C

-150

-200

-150

-200

läilsSl clay silt

^^ boundary Tertiary/

Figure 10.2 Geological section showing the major hydrogeological units 1-5. Location of the section in Figure 10.1.

till sand gravel läilsSl clay silt brown bound Quaternary

^^ boundary Tertiary/

Figure 10.2 Geological section showing the major hydrogeological units 1-5. Location of the section in Figure 10.1.

Table 10.1 Water discharge at the ice-sheet margin for different scenarios including permafrost and a subglacial channel

Basic model without permafrost and 4.0

without subglacial channel

Without permafrost and with 5.3

subglacial channel

With permafrost and without 3.7

subglacial channel

With permafrost and with subglacial 4.9 channel

Germany modelled by Piotrowski (1997a,b). This in turn implies a likelihood of hydraulic decoupling, and formation of more efficient drainage mechanisms for the surplus meltwater, such as subglacial sheet floods or channelized flow. Tunnel valleys, occurring abundantly across the entire central European lowland, yield convincing support for the latter. We therefore suggest that tunnel valleys formed to secure the stability of the ice sheet by reducing the water pressure at the ice-bed interface, thereby preventing catastrophic surges and ice-sheet collapse.

Table 10.1 Water discharge at the ice-sheet margin for different scenarios including permafrost and a subglacial channel

Scenario

Discharge at ice margin

(m3s-1)

Basic model without permafrost and 4.0

without subglacial channel

Without permafrost and with 5.3

subglacial channel

With permafrost and without 3.7

subglacial channel

With permafrost and with subglacial 4.9 channel

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