High-resolution seismic imaging of a Younger Dryas and Holocene mass movement complex in glacial lake Windermere, UK

The stratigraphy and sedimentological processes operating over the last 15,000 years within glacial lake Windermere (UK), at the mouth of Cunsey Beck, were imaged by a decimetre-resolution seismic reflection survey. A complex of fifteen mass movement deposits was identified as contemporaneous with the Younger Dryas, and two within the overlying Holocene drape. The high vertical resolution and dense grid of profiles allowed pseudo three-dimensional mapping of individual events, along with the determination of their relative temporal relationships. The size of the mass wasting deposits has been estimated to range between 2100 and > 100,000 m3. The geometry, structure and relationship to the existing stratigraphy suggest a rapid emplacement of the Younger Dryas mass movement deposits, facilitated by climatic changes making subaqueous slopes unstable, with possible triggering by seismic activity. Morphometric parameters, such as volume and planar surface area, indicate a greater mobility of the Younger Dryas mass movement deposits compared to the Holocene events. The sediments of all imaged mass movement deposits are believed to originate from the slope deposits of the lake. The age of two Holocene mass movement deposits, triggered by flooding or terrestrial debris flows, is estimated to be 2400 and 4400 years BP.