Offshore Tsunami Deposits: Evidence from Sediment Cores and Numerical Wave Propagation of the 1601 CE Lake Lucerne Event

Abstract

The 1601 Common Era earthquake (Mw ca. 5.9) in "Unterwalden", Central Switzerland triggered multiple subaqueous mass movements and a subaerial rockfall that generated tsunami waves with devastating run-up heights of up to 4 m and several hundred meters of inundation along the coastal lowland plain of Lake Lucerne. In the shallow Lucerne Bay at the outlet of the perialpine lake, historical chronicles reported a seiche with an initial amplitude of ˜1-2 m and a period of 10 min that decreased with time but persisted for several days after the event. The impact and erosion potential of the tsunami wave on the Lucerne Bay is assessed with sediment core analysis and numerical simulation of wave propagation. A 60 cm thick offshore event deposit was recovered and radiocarbon dated along a sediment-core transect. The event deposit has a sharp basal contact with carbonate shell fragments and a normal graded succession of siliciclastic sand to silt with high amount of terrestrial-derived horizontally bedded wooden particles. The simulated tsunami waves have a water-surface displacement of up to 1.5 m and bed shear-stresses that are likely capable of remobilizing large amounts of sediment in the Lucerne Bay area. Our study thus successfully links the sedimentology of event deposits with physical principles of sediment mobilization derived from numerical wave modeling, providing a tool to improve the identification and interpretation of potential tsunami deposits.

Shallow‐Water Tsunami Deposits: Evidence From Sediment Cores and Numerical Wave Propagation of the 1601 CE Lake Lucerne Event

“…In Lake Sils, Nigg, Wohlwend, et al. (2021) observed thick, normally graded sand deposits that were likely formed by the backwash currents of a prehistoric lake tsunami.…”

“…Data of core scans (MSCL and XRF), LDA particle‐size measurements, virtual gauge used for the sensitivity analysis, interpolated lake bathymetry of the area used for numerical wave‐propagation simulation, and coordinates of sediment cores, lake‐bed samples, and virtual gauges used in this research are available from the data repository Pangaea (https://doi.org/10.1594/PANGAEA.938716) by Nigg, Bacigaluppi, et al. (2021). The BASEMENT software used in this research is described in detail in Vetsch et al.…”

“…Nigg, Wohlwend, et al. (2021) found sedimentary evidence of a prehistoric tsunami in the shallow‐water and coastal area of Lake Sils, Switzerland, that are comparable to marine tsunami deposits.…”