The Lateglacial history of Bassenthwaite Lake and adjacent areas, Lake District, UK; a sub-bottom profiling and geomorphological investigation

Abstract

The glacial history of Bassenthwaite Lake and adjacent areas is poorly understood despite the English Lake District being a key area for assessing the dynamics of the British-Irish ice sheet. This project undertook geomorphological mapping and sub-surface geophysical investigations in order to investigate the glacial history of Bassenthwaite Lake. Drumlins and moraine ridges adjacent to the lake point to a relatively simple ice advance and retreat during the Last Glacial Maximum (LGM), but sub-bottom profile data from the lake floor suggests a more complex glacial history with a lower basement till or bedrock overlain by glaciolacustrine and glaciofluvial sediments. An eroded lower till or bedrock illustrates erosion potentially taking place during LGM ice coverage with the Bassenthwaite basin entirely inundated at this period. Moraine ridges along the length of Bassenthwaite Lake illustrate punctuated retreat of a constrained Lateglacial valley glacier. In addition to this, ice-marginal fluctuations are recorded through localised deformation within glaciolacustrine sediments. Continued retreat of the glacier results in the deposition of an upper glaciolacustrine sequence with ice-berg rafted debris identified. The identification of a re-advance till unit and the deformation of a lower glaciolacustrine sequence illustrates a fluctuating ice margin, which in some places re-advanced up to ~ 1 km and points to a dynamic ice mass occupying the Bassenthwaite basin. A drumlin was also investigated through sub-bottom profiling and was interpreted to have been created through erosion of the underlying bedrock. Following this, sedimentary packages overlie and infill the drumlin with two glacier re-advance events resulting in drumlinisation. It is clear that sub-bottom profiling has the potential to illustrate the internal composition and structure of submerged drumlins in addition to providing valuable information into Lateglacial glacier retreat dynamics.