Foreland evolution of Blåisen, Norway, over the course of an ablation season

Sammanfattning: This study presents a detailed investigation into the evolution of sedimentary landforms over an ablation season at Blåisen, an outlet of the Hardangerjøkulen Icecap, Norway. The two visits to Blåisen, one each side of the ablation season, allowed the preservation and evolution of the landforms to be studied. Much research is conducted studying glacial landforms, which are key in our understanding of past and future ice behaviour. This is important in researching the past, present and future response of the cryosphere to climate forcing, and the impact of such changes. A smaller portion of glacial geomorphological studies are now conducted using predominantly fieldwork with even fewer making repeated visits to sites in short succession. Many now use remote sensing which, while being a powerful tool to understand ice behaviour, means that smaller scale features (both in the temporal and spatial sense) may be missed. An awareness of what may be missing when studying forelands that are a few years to many millennia old is important to gaining a more holistic understanding of the ice behaviour and the processes occurring. This study focuses on the younger landforms in the immediate vicinity of the ice margin. GPS mapping, field observations and Structure from Motion Photogrammetry was used over two visits to Blåisen in June and September to identify four such landform types: snowbank squeeze moraines, flutes, minor moraines and an ice-cored wedged shaped ridge system (called a sediment wedge in this study after its characteristic shape). The foreland of Blåisen was characterised by a number of areas where a reverse bedrock was present (bedrock that slopes in the opposite direction to ice flow); this had the effect of inhibiting drainage leading to saturated sediments around the ice margin. These sediments are easily deformable, so play an important role in the formation of the Snowbank Squeeze Moraines, Flutes, Minor Moraines in particular. The processes of formation are explored using the geomorphological and sedimentological evidence to devise genesis and evolution models for each landform type. The model for the formation of the sediment wedge presents freeze-on as a prominent mechanism, facilitating the transport of debris in a band from the base of the glacier to the margin where, due to differential melting, the underlying ice is isolated from the rest of the glacier. Snowbank Squeeze Moraines were observed as ridges of sediment protruding out of the snow in June formed by the deformation of sediments between the ice margin and the winter snowbank lying over the margin. The ‘squeeze’ form of snowbank moraines has not been widely documented in part due to their poor preservation, illustrated by the lack of remaining evidence for them in September. Few flutes were recorded aside from those mapped in September, indicating that either in past seasons, conditions had not been favourable for formation, or that preservation was poor. The latter is supported by the lack of remaining evidence of the snowbank squeeze ridges in September. The poor preservation of these landforms highlights how they may be missed in other studies and the need for further research in this area.