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

Sammartini, M.; Moernaut, J.; Kopf, A.; Stegmann, S.; Fabbri, S. C.; Anselmetti, F. S.; Strasser, M. (2021). Propagation of frontally confined subaqueous landslides: Insights from combining geophysical, sedimentological, and geotechnical analysis. Sedimentary geology, 416, p. 105877. Elsevier 10.1016/j.sedgeo.2021.105877

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Subaquatic mass movements are common in marine and lacustrine environments, but due to their barely pre- dictable nature, direct observations of these processes are limited so that knowledge is only indirectly obtained by investigating the resulting mass-transport deposits (MTDs). Most research focuses on the most common fron- tally emergent slides, fast-moving events able to generate turbidity currents and tsunamis. Geohazards of fron- tally confined slides and mechanisms behind their typical fold-and-thrust deformation structures are however still poorly understood.
We investigate frontally confined MTDs in Lake Lucerne (Switzerland) by integrating bathymetric and high-res- olution 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 sed- iments 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 sedi- ments by the bulldozing sliding mass. Relative kinematic indicators document that the fold-and-thrust deforma- tion 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 sta- bility and propagation of basin-plain deformations, respectively. Our integrated study supports and refines prop- agation models proposed in marine environments, revealing the potential of investigating smaller-scale easier- to-access MTDs in lakes.

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