Ice calving

Ice calving

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Ice calving, also known as glacier calving or iceberg calving, is a form of ice ablation
Ablation zone
Ablation zone refers to the low altitude area of a glacier or ice sheet where there is a net loss in ice mass due to melting, sublimation, evaporation, or calving. The ablation zone is delineated by the equilibrium line altitude , or snow line, which separates the ablation zone and the high...

 or ice disruption. It is the sudden release and breaking away of a mass of ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 from a glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

, iceberg
Iceberg
An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...

, ice front
Ice front
An ice front is the place where a glacier thins and ends. The ice front's position changes as the glacier moves or melts....

, ice shelf
Ice shelf
An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland and Canada. The boundary between the floating ice shelf and the grounded ice that feeds it is called...

, or crevasse
Crevasse
A crevasse is a deep crack in an ice sheet rhys glacier . Crevasses form as a result of the movement and resulting stress associated with the sheer stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement...

. The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway.

Calving of glaciers is often preceded by a loud cracking or booming sound before blocks of ice up to 200 feet high break loose and crash into the water. The entry of the ice into the water causes large, and often hazardous wakes. The wakes formed in locations like Johns Hopkins Glacier
Johns Hopkins Glacier
Johns Hopkins Glacier is a long glacier located in Glacier Bay National Park and Preserve in the U.S. state of Alaska. It begins on the east slopes of Lituya Mountain and Mount Salisbury, and trends east to the head of Johns Hopkins Inlet, southwest of the terminus of Clark Glacier and northwest...

 can be so large that boats cannot approach closer than two miles. These events have become major tourist attractions in locations such as Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

.

Many glaciers terminate at oceans or freshwater lakes which results naturally with the calving of large numbers of icebergs. Calving of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

's glaciers produce 12,000 to 15,000 icebergs each year alone.

Calving of ice shelves is usually preceded by a rift. These events are not often observed.

Etymologically, calving is cognatic with calving as in birthing a calf
Calf
Calves are the young of domestic cattle. Calves are reared to become adult cattle, or are slaughtered for their meat, called veal.-Terminology:...

.

Causes



It is useful to classify causes of calving into first, second, and third order processes. 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
Crevasse
A crevasse is a deep crack in an ice sheet rhys glacier . Crevasses form as a result of the movement and resulting stress associated with the sheer stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement...

. When crevasses penetrate the full thickness of the ice, calving will occur. Longitudinal stretching is controlled by friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of 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
Subaerial
The term subaerial is mainly used in geology to describe events or structures that are located at the Earth's surface...

 ice, leading to collapse. Other second order processes include tidal and seismic events, buoyant
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 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 300m from the glacier terminus.

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
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

, c-axis fabric, impurity loading, though 'ice front normal spreading stress', is likely the most important variable, however it is usually not measured.

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. Another theory, based on preliminary research, shows that the calving rate increases as a power of the spreading rate near the calving front.

Major calving events



Filchner-Ronne Ice Shelf
Filchner-Ronne Ice Shelf
The Filchner-Ronne Ice Shelf, also known as Ronne-Filchner Ice Shelf, is an Antarctic ice shelf bordering the Weddell Sea.-Description:...


In October, 1988, the A-38 iceberg broke away from the Filchner-Ronne Ice Shelf. It was about 150 km x 50 km, a mass of ice bigger than the area of Delaware
Delaware
Delaware is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, and to the north by Pennsylvania...

. A second calving occurred in May 2000 and created an iceberg 167 km x 32 km.

Amery Ice Shelf
Amery Ice Shelf
The Amery Ice Shelf is a broad ice shelf in Antarctica at the head of Prydz Bay between the Lars Christensen Coast and Ingrid Christensen Coast. It is part of Mac. Robertson Land. The name "Cape Amery" was applied to a coastal angle mapped on February 11, 1931 by the British Australian New Zealand...


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 per day and is expected to eventually calve away.

Ward Hunt Ice Shelf
Ward Hunt Ice Shelf
The Ward Hunt Ice Shelf is the largest ice shelf in the Arctic, located on the north coast of Ellesmere Island, Nunavut, Canada. During the 20th century the Ellesmere Ice Shelf broke up into six separate shelves, the largest being Ward Hunt...


The largest observed calving of an ice island happened at Ward Hunt Ice Shelf. Sometime between August 1961 and April 1962 almost 600 km2 of ice broke away.

Ayles Ice Shelf
Ayles Ice Shelf
The Ayles Ice Shelf was one of six major ice shelves in Canada, all located on the northern coast of Ellesmere Island, Nunavut. The ice shelf broke off from the coast on August 13, 2005, forming a giant ice island thick and measuring around by in size . The oldest ice in the ice shelf is...


In 2005, nearly the entire shelf calved from the northern edge of Ellesmere Island
Ellesmere Island
Ellesmere Island is part of the Qikiqtaaluk Region of the Canadian territory of Nunavut. Lying within the Canadian Arctic Archipelago, it is considered part of the Queen Elizabeth Islands, with Cape Columbia being the most northerly point of land in Canada...

. 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 (33.6 sq mi) of ice was lost in this event. The largest piece was 66.4 km² (25.6 sq mi) in area, (equivalent in area to approximately 11,000 football fields or slightly larger than the City of Manhattan
Manhattan
Manhattan is the oldest and the most densely populated of the five boroughs of New York City. Located primarily on the island of Manhattan at the mouth of the Hudson River, the boundaries of the borough are identical to those of New York County, an original county of the state of New York...

.

Larsen Ice Shelf
Larsen Ice Shelf
The Larsen Ice Shelf is a long, fringing ice shelf in the northwest part of the Weddell Sea, extending along the east coast of Antarctic Peninsula from Cape Longing to the area just southward of Hearst Island...


This large ice shelf, located in the Weddell Sea
Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha Coast, Queen Maud Land. To the east of Cape Norvegia is...

, extending along the east coast of Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....

, consists of three segments, two of which have calved. The Larsen B Ice Shelf calved and disintegrated in February 2002. Then in January 1995, the Larsen A Ice Shelf containing 3,250 km² of ice 220 m thick calved and disintegrated.

Jakobshavn Isbrae Glacier


Also known as the Jakobshavn Glacier or Sermeq Kujalleq, in an ongoing event, 35 billion tonnes of icebergs calve off and pass out of the fjord
Fjord
Geologically, a fjord is a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity.-Formation:A fjord is formed when a glacier cuts a U-shaped valley by abrasion of the surrounding bedrock. Glacial melting is accompanied by rebound of Earth's crust as the ice...

 every year.

Glacier surfing


First conceived in 1995 by Ryan Casey while filming for IMAX
IMAX
IMAX is a motion picture film format and a set of proprietary cinema projection standards created by the Canadian company IMAX Corporation. IMAX has the capacity to record and display images of far greater size and resolution than conventional film systems...

, this sport involves a surfer
Surfing
Surfing' is a surface water sport in which the surfer rides a surfboard on the crest and face of a wave which is carrying the surfer towards the shore...

 being towed into range by a jet ski
Jet ski
Jet Ski is the brand name of a personal watercraft manufactured by Kawasaki Heavy Industries. The name is sometimes mistakenly used by those unfamiliar with the personal watercraft industry to refer to any type of personal watercraft; however, the name is a valid trademark registered with the...

 and waiting for a mass of ice to calve from a glacier. Surfers can wait for several hours in the icy water for an event. When a glacier calves, the mass of ice can produce 8 metre waves. Rides of 300 metres lasting for one minute can be achieved. This sport
Sport
A Sport is all forms of physical activity which, through casual or organised participation, aim to use, maintain or improve physical fitness and provide entertainment to participants. Sport may be competitive, where a winner or winners can be identified by objective means, and may require a degree...

 is considered to be dangerous.

See also


  • Ice sheet dynamics
    Ice sheet dynamics
    Ice sheet dynamics describe the motion within large bodies of ice, such those currently on Greenland and Antarctica. Ice motion is dominated by the movement of glaciers, whose gravity-driven activity is controlled by two main variable factors: the temperature and strength of their bases...

  • Ice shelf
    Ice shelf
    An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland and Canada. The boundary between the floating ice shelf and the grounded ice that feeds it is called...

  • Glacier
    Glacier
    A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

  • Ablation
    Ablation
    Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. This occurs in spaceflight during ascent and atmospheric reentry, glaciology, medicine, and passive fire protection.-Spaceflight:...


Further reading

  • Holdsworth, G. 1971. Calving From Ward Hunt Ice Shelf, 1961-1962., Canadian Journal Of Earth Sciences 8:299-305.

  • Jeffries, M. 1982. Ward Hunt Ice Shelf, Spring 1982. Arctic 35542-544.

  • Jeffries, M.O., And Serson, H. 1983. Recent Changes At The Front Of Ward Nwt. Arctic 36:289-290. Hunt Ice Shelf, Ellesmere Island, Koenig, L.S., Greenaway, K.R., Dunbar, M., And Haitersley

  • Smith, G. 1952. Arctic Ice Islands. Arctic 5:67-103.

  • Lyons, J.B., And Ragle, R.H. 1962. Thermal History And Growth Of The Ward Hunt Ice Shelf. International Union Of Geodesy And Geophysics International Association Of Hydrological Sciences, Colloque D’obergurgl, 10-18 September 1962. 88-97.

  • Rectic And Maykut, G.A., And Untersteiner, N. 1971. Some Results From A Time Of Geophysical Research Dependent Thermodynamic Model Of Sea Ice. Journal 761550-1575.

External links