Relict landscapes

The existence of well-preserved relict landscapes with early Weichselian eskers, frost shattered bedrock and the absence of erosional and depositional forms reflecting the flow of the late Weichselian ice sheet have been used by Kleman & Hätterstrand (1999) to map areas where the late Weichselian ice sheet was frozen to its bed and where there was therefore no sliding and little or no erosion (Plate 2.1c; see also Stroeven et al., this volume, Chapter 90). The fact that erosion can occur below cold ice (section 2.4.1) does not affect the inference that the relict zone in Plate 2.1 was a cold ice zone. It could be that this zone was more extensive than mapped by Kleman & Hätterstrand (1999), but this seems unlikely because of the probable low rates of cold ice erosion. The data provide a strong constraint on palaeoglaciolog-ical reconstruction of the ice sheet, and particularly on the glacier-climate parameters that are used in ice-sheet simulation models. Plate 2.1a & b shows a simulation of the basal temperature distribution in the European ice sheet as it approached its maximum extent at the LGM. The simulations show that the areas of the ice sheet mapped by Kleman & Hätterstrand (1999) as having relict features coincides with an area that had persistent freezing conditions during the last glacial expansion, although they suggest that areas outwith this zone had chequered histories of basal thermal regime as the dynamic structure of the ice sheet evolved.

Plate 2.2 shows a time-distance simulation of the evolution of basal temperature in space and time along the given transect through the ice sheet. It shows that during the early part of the glacial cycle (100 ka) temperate bed conditions extended almost up to the ice divide, whereas during the last glacial maximum (LGM) there was a 250-km-wide zone of basal freezing in the divide zone. This matches well with the Kleman & Hätterstrand (1999) reconstruction of basal thermal regime for the LGM and the evidence of early Weichselian temperate conditions in the ice divide zone, under which eskers formed, but which were later preserved because of frozen bed conditions (Lagerbäck, 1988). It also suggests that during parts of the retreat from the LGM, the rate

African Geophysical Images

Figure 2.13 The large scale pattern of lineations lying within the area of the last European ice sheet (Boulton et al., 2001c). Individual lines represent generalizations of more detailed mapping of lineations from Landsat images. The paucity of lineations in the southeastern region reflects the greater difficulty of resolving lineations in areas of arable agriculture.

Figure 2.13 The large scale pattern of lineations lying within the area of the last European ice sheet (Boulton et al., 2001c). Individual lines represent generalizations of more detailed mapping of lineations from Landsat images. The paucity of lineations in the southeastern region reflects the greater difficulty of resolving lineations in areas of arable agriculture.

of ice margin retreat was greater than the retreat rate of the junction between the outer temperate and inner cold ice-sheet zone, producing frozen bed conditions in the terminal zone (see also Boulton et al., 2001c), a result consistent with the deduction of Hattestrand & Clark (this volume, Chapter 39) for part of the deglaciation of the Kola Peninsula.

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