| Summary: | This thesis consists of an introduction and three individual papers that investigate the possibility for identifying the sedimentary imprint of catchment processes in lake sediments, emphasising on extreme events and in particular those deposited by river floods. Three individual lake sediment basins in southern Norway have been studied and changes in the frequency of such events are reconstructed for the last c. 10,000 years. In Paper I, the sediments of the glacier-fed Lake Russvatnet in eastern Jotunheimen (61′ N 8′ E) were studied. The record comprises a combination of glacier-derived material produced by the glacier Blackwellbreen and also several episodic processes in the catchment area such as floods and debris flows. In order to distinguish late- Holocene (last 4000 years) river floods and mass movements from glacier fluctuations, the sedimentary record from Russvatnet was analysed for grain-size distribution and minerogenic content, which allowed for discrete mass-movement and river-flood deposits to be recognized. Twenty-two such episodic events were identified; 11 mass movement events and 11 river-flood events. Enhanced river-flood and colluvial activity are observed at 4000–3400, 2900–2500, 2000–1400 and 1000– 500 cal. years BP, suggesting a decreasing trend over the last 4000 years. At c. 2300 cal. years BP a shift in sedimentation regime from a paraglacial to a glacially dominated regime was observed, followed by a Neoglacial expansion period after 2300 cal. years BP. In Paper II we examine the possibility for objectively identifying flood deposits in lake sediments and hence construct Holocene flood records that may reveal changes in the long-term frequency of river floods. The method for identifying flood deposits was successfully applied to a high-resolution lake sediment core retrieved from Meringsdalsvatnet in eastern Jotunheimen (61′ N 9′ E) resulting in a detailed record of river-flood activity covering the last c. 10,000 years, including floods that have also been recorded by instrumental ...
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