Living landslides: do carbonate mass transport events pose greater socio-economic risks?

Submarine landslides are major geohazards that can trigger tsunamis, and pose a threat to critical seafloor infrastructure such as telecommunication cables and energy pipelines. To improve assessments of the socio-economic risks linked to submarine landslide-related geohazards requires an understanding of the pre-requisite conditions (e.g. substrate character, excess subsurface pore pressures), and the sedimentary processes occurring during transport (e.g. which may change flow rheology and speed). Advances are only achievable through integrated studies using seabed data from recent events, detailed observations of ancient analogues, and physical experiments and numerical simulations.

One factor rarely considered in the hazard assessment of submarine landslides is whether the source and substrate sediment is siliciclastic, carbonate, or mixed. Most studies have focused on siliciclastic landslides, despite carbonate oozes comprising a significant proportion (c. 30%) of the world’s ocean floor (Dutkiewicz et al., 2015). However, carbonate successions strongly contrast with siliciclastic successions in terms of grain character (e.g., cohesion), diagenetic rates and processes, and therefore strength.

Fragile foraminifera and nanofossils dominate Cenozoic carbonate ooze successions, and they become weakly cemented at their contacts during early burial. This cementation creates a higher initial strength than (uncemented) siliciclastic sediments at the same time as preserving unusually high near-surface porosities. Upon burial these fragile biogenic particles may be crushed, generating excess near-seabed pore pressures and a dramatic loss of strength (Urlaub et al., 2015). When carbonate oozes fail, their residual strength can be only 10% of their initial strength, whereas the residual strength of siliciclastic sediments can be up to 55% of their initial strength (Gaudin and White, 2009).

Left: Photographs of exhumed ancient carbonate submarine landslides. Right: An example of a submarine landslide imaged offshore Australia

In addition, submarine landslide emplacement dynamics, including run-out distances, will be influenced by the composition of the substrate. However, the recognition that sedimentary processes are strongly influenced by extracellular polymeric substances (EPS), and other cohesive fine-grained material, complicates understanding flow-substrate interactions, which could be particularly important for carbonate systems. Nonetheless, submarine landslides involving carbonate ooze-dominated substrate may be more erosive than siliciclastic counterparts (Winterwerp et al., 2012), and therefore possibly present a greater socio-economic risk.

Aims and objectives

This studentship aims to advance our understanding of carbonate submarine landslides as geohazards, and will integrate a range of analytical approaches via the following objectives:

  • To document recent submarine landslides on margins with carbonate ooze, and develop a morphometric assessment of their dimensions to compare them to submarine landslides formed in siliciclastic settings
  • To investigate the composition and sedimentology of exhumed carbonate submarine landslides in Italy and Greece (Fig. 1), which will improve our understanding of the flow transport processes and interactions with its substrate
  • To design and run physical experiments of mass movements using a range of materials, using the flume tank facilities in the Sorby Environmental Fluid Dynamics Laboratory (University of Leeds)

Potential for high impact outputs

The PhD studentship is novel in integrating a range of analytical approaches in the assessment of submarine landslides. It is expected that high-quality research papers will arise from this studentship that will have a significant impact within the field of geohazard research.

Training

This PhD will commence before the end of 2022 and run for 3.5 years. During this period, the student will be eligible for all the postgraduate training typically provided to students attending the University as part of the PANORAMA DTP. The PhD will provide an excellent training in state-of-the-art experimental and field techniques, a key skill set for both future academic and industrial based employment. Research skills and impact will be supported by a supervisory team with leading expertise in fieldwork, sedimentological modelling, and geotechnical assessments. The PhD will benefit from access and training to use state-of-the-art equipment and facilities at the University of Leeds, and the student will visit the National Oceanographic Centre for training in analysis of sediment cores and Autonomous Underwater Vehicle-acquired and Remotely Operated Vehicle-acquired high-resolution data from carbonate systems with submarine landslides.

Student Profile

A numerate student with a background in Geography, Earth Sciences or Civil Engineering related degree is sought. Experience and interest in fieldwork, laboratory fluid dynamics and / or field measurements is desired.

References

Dutkiewicz, A., Müller, R. D., O’Callaghan, S., and Jónasson, H., 2015, Census of seafloor sediments in the world’s ocean: Geology, v. 43, no. 9, p. 795-798.

Gaudin, C., and White, D., 2009, New centrifuge modelling techniques for investigating seabed pipeline behaviour, in Proceedings 17th International Conference on Soil Mechanics and Geotechnical Engineering, Alexandria, 2009, p. 448-451.

Nugraha, H.D., Jackson, C.A-L. , Johnson, H., Hodgson, D.M., Clare, M., 2019, How erosive are submarine landslides? Eartharxiv, doi: https://doi.org/10.31223/osf.io/cpx9e

Ogata, K., Pogačnik, Ž., Pini, G. A., Tunis, G., Festa, A., Camerlenghi, A., and Rebesco, M., 2014, The carbonate mass transport deposits of the Paleogene Friuli Basin (Italy/Slovenia): internal anatomy and inferred genetic processes: Marine geology, v. 356, p. 88-110.

Ten Brink, U.S., Geist, E.L. and Andrews, B.D., 2006. Size distribution of submarine landslides and its implication to tsunami hazard in Puerto Rico. Geophysical Research Letters, 33, L11307.

Urlaub, M., Talling, P.J., Zervos, A. and Masson, D., 2015. What causes large submarine landslides on low gradient (< 2°) continental slopes with slow (∼ 0.15 m/kyr) sediment accumulation? Journal of Geophysical Research: Solid Earth, 120, 6722-6739.

Winterwerp, J., Kesteren, W., Prooijen, B., and Jacobs, W., 2012, A conceptual framework for shear flow–induced erosion of soft cohesive sediment beds: Journal of Geophysical Research: Oceans, v. 117, no. C10.