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International audience; In this paper, we analyze the relevance of the use of the shallow water model and the Boussinesq model to simulate tsunamis generated by a landslide. In a first part, we determine if the two models are able to reproduce waves generated by a landslide. Each model has drawbacks but it seems that it is possible to use them together to improve the simulations. In a second part we try to recover the landslide displacement from the generated wave. This problem is formulated as a minimization problem and we limit the number of parameters to determine assuming that the bottom can be well described by an empirical law.; Dans cet article, nous analysons la pertinence de l'utilisation de modèles intégrés suivant la verticale tels que le modèle de Saint-Venant et le modèle de Boussinesq pour simuler les tsunamis générés par un glissement de terrain. Dans une première partie, nous déterminons si les deux modèles sont capables de reproduire les vagues générées par un glissement de terrain. Chaque modèle présente des inconvénients mais il semble qu'il soit possible de les utiliser ensemble pour améliorer les simulations. Dans une deuxième partie, nous essayons de retrouver le déplacement du glissement de terrain à partir de la vague générée. Ce problème a été formulé comme un problème de minimisation et nous limitons le nombre de paramètres à déterminer en supposant que le fond peut être bien décrit par une loi empirique.

On June 17 2017, the western coast of Greenland was the site of a tsunami which flooded several villages, killing 4 people and destroying 11 houses in the village of Nuugaatsiaq. This tsunami was triggered by a subaerial landslide which occurred in a fjord 32 km ENE of Nuugaatsiaq. This paper presents the numerical modeling of this landslide of $$\sim$$ 50 million $$\hbox {m}^{3}$$ and of the tsunami propagation from its source to Nuugaatsiaq. The landslide is considered as a granular flow under gravity forces and the water waves generated are related to the displacement of the sea bottom. The results obtained are similar in amplitude to our inferences from videos, i.e., three water waves between 1 and 1.5 m arriving at Nuugaatsiaq with a period of roughly 3 min, and are also in general agreement with the amplitude (1 m) resulting from deconvolution of oscillations recorded on a horizontal seismogram operating at Nuugaatsiaq (NUUG). According to the field survey performed by Fritz et al. (EGU General Assembly Conference Abstracts, Vol. 20 of EGU General Assembly Conference Abstracts, p 18345, 2018a) on July 2017, a second mass next to the landslide is threatening Karrat Fjord. A sensitivity study is realized on its volume, with 2, 7, 14 and 38 million $$\hbox {m}^{3}$$ reaching the sea. The shape of the water waves is found to be independent of volume, and linearity is observed between the volume and the water wave heights. Finally, the orientation of the slide does not seem to influence either the period or the shape of the generated water waves.

In the literature, OpenFOAM has been used to simulate landslide tsunamis, modeling the landslide as a solid or a two-phase flow. Here we present an approach using three phases (air, water and sediment) modeled as Newtonian fluids. This 3D model is validated against two benchmarks with deformable landslides: one subaerial (Viroulet et al. 2016) and one submarine (Grilli et al. 2017). These benchmarks are also run by a 2D depth-integrated model, AVALANCHE, recently used to reproduce the 2017 Karrat Fjord, Greenland and the 2018 Anak Krakatau, Indonesia events. Both models are able to reproduce either the water waves or the landslide behavior but not both at the same time.Considering OpenFOAM as a reference code, sensitivity studies on the slope angle, the landslide viscosity and the landslide initial submergence showed that AVALANCHE produces similar results for slope angles between 10 and 45°, for subaerial or close to the surface landslide and/or for low viscosity values. In the other cases (submarine landslides and higher viscosity values) results indicated that OpenFOAM should be preferred to a 2D depth-integrated model. References:Grilli, S., Shelby, M. & Kimmoun, O. (2017), ‘Modeling coastal tsunami hazard from submarine mass failures: effect of slide rheology, experimental validation, and case studies off the US East Coast’, Natural Hazards 86, 353-391.Viroulet, S., Sauret, A., Kimmoun, O. & Kharif, C. (2016), Tsunami waves generated by cliff collapse: comparison between experiments and triphasic simulations, in E. Pelinovsky & C. Kharif, eds, ‘Extreme Ocean Waves’, Springer International Publishing, Cham, pp. 173-190.

The arc of the Lesser Antilles is associated with a significant tectonic activity due to the subduction of the Atlantic oceanic plate under the Caribbean plate. Earthquakes in this context have the potential to trigger landslides and tsunamis due to the important vertical seafloor displacement. The historical tsunamigenic earthquakes in this region are rare, but the damages they may have generated before along the coasts show that they pose a considerable threat to the closest inhabited islands. The most recent tsunamigenic earthquake occurred in 2004 in the area of Les Saintes, along a normal fault system located in the back-arc of the subduction. This $$M_{w}=6.3$$ earthquake generated small waves with 2 m of run-up in several bays of Les Saintes, a group of islands in the South of Guadeloupe. A recent survey conducted in the source area using deep-sea vehicles revealed for the first time an important coseismic slip on the Roseau fault plane, attributed to the 2004 event, which had not been predicted in the seismic inversion models. This event and the dataset on the Roseau fault gives the opportunity to model precisely the earthquake, to compare the simulation results with the observations and to evaluate the impact of the rupture heterogeneity and rupture shallowness on the height of the tsunami waves. Extending our earlier work (Cordrie et al. in OCEANS 2019—Marseille, Jun 2019, Marseille, France, pp 1–9, 2019. https://doi.org/10.1109/OCEANSE.2019.8867447 ) and in order to avoid a loss of quality from the dataset in the modeling of the initial sea-surface deformation especially in shallow depth and near field context, a transfer function of the deformation from the seafloor to the sea surface and different numerical schemes were used. Results on the tsunami height distribution indicate some local tsunami amplification phenomena linked to the bathymetry or the coastline geometry and highlight the most endangered areas of the islands. The simulations give additional constraints on the source, show the impact of the slip heterogeneities on the tsunami and finally provide a complementary estimation of the 2004 coseismic slip intensity.

International audience; On the evening of December 22, 2018, the coasts of the Sunda Strait, Indonesia, were hit by a tsunami generated by the collapse of a part of the Anak Krakatau volcano. Hundreds of people were killed, thousands were injured and displaced. This paper presents a preliminary modeling of the volcano flank collapse and the tsunami generated based on the results of a 2D depth-averaged coupled model involving a granular rheology and a Coulomb friction for the slide description and dispersive effects for the water flow part. With a reconstructed total volume (subaerial and submarine) of the landslide of 150 million m 3 inferred from pre and post-collapse satellite and aerial images , the comparison of the simulated water waves with the observations (tide gauges located all around the strait, photographs and field surveys) is satisfactory. Due to the lack of information for the submarine part of the landslide, 2 Alexandre Paris et al. the reconstructed submarine slope is assumed to be approximately constant. A significant time delay on the results and particularly in the Bandar Lampung Bay could be attributed to imprecisions of bathymetric data. The sensitivity to the basal friction and to dispersive effects is analyzed through numerical tests. Results show that the influence of the basal friction angle on the simulated wave heights decreases with distance and that a value of 2°gives consistent results with the observations. The dispersive effects are assessed by comparing water waves simulated by a shallow water model and a Boussinesq model. Simulations with frequency dispersion produce longer wave periods and smaller wave amplitudes in the Sunda Strait and particularly in deep waters.

Two approaches are proposed to simulate tsunamis generated by granular landslides: a depth-averaged model, AVALANCHE, and laminar Navier–Stokes simulations using the OpenFOAM model. Both models are validated against two 2D benchmarks, a subaerial and a submerged one involving a triangle initial slide shape. In both models, the landslide is defined as a viscous fluid flowing downslope. Except in the first instants, both models can reproduce either the landslide behavior or the generated first water waves but cannot reproduce simultaneously both the landslide and the water surface. There is an overlap in the optimal viscosity range between both models. Sensitivity studies are carried out by varying the slope angle and the landslide submergence for the subaerial benchmark. The largest waves are obtained for initial landslide position close to the free surface. The height of the generated waves increases linearly with the slope angle and the landslide Reynolds number in the depth-averaged model. The relationships are more complex in the Navier–Stokes model. For low slide Reynolds numbers and with an initial slide close to the free surface, both models produce similar waves. Nine additional cases are performed with a k − e turbulence closure model and varying the submergence and the slope angle.

This paper aims at best describing the submarine landslide which induced partial submersion of the atolls of Mururoa and Fangataufa in 1979. More precisely, waves propagated along the south coast of Mururoa atoll and penetrated into its lagoon some minutes after the landslide triggering (t = 0 s), whereas a train of eight water waves reached the runway located on the north-east coast of Fangataufa (40 km south of Mururoa) between t = 7 min 30 s and t = 20 min. A numerical model based on shallow water equations is used to simulate the landslide as well as the associated tsunami. Saint-Venant equations are used to propagate the tsunami in coastal areas, whereas the offshore propagation is simulated by solving weakly nonlinear Boussinesq equations. Low- and high-resolution nested grids are used to simulate the tsunami propagation in deep sea and in shallow waters, respectively. Several scenarios have been tested to reproduce the observed water and run-up heights in the near and far fields. The best scenarios correspond to a landslide with a volume in the range (75–90 Mm3) (for a basal friction angle of 35°) and with a basal friction angle in the range (30°–40°) (for a volume of 80 Mm3). These results have been completed by a parametric study on the slide parameters.

In this paper, we present a new source assessment of the La Palma collapse scenario previously described and studied in Abadie et al. (2012). Three scenarios (i.e., slide volumes of 20, 40 and 80 km3) are considered, from the initiation of the slide to the water waves generation, using THETIS, a 3D Navier–Stokes model. The slide is considered as a Newtonian fluid whose viscosity is adjusted to approximate a granular behavior. After 5 minutes of propagation with THETIS, the generated water wave is transferred into FUNWAVE-TVD for 15 minutes of Boussinesq model simulation. Then, four different depth-averaged codes are used to propagate the wave to the Guadeloupe area, Europe and French coasts. Finally, the wave impact in terms of run-up is evaluated through direct computations in specific areas or using theoretical formulas. Although the wave source appears reduced due to the rheology used compared to former works, the wave impact is still significant for the maximum slide volume considered on surrounding islands and coasts, as well as on remote most exposed coasts such as Guadeloupe. In Europe and in France, the wave impact is moderate (for specific areas in Spain and Portugal) to weak (Atlantic French coast). The comparison between the different wave models in overlapping computational regions shows an overall agreement in terms of first wave amplitude and time of arrival, but differences appear in the trailing waves.

In the evening on December 22, 2018, the Sunda Strait, Indonesia, suffered a destructive tsunami that no one had seen coming. It killed more than 400 people, injured and displaced thousands more. Post event satellite images indicate that the tsunami was probably caused by the collapse of a part of the southwestern flank of the Anak Krakatau volcano. Assuming a landslide volume of 150 million m3 sliding into water as a granular flow under gravity forces, the simulated water waves are in general agreement with the tide gauges that recorded the tsunami.

Modest earthquakes may trigger large submarine landslides, responsible for disastrous tsunami waves, as demonstrated by the Papua New Guinea event of July 17, 1998. The relatively small earthquake was followed by unexpectedly high waves, up to 15 m, wiping out 3 villages and killing more than 2200 people. Numerical simulations show that seismic dislocation sources are not energetic enough to reproduce the observed tsunami along the coast. Tsunami generation by a submarine landslide has been simulated by a finite-difference model, assimilating the landslide to a flow of granular material. Long-wave approximation is adopted for both water waves and the slide. Numerical results show that observed inundation heights are well reproduced for a volume of 4 km³ located 20 km offshore, sliding downslope with a Coulomb-type friction.

The evolution of the volcano activity in Montserrat could lead to the collapse of a portion of the lava dome in the Tar River Valley and to a sudden entry of debris avalanche into the Caribbean Sea. The impact of a debris avalanche with a volume of 40× 10 6 m 3 into the sea and the generated tsunami have been simulated numerically by a mixture model solving the 3D Euler's equations. The mixture is composed of sediments considered as an homogeneous fluid of density 2 and of water. Numerical tests show that the generated waves are sensitive to both initial impact velocities and avalanche fronts of the landslide. The water surface and velocities calculated by the 3D mixture model are used as input data in a non-linear shallow water model, to calculate tsunami propagation along the coasts of Montserrat. The hydraulic risks in Montserrat are roughly assessed for a tsunami generated by a mass of 40×10 6 m 3 entering the sea.

[1] On September 13, 1999, Omoa Bay (Fatu Hiva Island, French Polynesia) was struck by 2 to 5 m high water waves: several buildings were flooded and destroyed but no lives were lost. Observations gathered during a post-event survey revealed the recent collapse into the sea of a 300 × 300 m2, at least 20-m thick, cliff located 5 km southeast of Omoa. This cliff failure most certainly triggered the tsunami waves since the cliff was reported intact 45 min earlier. We simulate the tsunami generation due to a subaerial landslide, using a finite-difference model assimilating the landslide to a flow of granular material. Numerical modeling shows that a 0.0024-km3 landslide located in the presumed source area accounts for the tsunami waves reported in Omoa Bay. We show that the striking amplification observed in Omoa Bay is related to the trapping of waves due to the shallow submarine shelf surrounding the island.