A detailed investigation into the legacy of glacial readvances and ice-dammed lakes around Sellafield, West Cumbria: implications for 3D modelling, hydrogeology and ground engineering

The glacial evolution of western Cumbria, England is reassessed following a comprehensive review of both published and extensive unpublished records from the Sellafield area, together with targeted fieldwork. The exercise scrutinises evidence for glacial readvances across former ice-dammed lakes, determining their occurrence, relative age, extent and legacy. It is concluded that the area was affected by at least two substantial glacial readvances following the maximum build-up of ice during the last, Late Devensian (Weichselian/Wisconsin) glaciation. The earlier Gosforth Oscillation involved locally sourced ice together with ice that circulated around the north of the Lake District into the Irish Sea basin whilst most of the region was substantially glaciated. The subsequent Fishgarth Wood Readvance involved ice flowing from the north, but when an ice centre positioned over the western Southern Uplands of Scotland had become dominant. Glacial oscillations across the coastal plain have resulted in a complex interdigitating sequence of sediments of contrasting permeability and physical properties, commonly preserved within buried valleys. The genesis of some thin units of clay-rich diamicton and pebbly clay previously interpreted as till is discussed in the light of ongoing debate concerning their possible glaciolacustrine origin.