Ice calving or iceberg calving 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.[1]
Calving of glaciers is often preceded by a loud cracking or booming sound[2] 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.[3] The wakes formed in locations like Johns Hopkins Glacier can be so large that boats cannot approach closer than two miles. These events have become major tourist attractions in locations such as Alaska.
Many glaciers terminate at oceans or freshwater lakes which results naturally[4] with the calving of large numbers of icebergs. Calving of Greenland's glaciers produce 12,000 to 15,000 icebergs each year alone.[5]
Calving of ice shelves is usually preceded by a rift.[6] These events are infrequent and not often observed.
Etymologically, calving is cognatic with calving as in birthing a calf. [7]
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Although calving can be caused by tidal and seismic events, periodic calving and disintegration of ice masses are considered normal geological processes.[4] One of the most important causal factors in glacial calving is the tendency of the ice to spread out at the terminus of the glacier.[8] Other important variables include tidal fluctuations, storm surges, collisions from other ice masses, melt water wedging into crevasses, and pre-existing flaws along which calving might occur.
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, 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. [9] Another theory, based on preliminary research, shows that the calving rate increases as a power of the spreading rate near the calving front.
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. A second calving occurred in May 2000 and created an iceberg 167 km x 32 km.
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.[10]
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.[11]
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 (33.6 sq miles) of ice was lost in this event. The largest piece was 66.4 km2 (25.6 sq. miles) in area, (equivalent in area to approximately 11,000 football fields or slightly larger than the City of Manhattan.[12]
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. 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.
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 every year.
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.[13] 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.[14] This sport is considered to be dangerous.
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