Huge landslides, mobilizing hundreds to thousands of km3 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.

Submarine landslides: processes, triggers and hazard prediction

https://earthweb.ess.washington.edu/tsunami2/deposits/downloads/recommendedreading/Morton_SedGeoAcpt_tsunamiVstorm_Deposits.pdf

Physical criteria for distinguishing sandy tsunami and storm deposits using modern examples

Part 1 Tsunami as a known hazard.- 1. Introduction.- 2. Tsunami dynamics.- Part 2 Tsunami-Formed Landscapes.- 3. Signatures of tsunami in the coastal landscape.- 4. Coastal Landscape Evolution.- Part 3 Causes of Tsunami.- 5. Earthquake-Generated Tsunami.- 6. Great Tsunamigenic Earthquakes.- 7. Great Landslides.- 8. Volcanic Eruptions.- 9. Comets and Asteroids.- Part 4 Modern Risk of Tsunami.- 10. Risk and Avoidance.- 11. Epilogue.- References.- Index.

Tsunami: The Underrated Hazard

Submarine mass movements represent major offshore geohazards due to their destructive and tsunami-generation potential. This potential poses a threat to human life as well as to coastal, near shore and offshore engineering structures. Recent examples of catastrophic submarine landslide events that affected human populations (including tsunamis) are numerous; e.g., Nice airport in 1979 (Dan et al. 2007), Finneidfjord in 1996 (e.g., L’Heureux et al., this volume, Steiner et al., this volume), Papua-New Guinea in 1998 (Tappin et al. 2001), Stromboli in 2002 (Chiocci et al. 2008), and the 2006 and 2009 failures in the submarine cable network around Taiwan (Hsu et al. 2008). The Great East Japan Earthquake of March 2011 also generated submarine landslides that may have amplified effects of the devastating tsunami as shown in Fryer et al. (2004). Given that 30% of the World’s population lives within 60 km of the coast, the hazard posed by submarine landslides is expected to grow as global sea level rises. In addition, the deposits resulting from such processes provide-various types of constraints to offshore development (Shipp et al. 2004), and have significant implications for non-renewable energy resource exploration and production (Weimer and Shipp 2004; Beaubouef and Abreu 2010).

http://www.gbv.de/dms/goettingen/600607267.pdf

Submarine Mass Movements and Their Consequences

The origin of the Papua New Guinea tsunami that killed over 2100 people on 17 July 1998 has remained controversial, as dislocation sources based on the parent earthquake fail to model its extreme run–up amplitude. The generation of tsunamis by submarine mass failure had been considered a rare phenomenon which had aroused virtually no attention in terms of tsunami hazard mitigation. We report on recently acquired high–resolution seismic reflection data which yield new images of a large underwater slump, coincident with photographic and bathymetric evidence of the same feature, suspected of having generated the tsunami. T–phase records from an unblocked hydrophone at Wake Island provide new evidence for the timing of the slump. By merging geological data with hydrodynamic modelling, we reproduce the observed tsunami amplitude and timing in a manner consistent with eyewitness accounts. Submarine mass failure is predicted based on fundamental geological and geotechnical information.

The slump origin of the 1998 Papua New Guinea Tsunami

The Sissano, Papua New Guinea tsunami of July 1998 — offshore evidence on the source mechanism

After considerable controversy over the origin of the July 1998 PNG tsunami, there is now a large body of evidence that supports a sediment slump offshore of the devastated area. Between 1999 and 2000, four surveys were carried out offshore of the affected area, acquiring bathymetry, sediment cores, 3.5kHz seismic, multi-channel seismic and seabed imagery. In 2001, the same area was surveyed using single channel seismic that has been used to interpret the northern margin of PNG and the internal architecture of the slump. The susceptibility to slumping of the area offshore of northern PNG can be more definitively assessed.

T. Matsumoto

Papers

The Sissano, Papua New Guinea tsunami of July 1998 — offshore evidence on the source mechanism

Architecture and Failure Mechanism of the Offshore Slump Responsible For the 1998 Papua New Guinea Tsunami