Calving glaciers

Based on a review of observations on different types of calving glaciers, a simple calving model is proposed. Glaciers that exist in a sufficiently cold climate can form floating ice shelves and ice tongues that typically do not extend beyond confinements such as lateral fjord walls or mountains, and ice rises. If the local climate exceeds the thermal limit of ice shelf viability, as is the case for temperate glaciers, no floating tongue can be maintained and the position of the terminus is determined by the thickness in excess of flotation. If the snout is sufficiently thick, a stable terminus position at the mouth of the confining fjord - usually marked by a terminal shoal - can be maintained. Further advance is not possible because of increasing sea-floor depth and diverging flow resulting from lack of lateral constraints. If a mass balance deficiency causes the terminal region to thin, retreat is initiated with the calving front retreating to where the thickness is slightly in excess of flotation. In that case, the calving rate is determined by glacier speed and thickness change at the glacier snout. Advance or retreat of the calving front is not driven by changes in the calving rate, but by flow-induced changes in the geometry of the terminal region. This model is essentially different from prior suggestions in which some empirical relation - most commonly the water-depth model - is used to calculate calving rate and the rate of retreat or advance of the terminus.