Ice sheet unzipping in the mountain-piedmont region of west-central Sweden: complex late-deglaciation of the Scandinavian ice sheet

Regional-scale glacial geomorphological maps provide important empirical data for reconstructions of former ice sheets, which may serve as analogues for the behaviour of modern ice sheets under climate warming. In particular, the extensive LiDAR-derived record of former ice sheet beds, provides an outstanding archive from which to infer former ice sheet behaviour. The stacking together and analysis of, tens of thousands of individual landforms, based on their spatial coherency, provides a powerful tool to reconstruct ice flow dynamics, temporally evolving ice divide positions and the “unzipping” of ice sheets into separate masses during deglaciation. In this study, we develop a glacial geomorphological dataset focussing on the mountain-piedmont region of Jämtland in west-central Sweden. We focus on this region because it is where the last (Weichselian) ice sheet is believed to have unzipped into separate domes and was inundated by vast ice dammed lakes. Jämtland also records a complex temporal evolution of subglacial processes and was formerly mapped without the benefit of a LiDAR-based elevation model. The dataset was created by mapping in GIS and covers an area of 50 000 km² and almost 88 000 landforms, including glacial lineations, crag-and-tails, ice marginal moraines, lateral meltwater channels, eskers, and glacial lake shorelines. We use this unique dataset–in terms of spatial density and resolution–and quantitatively analyse cross-cutting relationships to establish a relative ice flow chronology. Our key findings include 1) a previously unmapped landform system, formed by the Early-to-Middle Weichselian westward expansion of a mountain centred ice sheet, and 2) a complex early Holocene deglaciation sequence with ice sheet unzipping occurring in southern and east-central Jämtland. The ice sheet split into a larger sheet retreating northward and a smaller ice sheet remaining southeast of the mountain piedmont. Our results provide new insights into the late deglaciation of the Scandinavian Ice Sheet.