Failure processes in submarine landslides: a geomorphological approach

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

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2007

Author dc:creator

• Micallef, Aaron