Impact of sea level fluctuations on the sedimentation patterns of the SE African margin:Implications for slope instability

The sheared-passive margin offshore Durban (South Africa) is characterised by a narrow continental shelf and steep slope hosting numerous submarine canyons. Supply of sediment to the margin is predominantly terrigenous, dominated by discharge from several short but fast-flowing rivers. IODP Expedition 361 provides a unique opportunity to investigate the role of sea level fluctuations on the sedimentation patterns and slope instability along the South African margin. We analysed >300 sediment samples and downcore variations in P-wave, magnetic susceptibility, bioturbation intensity, and bulk density from site U1474, as well as regional seismic reflection profiles to: (i) document an increase in sand input since the mid-Pliocene; (ii) associate this change to a drop in sea level and extension of subaerial drainage systems towards the shelf-edge; (iii) demonstrate that slope instability has played a key role in the evolution of the South Africa margin facing the Natal Valley. Furthermore, we highlight how the widespread occurrence of failure events reflects the tectonic control on the morphology of the shelf and slope, as well as bottom current scour and instability of fan complexes. This information in important to improve hazard assessment in a populated coastal region with growing offshore hydrocarbon activities

Subaqueous mass movements in the context of observations of contemporary slope failure

The consequences of subaqueous landslides have been at the forefront of societal conscience more than ever in the last few years, with devastating and fatal events in the Indonesian Archipelago making global news. The new research presented in this volume demonstrates the breadth of ongoing investigation into subaqueous landslides, and shows that while events like the recent ones can be devastating, they are smaller in scale than those Earth has experienced in the past. Understanding the spectrum of subaqueous landslide processes, and therefore the potential societal impact, requires research across all spatial and temporal scales. This volume delivers a compilation of state-of-the-art papers covering regional landslide databases, advanced techniques for in situ measurements, numerical modelling of processes and hazard

Processes on the precipice : seafloor dynamics across the upper Malta-Sicily escarpment

The Malta-Sicily Escarpment (MSE) is a steep, sediment-undersupplied, carbonate escarpment incised by a series of submarine canyons. In this study we present data acquired from the upper MSE during the Eurofleets-funded CUMECS cruise to document a complex seafloor morphology comprising gullies, canyon heads, mass movement scars, channels, contourites and escarpments. The evolution of the upper MSE has been driven by the interaction of fault activity, sedimentary activity related to hemipelagic, pelagic and contouritic sedimentation, and seafloor incision by bottom current activity. Submarine mass movements play a key role in canyon development – they control the extent of lateral and headward extension, facilitate tributary development, remove material from the continental shelf and slope, and feed sediment into the canyons.peer-reviewe

A new depositional model for the Tuaheni Landslide Complex, Hikurangi Margin, New Zealand

The Tuaheni Landslide Complex (TLC) is characterised by areas of compression upslope and extension downslope. It has been thought to consist of a stack of two genetically linked landslide units identified on seismic data. We use 3D seismic reflection, bathymetry data, and IODP core U1517C (Expedition 372), to understand the internal structures, deformation mechanisms and depositional processes of the TLC deposits. Unit II and Unit III of U1517C correspond to the two chaotic units in 3D seismic data. In the core, Unit II shows deformation whereas Unit III appears more like an in situ sequence. Variance attribute analysis shows that Unit II is split in lobes around a coherent stratified central ridge and is bounded by scarps. By contrast, we find that Unit III is continuous beneath the central ridge and has an upslope geometry that we interpret as a channellevee system. Both units show evidence of lateral spreading due to the presence of the Tuaheni Canyon removing support from the toe. Our results suggest that Unit II and Unit III are not genetically linked, that they are separated substantially in time and they had different emplacement mechanisms, but fail under similar circumstances