Subaqueous morphology of Lake Lucerne (Central Switzerland): implications for mass movements and glacial history

Bathymetric data available for Swiss lakes have typically only low to moderate resolution and variable quality, making them insufficient for detailed underwater geomorphological studies. This article presents results of a new bathymetric survey in perialpine Lake Lucerne using modern hydrographic equipment. A digital terrain model (DTM) of the lake floor (raster dataset with 1 m cell size) covering the Chrüztrichter and Vitznau basins documents signatures of major Holocene mass movements and relics from the glacial history of the lake. Combining the bathymetry data with reflection seismic profiles and an existing event chronology allows investigating the morphology in its geological context. Subaqueous sediment slide scars with sharp headwalls cover large areas on moderately inclined slopes. The particularly large Weggis slide complex, correlated with an historical earthquake (ad 1601), features a ~9 km long and 4–7 m high headwall and covers an area of several square kilometers. Large debris cones of prehistoric rockfalls and the deposits of recent rockfall events imaged on the almost flat basin plain document mass-movement activity on steep slopes above the lake. Six transverse moraines, visible as subaqueous ridges, as lake-floor lineaments, or only imaged on reflection seismic profiles, indicate a complex glacial-inherited morphology. As many of the documented features result from potentially catastrophic events, high-resolution bathymetry can significantly improve natural hazard assessment for lakeshore communities by extending classical hazard maps to the subaqueous domain.