Reconstructing the character of the eastern sector of the Scandinavian ice sheet using remote sensing

Abstract

The extensive glacial landforms in the Baltic States and neighbouring countries have been used to infer the dynamic behaviour of the Scandinavian ice sheet.Landsat TM imagery was acquired of the Baltic States and neighbouring regions south of the Gulf of Finland (the Eastern Baltic region) in digital form. Computer image processing techniques were used to enhance the glacial geomorphology without enhancing the pattern of agricultural land usage. Mapping of glacial landforms was done (on-screen) using computer software. Using computers allowed the interpretations to be manipulated, analysed and compared with further information from digital elevation models, land cover maps and published literature /maps. This allowed the limit of Weichselian ice to be delineated using four different methods.Streamlined glacial lineations, including megaflutes, drumlins, megadrumlins and elongated hills have been mapped using this technique. Coherent groups of lineations were identified as flow sets, which were considered to have been formed by the same phase of ice flow. Where the lineations of different flow sets intersect, the temporal relationship between the flow sets, and therefore between the ice flows, was determined.While pre- Weichselian phases of ice flow were identified, it was concluded that the majority of lineations within the Eastern Baltic formed during the Late Weichselian. Long (up to 21 km), well-defined lineations were found to have formed during the Late Weichselian maximum when the ice velocities were greatest. These form flow sets with a north -south trend. Lineations from the final deglaciation are shorter in length and form flow sets orientated at 170 °. During the final deglaciation ice streams developed. Interstream areas generally coincide with regions of elevated bed rock.The interpretations resulting from these observations were combined with similar data from Finland to create a data set covering the area from the ice divide to beyond the limit of Weichselian ice. The spatial distribution of lineation size was examined using this data set and compared to output from a glaciological model. It was concluded that flow -parallel lineations were most likely formed by a single mechanism. The most likely mechanism was concluded to be subglacial deformation with the most active zone of lineation formation occurring within 100 km of the ice sheet margin.Variations in the frequency distribution of lineation length between Finland and the Eastern Baltic regions point to differences in the controls on lineation formation. Differences in the character of deglaciation between Finland and the Eastern Baltic were identified. Ice streams in Finland appear to have been more stable in location and about twice the width of those observed in the Eastern Baltic region. These differences may be explained by the interaction between the ice sheet and its substratum.