Laboratory Investigation of Lake Tsunamis Generated by Granular Submarine Slides

Lake tsunamis are triggered in mountain lakes or reservoirs by various mass-movement mechanisms, such as landslides, rockfalls, snow and ice avalanches or glacier calvings. With the usually short propagation distances, the wave attenuation is small, resulting in a high damage potential at the surrounding shoreline. For a number of large natural lakes in Switzerland, evidences of large historical tsunamis have been documented, with many of them also causing casualties (e.g. 1584 in Lake Geneva, 1601 and 1687 in Lake Lucerne, 1806 in Lake Lauerz). In contrast to subaerial slides, only few experimental investigations on submarine slides are reported in literature. Field observations are difficult since the slide events and their locations often remain unnoticed. Whereas subaerial mass movements are triggered only on rather steep slopes, underwater slope failures may occur for relatively small angles (α ≤ 20°), since buoyancy and pore water pressure reduce the slope stability. Even weak earthquakes can then trigger slope failures.

Physical model tests were conducted in the 11.0 m long, 0.5 m wide and 1.0 m deep impulse wave channel at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zurich. The granular slide was triggered by a retracting metal sheet and recorded through the glass side wall using a high-speed camera. The slide characteristics (e.g. the slide centroid location, slide length and slide velocity) and the wave characteristics (wave amplitudes and wave length) were determined from still images. The downstream water surface deformation was recorded pointwise using Ultrasonic Distance Sensors. The wave generation process was investigated for a wide parameter range including the slope angle, the initial slide submergence, the slide mass, the slide length, the grain diameter and the still water depth. Prediction equations for the resulting wave features were derived based on the parameter study. The obtained data will be used in the future to validate a numerical model. In addition to the free granular slides, granular slides packed into high-permeable mesh-bags and a solid body slide were investigated. The selected experimental results to be presented at the 38th IAHR World Congress in Panama City will cover the above descriptions with a focus on the different slide approximations: free granular slides, mesh-bag slides, and solid body slides.