Failure processes in submarine landslides: a geomorphological approach

Abstract

This thesis presents a novel technique for the quantitative characterisation of bathymetric
data sets. The technique integrates three main geomorphometric methods: morphometric
attributes and their statistical analyses, feature-based quantitative representation, and
automated topographic classification. These methods allow useful morphological
information to be extracted from bathymetric data and can significantly enhance submarine
geomorphological investigations. The methods are applied to bathymetric data from the
Storegga Slide, one of the largest known submarine landslides, to investigate three aspects
of submarine mass movements: spreading, fractal statistics and morphology and slide
development.
The morphological signature of spreading, in the form of a repetitive pattern of ridges and
troughs, covers at least 25% of the Storegga Slide scar. Two modes of failure can be
identified for submarine spreading. The first involves retrogressive slide development via
the unloading of the headwall. The second entails the extension of a thin coherent slab of
semi-consolidated material downslope by gravity. Both modes of failure involve the break
up of surface sediment units into coherent blocks and their displacement along planar slip
surfaces. The block movement pattern entails an exponential increase of displacement, and
thinning of the failing sediment, with distance downslope. Loss of support and seismic
loading are the main potential triggering mechanisms of submarine spreading.
Analysis of headwall morphologies within the Storegga Slide reveals the occurrence of
spatial scale invariance. One explanation for this scale invariance is that the Storegga Slide
is a geomorphological system that may exhibit self-organised criticality. Spatial scale
invariance may also be linked to the retrogressive nature of the Storegga Slide. The shape
and fractal dimension of headwalls, on the other hand, can be used as a proxy for the type
and number of the formative mass movements.
A detailed reconstruction of the development of the north-eastern Storegga Slide shows
that after the initial evacuation of the surface sediment as turbidity currents, the area failed
as an extensive spread. The spreading blocks subsequently underwent higher displacement
and remoulding, and were partly removed by debris flows and turbidity currents. The
renewed instability within the spreading areas may have been related to gas hydrate
dissociation and pore pressure increases due in response to the changing overburden, and
the distribution of contourite drift deposits within underlying palaeoslide scars.

More information

Identifiers

Catalogue record

Export record