UNDER THE SCANDINAVIAN ICE SHEET: PROCESSES, DEPOSITS AND LANDFORMS

Glaciers are arguably the most powerful, climatically driven agents of large-scale sediment redistribution and landscape formation in the Earth system. Repeated waxing and waning of continental ice sheets during the Quaternary contributed to a profound reshaping of the Earth surface and set the scene for the development of ecosystems in the post-glacial time. Despite the well-established impact of glaciers on the upper lithosphere the specific processes of glacial erosion, transport and deposition, and the formation landforms at the ice-bed interface often remain contentious. In particular, the relative importance of direct ice impact versus the impact of glacial meltwater is controversial. Here, we focus on the southern peripheral area of the Scandinavian Ice Sheet hosting thick successions of soft, deformable sediments and examine some spectacular assemblages of glacial deposits and landforms to illustrate the nature of the subglacial processes. In order to decipher the behavior of the ice sheet we combine field, experimental and numerical approaches. It is shown that the strength of the coupling between the ice and the bed that controls the response of the substratum to ice overriding and stress propagation depends primarily on the ability of the glacial system to evacuate meltwater from ice-bed interface. Strong coupling, locally enhanced by subglacial permafrost resulted in deeply rooted (100’s of meters) glaciotectonic deformation whereas weak coupling promoted by water ponding under the ice triggered the formation of deep (100’s of meters) tunnel valley networks. Under the arteries of fast-flowing ice streams, remoulding of soft sediments generated mega-scale glacial lineations and drumlins that hold the key to the understanding of glacier dynamics. The subglacial environment is envisaged as a four-dimensional mosaic of stable and deforming spots transient in time and space whose impact is embedded in the properties of the sediment-landform systems.