The timing and frequency of large-volume submarine landslides and turbidity currents along the north-eastern Atlantic Margin

Submarine landslides and turbidity currents are one of the most voluminous sediment transport mechanisms operating on our planet. Due to their potential size (>100 km3) and speed (>20 m/s) they pose considerable risk to coastal settlements and strategic marine infrastructure. This thesis aims to investigate the processes that precondition and trigger submarine landslides and turbidity currents within submarine canyons and on open continental slopes. Sediment cores, age models, and statistical analyses are used initially to test the effects of eustatic sea level on the recurrence rates of turbidity currents that fill and flush the Nazaré Canyon. Recurrence rates of turbidity currents that fill the canyon are strongly influenced by eustatic sea level, while more infrequent flows that flush the canyon are only associated with shifts in eustatic sea level periodicity and amplitude. The form of the frequency distribution of canyon filling and flushing turbidity currents also differ markedly, suggesting they have different triggers. This thesis also aims to understand the geohazard implications of large submarine landslides. The Trænadjupet Slide is a large (>400 km3) submarine landslide that occurred approximately 4,000 years ago on the Norwegian Margin. Unlike some other large submarine landslides, the Trænadjupet Slide did not trigger a widespread tsunami based on available coastal studies. The age of the Trænadjupet Slide is refined here to between ~2,600 and ~3,400 cal BP. The absence of a widespread tsunami associated with the Trænadjupet Slide may be explained by its emplacement dynamics (e.g. speed, acceleration, or time gaps between stages of failure). These findings have importance for landslide geohazards in the North Atlantic, as they suggest that other similarly-sized slides on the Norwegian Margin or elsewhere may not have produced very damaging tsunamis