Continuous and episodic sedimentation in western Norwegian fjord lakes. A Holocene climatic perspective

• Published in: The Holocene
• Main Author: Vasskog, Kristian
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2011
• Subjects: VDP::Mathematics and natural science: 400::Geosciences: 450::Quaternary geology; glaciology: 465; Norway; glacier
• Online Access: https://hdl.handle.net/1956/5291

A Holocene chronology of hazardous events has been constructed in parallel with a new record of glacier variability from inner Nordfjord in western Norway, based on the analysis of seismic profiles and sediment cores from the lakes Oldevatnet (8 km2), Nerfloen (1 km2) and Oppstrynsvatnet (30 km2). In paper I the frequency of episodic sedimentation events over the last 7300 years was investigated in a sediment core retrieved from Oldevatnet in inner Nordfjord, western Norway. Our data suggest that the event record is dominated by snow-avalanches, whereas inferred floods and density currents are too infrequent to be of any palaeoclimatic significance. Altogether forty-seven snow-avalanche events are recorded over the investigated interval. Periods of enhanced snow-avalanche activity are recorded at 5500– 5400, 5000–4900, 1200–1100 cal. yr BP and during the ‘Little Ice Age’ (LIA) glacier maximum (c. 400–100 cal. yr BP). Periods without any large snow-avalanches entering the lake are seen between 7100-5700, 4200-3700, 3200-2800, and 1400-1300 cal. yr BP. A compilation of snow-avalanche records from western Norway reflect an increasing trend through the Holocene, similar to what is seen in records of other types of extreme events such as floods. It seems likely that regional changes in winter precipitation are crucial for the fluctuations observed in snow-avalanche activity, although local effects may give rise to site-specific responses. Around Oldevatnet, the glacier expansion during the LIA probably served to increase the local snow-avalanche activity as the glacier fronts expanded into the steep slopes surrounding the lake. In paper II a Principal Component Analysis (PCA) was applied to a suite of different sedimentary parameters with the purpose of reconstructing past glacier activity in the 440 km2 upstream catchment of lake Nerfloen in Stryn, western Norway. The PCA reveals a strong signal contained in the sediment record, and is able to express 76% of the total variability of the fifteen investigated ...