Altered volcanic deposits as basal failure surfaces of submarine landslides

Abstract

One of the main concerns regarding the development of submarine landslides is the role played by weak layers in the failure process and, in particular, their impact in terms of volume, shape and evolution of mass movements. In the present study we identified a weak layer in the eastern margin of the Corsica Trough (northern Tyrrhenian Sea) that formed the basal failure surface of the Pianosa Slump at 42-50 ka. This layer is characterized by high water content, high plasticity, high compressibility, and post-peak strain softening behavior (i.e., strength loss with increasing strain). These specific mechanical and sedimentological properties seem to be related to the presence of analcime zeolites with a concentration of 2-4% in the muddy sediment. Zeolites commonly form by the alteration of volcanic rocks and were deposited on the slope during a sea level low-stand. The influence of the zeolitic layer on slope instability was tested numerically using an elastic-perfectly plastic model that exhibits strain softening. Modeling results show that erosion at the foot of the slope could lead to enough strain to reduce the shear strength of the zeolitic layer and lead to slip in this layer. We conclude that the strain softening behavior of muddy zeolitic sediment plays an important role in predisposing submarine landslides on continental slopes.

How Clay Mineral Assemblages Affect Instability on the Upper Slope of the Hikurangi Subduction Zone, New Zealand

“…Rapid accumulation of low‐permeability, muddy sediments in environments such as Hikurangi often contributes to overpressured conditions (e.g., Micallef et al., 2015; Stoecklin et al., 2017), and fluid pressures can be exacerbated by trapping or seepage of free gas (e.g., Crutchley et al., 2022; Faure et al., 2006; Gross et al., 2018). Contourite drifts elsewhere are known to be susceptible to failure due to localized oversteepening of the seafloor, scouring by currents, and/or pronounced climate‐induced changes of lithology (e.g., Gatter et al., 2020; Laberg et al., 2016; Miramontes, Garziglia, et al., 2018; Miramontes, Sultan, et al., 2018; Prieto et al., 2016). The Hikurangi margin, in addition, has a propensity for moderate to large subduction‐induced earthquakes (Cubrinovski et al., 2022; Dowrick & Rhoades, 1998), so it is logical to expect dynamic loading coupled with transient increases of fluid pressure (e.g., Stegmann et al., 2007).…”

“…Weak layers elsewhere are known to occur in diverse lithologies (Gatter et al., 2021). In some examples, tephra beds act as weak layers; their suggested causes include fabric rearrangement and volume reduction during shearing (Harders et al., 2010), alteration of the volcanic glass to smectite (Miramontes, Garziglia, et al., 2018; Miramontes, Sultan, et al., 2018), or the tephra's role in focusing transient perturbations of pore‐fluid pressure (Kuhlmann et al., 2016; Wiemer & Kopf, 2015). Some weak layers evidently predate failure and function as the preferred glide planes, whereas others form during failure events due to realignment of grain fabric (Gatter et al., 2021; Locat et al., 2014).…”

The Subantarctic Front as a sedimentary conveyor belt for tsunamigenic submarine landslides

“…However, there are some significant differences, including the presence of ash as a weak layer promoting failure (Miramontes et al, 2018b), and downslope sediment supply from the adjacent landmasses.…”

Integrated geophysical, sedimentological and geotechnical investigation of submarine landslides in the Gulf of Lions (Western Mediterranean)

“…Therefore, only a few studies have reported information about failure-related weak layers and basal surfaces of submarine landslides (e.g. Kvalstad et al 2005;Dan et al 2007;L'Heureux et al 2012;Baeten et al 2014;Miramontes et al 2018;Urlaub et al 2018) Submarine landslides in the Gulf of Lions (GoL) are widespread from the upper slope to the deep basin, within the canyon flanks and in the interfluves of major canyons (Fig. 1).…”