Lake shoreline development, frost weathering and rock platform erosion in an alpine periglacial environment, Jotunheimen, southern Norway
Ice‐dammed lake Boverbrevatnet existed for 75–125 years in the ‘Little Ice Age’. After about A.D. 1826, glacier retreat led to a fall in lake level and to exposure of the former shoreline, which includes well‐developed platforms cut in metamorphic bedrock. The rock platforms, up to 5.3 m wide and ba...
| Published in: | Boreas |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Wiley
1986
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1111/j.1502-3885.1986.tb00741.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1502-3885.1986.tb00741.x https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1502-3885.1986.tb00741.x |
| Summary: | Ice‐dammed lake Boverbrevatnet existed for 75–125 years in the ‘Little Ice Age’. After about A.D. 1826, glacier retreat led to a fall in lake level and to exposure of the former shoreline, which includes well‐developed platforms cut in metamorphic bedrock. The rock platforms, up to 5.3 m wide and backed by cliffs up to 1.55 m high, are partially covered by large angular boulders which form pavements. Accurate levelling has permitted correlation of platform fragments, overflow cols and related features of the shoreline, such as benches eroded in moraines, ice‐push ridges, a perched delta, vegetation trim‐lines, lichen limits and a ‘lichen‐kill’ zone. The evolution of the lake, the chronology of deglaciation and the period of formation of the rock platforms have been dated by lichenometry, supported by 14 C dating, Schmidt hammer ‘R’‐values and historical data. The morphology of the rock platforms, together with estimates of their rate of erosion ranging from 1.4 to 7.1 cm/year, indicate the importance of frost shattering (frost riving, frost wedging or macrogelivation) at the lake margin under a periglacial climate, while the permanence of such platforms as landscape features suggests their use in the reconstruction of former periglacial environments. A semi‐quantitative model is outlined for the development of rock platforms which emphasises deep penetration of the annual freeze‐thaw cycle, the movement of unfrozen lake water towards the freezing plane, and the growth of segregation ice in fissures and cracks at the interface between lake ice and bedrock. Ice‐push and ice‐pull processes are involved primarily as transporting agents in the formation of boulder pavements and in the removal of debris from the platforms. Analogous processes may occur on polar coasts producing coastal rock platforms. |
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