Propagation of frontally confined subaqueous landslides: Insights from combining geophysical, sedimentological, and geotechnical analysis

Subaquatic mass movements are common in marine and lacustrine environments, but due to their barely predictable nature, direct observations of these processes are limited so that knowledge is only indirectly obtained by investigating the resultingmass-transport deposits (MTDs). Most research focuses on themost common frontally emergent slides, fast-moving events able to generate turbidity currents and tsunamis. Geohazards of frontally confined slides and mechanisms behind their typical fold-and-thrust deformation structures are however still poorly understood. We investigate frontally confinedMTDs in Lake Lucerne (Switzerland) by integrating bathymetric and high-resolution seismic data with geotechnical information derived from in situ Cone Penetrometer Tests and short core analysis. Investigated MTDs consist of three units: i) a mass-slide deposit, located at the base of the slope consisting of a coherent slope sequence, ii) a fold-and-thrust system developed in basin sediments, and iii) an overrunning mass flow deposit, consisting of remolded slope sediments. The deformed and thrusted basin sediments show higher undrained shear strength compared to the undisturbed basin sequence. We propose that this strengthening is caused by lateral compression leading to fluid expulsion in the high-plasticity basin sediments by the bulldozing slidingmass. Relative kinematic indicators document that the fold-and-thrust deformation structures occur rapidly. Thus, they should be considered in tsunami hazard analysis. Furthermore, our data highlight that the slope angle of the gliding surface and basin topography are key controlling factors for slope stability and propagation of basin-plain deformations, respectively. Our integrated study supports and refines propagation models proposed in marine environments, revealing the potential of investigating smaller-scale easierto-access MTDs in lakes. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

Subaquatic mass movements are common in marine and lacustrine environments, but direct observations are limited, leading to a focus on investigating resulting mass-transport deposits. This study in Lake Lucerne integrates various data types to explore frontally confined MTDs, finding that the deformed basin sediments have higher shear strength due to lateral compression. The rapid occurrence of fold-and-thrust deformation structures should be considered in tsunami hazard analysis.