Volcanic arc island flank collapse emplacement : The complex interplay of depositional processes and longterm deposit stability

Volcanic island flank collapses are the most voluminous mass movements on Earth and can trigger devastating tsunamis. With nine major events and more than 15000 casualties over the last 400 years, they pose a serious geohazard on a non-geological time scale. Hazard assessments for volcanic flank collapses require a detailed understanding of pre-condition, failure and emplacement mechanisms. However, the different processes during emplacement, the controls on the dynamics of the associated landslides, and the potential consequences of emplacement for the stability of the slope sediments are poorly constrained. Studies on ancient volcanic flank collapse deposits using high-resolution seismic data combined with drilling operations provide insight into these processes and their complex interplay. This cumulative doctoral thesis shows that the emplacement of volcanic flank collapse is an interplay of different processes over multiple phases, including initial failure of the volcanic flank and versatile interaction of the failure mass with seafloor sediments. This work also shows that the slope topography and the nature of the substrate sediment are major controls on slide dynamics and morphology, and that once a slope failure occurred on a slope, the propensity for subsequent failure is enhanced.

Failure of a volcanic flank and the emplacement of the associated landslides are complex interplays of different geological and physical processes. This thesis - using the exceptional opportunity to combine high-resolution 2D and 3D seismic with drilling data from volcanic flank collapse deposits - provides new insights into this complexity.