Identifying fast ice flow from landform assemblages in the geological record: a discussion
Different types of fast ice flow (both spatial and temporal) in valley glaciers (surging glaciers, tidewater glaciers and deforming-bed glaciers) and ice sheets (ice streams and deforming-bed ice-sheet flow) are discussed briefly. Although there are unlikely to be any specific individual landforms associated with fast ice flow, there may be landform assemblages.
At valley glacier scale, it is suggested that there are two landform assemblages: (1) an ice-thrust type, dominated by bulldozed push moraines and hummocky moraines (associated with glaciers with a high supraglacial sediment supply, a coarse-grained substrate and a coarse-grained proglacial sediment wedge); and (2) a bed-flow type dominated by "squeeze" push moraines, flutes and drumlins (associated with glaciers with a low supraglacial sediment supply and fine-grained substrate). The ice-thrust type alone is only associated with discontinuous fast flow (on both rigid and deforming beds); whilst the bed-flow type is associated with both continuous and discontinuous fast flow.
It is suggested that these two landform assemblages may also be indicative of fast ice flow at ice-sheet scale, in particular the bed-flow style. If that is the case, then discontinuous fast ice flow may be indicated by the ice-thrust landform assemblage and the bed-flow style where drumlins are present.
It is also suggested that specific evidence for ice streams includes the distinctive land-form assemblages within valley or fan-like locations, and a predictable pattern of velocity reflected by drumlin elongation ratios.
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