Undersea landslides: extent and significance in the Pacific Ocean, an update

Nat. Hazards Earth Syst. Sci.

Watts²,

Grilli

2008

242

150

Abstract. The Papua New Guinea (PNG) tsunami of July 1998 was a seminal event because it demonstrated that relatively small and relatively deepwater Submarine Mass Failures (SMFs) can cause devastating local tsunamis that strike without warning. There is a comprehensive data set that proves this event was caused by a submarine slump. Yet, the source of the tsunami has remained controversial. This controversy is attributed to several causes. Before the PNG event, it was questionable as to whether SMFs could cause devastating tsunamis. As a result, only limited modelling of SMFs as tsunami sources had been undertaken, and these excluded slumps. The results of these models were that SMFs in general were not considered to be a potential source of catastrophic tsunamis. To effectively model a SMF requires fairly detailed geological data, and these too had been lacking. In addition, qualitative data, such as evidence from survivors, tended to be disregarded in assessing alternative tsunami sources. The use of marine geological data to identify areas of recent submarine failure was not widely applied.The disastrous loss of life caused by the PNG tsunami resulted in a major investigation into the area offshore of the devastated coastline, with five marine expeditions taking place. This was the first time that a focussed, large-scale, international programme of marine surveying had taken place so soon after a major tsunami. It was also the first time that such a comprehensive data set became the basis for tsunami simulations. The use of marine mapping subsequently led to a larger involvement of marine geologists in the study of tsunamis, expanding the knowledge base of those studying the threat from SMF hazards. This paper provides an overview of the PNG tsunami and its impact on tsunami science. It presents revised interpretations of the slump arCorrespondence to: D. R. Tappin (drta@bgs.ac.uk) chitecture based on new seabed relief images and, using these, the most comprehensive tsunami simulation of the PNG event to date. Simulation results explain the measured runups to a high degree. The PNG tsunami has made a major impact on tsunami science. It is one of the most studied SMF tsunamis, yet it remains the only one known of its type: a slump.

Section: R Tappin Et Al: the Png Tsunami Of 1998 -A Catastrophicmentioning

confidence: 99%

The Papua New Guinea tsunami of 17 July 1998: anatomy of a catastrophic event

Nat. Hazards Earth Syst. Sci.

Watts²,

Grilli

2008

242

150

“…Prior et al 1986a). For example, at Kitimat Fjord in British Columbia in 1975, a landslide was triggered by a low tide, creating a tsunami up to 8.2 m in height (Prior et al 1982a;Lee 1989). Although there was significant damage, no lives were lost.…”

Section: (B) Fjordsmentioning

confidence: 99%

“…These environments include the open continental shelf, submarine canyon/fan systems, fjords, active river deltas and volcanic islands. In addition, Lee (2005) identified convergent margins as an environment where submarine landslides also take place. Recent research in the South Pacific on reef-front environments suggests that these too may prove to be a location where SMFs can cause hazardous tsunamis, as in the Suva, Fiji, event of 1953 (Rahiman et al 2007).…”

Section: Landslide Territoriesmentioning

confidence: 99%

“…Weak delta sediments can also fail through earthquake loading, as happened during the great Alaska earthquake of 1964. The resulting tsunamis were enormously destructive, with loss of lives and damage to infrastructure (Plafker et al 1969;Lee 1989;Hampton et al 1993). At Seward a 1 km section of the waterfront collapsed as a result of submarine failure, creating a 10 m high tsunami (Lemke 1967).…”

Section: (B) Fjordsmentioning

confidence: 99%

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Submarine mass failures as tsunami sources: their climate control

Phil. Trans. R. Soc. A.

2010

Recent research on submarine mass failures (SMFs) shows that they are a source of hazardous tsunamis, with the tsunami magnitude mainly dependent on water depth of failure, SMF volume and failure mechanism, cohesive slump or fragmental landslide. A major control on the mechanism of SMFs is the sediment type, together with its post-depositional alteration. The type of sediment, fine- or coarse-grained, its rate of deposition together with post-depositional processes may all be influenced by climate. Post-depositional processes, termed sediment ‘preconditioning’, are known to promote instability and failure. Climate may also control the triggering of SMFs, for example through earthquake loading or cyclic loading from storm waves or tides. Instantaneous triggering by other mechanisms such as fluid overpressuring and hydrate instability is controversial, but is here considered unlikely. However, these mechanisms are known to promote sediment instability. SMFs occur in numerous environments, including the open continental shelf, submarine canyon/fan systems, fjords, active river deltas and convergent margins. In all these environments there is a latitudinal variation in the scale of SMFs. The database is limited, but the greatest climate influence appears to be in high latitudes where glacial/interglacial cyclicity has considerable control on sedimentation, preconditioning and triggering. Consideration of the different types of SMFs in the context of their climate controls provides additional insight into their potential hazard in sourcing tsunamis. For example, in the Atlantic, where SMFs are common, the tsunami hazard under the present-day climate may not be as great as their common occurrence suggests.

“…The environments recognized include the open continental shelf, submarine canyon/fan systems, fjords, active river deltas and volcanic islands. In addition, Lee (2005) identified convergent margins as an important environment where submarine landslides also take place. Consideration of these landslide environments indicates several dominant controls on slope stability, that have been elucidated by Lee (in press) as: i) sediment delivery to the continental margins; its rate, volume and type, ii) sediment thickness, iii) changes in seafloor conditions, which can influence hydrate stability and the possible generation of free gas, iv) variations in seismicity and, v) changes in groundwater flow.…”

Section: Mass Transport Eventsmentioning

confidence: 99%

Mass Transport Events and Their Tsunami Hazard

Submarine Mass Movements and Their Consequences

2010

Mass transport events, such as those from submarine landslides, volcanic flank collapse at convergent margins and on oceanic islands, and subaerial failure are reviewed and found to be all potential tsunami sources. The intensity and frequency of the tsunamis resulting is dependent upon the source. Most historical records are of devastating tsunamis from volcanic collapse at convergent margins. Although the database is limited, tsunamis sourced from submarine landslides and from collapse on oceanic volcanoes have a climate influence and may not be as hazardous as their frequency suggests. Conversely, tsunamis sourced from submarine landslides at convergent margins may be more frequent historically than previously recognized and more hazardous.