Abstract
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 resulting mass-transport deposits (MTDs). Most research focuses on the most 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 confined MTDs 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 sliding mass. 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 easier-to-access MTDs in lakes.
Highlights
Subaqueous mass movements are common processes in marine as well as in lacustrine environments, capable of mobilizing and transporting large volumes of sediments from submerged slopes to deep basins (Masson et al, 2006; Urgeles and Camerlenghi, 2013; Sammartini et al, 2019; Mountjoy et al, 2020; Strasser et al, 2020)
Since general characteristics of submarine mass-transport deposits (MTDs), as well as their transport and initiation processes, are often comparable with MTDs in the lacustrine environment (Sammartini et al, 2019), this paper focuses on a multidisciplinary investigation of some outstanding examples of frontally confined slides in Lake Lucerne, which was already used as a case study by Schnellmann et al (2005) for the proposed data-based conceptual model
The upper 15 cm is composed of low density (~1.15 g cm−3), very high water content (>450%) organic-rich sediments, with a comparably higher sand (~10–15%) and a lower clay (~10%) content, and likely links to the human-induced eutrophication of the lake in the last century (Kelts, 1978). τu of this uppermost interval is below detection limit
Summary
Subaqueous mass movements are common processes in marine as well as in lacustrine environments, capable of mobilizing and transporting large volumes of sediments from submerged slopes to deep basins (Masson et al, 2006; Urgeles and Camerlenghi, 2013; Sammartini et al, 2019; Mountjoy et al, 2020; Strasser et al, 2020). Frey-Martínez et al (2006) proposed two end members in the frontal emplacement style of a deposit: i) frontally emergent MTDs, when the failing mass is able to ramp up from its stratigraphic confinement and travels downslope on the seafloor; and ii) frontally confined MTDs, in which the translating mass is buttressed against the undisturbed basin sequence (see Fig. 4 in Clare et al, 2018) In the latter type, forming the focus of this study, the toe domain is morphologically characterized by compressional ridges as superficial expression of fold-and-thrust systems, the main thrusts of which are propagating from the basal shear surface towards the top of the deposit (Frey-Martínez et al, 2006; Bull et al, 2009; Moernaut and De Batist, 2011)
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