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Ice calving, also known as glacier calving or iceberg calving, is the breaking off of chunks of ice at 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, 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.〔(Glossary of Glacier Terms ), Ellin Beltz, 2006. Retrieved July 2009.〕 Calving of glaciers is often accompanied by a loud cracking or booming sound〔(Glacier Bay ), National Park Service. Retrieved July 2009.〕 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.〔(Glacier Calving photos ). Retrieved July 2009.〕 The waves formed in locations like Johns Hopkins Glacier can be so large that boats cannot approach closer than . These events have become major tourist attractions in locations such as Alaska. Many glaciers terminate at oceans or freshwater lakes which results naturally〔(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.'' ), Martin O. Jeffries, 1985, University of Calgary. Retrieved 18 July 2009.〕 with the calving of large numbers of icebergs. Calving of Greenland's glaciers produce 12,000 to 15,000 icebergs each year alone.〔(Oceans ), Oxfam. Retrieved June 2009.〕 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. ==Causes== It is useful to classify causes of calving into first, second, and third order processes.〔(Benn, D., Warren, C. & Mottram, R. 2007. Calving processes and the dynamics of calving glaciers. Earth-Science Reviews, 82, 143-179. )〕 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.〔(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, 781. )〕 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 300m from the glacier terminus.〔(How close should boats come to the fronts of Svalbard’s calving glaciers? )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ice calving」の詳細全文を読む スポンサード リンク
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