The formation of icebergs, known as “calving”, is part of the natural lifecycle of glaciers and ice sheets. So long as the rate of snow accumulation balances mass loss via calving and direct melting of ice into the oceans, an ice mass can remain in equilibrium. However, in recent years, glaciologists observing the retreating glaciers and ice shelves of Greenland and Antarctica have begun to understand the many environmental factors that can upset this equilibrium. Air temperatures, sea temperature, and glacier flow-speed and thickness have all been shown to play a part. This progress formed a crucial component in predictive ice-sheet and glacier models, but we have yet to formulate a complete theory that will allow us to predict calving rates for individual glaciers.

Ice2sea researchers have been testing new calving criteria, i.e. sets of assumptions in models, which begin to resolve these issues. The criteria are based on calculations of stretching forces in the ice which create crevasses in the surface and base of the ice. Calving is predicted where these crevasses are calculated to either reach the waterline or go through the ice completely. The criteria have performed reasonably well in predicting the position and behaviour of calving fronts, including the seasonal cycles of retreat and advance observed at Greenland marine outlet glaciers.

This study highlights the requirement for more observations with which to validate and test the calving criteria, but we anticipate that the new calving criteria will be incorporated into the predictive glacier and ice-sheet models that ice2sea will eventually use to estimate the contribution of continental ice to sea-level rise.

Ice2sea Work Package: WPs2.3, 3.4

Publication: Nick, F. M., C. J. van der Veen, A. Vieli, and D. Benn (2010), A physically based calving model applied to marine outlet glaciers and implications for their dynamics, Journal of Glaciology, 56, 781-794.