The Younger Dryas in the English Lake District: reconciling geomorphological evidence with numerical model outputs

The geomorphology of the south‐western and central L ake D istrict, E ngland is used to reconstruct the mountain palaeoglaciology pertaining to the L ateglacial and Y ounger D ryas. Limitations to previous ice‐mass reconstructions and consequent palaeoclimatic inferences include: (i) the use of static (steady‐state) glacier reconstructions, (ii) the assumption of a single‐stage Y ounger D ryas advance, (iii) greatly varying ice‐volume estimates, (iv) inexplicable spatial variations in ELA ( E quilibrium L ine A ltitude), and (v) a lack of robust extent chronology. Here we present geomorphological mapping based on aerial photography and the N ext M ap B ritain D igital E levation M odel, checked by ground survey. Former glacier extents were inferred and ELAs were calculated using the Balance Ratio method of O smaston. Independently, a time‐dependant 2‐D ice‐flow model was forced by a regional ELA history that was scaled to the GRIP record. This provided a dynamic reconstruction of a mountain ice field that allowed for non‐steady‐state glacier evolution. Fluctuations in climate during the Y ounger D ryas resulted in multiple glacial advance positions that show agreement with the location of mapped moraines, and may further explain some of the ELA variations found in previous local and static reconstructions. Modelling based on the GRIP record predicts three phases: an initial maximum extent, a middle minor advance or stillstand, and a pronounced but less extensive final advance. The comparisons find that the reconstructions derived from geomorphological evidence are effective representations of steady‐state glacier geometries, but we do propose different extents for some glaciers and, in particular, a large former glacier in U pper E skdale.