Sognefjorden in western Norway – physiography, geomorphology, marine levels and deglaciation history
Journal article, Peer reviewed
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Date
2024Metadata
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- Department of Earth Science [1133]
- Registrations from Cristin [11366]
Abstract
The landscape formation along Sognefjorden, Norway’s longest and the world’s second longest fjord, involves tectonic activity, glacial erosion during numerous Quaternary ice ages, and mass movements during interglacials and interstadials. As previously observed, segments of the strandflat are present between the coast and the Balestrand / Vangsnes area. Based on an equidistant shoreline diagram from the Bergen area (Sotra–Tørvikbygd transect) an equidistant shoreline diagram was constructed for the Sognefjorden region. This diagram was used to obtain age estimates of marine limits / levels along Sognefjorden. Ice-marginal deposits at the mouths of tributary valleys in the inner Sognefjorden region have, according to the shoreline diagram, ages in the range of 11.34–10.93 cal. ka BP, which are in close agreement with previous ages estimates for these frontal deposits. Reconstruction of the course of the last deglaciation indicates a frontal retreat rate of about 270 m a-1 from the Younger Dryas (YD) ice-sheet margin in the coastal area in Solund to Leikanger, ~122 km to the east of the YD ice-sheet margin. Farther inland, the average deglaciation rate was in the order of 185 m a-1 between Leikanger and along Lustrafjorden to Skjolden in the innermost part of the fjord. In an east-facing cirque below a modern local glacier east of the summit of Bleia, marginal moraines down to 1080 m a.s.l. are interpreted to have been formed by a local glacier. The ELA difference between the modern glacier and the reconstructed glacier has been estimated to 470, 460, and 485 ± 11 m with the MELM, THAR, and AAR approaches, respectively. These land-uplift corrected ELA calculations are in close agreement with estimates for ELA depressions of YD valley and cirque glaciers in western Norway. A mean basal shear stress of the contemporaneous glacier in Sognefjorden has been calculated to ~19 kPa. Similar basal shear stress values are commonly associated with low-gradient, fjord- and tidewater glaciers and / or glaciers resting on soft, deformable beds.