STREAMING FLOW IN THE LAST EUROPEAN ICE SHEET

The locations of fast ice streams have been inferred within the area of the last European ice sheet from extensive and well-integrated sets of glacial lineations (often drumlins and mega-flutes) and protrusions of the contemporary ice margin marked by moraines or fanning of the flow lineations. Zones of streaming flow have been identified for the whole period of retreat of the ice sheet, a period of about 8-10,000 years. Some appear to have been sustained for the whole period of retreat, others appear to have been ephemeral, reflecting an imbalance between the accumulation flux and flow. In some cases, the length of time for which ephemeral fast streams were sustained can be estimated.

A high resolution, numerical ice sheet model has been used to simulate streaming flow in the European ice sheet. It permits model results to be compared with glacial geological and geophysical observations on the scale at which they are made, and yields velocity and shear stress estimates for the streams. In some cases there is a very close correspondence between model output and reconstructions based on geological data. The overall pattern of fast streaming permits aspects of glacial geology that had hitherto been highly problematic to be explained. However, it is clear in detail that the basal boundary that has been selected does not permit some aspects of geological and geophysical evidence to be explained, and requires coupling between basal melting/drainage and basal decollement. The extent to which sediment deformation has facilitated this decollement and streaming flow is discussed.