What causes large submarine landslides on low gradient (&lt;2°) continental slopes with slow (∼0.15 m/kyr) sediment accumulation?

Morelia Urlaub,Peter J Talling,Antonis Zervos,Douglas Masson

doi:10.1002/2015jb012347

Abstract

AbstractSubmarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine megaslides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (<0.15 m/kyr), such as off northwest Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties, and stratigraphic layer configurations. The simulations show that, in general, it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes.

Highlights

Submarine landslides include the largest mass flows on Earth and can be up to 2 orders of magnitude larger than landslides on land [Hampton et al, 1996; Korup et al, 2007]
Aims and Objectives This study focuses on open continental slopes at passive margins with headwall heights in excess of 100 m, because they host many of the largest submarine landslides
We investigate the dependence of stability on three main factors that can control the development of overpressure: spatial as well as temporal sedimentation patterns, hydromechanical properties of deep sea sediments, and the pore fluid flow pattern caused by permeability contrasts

Summary

Introduction

Submarine landslides include the largest mass flows on Earth and can be up to 2 orders of magnitude larger than landslides on land [Hampton et al, 1996; Korup et al, 2007]. Submarine landslides are one of the major processes for moving large amounts of sediment from the continental shelf and slope into the deep ocean and play an important role in the Earth’s sedimentary budget [Masson et al, 2006; Korup et al, 2007]. The Storegga Slide that occurred 8200 years ago triggered a tsunami that affected the whole Nordic and North Sea region [Bondevik et al, 2005]. The landslides themselves can damage seafloor infrastructure, such as that used for hydrocarbon exploration. They may generate longer runout sediment flows called turbidity currents that break offshore telecommunication cables, as occurred offshore from the Grand Banks, Canada, in 1929 [Piper and Aksu, 1987]

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