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Retreat of the grounding lines of West Antarctic ice streams may lead to the collapse of the West Antarctic ice sheet. Pine Island Glacier has been pinpointed as an ice stream in which rapid retreat is likely, especially as it is not buttressed by an ice shelf. Radio echo-sounding flights have produced a longitudinal thickness profile for the glacier. The ice presently rests on a bedrock sill which may play a crucial role in controlling the position of the grounding line. The profile can be fitted to a steadystate model but this alone is not adequate to determine steady- or non-steady-state behaviour. Landsat images show that the ice front undergoes periodic calving. Mass-balance calculations suggest that accumulation in the catchment may exceed ablation by a factor of 2. However, accumulation data are poor and there is no firm evidence of a build-up of ice within the Pine Island Glacier drainage basin.
Crabtree et al. (Fri,) studied this question.