Crevasses can be ignored in studying the dynamics of most glaciers because they are only about 20 m deep, a small fraction of ice thickness. In ice shelves, however, s urface crevasses 20 m deep often reach sealevel and bottom crevasses can move upward to sea-level (Clough, 1974; Weertman, 1980). The ice shelf is fractured completely through if surface and basal crevasses meet (Barrett, 1975; Hughes, 1979). This is especially likely if surface melt water fills surface crevasses (Weertman, 1973; Pfeffer, 1982; Fastook and Schmidt, 1982). Fracture may therefore play an important role i n the disintegration of ice shelves. Two fracture criteria which can be evaluated experimentally and applied to ice shelves, are presented. Fracture is then examined for the general strain field of an ice shelf and for local strain fields caused by shear rupture alongside ice streams entering the ice shelf, fatigue rupture along ice shelf grounding lines, and buckling up-stream from ice rises. The effect of these fracture patterns on the stability of Antarctic ice shelves and the West Antarctic ice sheet is then discussed.
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