V

Bedrock

Ice surface

Point of maximum erosion

Bedrock

Point of maximum erosion

Increasing erosion rate

Increasing erosion rate

Increasing erosion rate

Bedrock

Source: Harbor, J.M., Hallet, B. and Raymond, C.F. (1988) A numerical model of landform development by glacial erosion. Nature, 333, 347-9.[Diagram modified from: Harbor et al. (1988) Nature, 333, figure 1, p. 348]

an area when it is first glaciated, and once an efficient system of glacial troughs and other ice discharge routes has been established little modification may occur.

The longitudinal profile of glacial troughs usually contains a series of enclosed basins within it (Box 6.6). These are excavated as outlined in Section 6.2.3 through the operation of positive feedback between compressional flow and basin development. Hanging valleys are formed where two glacial troughs have been eroded into the landscape at different rates. If one trough is cut at a faster rate, perhaps because of a greater drainage area than its tributary, then the floor of the tributary will become perched at a higher altitude than that of the first trough. There may be a substantial height difference between the altitude of the two valley floors, and the highest is said to be left 'hanging' above the lowest.

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