "Antarctic calving loss rivals ice-shelf thinning". Nature. 609 (7929): 948–953. Bibcode:2022Natur.609..948G. doi:10.1038/s41586-022-05037-w. PMID   35948639. S2CID   251495070.
  11. ↑ Benn, D.; Warren, C.; Mottram, R. (2007). "Calving processes and the dynamics of calving glaciers" (PDF). Earth-Science Reviews. 82 (3–4): 143–179. Bibcode:2007ESRv...82..143B. doi:10.1016/j.earscirev.2007.02.002.
  12. ↑ Nick, F.; Van der Veen, C.; Vieli, A.; Benn, D. (2010). "A physically based calving model applied to marine outlet glaciers and implications for the glacier dynamics". Journal of Glaciology. 56 (199): 781. Bibcode:2010JGlac..56..781N. doi: 10.3189/002214310794457344 . hdl: 1808/17292 .
  13. ↑ Kohler, Jack (September 28, 2010). "How close should boats come to the fronts of Svalbard's calving glaciers?" (PDF). Norwegian Polar Institute. Archived from the original (PDF) on 2010-09-28. Retrieved 18 January 2018.
  14. ↑ Bassis, J. N.; MacAyeal, D. R.; Alley, R. (2008). "Modeling Iceberg Calving From Ice Shelves Using a Stress Based Calving Law: The". AGU Fall Meeting Abstracts. 2008. Adsabs.harvard.edu. Bibcode:2008AGUFM.C41D..03B.
  15. ↑ Coleman, Richard (2009-05-18). "Rifting and calving of the Amery Ice Shelf - Australian Antarctic Division". Aad.gov.au. Archived from the original on September 30, 2009. Retrieved 2010-07-30.
  16. ↑ "ARCTIC, Vol. 39, No. 1 (March 1986) P. 15-19, Ice Island Calvings and Ice Shelf Changes, Milne Ice Shelf and Ayles Ice Shelf, Ellesmere Island, N.W.T." (PDF). Archived from the original (PDF) on 2019-09-28. Retrieved 2009-07-10.
  17. ↑ "Ayles Ice Shelf - Dr. Luke Copland". Geomatics.uottawa.ca. Archived from the original on 9 February 2007. Retrieved 27 January 2017.
  18. ↑ "Video: Largest glacier calving ever caught on film | EarthSky.org". earthsky.org. 5 February 2013. Retrieved 2017-02-20.
  19. ↑ McNamara, Garrett. "Garrett McNamara Extreme Waterman".
  20. ↑ "Glacier Surfing". June 30, 2008. Archived from the original on February 1, 2009.

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