10 000 years of snow avalanche activity in western Norway: a multiproxy lake sediment record from Lake Vatnasetvatnet, Hardanger

Abstract. Long-term reconstructions provide critical insights into the interplay between large-scale climatic systems and snow avalanche frequency over millennial timescales. This study presents a ∼ 10 000-year-long snow avalanche record reconstructed from a continuous sediment sequence in a lake in western Norway. A multi-proxy approach, combining bulk sediment analysis (LOI, DBD, and grain size) with high-resolution scanning techniques (MS, XRF, CT scanning), was used to characterise the sediments. The avalanche layers consist of a sand-rich base, dispersed organic fragments, and a fining-upward sequence of silt and clay. We applied two independent, semi-automatic detection methods to quantify event frequency and sediment influx over time: the rate of change (RoC) of Ti and interactive thresholding of CT greyscale data. Sedimentation in the early Holocene (> 10 100 cal yr BP) was dominated by glacial and periglacial processes linked to the study area's deglaciation. A period of low avalanche activity followed during the Holocene Thermal Maximum (> 6500 cal yr BP). The avalanche frequency increased during the mid-Holocene (6500–5000 cal yr BP) and intensified further in the late Holocene, with peak activity from 2300 cal yr BP to the present, a period characterised by large inter-centennial fluctuations and abrupt shifts in avalanche frequency. Comparison with regional palaeoclimatic and palaeo-environmental records suggests that the snow avalanche frequency is primarily controlled by large-scale atmospheric circulation patterns, particularly the intensity of the predominant westerly winds and humidity along the western coast of Norway. These fluctuations are closely linked to North Atlantic Sea surface temperature variability, shifts in the North Atlantic Oscillation, and broader synoptic climate dynamics.