Separation of late-Holocene episodic paraglacial events and glacier fluctuations in eastern Jotunheimen, central southern Norway

Abstract

The lacustrine sediments of proglacial lake Russvatnet in eastern Jotunheimen, central southern Norway, comprise a combination of glacier-derived material from the glacier Blackwellbreen and several episodic paraglacial processes in the catchment. This study focuses on the characteristics of lake sediments, and the decomposition of a 4000-yr complex multiprocess record from Russvatnet, in order to separate late-Holocene river floods, mass movements and glacier fluctuations. Facies models based on grain-size distribution, minerogenic content and amount of terrestrial macrofossils are used to recognize discrete mass movement and river flood deposits. Twenty-two episodic events are identified during the late Holocene, classified as 11 mass movement events (debris flows, high density turbidity currents and low density turbidity currents) and 11 river flood events. Enhanced river flood and colluvial activity is inferred at 4000—3400, 2900—2500, 2000—1400 and 1000—500 cal. yr BP. Glaciolacustrine core segments were analysed based on magnetic susceptibility, bulk density and loss-on-ignition to reconstruct variations in late-Holocene glacier magnitude. At c. 2300 cal. yr BP a shift in sedimentation regime from a paraglacial to a glacially dominated regime is recorded, and a Neoglacial expansion period after 2300 cal. yr BP is suggested. A contrasting pattern of climate deterioration and rapid episodic events are recorded in lake Russvatnet. Large regional variations in the timing of episodic events emphasize the importance of local triggering factors compared with more large-scale effects of climate change.