Streamlined landform distribution in south-west Sweden

Abstract

Streamlined landforms are forming underneath today’s glaciers. Since the Earth is undergoing a deglaciation it is important to understand how the glaciers move over the landscape to be able to predict future changes. In order to better understand the current deglaciation we can look to the past one and to that end a 14 085 km² area of south-western Sweden was mapped. Using a high resolution hillshaded DTM derived from a DEM created using LiDAR data (spatial resolution of 2 m) a map of the distribution and the ice flow direction of streamlined glacial landforms, with a focus on stoss-side moraines and crag-and-tails was created. It was found that the dominant ice flow direction was towards the south-west in south-western Sweden. Furthermore, stoss-side moraines were more common towards the coastline where the land is well below the highest coastline, whereas the number of crag-and-tails were few. Only the two most narrow bedrock knobs of the stoss-side moraines were smaller than the biggest bedrock knob of the crag-and-tails and on average the stoss-side moraines bedrock knob was 10,3 times wider than that of the crag-and-tails. The stoss-side moraines and crag-and-tails are both formed around a bedrock knob. The stoss-side moraines have sediment on the proximal (i.e. up-ice) side, whereas the crag-and-tails have sediment on the distal (i.e. down-ice) side of the bedrock knob. Streamlined till patches often contained multiple streamlined features which had merged into one suggesting that they are deposited wherever their formation is promoted. Another key finding was that there is always a taller mountain peak up-ice from every stoss-side moraine and often also a low laying flat directly up-ice from the stoss-side moraine, both of which appear to be crucial to their formation. Furthermore, two primary flow directions were indicated by the crag-and-tails, the first towards approximately 210° and the second towards approximately 240°. This is explained by their position on the land with all of the crag-and-tails with an azimuth of 220° or less being on the eastern side. An alternative explanation is that the crag-and-tails trending towards 240° are older, forming during the initial advance and those trending towards 210° being deposited during a readvance or during a retreat.