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Eivind Nagel Støren, University of Bergen, Department of Earth Science (Norway)
Kristian Vasskog, University of Bergen, Department of Earth Science (Norway)
Atle Nesje, University of Bergen, Department of Earth Science (Norway)
Svein Olaf Dahl, University of Bergen, Department of Geography (Norway)
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During recent years extreme weather events and related geohazards are given increased attention, especially related to future scenarios. Accurate predictions and models of future extreme events have, however, proven difficult to accomplish mainly because of their rarity, brevity and often very local nature. Prehistoric records may shed light on the structure of such episodic events, and increase the understanding of which geohazards that dominate different prevailing climate regimes, and how their frequency have changed under changing climatic conditions.
The proglacial lake Russvatnet is situated at 1175 m a.s.l. in the eastern part of Jotunheimen national park, central southern Norway. The prevailing west-southwesterly wind direction leads to a strong west-east precipitation gradient across southern Norway. The Russvatnet catchment is located in the precipitation shadow of western-central Jotunheimen and it is characterized by a semi-continental climate regime. Three glaciers deliver melt water to the lake, and thick till and talus deposits on the steep slopes around the lake form source areas for slope processes. Approximately 55% of the lake catchment is located above the regional lower permafrost limit that lies at ca 1500 m a.s.l. The local tree line in the area lies at ca 1000 m a.s.l. and vegetation is consequently sparse.
In this study we present a transect of sediment cores from the lake Russvatnet, recording a complex combination of direct glacier-derived material from the three glaciers in the catchment, and material from a variety of different episodic mass movements developed on the slopes around the lake. Well-established facies models from marine studies are adopted and combined with calculated sediment parameters such as mean grain-size and sorting values to develop facies models of river floods and mass movement sequences suitable for a lacustrine environment. The complex multi-process record of Russvatnet is broken down, and records of river floods, mass movements, and glacier fluctuations are differentiated. Each of these complimentary process-records creates the basis for palaeo-environmental reconstructions, and thus the possibility to make a direct comparative study between different processes in the Russvatnet catchment during the Holocene. Results are compared to a similar study in the maritime western Norway, showing regional differences in the timing of extreme weather events in southern Norway.
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