Refining gravity flow and snow avalanche signatures in lacustrine sediments—a novel facies model

ABSTRACT Lacustrine sediments can preserve high‐resolution records of mass movement events, offering insights into past natural hazards beyond the instrumental period. The unequivocal identification of lacustrine and terrestrial parent processes requires detailed lithofacies analysis of cores from multiple locations including shore‐proximal settings. This study refines existing lithofacies models for lacustrine deposits by distinguishing deposits both from gravity flows and snow avalanche processes. The application of refined models contributes to more robust reconstructions of the frequencies and magnitudes of past mass movement events, thereby improving hazard assessments. Ten short gravity cores from a cross‐lake transect at Lake Anestølsvatnet, Western Norway, are analysed based on records of grain size, magnetic properties, organic content and sediment structures supported by micro computed tomography for visualisation. The sediment cores are correlated based on a distinct pattern of silt laminae in the background sedimentation reflecting glacier meltwater pulses during periods of larger glacier extent in the catchment. Interspersed throughout the background sediment, three sets of proximal to distal sediment signatures derived from terrestrial gravity flows are discriminated into: (i) sedimentary unit GF 1 triggered by a terrestrial debris flow which translates into lake deposits resembling intrabasinal turbidites and (ii) sedimentary unit GF 2 triggered by longer‐lived flood events which produce sand‐rich hyperpycnites. Further, the following snow avalanche‐derived sedimentary signatures are distinguished: (i) sedimentary unit SA 1 attributed to snow avalanche debris melting out from lake ice and (ii) sedimentary unit SA 2 suggested to originate from snow avalanches breaking through lake ice. While not observed in this study, the presented novel facies model also considers the process of snow avalanches hitting an ice‐free lake, producing highly localised lacustrine deposition in shore‐proximal pools. By refining existing criteria, this study offers a novel approach to distinguish between different snow avalanche deposits, ultimately improving the reliability of palaeohazard reconstruction from lacustrine sediments.