Geological Quarterly, 1999,43 (2): 153-162 Channelized subglacial drainage under soft-bedded ice sheets: evidence from small N-channels in Central European Lowland

Examples of small (m-scalc) subglacial meltwater channels of Nyc-type from central Europe coupled with the occurrence of large tunnel valleys suggest a signi fican! role of noo-d istri butcd drainage system during major Pleistocene glaciations in this area. Hydraulic transmissivity of unconsolidated sediments overridden by the ice sheets was not sufficient to drain all basal meltwater as groundwater flow, so that the excess water volume was evacuated in hydraulically efficient channels incised into the bed, well preserved in the geological record. The channels are steep-sided, surrounded by undisturbed sediments and filled mainly with till, and they are bound by sharp. undulating erosional contacts. Their occurrence in sub-marginal areas of past ice sheets is consistent with the glaciological theory