Symmetrical till-cored drumlins highlight where past ice sheets flowed faster

For over 100 years, from school textbook to research, glacially sculpted landforms called drumlins have been considered asymmetrical, tear-drop shaped. Recent work has securely demonstrated that, in the absence of bedrock, this asymmetry is measurable but tiny – non-existent to visual inspection. High-resolution DEMs and a novel application of statistics to flow-sets demonstrate that a well-studied a Swedish site exhibits a transition from asymmetrical bedrock-cored drumlins to symmetrical till-cored ones within just a few 10s of m of till. We believe that this is the first direct observational constraint upon the thickness of till required to effectively decouple flowing ice from rough bedrock topography. Understanding where till lubrication has the potential to speed up ice flow has large implications for modelling current ice sheets and Antarctic deglaciation, so we are hoping for ideas of how to best assess this last part.