Overlaps with other Glacigenic Landsystems

Important questions are how unique is the sub-polar glacier landsystem and to what extent can it be differentiated from other terrestrial and subaquatic glacigenic landsystems? This is important for understanding the nature of glaciers and ice sheets in the geological record, particularly in terms of their basal thermal regime and, hence, past climate. The sub-polar glacier landsystem contains elements that are common to several other landsystems discussed in this book. Thrust-block moraines have been described from modern surge-type, temperate glaciers in Iceland (Evans and Rea, Chapter 11). Temperate, marine-terminating tidewater glaciers in environments such as southeast Alaska, deposit subaquatic morainal banks, grounding-line fans and ice-contact deltas (Powell and Molnia, 1989; Powell, 1990, Chapter 13). Additionally, plateau ice fields in the

Black Dahlia Coroner Photos
Figure 3.14 Ice-dammed lake, produced by the blocking of a valley by a plateau-outlet glacier (see also Chapter 16), Viking Ice Cap, northeastern Ellesmere Island. (Photograph T404L-56, Energy, Mines and Resources, Canada).

Canadian and Greenland high arctic are characterized by a suite of landforms and sediments that are diagnostic of the plateau ice field landsystem (see Rea and Evans, Chapter 16). The mountainous setting of much of the Canadian and Greenland high arctic, in which outlet glaciers extend towards sea level through valleys, means that the processes and landforms characteristic of the high-relief glaciated valley landsystem (see Benn et al., Chapter 15) may also occur in the subpolar glacier landsystem. These include rock glacierization, melt-out of supraglacial and englacial debris to produce buried glacier snouts (see Dyke and Evans, Chapter 7) and subaerial debris flow deposition.

As has been stressed for the other landsystems in this volume, it is apparent that no single criterion is diagnostic of the sub-polar glacier landsystem other than the exceptional detail provided by nested lateral meltwater channels. Rather it is important to consider the criteria collectively, particularly in investigations of the geological record. It is the combination of evidence for both a warm-based glacier bed with frozen glacier margins that is diagnostic of the sub-polar glacier regime. For example, the juxtaposition of thick accumulations of meltwater-derived glacimarine sediments related to the subglacial drainage system, with nested suites of lateral meltwater channels in the same fjord system, suggests the former presence of a sub-polar glacier margin rather than a temperate southeast Alaska-type regime. In the latter, the temperate glaciological regime would facilitate rapid penetration of supraglacial meltwater to the bed and preferential evacuation to the glacier terminus via the subglacial meltwater system.

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