Landslide-generated Tsunamis Research Articles

Growth and collapse of the Reunion Island volcanoes

This work presents the first exhaustive study of the entire surface of the Reunion Island volcanic system. The focus is on the submarine part, for which a compilation of all multibeam data collected during the last 20 years has been made. Different types of submarine features have been identified: a coastal shelf, debris avalanches and sedimentary deposits, erosion canyons, volcanic constructions near the coast, and seamounts offshore. Criteria have been defined to differentiate the types of surfaces and to establish their relative chronology where possible. Debris avalanche deposits are by far the most extensive and voluminous formations in the submarine domain. They have built four huge Submarine Bulges to the east, north, west, and south of the island. They form fans 20–30 km wide at the coastline and 100–150 km wide at their ends, 70–80 km offshore. They were built gradually by the superimposition and/or juxtaposition of products moved during landslide episodes, involving up to several hundred cubic kilometers of material. About 50 individual events deposits can be recognized at the surface. The landslides have recurrently dismantled Piton des Neiges, Les Alizes, and Piton de La Fournaise volcanoes since 2 Ma. About one third are interpreted as secondary landslides, affecting previously emplaced debris avalanche deposits. On land, landslide deposits are observed in the extensively eroded central area of Piton des Neiges and in its coastal areas. Analysis of the present-day topography and of geology allows us to identify presumed faults and scars of previous large landslides. The Submarine Bulges are dissected and bound by canyons up to 200 m deep and 40 km long, filled with coarse-grained sediments, and generally connected to streams onshore. A large zone of sedimentary accumulation exists to the north–east of the island. It covers a zone 20 km in width, extending up to 15 km offshore. Volcanic constructions are observed near the coast on both Piton des Neiges and Piton de la Fournaise volcanoes and are continuations of subaerial structures. Individual seamounts are present on the submarine flanks and the surrounding ocean floor. A few seem to be young volcanoes, but the majority are probably old, eroded seamounts. This study suggests a larger scale and frequency of mass-wasting events on Reunion Island compared to similar islands. The virtual absence of downward flexure of the lithosphere beneath the island probably contributes to this feature. The increased number of known flank–failure events has to be taken into consideration when assessing hazards from future landslides, in particular, the probability of landslide-generated tsunamis.

Researchers Replicate Landslide-Generated Tsunamis

Researchers Replicate Landslide-Generated Tsunamis

Meteotsunamis: atmospherically induced destructive ocean waves in the tsunami frequency band

Abstract. In light of the recent enhanced activity in the study of tsunami waves and their source mechanisms, we consider tsunami-like waves that are induced by atmospheric processes rather than by seismic sources. These waves are mainly associated with atmospheric gravity waves, pressure jumps, frontal passages, squalls and other types of atmospheric disturbances, which normally generate barotropic ocean waves in the open ocean and amplify them near the coast through specific resonance mechanisms (Proudman, Greenspan, shelf, harbour). The main purpose of the present study is to describe this hazardous phenomenon, to show similarities and differences between seismic and meteorological tsunamis and to provide an overview of meteorological tsunamis in the World Ocean. It is shown that tsunamis and meteotsunamis have the same periods, same spatial scales, similar physical properties and affect the coast in a comparably destructive way. Some specific features of meteotsunamis make them akin to landslide-generated tsunamis. The generation efficiency of both phenomena depend on the Froude number (Fr), with resonance taking place when Fr~1.0. Meteotsunamis are much less energetic than seismic tsunamis and that is why they are always local, while seismic tsunamis can have globally destructive effects. Destructive meteotsunamis are always the result of a combination of several resonant factors; the low probability of such a combination is the main reason why major meteotsunamis are infrequent and observed only at some specific locations in the ocean.

Submarine landslides: processes, triggers and hazard prediction

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.

Geology and tsunamigenic potential of submarine landslides in Santa Barbara Channel, Southern California

A large submarine landslide complex and four small landslides developed under the Santa Barbara Channel, suggesting a potential hazard from landslide-generated tsunamis. We integrate offshore stratigraphy and geologic structure, multibeam bathymetric information, and several kinds of seismic-reflection data to understand how and when the submarine landslides formed. Seismic-reflection data show that mass failure along the slope began at least 200 ka ago. Landslides appear as zones of poor reflectivity having an irregular upper surface, and these zones alternate vertically with strong parallel reflections. The emplacement ages of two of the three main landslide lobes are well established at 8 and 10 ka. The source material for the youngest part of the landslide complex was sediment of probable late Pleistocene and Holocene age that accumulated in a shelf-edge delta. Directly under this delta, growth of faults and anticlines was particularly intense and tended to oversteepen the deltaic deposits. These active structures also formed migration pathways and reservoirs for aqueous and hydrocarbon fluids from the deep basin. Tsunami deposits have been described from a low-lying area near Santa Barbara, and numerical modeling of tsunamis generated by hypothetical landslides in Santa Barbara Channel indicates a moderate to severe threat [Borrero, J.C., Dolan, J.F. and Synolakis, C.E., 2001. Tsunamis within the eastern Santa Barbara Channel. Geophys. Res. Lett., 28(4): 643–646.], involving wave runups of 2–20 m, for a range of assumed landslide volumes. Inundation from these waves, however, is expected to be highly focused so that only narrow (∼10-km) sections of the shoreline would be affected.

The Grand Banks landslide-generated tsunami of November 18, 1929: preliminary analysis and numerical modeling

On November 18, 1929, a M=7.2 earthquake occurred at the southern edge of the Grand Banks, 280 km south of Newfoundland. The earthquake triggered a large submarine slope failure (200 km 3), which was transformed into a turbidity current carrying mud and sand eastward up to 1000 km at estimated speeds of about 60–100 km/h, breaking 12 telegraph cables. The tsunami generated by this failure killed 28 people, making it the most catastrophic tsunami in Canadian history. Tsunami waves also were observed along other parts of the Atlantic coast of Canada and the United States. Waves crossing the Atlantic were recorded on the coasts of Portugal and the Azores Islands. Tsunami waves had amplitudes of 3–8 m and runup of up to 13 m along the coast of the Burin Peninsula (Newfoundland). To simulate the slide-generated tsunami from this event, our initial analysis uses a shallow-water model; the slide was assumed to be a viscous, incompressible fluid layer; water was inviscid and incompressible. The preliminary results of the numerical modeling are encouraging, with computed and observed tsunami arrival times in reasonable agreement.

Storms and tsunamis: evidence of event sedimentation in the Late Jurassic Tendaguru Beds of southeastern Tanzania

In Late Jurassic shallow marine siliciclastic sediments of the dinosaur-bearing Tendaguru Beds from the Mandawa Basin of southeastern Tanzania we identified several event deposits. Based on an analysis of their sedimentological and palaeontological features, a storm-induced origin can be assumed for the majority of these deposits. This interpretation is in agreement with the regional palaeogeography and palaeoclimatological data, and is further supported by the widespread evidence of Late Jurassic storm-controlled sedimentation in adjacent basins along the East African margin. A particularly striking feature is a laterally extensive, conglomeratic bed with gravel components up to 30 cm in diameter, and megaripples indicating southward transport directions. The troughs between ripples are filled by cross-bedded fine-grained sandstones and siltsones with inferred transport directions to the north. Giant bedforms, a mixture of clasts of marine and continental origin, and evidence of opposite current directions suggest that this chaotically deposited sediment may have formed from a tsunami. Within the available time resolution this event is synchronous with the Morokweng impact structure in South Africa. However, because of the considerable distance of Morokweng from the Jurassic sea, direct links between both events cannot be established. Alternative mechanisms such as a landslide-generated tsunami are plausible, but not yet supported by geophysical data.

Tsunami hazard from submarine landslides on the Oregon continental slope

The morphometric analysis of submarine landslides on the continental slope of Oregon provides insight into tsunami hazard, including the locations of mass movements, the sizes of mass failures, their relative importance to the structure of a given margin, and the potential for landslide-generated tsunami hazards. Numerous, often overlapping failures, including two super-scale slumps in the southern Oregon margin, may have had the capacity to produce very large tsunamis, and should be considered when assessing earthquake and tsunami hazard in the Cascadia Subduction Zone. We use various aspects of the slides, including the mean water depth, width, run-out distance, and thickness, along with the slope gradient in the scar and adjacent slopes (and radius of curvature of the failure plane for slumps) to predict maximum tsunami amplitudes directly above the failure. Cohesive landslides tend to have higher headscarps than the slides that lose cohesion, suggesting that they occur in stronger sediment, and have the potential to produce larger tsunamis. On other continental margins (California, Texas/Louisiana, and New Jersey/Maryland), landslides tend to occur on slopes less than 4°, however offshore Oregon, most of the landslides occur on slopes over 15°; the failures on the steeper slopes tend to produce larger tsunamis. There are surprisingly few large failures along the seismically active northern margin, implying that strong shaking maybe limited in this region, and tsunami generation may be due to coincident movement along faults on the upper plate.

Landslide tsunami case studies using a Boussinesq model and a fully nonlinear tsunami generation model

Abstract. Case studies of landslide tsunamis require integration of marine geology data and interpretations into numerical simulations of tsunami attack. Many landslide tsunami generation and propagation models have been proposed in recent time, further motivated by the 1998 Papua New Guinea event. However, few of these models have proven capable of integrating the best available marine geology data and interpretations into successful case studies that reproduce all available tsunami observations and records. We show that nonlinear and dispersive tsunami propagation models may be necessary for many landslide tsunami case studies. GEOWAVE is a comprehensive tsunami simulation model formed in part by combining the Tsunami Open and Progressive Initial Conditions System (TOPICS) with the fully non-linear Boussinesq water wave model FUNWAVE. TOPICS uses curve fits of numerical results from a fully nonlinear potential flow model to provide approximate landslide tsunami sources for tsunami propagation models, based on marine geology data and interpretations. In this work, we validate GEOWAVE with successful case studies of the 1946 Unimak, Alaska, the 1994 Skagway, Alaska, and the 1998 Papua New Guinea events. GEOWAVE simulates accurate runup and inundation at the same time, with no additional user interference or effort, using a slot technique. Wave breaking, if it occurs during shoaling or runup, is also accounted for with a dissipative breaking model acting on the wave front. The success of our case studies depends on the combination of accurate tsunami sources and an advanced tsunami propagation and inundation model.

Field Survey and Numerical Simulations: A Review of the 1998 Papua New Guinea Tsunami

The Papua New Guinea (PNG) tsunami of 1998 is re-examined through a detailed review of the field survey as well as numerous numerical computations. The discussion of the field survey explores a number of possible misinterpretations of the recorded data. The survey data are then employed by a numerical model as a validation tool. A Boussinesq model and a nonlinear shallow water wave (NLSW) model are compared in order to quantify the effect of frequency dispersion on the landslide-generated tsunami. The numerical comparisons indicate that the NLSW model is a poor estimator of offshore wave heights. However, due to what appears to be depth-limited breaking seaward of Sissano spit, both numerical models are in agreement in the prediction of maximum water elevations at the overtopped spit. By comparing three different hot-start initial profiles of the tsunami wave, it is shown that the initial shape and orientation of the tsunami wave is secondary to the initial displaced water mass in regard to prediction of water elevations on the spit. These numerical results indicate that agreement between numerical prediction of runup values with field recorded values at PNG cannot be used to validate either a NLSW tsunami propagation model or a specific landslide tsunami hot-start initial condition. Finally, with the use of traditional tsunami codes, a new interpretation of the PNG runup measurements is presented.

Landslide-generated Tsunamis: Geotechnical Considerations

Landslide-induced tsunamis are particularly dangerous because the warning time is very short in the coastal area. Therefore it is critical to identify the potential for coastal landslides involving large masses of material. Almost invariably such large landslides will occur in material susceptible to liquefaction, particularly during earthquakes. This paper discusses characteristics of such materials, how they may be identified, and offers suggestions for estimating the potential for large deformations.

Mitigation Lessons from the July 17, 1998 Papua New Guinea Tsunami

The July 17, 1998 tsunami killed over 2,100 people, injured at least 800 severely enough to require hospitalization, permanently displaced over 10,000 and disrupted the social and economic framework of the coastal communities of eastern Saundaun Province, Papua New Guinea. Initial response to the disaster was delayed 16 hours because of the failure to communicate the magnitude of the impact outside the affected area. Once the scope of the disaster was known, international assistance was rapid and substantial. Medical teams, supplies, air transport and mobile field hospitals were provided to assist national medical personnel and facilities. Seven care centers were established for the displaced survivors. Nineteen countries and 17 NGOs (Non-Governmental Organizations) donated money, relief and rebuilding supplies valued at over 6 million US$ in addition to substantial contributions from national recovery funds and the Catholic Diocese. The three Malol villages, two Arop, four Sissano and the Warupu village were permanently abandoned and new villages established inland. Closure of the lagoon and restriction of coastal fishing impacted adjacent villages as well as tsunami survivors. By the second anniversary of the tsunami construction of schools, water and sanitation systems and some roads had been completed. Survivors were provided tools and building supplies to construct new homes, canoes and fishing equipment. Relief and recovery efforts were complicated by coordination difficulties among the many responding agencies and organizations, the disruption of daily routines for both survivors and villages hosting the care centers, and the intrusion of outside aid workers in a region that had been isolated before the disaster. Adaptation to the new village sites has been difficult due to their inland locations that are hotter, more insect-infested and have water and sanitation difficulties. The high number of casualties from the tsunami was the result of several factors: Population concentrated in the area of maximum tsunami impact. Date and time of occurrence. Siting of villages on vulnerable sand spits. Failure of residents to self-evacuate after feeling the earthquake. Substantial delay in mobilizing response. However, further losses were likely reduced because of the rapid deployment of air transport and medical teams, and massive international relief support. The tsunami has affected long-term tsunami mitigation in the Sissano region through the relocation of villages, heightened awareness and education programs. It has also had a significant effect on mitigation in other countries by illuminating the potential dangers of landslide-generated tsunamis and in media coverage of tsunami hazards.

Re-examination of the Source Mechanism of the 1998 Papua New Guinea Earthquake and Tsunami

Simulation of tsunami propagation and runup of the 1998 Papua New Guinea (PNG) earthquake tsunami using the detailed bathymetry measured by JAMSTEC and adding bathymetric data at depths less than 60 m is carried out, reproducing the tsunami energy focus into Warapu and Arop along the Sissano Lagoon. However, the computed runup heights in the lagoon are still lower than those measured. Even if the error in estimating the fault parameters is taken into consideration, computational results are similar. Analysis by the wave ray method using several scenarios of the source size of the tsunami and location by the wave ray method suggests that a source characterized by small size in water 1,000-m deep approximately 25 km offshore the lagoon, best fits the arrival determined from the interviews with eyewitnesses. A two-layer numerical model simulating the interaction of the tsunami with a landslide is employed to study the behavior of a landslide-generated tsunami with different size sand depths of the initial slide just outside the lagoon. A landslide model with a volume of 4-8 x 109 m3 is selected as the best in order to reproduce the distribution of the measured tsunami runup in the lagoon. The simulation of a tsunami generated in two stages, fault and landslide, could show good agreement with the runup heights and distribution of the arrival time, but a time gap of around 10 minutes remains, suggesting that a tsunami generated by the mainshock at 6:49 PM local time is too small for people to notice, and the following tsunami triggered by landslide or mass movement near the lagoon about ten minutes after the mainshock attacked the coast and caused the huge damage.

Analytical solutions for forced long waves on a sloping beach

We derive analytic solutions for the forced linear shallow water equation of the following form:<?TeX \partial^2 Y \over \partial t^2}-b{\partial \over \partial x}\left(x {\partial Y \over \partial x}\right)={\partial^2 f\over \partial t^2 ?>for x>0, in which Y(x,t) denotes an unknown variable, f(x,t) a prescribed forcing function and b a positive constant. This equation has been used to describe landslide-generated tsunamis and also long waves induced by moving atmospheric pressure distributions. We discuss particular and general solutions. We then compare our results with numerical solutions of the same equation and with the corresponding solutions of the nonlinear depth-integrated equations and discuss them in terms of landslide-generated tsunamis.

Numerical Modelling of a Landslide-generated Tsunami: The 1979 Nice Event

—On the 16th of October 1979, a part of the Nice new harbour extension, close to the Nice international airport (French Riviera), slumped into the Mediterranean Sea during landfilling operations. A submarine slide with initial volume close to seashore of about 10 millions m3, which could have evolved later into an avalanche, was followed by a small tsunami, noticed by several witnesses in the “Baie des Anges.” The maximum tsunami effects were observed 10 km from the slide location near Antibes city, which was inundated. Previous analyses used rough approximate methods and produced models which did not conveniently fit data. In this paper, both the slide and the generated water waves are numerically simulated on the basis of the shallow water approximation. The landslide is assimilated to a heavy Newtonian homogeneous fluid downslope under gravity. Water waves are generated by sea-bottom displacements induced by the landslide. Taking into account a very accurate multibeam bathymetric map, the Nice slide of 10 millions m3 is simulated by this model. The numerical results are generally consistent with the observed hydraulic local effects in front of the Nice airport, however they are not in agreement in the far field. A larger and deeper landslide 2 km off Nice airport is tested to quantitatively study the effects of the landslide volume on water waves generation.

Numerical modeling of a landslide-generated tsunami following a potential explosion of the Montserrat volcano

The explosion of the Montserrat volcano (Caribbean Sea) could trigger a major landslide and lead to the generation of a tsunami in the Caribbean Sea. In the worst case scenario, the volume of material reaching the sea has been estimated at 80 millions of cubic meters. The sliding of this mass and the generation of the associated tsunami have been simulated numerically, assuming that the debris behave like a heavy fluid flowing into the sea. The numerical model solves the 3D Navier-Stokes equations for a mixture composed of rocks and water. The generated water waves is then propagated around the coast of Montserrat by means of a shallow water model. The numerical results show that the water heights above sea level are higher than 5 meters within a radius of 5 km of the source.

Tsunami waves generated by volcanic landslides: an assessment of the hazard associated with Kick ’em Jenny

Abstract Landslides and rock falls generating tsunamis constitute a serious element of risk at steep-sided volcanoes located in close proximity to water, especially when the volcano’s structure is cut by faults or altered by fumaroles and where there has been a history of subsidence or signs of incipient caldera formation. Approximately 5% of known tsunami events have been generated by volcanoes, producing some of the most destructive tsunamis on record. A preliminary study suggests that Kick ’em Jenny is a prime candidate for tsunamigenic events on a potentially hazardous scale, possibly affecting the whole of the eastern Caribbean region. An estimate of the potential height of tsunami waves generated following slope failure on the flanks of Kick ’em Jenny has been found using the basic solitary wave theory combined with equations of energy conservation. Generally, landslide-generated tsunamis possess little energy and, unless they are confined in a bay or channel, are only hazardous close to the source. However, the results show that with the low-lying Grenadine Islands situated a few kilometres to the east, even a relatively small landslide event at Kick ’em Jenny has the potential to produce waves that would prove hazardous to both coastal populations and ships.