Ice Lake

At the close of the last glacial cycle a very large lake lay along the southern margin of the Scandinavian Ice Sheet across what is the Baltic Sea today. Large delta moraines accumulated along the southern margin of the ice sheet. These are best developed in southern Finland where the Salpausselka moraines occur. The moraines extend for over 600 km and are composed for the most part of outwash sediments deposited along a stationary ice margin. Fyfe (1990) studied the morphology and sedimentology of one of the three Salpausselka moraines. She found that it was composed along its length of three geomorphological components.

1. Large individual deltas with braided tops, ice-contact deltas, which built up to the water level and were produced in relatively shallow water where the meltwater outflow was concentrated into a small number of concentrated outflows or portals.

2. Low narrow fans, grounding-line fans, which coalesce along the former ice margin and were formed in deeper water where the meltwater outflow was more distributed along the ice margin.

3. Small laterally overlapping subaqueous fans formed where the location of the meltwater portals was unstable due to calving into deep water. Consequently a large number of small fans developed along the margin.

The water depth and the nature of the subglacial drainage system - concentrated, distributed, stable or unstable - controlled the nature of the outwash accumulation that formed along the former ice margin, and therefore control the morphology of the delta moraine formed.

Source: Fyfe, G.J. (1990) The effect of water depth on ice-proximal glaciolacustrine sedimentation: Salpausselka I, southern Finland. Boreas, 19,147-64.

distance behind the ice margin. Exceptionally fine examples have recently been revealed by sonar imagery from the German Bank area of the Scotian Shelf southwest of Nova Scotia (Box 11.2). There is considerable confusion surrounding the nomenclature and formation of these ridges. This in part reflects the fact that these ridges may form in several different ways (Figure 11.4); a concept known within geomorphology as equifinality. Some of these features form as seasonal push moraines produced by winter readvances of the grounding line in the same way as terrestrial push moraines (Figure 11.4A). It has been suggested that the calving of large icebergs may play a role in pushing up these ridges (see Figure 9.1B). Other examples may form as a consequence of the subglacial advection of deformation till to the ice margin and subsequent distal redistribution via a variety of sediment gravity flows. The internal structure of some larger ridges supports this model, with crude foreset beds of diamict dipping in a down-glacier direction

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