Glacial and post-glacial history of Lake Windermere, The Lake District, UK: integrating high resolution multibeam bathymetry, airborne LiDAR, and sediment cores

High resolution multibeam bathymetry and airborne LiDAR (light detection and ranging) data, supplemented by geomorphological and geological field mapping have been used to investigate the glacial and post-glacial history of Windermere, the largest natural lake in England. In addition, recently acquired piston cores, supplemented with 2D and 3D seismic reflection data from previous surveys have been used to examine the well preserved sequence stratigraphy. The data is used to generate a present-day landscape map, revealing a complex landform record, characterised by nine sub-basins separated by steps, ridges and isolated topographic highs related to the retreat of the British and Irish Ice Sheet (BIIS). Debris flows and anthropogenic features are superimposed on the general bathymetric framework formed since the Last Glacial Maximum. There is also evidence of glacial features preserved onshore, which identify a series of depositional environments that accompanied ice advance, ice retreat and post-glacial deposition within the Lake District. Core analysis has identified a sequence of sand with finely laminated sand, silt and clay, fining upwards into varved clays, overlain by organic rich lacustrine gyttja. The stratigraphic units correlate with existing seismic stratigraphic facies, suggesting the sequence extends through an overlying drape of Holocene gyttja into glaciolacustrine and lacustrine sediment fill relating to Interstadial/BIIS retreat, and further penetrates to the till surface. Analysis of geophysical core properties reveals coarser layers in the varved clay are correlated with peaks in magnetic susceptibility and iron, suggesting retreat was punctuated by surges in ice movement leading to the deposition of coarser layers rich in iron bearing minerals. This study indicates that an integrated approach, using high resolution geophysical datasets combined with sediment coring is capable of deriving an in-depth understanding of glacial and post-glacial activity within a lacustrine setting. The results complement existing high resolution geophysical data and can be used to inform wider ice sheet glacial reconstructions.