15,000 Years of mass-movement history in Lake Lucerne: Implications for seismic and tsunami hazards

Abstract.: A chronological catalogue of Late Glacial and Holocene mass-movement deposits in Chrüztrichter and Vitznau Basins of Lake Lucerne (Vierwaldstättersee) reveals a complex history of natural hazards affecting the lake and its shores. Ninety-one mass-flow and six megaturbidite deposits have been identified and mapped out with a grid of more than 300 km high-resolution seismic profiles. An age model based on the analyses of 10 long piston cores, 2 tephra layers and 32 AMS-14C ages allowed building up a chronological event catalogue covering the last 15,000 years. Most of the identified mass-flow deposits relate to subaqueous sliding and subaerial rockfalling, as indicated by slide scars and rockfall cones on the lake floor. Deposits related to subaqueous sliding occur at the toe of slopes with inclinations >10° and reach their largest extents below slopes with inclinations between 10 and 20°. On subaqueous slopes >25° there is hardly any sediment accumulation. Rockfall cones and related mass-flow deposits in the northeastern and southern part of Vitznau basin evidence repeated rockfall activity, particularly along two zones on the northern face of Bürgenstock Mountain. Historic examples indicate that such rockfalls, as well as large subaqueous slides, can induce considerable tsunami waves in the lake. All of the 91 identified mass-flow deposits are associated with 19 seismic- stratigraphic event horizons. One of them comprises 13 mass-flow deposits and 2 megaturbidites and relates to the 1601 A.D. Mw ~ 6.2 earthquake. By analogy, five older multiple mass-movement horizons, each including six or more coeval deposits, are interpreted to result from strong prehistoric earthquake