Submarine landslides: processes, triggers and hazard prediction

Abstract

Huge landslides, mobilizing hundreds to thousands of km(3) of sediment and rock are ubiquitous in submarine settings ranging from the steepest volcanic island slopes to the gentlest muddy slopes of submarine deltas. Here, we summarize current knowledge of such landslides and the problems of assessing their hazard potential. The major hazards related to submarine landslides include destruction of seabed infrastructure, collapse of coastal areas into the sea and landslide-generated tsunamis. Most submarine slopes are inherently stable. Elevated pore pressures (leading to decreased frictional resistance to sliding) and specific weak layers within stratified sequences appear to be the key factors influencing landslide occurrence. Elevated pore pressures can result from normal depositional processes or from transient processes such as earthquake shaking; historical evidence suggests that the majority of large submarine landslides are triggered by earthquakes. Because of their tsunamigenic potential, ocean-island flank collapses and rockslides in fjords have been identified as the most dangerous of all landslide related hazards. Published models of ocean-island landslides mainly examine 'worst-case scenarios' that have a low probability of occurrence. Areas prone to submarine landsliding are relatively easy to identify, but we are still some way from being able to forecast individual events with precision. Monitoring of critical areas where landslides might be imminent and modelling landslide consequences so that appropriate mitigation strategies can be developed would appear to be areas where advances on current practice are possible.

Late Cenozoic shelf delta development and Mass Transport Deposits in the Dutch offshore area – results of 3D seismic interpretation

“…A plausible mechanism is that the concentrated increase in sediment supply across headwall scars following events of slope failure (see above) uphold the low A'/S' conditions and favour a continuation of the instable slope conditions (c.f. Masson et al, 2005). Subsequently, a new MTD develops after which the sediment delivery through incised valleys is localised again.…”

“…Seismic events are considered the most common trigger for slope failures (Hampton et al, 1996;Locat & Lee, 2002;Canals et al, 2004 and references therein; Masson et al, 2005;Owen et al, 2007;Lee, 2009). Since important faults in the study area are supposed to have been inactive from Early Cretaceous onwards (Ziegler, 1990), large-scale tectonics has not been considered an important triggering factor for the studied slope failure events.…”

“…when clinoforms were not formed). Clay content may therefore play a role in determining the position of the basal shear surface; high pore water pressures are more likely to develop in layers with lower permeability (Popenoe et al, 1993;Hampton et al, 1996;Locat & Lee, 2002;Canals et al, 2004;Masson et al, 2005;Owen et al, 2007;Lee, 2009;Fig. 13).…”

“…It is suggested that a specific slope-failure trigger is required in order to overcome the shear strength of the sediment (Popenoe et al, 1993;Mc Gregor et al, 1993;Hampton et al, 1996;Locat & Lee, 2002;Canals et al, 2004;Owen et al, 2007;Masson et al, 2005;Lee, 2009). Seismic events are considered the most common trigger for slope failures (Hampton et al, 1996;Locat & Lee, 2002;Canals et al, 2004 and references therein; Masson et al, 2005;Owen et al, 2007;Lee, 2009).…”

“…They are very common in tectonic active areas, but also occur in numerous tectonically quiet settings. Fjords, active river deltas on the continental margin, submarine canyon-fan systems, open continental slopes and oceanic island flanks and -ridges are the areas where slope failures mostly occur (Hampton et al, 1996), especially where the slope consists of fine-grained sediment (Masson et al, 2005). In the absence of seismic triggers, such as on passive margins, climate can play an important role in the timing of slope failure.…”