Spatial distribution and diversity of hummocky tracts in Southern Sweden - an analog to subglacial drainage in present large ice sheets?

Abstract:

Robust knowledge about processes involved in glacial melt-water drainage is crucial for a complete understanding of ice sheets. Investigating sediments and geomorphology of drainage systems below ice sheets is complicated; however, formerly glaciated regions are easily accessible. On the South Swedish Uplands, in the area covered by Fennoscandian ice sheets (FIS) during the late Quaternary, there is a diversity of hummocky tracts. For over a century, the hummocky characteristics of this region have been recognized, and several explanations have been proposed since. Most of these studies describe hummocks shown to be products of stagnant ice. The advent of LiDAR has revealed details of the landscape never before seen. We have mapped and analyzed glacial landforms on detailed DEMs from the region, and can present a more diverse view of the hummocky tracts. The four most striking features apart from the diversity are the spatial distribution and morphology. First, there are distinct elongate zones of hummocks with a radial pattern. Second, the hummocky zones in some places show an anastamosing and in other place a dendritic pattern. Third, in analyzing these elongate zones, it is clear that they do not follow regional lows but instead runs over highlands. Fourth, in these zones there are localities with eskers superposed on hummocks. These observations let us propose that stagnant ice cannot be the only process responsible for the hummocky tracts of SSU. In the field we have investigated the stratigraphy in sections. Preliminary results show that the stratigraphy cannot be readily interpreted as till from stagnant ice. Taken together, these observations can possibly explain the elongate hummocky zones invoking processes of subglacial meltwater eroding hummocks in the bottom of tunnel valleys. If these distinct elongate hummocky zones are not stagnant ice features but produced by subglacial meltwater they would alter the view of the FIS deglaciation significantly.