Largescale drift lineations

Figure 2.13 shows a compilation of the large-scale trends of lineations (primarily produced by drumlins) from the area of the last European ice sheet (Boulton et al., 2001c). It reveals major crossing lineation sets, reflecting shifts in the centre of mass of the ice sheet through the last glacial cycle, and consequent changes in the pattern of flow. It shows that these lineations cross at particularly high angles in northern Sweden, in the ice divide zone, where Lagerb├Ąck (1988) and Kleman et al. (1997) have shown that glacial geomorphological features have survived unaltered from the early part of the Weichselian glacial cycle. It shows the locations of former ice streams, particularly in the eastern and northeastern area of the Fennoscandian Shield. Submarine bathymetric studies can reveal even more complete patterns, and have been used by Clark et al. (2003b) to demonstrate the megaflute lin-eations created by the ice stream that flowed along the Skaggerak and thence along the Norwegian channel towards the continen tal shelf edge during the Last Glacial Maximum. Large-scale lin-eation patterns are now a rich source of information about the locations of palaeo-ice streams in former ice sheets (see Stokes and Clark, this volume, Chapter 26).

In a series of papers over the past 20yr, Shaw and collaborators (see Shaw, this volume, Chapter 4) have argued that drumlins are erosion marks created by subglacial water flow, and in the case of the North American Wisconsinan ice sheet were generated by very large outburst floods that, during one phase, are postulated to have generated a flow volume of 84,000 km3. The discovery of very large lakes beneath the Antarctic ice sheet (Robin et al., 1977; Kwok et al., 2000) suggested how a possible source for such floods might have existed beneath the North American ice sheet. Although it would be premature, at this stage of our knowledge, to suggest that such floods cannot or did not happen, there are no characteristics of drumlin fields that have been described that cannot be explained by glacial transport processes that are known to occur. It would therefore also be premature to prefer a speculative flooding process for their origin.

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