Project title: Characteristics of slow-moving submarine landslides
Researcher: Benjamin Couvin
Landslides are generally thought of as catastrophic events occurring on land. However, many observations in the past have shown that landslides could also occur underwater, generally at the continental slopes. They can displace a large amount of material (much more than continental ones) and can therefore trigger tsunamis and damage human installations on the seafloor or on coastal land. The Tuaheni Landslide Complex (TLC), on the Hikurangi Margin, offshore New Zealand, presents large landslide deposits that appear to have a creeping behaviour. The deformation observed in the debris is also unlike what we would expect of such submarine mass movements. As a result, we seek to investigate the factors at the origin of deformation within the TLC. More insights in the mechanisms involved in slow-moving landslides such as this one could be compared to other slow-moving mass movements, on the seafloor as well as on land, the end objective being to characterise their mechanics at a global scale.
We present here several hypotheses that we wish to test. We hypothesise that :
1) Of the two distinct sedimentary units that compose the slide deposit, the lower debris unit is more extensive than previously thought. If this is the case, the stratigraphy of the Hikurangi margin, as well as the TLC morphology, may need to be characterised anew.
2) The presence of gas hydrates and free gas under the slide plays a role in driving the deformation, either by modifying the rheology of the sediment or by fracturation.
3) Some force other than gas drives in part or entirely the deformation, in which case we intend to find what it is.
The central research question that this project addresses is “What are the lithological and rheological properties of slow-moving submarine landslides?” This question is important in understanding these relatively under-studied processes. Submarine landslides are commonly considered to happen catastrophically implying that if not all, most submarine landslides move rapidly, which has implications for tsunami generation and seafloor installation hazard. Yet there is evidence that some events exhibit creeping behaviour and might even be active presently, such as the TLC (Mountjoy et al., 2014). The aims of this project will be: a) to examine the deformation style of slow-moving submarine landslides, and b) to identify whether multiple stacked events are responsible for the creeping behaviour observed on seismic data.