LiDAR-based Volume Assessment of the Wadena Drumlin Field and End Moraines, Minnesota, USA: Evaluating an Erosional Origin for Mega-scale Glacially Lineated Terrains

English Abstract:

Mega-scale glacially lineated terrains (MSGL) are widely recognised as the geomorphic footprint of fast-flowing paleo ice streams within otherwise slowly moving ice sheets. MSGL is common in Minnesota, USA, reflecting the convergence of several ice streams within the southern sector of the Laurentide Ice Sheet. The Wadena drumlin field of west central Minnesota consists of an estimated 2000 streamlined subglacial bedforms over an area of about 7500 km2. The field lies within a complex upland interlobate area surrounded by prominent end moraines with the Alexandria Moraine on its southern and western margins possibly marking the outer extent of the southwesterly-flowing Wadena Ice Stream at the time of drumlin formation. Light Detection and Ranging (LiDAR) data are revealing much new detail of the morphology of drumlins. This presentation posits that they are primarily residual landforms formed by erosion of a pre-existing sediment bed by a thin mobile ‘erodent layer’ of deforming diamictic debris that delivered subglacial debris to build morainal landforms at the outer margin of the drumlin field. We evaluate the erosional hypothesis by using a newly developed quantitative methodology based on relief curvature analysis of LiDAR imagery to evaluate subglacial debris fluxes below the Wadena Lobe.