It has been more than 400 years since a tsunami flooded the banks of Lake Lucerne and the city of Lucerne. The tidal wave was caused by a 5.9-magnitude earthquake, which triggered several underwater landslides as well as a rockslide on the Bürgenstock. These events subsequently caused a shock wave that spread across the entire lake. Based on historical records, it was estimated that the wave was four metres high: near Ennetbürgen, reports describe flooding “1,000 paces or three rifle shots” into the hinterland.
Today, the lowlands and shores around Ennetbürgen are fully civilized: the shore is dotted with buildings, a marina, a camp site and a water sports centre, while intensively used meadowland stretches far into the hinterland. The risk of tsunamis on Lake Lucerne and other Swiss lakes has not disappeared, however, and the one in 1601 was not a one-off event. They happen rarely, but the possibility cannot be fully ruled out.
Researching tsunami hazards
This is why researchers from ETH Zurich, the University of Bern and the Center for Marine Environmental Sciences in Bremen began a major research project to learn about the hazards posed by lake tsunamis, how often they have occurred in the past, what triggers them and what effects they have.
The project focuses on taking seismic measurements in Lake Lucerne. The researchers place special underwater seismometers in various locations to obtain seismic and geotechnical measurements on the lake floor.
The researchers are also studying landslides in river deltas. In 1687, for example, sections of the Muotha delta slid, causing a tidal wave on Lake Lucerne. By examining cores drilled on the shoreline and in the lake bed, researchers are searching for deposits caused by tsunamis. They are also using computer models to simulate how tidal waves might spread across the lake.
Extensive sediment testing
ETH professor Donat Fäh is in charge of the main part of the project. Fäh is Head of the Earthquake Hazard & Risk Assessment Section for the Swiss Seismological Service. He plans to closely examine the internal structure, volume and properties of lake sediments. The researchers also want to learn what processes unfold in the sediments and how stable they are. They hope to develop a geophysical and geotechnical 3D model to study the propagation of seismic waves or deformations caused by earthquakes, for example. Finally, they also want to develop computer simulations for earthquake scenarios.
