Ice calving, also known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier.Essentials of Geology, 3rd edition, Stephen Marshak 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 A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

iceberg An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...

, ice front, ice shelf, or

crevasse A crevasse is a deep crack, that forms in a glacier or ice sheet that can be a few inches across to over 40 feet. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid p ...

. The ice that breaks away can be classified as an iceberg, but may also be a growler, bergy bit, or a crevasse wall breakaway.Glossary of Glacier Terms
Ellin Beltz, 2006. Retrieved July 2009. Calving of glaciers is often accompanied by a loud cracking or booming sound before blocks of ice up to high break loose and crash into the water. The entry of the ice into the water causes large, and often hazardous waves. The waves formed in locations like

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, sout ...

can be so large that boats cannot approach closer than . These events have become major tourist attractions in locations such as

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U ...

. Many glaciers terminate at oceans or freshwater lakes which results naturallyARCTIC, 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.''
Martin O. Jeffries, 1985, University of Calgary. Retrieved 18 July 2009. with the calving of large numbers of icebergs. Calving of

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

's glaciers produce 12,000 to 15,000 icebergs each year alone. Calving of ice shelves is often preceded by a rift. An ice shelf in steady state calves at roughly the same rate as the influx of new ice, and calving events may occur on subannual 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.

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

s. When crevasses penetrate the full thickness of the ice, calving will occur. Longitudinal stretching is controlled by

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

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 In natural science, subaerial (literally "under the air"), has been used since 1833,Subaerial
in the Merriam ...

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 300m from the glacier terminus.

Calving law

Though many factors that contribute to calving have been identified, a reliable predictive

mathematical formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a '' chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship bet ...

is still under development. Data is currently being assembled from ice shelves in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

and Greenland to help establish a 'calving law'. Variables used in models include properties of the ice such as thickness, density,

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

, 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. 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

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 meters per day and is expected to eventually calve away.

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 of ice broke away.

Ayles Ice Shelf

In 2005, nearly the entire shelf calved from the northern edge of

Ellesmere Island Ellesmere Island ( iu, script=Latn, Umingmak Nuna, lit=land of muskoxen; french: île d'Ellesmere) is Canada's northernmost and third largest island, and the tenth largest in the world. It comprises an area of , slightly smaller than Great Br ...

. 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 of ice was lost in this event. The largest piece was in area, (slightly larger than the City of

Manhattan Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...

Larsen Ice Shelf

This large ice shelf, located in the Weddell Sea, extending along the east coast of

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

, consists of three segments, two of which have calved. In January 1995, the Larsen A Ice Shelf containing 3,250 km² of ice 220 m 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 In physical geography, a fjord or fiord () is a long, narrow inlet with steep sides or cliffs, created by a glacier. Fjords exist on the coasts of Alaska, Antarctica, British Columbia, Chile, Denmark, Germany, Greenland, the Faroe Islands, Icel ...

every year. Photographer

James Balog James Balog (pronounced ''BAY-log''; born July 15, 1952) sometimes referred to as Jim Balog, is an American photographer whose work explores the relationship between humans and nature. Since the early 1980s, Balog has photographed such subjects ...

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. 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 IMAX is a proprietary system of high-resolution cameras, film formats, film projectors, and theaters known for having very large screens with a tall aspect ratio (approximately either 1.43:1 or 1.90:1) and steep stadium seating. Graeme ...

, 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. 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.

References

External links

University of Chicago article"Chasing Ice" captures largest glacier calving ever filmed
{{glaciers Glaciers Glaciology Articles containing video clips