Characterisation of weak layers, physical controls on their global distribution and their role in submarine landslide formation

Gatter, R.; Clare, M.A. ORCID: https://orcid.org/0000-0003-1448-3878; Kuhlmann, J.; Huhn, K.. 2021 Characterisation of weak layers, physical controls on their global distribution and their role in submarine landslide formation. Earth-Science Reviews, 223, 103845. 10.1016/j.earscirev.2021.103845

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Abstract/Summary

Submarine landslides pose a hazard to coastal communities as they can generate powerful tsunamis, and threaten critical offshore infrastructure such as seafloor cable networks that underpin global communications. Such events can be orders of magnitude larger than their onshore equivalents. Despite the hazard they pose, many aspects of submarine landslides remain poorly understood, such as why they fail on low angle (<2°), seemingly stable slopes. Many studies have proposed that failure on low slope angles, and the large areal extent of submarine landslides, may be controlled by the presence of laterally-extensive weak layers embedded within the slope stratigraphy, which precondition slopes to failure. Little remains known, however, about the characteristics and processes that control and form weak layers. We conducted a comprehensive review of published submarine landslide studies that examine failure planes and apparent weak layers associated with historical and ancient submarine landslides. Based on a new global landslide catalogue that comprises 64 case studies, this review aims to investigate the types of sediment that form weak layers and to understand the controls on their global variability. Existing classification schemes are based on mechanical process(es), and do not readily enable a diagnosis of weak layers from unfailed sediments. Here, a new and complementary classification of weak layers based on lithology is introduced. This classification enables weak layer recognition from sediment cores (including those sampling unfailed sediments), and allows us to attribute failure mechanisms to different environmental settings where distinct types of weak layers are more likely. The results show that failure planes usually form in the vicinity of an interface between distinct lithologies that together comprise a weak layer. The weak layers of 22 of the 64 case studies were related to characteristic sediment sequences within the slope stratigraphy, of which 19 were classified based on direct measurements from sediment cores and in-situ measurements: 16 weak layers were classified as siliciclastic, four as volcaniclastic, and two as fossiliferous sediment sequences. Only three submarine landsides were related to clay-dominated weak layers. In addition, failure along lithological contrasts was inferred for six case studies. Based on global depositional models likely locations of these different types of weak layer can be inferred. These include oceanic gateways where long-term circulation can create distinct permeability interfaces within siliciclastic sequences, areas of high productivity where biogenic sediments may dominate, and regions that experience widespread ash fall from volcanic eruptions. We highlight that many submarine landslide studies have historically not collected sediment cores that characterise weak layers within intact sedimentary sequences and instead have focused on characterising the slope failure deposit. As weak layers can collapse or become heavily modified during failure, there is a widespread omission of key information required for geotechnical analysis to determine where and why certain slopes are predisposed to failure. We conclude by highlighting the need to combine detailed geotechnical measurements with sedimentological and geophysical analyses including grain-scale observations (e.g. micro-Computed Tomography 3D imagery), and emphasise the importance of a uniform workflow that will allow for a better comparison between individual studies.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.earscirev.2021.103845
ISSN:	00128252
Date made live:	05 Jan 2022 17:41 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/531375

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