Experiments on Tsunamis Generated by 3D Granular Landslides F. Mohammed and H.M. Fritz Abstract Subaerial and submarine landslides can trigger tsunamis with locally high amplitudes and runup, which can cause devastating effects in the near field region such as the 1958 Lituya bay, Alaska, 1998 Papua New Guinea and 2006 Java tsunamis. Tsunami generation by submarine and subaerial landslides were studied in the three dimensional NEES (George E. Brown, Jr. Network for Earthquake Engineering Simulation) tsunami wave basin (TWB) at Oregon State University based on the generalized Froude similarity. A novel pneumatic landslide generator was deployed to control the granular landslide geometry and kinematics. Measurement techniques such as particle image velocimetry (PIV), multiple above and underwater video cameras, multiple acoustic transducer arrays (MTA), as well as resistance wave and runup gauges were applied. The experimental data provided new insights on landslide deformation as it impacts the water surface, penetrates the water and finally deposits on the bottom of the basin. The influence of the landslide volume, shape and the impact speed on the generated tsunami waves were extensively studied. The instantaneous surface velocity fields measured using the PIV gave insight into the kinematics of the landslide and wave generation process. At high impact velocities, flow separation occurred on the slide shoulder resulting in a hydrodynamic impact crater. The measured wave profiles yielded information on the wave propagation and attenuation. The measured wave speed of the leading wave reaches the theoretical solitary wave celerity while the trailing waves are slower in nature. Attenuation functions of the leading wave crest amplitude, the wave length and the time period were obtained to study the wave behavior in the near field and far field regions. The measured wave data serves the validation and advancement of 3-dimensional numerical landslide tsunami and prediction models. F. Mohammed () and H.M. Fritz School of Civil and Environmental Engineering, Georgia Institute of Technology, 210 Technology Circle, Savannah, GA 31407, USA e-mail: [email protected]; [email protected] D.C. Mosher et al. (eds.), Submarine Mass Movements and Their Consequences, Advances in Natural and Technological Hazards Research, Vol 28, © Springer Science + Business Media B.V. 2010 705 706 F. Mohammed and H.M. Fritz Keywords Submarine landslide • granular landslide • tsunami • pneumatic landslide generator •particle image velocimetry •wave attenuation 1 Introduction Landslide generated tsunamis can occur in confined water bodies as well as at island and continental shelves and coasts where the waves can travel both in offshore and along the shore directions. These landslide generated tsunamis with locally high amplitudes and runup can be devastative in the near field regions. In the past, major tsunamis caused by landslides were recorded at Grand Banks in 1927 (Fine et al. 2005), Lituya Bay, Alaska in 1958 (Fritz et al. 2001, 2009; Weiss et al. 2009), Vajont dam in Italy in 1963 (Müller 1964), the more recent 1998 Papua New Guinea (Synolakis et al. 2002; Bardet et al. 2003), Stromboli (Tinti et al. 2005, 2006), Java tsunamis (Fritz et al. 2007) and the ancient Storegga slide (Bondevik et al. 2005). The resulting impulse waves can cause damage due to large local runup along the coastline and overtopping of dams and reservoirs. Hence a need arises to understand the effects of the landslide characteristics on the generated tsunami waves. Physical models of landslide generated tsunami scenarios provide a detailed understanding of the wave generation and propagation mechanism as well as simultaneously assist advancement of numerical model development. These analytical and numerical models will allow hazard assessments of landslide generated tsunamis. Majority of physical experiments on landslide generated tsunamis have focused on two dimensional tsunami waves generated by landslides. These experiments were performed by either using solid blocks sliding on an incline to simulate landslide tsunamis (Heinrich 1992; Watts 2000; Walder et al. 2003; Grilli and Watts 2005) or using granular landslides (Fritz 2002; Fritz et al. 2003, 2004). Waves generated by three dimensional solid block landslides were studied by Liu et al. 2005; Panizzo et al. 2005; Enet and Grilli 2005, 2007; DiRisio et al. 2009 on flat bottoms, on sloping beaches and conical islands. The aim of the present study is to understand the generation of tsunami waves by fully three dimensional deformable granular landslides. A realistic description of the landslide is attainable by using deformable materials for the landslide as compared with solid blocks, which do not account for the landslide deformation due to slide motion, interaction with the water body and bathymetry. Herein experiments conducted in the Tsunami Wave Basin at Oregon State University are presented. The study focused on understanding the granular landslide dynamics above and under water, the generation and propagation of the resulting tsunami waves as well as the lateral onshore runup. Three dimensionality of the physical model enabled to identify the wave amplitude attenuation functions in both the radial and the angular directions away from the landslide source thus enabling us to characterize the wave evolution in the near field as well as in the far field regions. Experiments on Tsunamis Generated by 3D Granular Landslides 2 707 Experiment Description The landslide tsunami generator experiments were conducted at the O. H. Hinsdale Wave Research Laboratory at the Oregon State University, Corvallis. The experiments were performed in the three-dimensional NEES Tsunami Wave Basin (TWB), which is 48.8 m long, 26.5 m wide and 2.1 m deep. A unique pneumatic landslide generator was designed and built at Georgia Tech in Savannah and then shipped and deployed at the Wave Research Lab in Corvallis. The landslide tsunami generator was constructed as an open aluminum box mounted on a steel slide. The box measures 2.1 by 1.2 by 0.3 m and is filled with 0.756 m3 (upto 1,350 kg) of naturally rounded river gravel. The granulate material has a bulk density of 2.557 and saturated-surface density of 2.617. The slide box can be subdivided to adjust for the initial slide length and thickness. The box accelerates down the slope by means of four parallel pneumatic pistons. The landslide tsunami generator is shown in Fig. 1a. This apparatus is capable of simulating landslides initiating both above and below the water surface. The pneumatic pistons accelerate the box to reach launch speeds up to 4 m/s at slide release. The granular landslide is accelerated in the box and released by opening the front tarp while the box is decelerated pneumatically. The entire landslide tsunami generator is positioned on a steel plate with slope 2 H:1 V. Upon deployment, the granulate slides out of the box, spreads down the slope and impacts the water surface at velocities up to 5 m/s, thereby generating the tsunami waves. After impacting the water surface, the granular landslide material deposits on a steel plate placed at the bottom of the wave basin. At the end of an experimental trial, the steel plate is lifted by means of an overhead crane and the granular material is filled back into a bucket and the box is reloaded for the next run. A typical experimental cycle is shown in Fig. 1b. During each experimental trial, a data acquisition system constantly records the entire process and measures the water surface elevation. Measurements are made relating to the shape and speed of the landslide, both above water and underwater, the wave generation process and Fig. 1 Landslide Tsunami Generator, LTG. (a) Pneumatic acceleration mechanism with four pneumatic pistons in the upper half of the image and the filled slide box with the front tarp; (b) experimental cycle of the landslide granulate portrays the sled loading, pneumatic launch, landslide recovery and reloading for the sub-sequent trial 708 F. Mohammed and H.M. Fritz the wave propagation away from the source and the shape of the deposited slide material on the bottom of the wave basin. After all the measurements are recorded, the steel plate with the landslide deposit is lifted, the recovered slide deposit dumped into a bucket and the box refilled for the next trial. A wide array of instrumentation is deployed in the wave basin to measure the characteristics of the granular landslide and the generated tsunami waves. Four parallel stringpots measure the box motion and provide information on the pneumatic acceleration and deceleration of the gravel filled box. Thus, before the landslide is released from the box, the slide front velocity corresponds to the box velocity. An array of above water and under water cameras is shown in Fig. 2a. These camera measurements provide an insight into the landslide kinematics and the slide shape evolution down the slope. A Multi Transducer Array (MTA) is used at the end of each trial to survey the landslide deposit and measure its shape, volume and the extent of the deposited granular material. An array of resistance wave gauges is deployed to measure the generated tsunami wave surface elevation and the tsunami runup wave elevation on the slope lateral to the landslide. The wave gauge array is shown in Fig. 2b. The wave gauges are positioned to measure the wave properties along both the radial and the angular direction in the wave basin. A high resolution (1,600 × 1,200 pixels) Particle Image Velocimetry (PIV) camera is setup to record the landslide on the slope and the water surface in the impact zone. The digital, high sensitivity PIV camera with 14-bit pixel-depth is positioned at a distance of 6.8 m perpendicular to the hill slope providing an approximate 15 m2 (4.5 by 3.38 m) viewing area. The PIV analysis provides an insight into the kinematics of the wave generation process and the landslide motion down the slope. All the cameras are calibrated in situ by placing calibration plates with regular dot patterns in the various measurement planes both above and underwater to account for optical refraction. 2.1 Experiment Trial Conditions A total of 62 trials were completed with the landslide tsunami generator in the tsunami wave basin to study the tsunami generation by granular landslides. The material used for the landslide is composed of naturally rounded fine gravel spanning sieve sizes Fig. 2 Instrumentation setup. (a) Underwater and above water camera setup to record the landslide kinematics; (b) Planform of the wave gauge array installed in the TWB to measure the landslide generated tsunami wave characteristics. Distances in (m) Experiments on Tsunamis Generated by 3D Granular Landslides 709 6.35 to 19 mm. Different trials were conducted to study the effects of varying water depths, landslide volumes and impact speeds on the generated tsunami waves. The trials were conducted at water depths of 0.3, 0.6, 0.9, 1.2 and 1.35 m. The varying water depths provide a wide range of generated waves from the shallow water depth wave regime to the intermediate water depth wave regime. Four different pneumatic launch pressures provide four different cases of landslide release velocities ranging from 2 to 4 m/s resulting in impact velocities up to 5.5 m/s. By fixing a plate midway along the length of the box, the initial mass loading of the box is restricted to half the original volume. This enables us to have two testing loads of the granular landslide material of roughly 1,350 and 675 kg. Thus the varying water depth conditions combined with the slide characteristics provide a wide range of non-dimensional parameters governing the generated tsunami wave data. This allows characterizing the effects of various slide properties and water depths on generated tsunami waves. 3 3.1 Data Analysis Pneumatic Landslide Generator Performance The pneumatic pistons accelerate the slide box over the first two thirds of the 2 m piston stroke, while the latter third is dedicated to pneumatic deceleration. At the maximum velocity of the box, it begins to decelerate thus releasing the landslide Fig. 3 Slide box displacement based on string pot recordings and landslide front veloc-ity measured from the PIV images for a case at 10 bar initial pneumatic firing pressure 710 F. Mohammed and H.M. Fritz material from the box. Until the release point, the landslide front velocity is the same as the box velocity. After the landslide releases from the box, the images recorded by the PIV camera are used to measure the front velocity. The landslide front velocity with the stringpot data along the slope direction is shown in Fig. 3. The coordinate system for measuring the landslide impact velocity is defined with the x-direction following the incline of the slope, the y-axis in the transverse direction along the lateral spreading of the landslide and the z-direction points perpendicularly upwards from the incline. The origin is the front of the box when at rest. By collecting all the data for similar landslide cases at all water depths and transforming to the slope fixed coordinate system, the complete evolution of the landslide front velocity above the water surface is obtained. The displacement curve of the landslide box is characterized by initial acceleration driven by the pneumatic pistons up to the release point as shown in Fig. 3. After the landslide is released from the box, further acceleration down the incline is purely influenced by gravity, friction and resistance by the surrounding fluid. Simultaneously the slide box is decelerated pneumatically to a stopping point. 3.2 Landslide Characteristics The generated tsunami wave characteristics depend on the normalized slide impact velocity and the shape of the slide at the impact, namely the maximum width and thickness of the slide relative to the water depth. The slide widths are measured from the PIV image sequences. A combination of time stacking and image processing techniques are used to extract the information on the slide widths. From a series of images, the time stacked image of one particular row is generated by subtracting an image from its previous image and stacking one below the other. This helps in enhancing the change in the image at the next time level. The time stacked image is filtered using a circular averaging filter of radius 32 pixels to eliminate individual grains that scatter on the lateral boundary of the landslide and do not form part of the bulk slide mass that generates the tsunami waves. By applying a threshold on the grayscale of the image, it is converted into a binary image, where the white region corresponds to the slide material and the black region is the background of the slope. Then the edge of this bulk material is extracted. By subtracting the edges along each row in the image, the evolution of the width with respect to time is obtained at that particular location. By repeating this process along the length of the slope above the water surface, the complete width evolution with respect to space and time is obtained. Then the maximum width is determined across the length of the slope at each time level to obtain the maximum width evolution over time of the landslide material. A sample time stacked image and the maximum extracted width is shown in Fig. 4a, b. The time t = 0 corresponds to the time of the landslide impact on the water surface. The extracted width shows the lateral spreading of the slide material to reach a maximum width followed by a gradual decrease in slide width. Experiments on Tsunamis Generated by 3D Granular Landslides 711 A corresponding raw image sequence is shown in Fig. 4c. Side cameras are used to extract information on the evolution of the slide thickness with respect to time both above water and under water. The underwater information is limited to cases where there is sufficient visibility to identify the landslide material and extract its thickness. An edge extraction is shown for a series of underwater images at a water depth of 0.6 m, pneumatic firing pressure of 10 bar and 1,350 kg of the granular material in Fig. 5a. The landslide deposit from the MTA survey is shown in Fig. 5b. This data is extrapolated linearly to obtain the full extent of the deposit and measure the volume of the slide material that gets deposited underwater. Fig. 4 Landslide width for water depth 0.6 m, 10 bar firing pressure and 1,350 kg of granular material. (a) Time Stacked image shown with the extracted edge of the slide material; (b). Landslide width evolution versus time. t = 0 corresponds to the moment when the landslide impacts the water surface; (c) Lateral spreading of the landslide material above the water surface Fig. 5 Experiment case of water depth 0.6 m, pneumatic firing pressure 10 bar and 1,350 kg of granular material. (a) Underwater landslide thickness estimation; (b) granular landslide deposit surveyed by the MTA 712 3.3 F. Mohammed and H.M. Fritz Tsunami Wave Characteristics The velocity on the landslide surface and the water surface is obtained from the cross-correlation analysis based processing of the PIV image sequences. The water surface is sprinkled with slightly buoyant seeding particles to enable the PIV analysis. The speckled pattern generated by the landslide granulate surface and the particles reflecting light on the water surface are used for iterative multi-pass cross correlation analysis with decreasing window sizes down to 32 by 32 pixels (Raffel et al. 1998; Fritz et al. 2003a). Since the landslide and the water surface are in two different planes, the image is rectified twice using calibration boards to obtain the PIV velocity measurements for the landslide and the water surface in m/s rather than in pixel/s. Measured velocity vectors on the landslide surface are shown in Fig. 6. The impact of the landslide on the water surface generates the first wave which travels radially away from the landslide source. The PIV analysis provides insight on the radial wave generation, the crater dynamics including the collapse and the subsequent runup with secondary wave formation after the rundown (Fritz et al. 2003b). Thus two distinct runup waves propagate in the transverse direction with high amplitudes. The water surface elevation measured by the wave gauges along the landslide direction (0°), along a ray which is at 30° from the landslide direction and the lateral runup along shore (90°) is shown in Fig. 7. The recorded wave profiles were strongly directional, unsteady, nonlinear and mostly in the intermediate water depth wave regime. The leading wave is followed by a train of dispersive waves as seen in Fig. 7. The waves display the characteristic shape of a large trough between two crests. The first crest is generated when the landslide impacts the water surface and pushes the water column away from the landslide. The impact creates a cavity Fig. 6 Velocity vectors computed with the cross-correlation PIV-analysis on the landslide surface during the wave generation process for 10 bar pneumatic launch pressure Fig. 7 Wave surface elevation measured at the resistance wave gage array: (a) The 0° offshore direction in prolongation of the landslide axis at X/h = 8.5, 14.2, 23.3 and 40.2; (b) Along a 30° ray at X/h = 6.5, 8.5 and 14.2; (c) Lateral along shore runup direction (90°) at Y/h = 3.3, 4.3, 6.3 and 9.3 Experiments on Tsunamis Generated by 3D Granular Landslides 713 714 F. Mohammed and H.M. Fritz which contributes the large trough. Then the collapse of this cavity creates a second hillslope runup and subsequently the rundown forms the second wave crest. This source oscillation is followed by decreasing repetitions of wave up rush and draw down resulting in a trailing wave train behind the first two initially dominant wave crests. By identifying the locations, where the water surface departs from the mean water level, the upcrossing points are identified. Then the water surface between two successive up crossing points is identified as a single wave and the subsequent wave crest and trough are identified. The wave celerity is determined by measuring the time taken for the wave crests and troughs to travel the distance between subsequent wave gauges. Figure 8 shows the measured speed of the crests and troughs of the first three waves. The first wave crest speed in many cases approaches the theoretical limit celerity of the non-linear solitary wave theory, which is governed only by water depth and amplitude dispersion. The speed of a solitary wave is given by Boussinesq (1872). c1 gh = 1+ a1 2h which compares with the wave celerity given by Tanaka (1986) (Glimsdal et al. 2007). However the second and the third waves are shorter in wave length and Fig. 8 Measured crest and trough speed of the first three waves between the wavegages for all the experimental trials. The amplitude is non-dimensionalized by the water depth and the speed by the shallow water speed (gh)1/2 Experiments on Tsunamis Generated by 3D Granular Landslides 715 Fig. 9 Wave amplitude attenuation for water depth 0.6 m, 10 bar firing pressure and roughly 1,350 kg of slide material: (a) The first wave crest amplitude versus the radial distance where it is measured in the wave basin; (b) First wave crest amplitude versus angle for the same case therefore travel at a reduced celerity as compared to the first wave. The source amplitudes of landslide generated tsunamis are only limited by the landslide Froude number and the relative slide thickness, and can therefore exceed source amplitudes of tectonic tsunamis. However radial spreading combined with both amplitude and frequency dispersion results in more rapid decrease in leading wave heights compared to tectonic tsunamis. Consequently landslide tsunamis can have devastating impacts on coastal communities near the source, while far field hazards are rapidly reduced. The first wave crest amplitude for an experimental case of water depth 0.6 m, firing pressure 10 bar and full load is shown in Fig. 9a. It is assumed that the wave amplitude depends on the radial coordinate as a1 = krn, where the coefficients 716 F. Mohammed and H.M. Fritz k and n account for the source parameters such as the landslide impact speed, width, thickness and water depth. The wave amplitude also decays rapidly in the angular direction away from the landslide direction. The first wave crest as a function of angular direction for the same case is shown in Fig. 9b. Here u = 0° correspond to the landslide direction. The results portray cos u dependency on the amplitude decay in the angular direction. The initial wave characteristics are governed by the non-dimensional landslide parameters, while the wave propagation is solely dependent upon the wave parameters and water depth. 4 Discussion The three dimensional pneumatic landslide tsunami generator was designed, constructed and successfully deployed in the NEES tsunami wave basin at OSU. The uniqueness of this apparatus lies in its large scale, ability to test with granular material and controlled acceleration of the slide. To date, 62 successful trials were completed to study the effects of landslide characteristics and water depth conditions on the generated tsunami wave. The landslide characteristics and the main tsunami parameters such as the wave speed and amplitude were determined. The generated waves are strongly directional, nonlinear and varyingly dispersive. The maximum wave amplitudes of the generated wave trains demonstrate an exponential decay with radial distance away from the landslide source and in the angular direction as well. The measured wave speed approaches the limiting theoretical approximation of the solitary wave theory, which can be used for predictions of tsunami arrival times. The landslide tsunamis exhibit more dispersive propagation than tectonic tsunamis (Glimsdal et al. 2006; Loualalen et al. 2007). Since water displacement can significantly exceed the landslide volume due to the impact cavity at high speeds, the generated wave amplitude is high at the impact location. Thus the landslide waves can be very destructive locally. However the localized tsunami source and radial spreading combined with dispersion result in rapid wave height decay with propagation distance. The PIV analysis provides an insight into the wave generation process and reveals potential for fully 3D surface and velocity reconstruction. Ultimately the analysis of landslide generated tsunami waves includes describing the entire landslide evolution as it traverses from the subaerial to the submarine regime. In particular, describing the slide width and thickness along the slope will provide an insight into rheological dependency of landslide deformation during the impact. The generated tsunami characteristics will be related to the impact velocity and shape of the slide. Further energy transfer rates between the slide and the water body will be determined. The slide and wave data is used to benchmark and advance numerical models for prediction and warning. Acknowledgements This research work is supported by the National Science Foundation under Grant N0. CMMI-0421090 and CMMI-0402490. Any opinions, findings, and conclusions or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Experiments on Tsunamis Generated by 3D Granular Landslides 717 References Bardet J-P, Synolakis C, Davis H, Imamura F and Okal E (2003) Landslide tsunamis: Recent findings and research directions. Pure Appl Geophys 160:1793–1809. Bondevik S, Løvholt F, Harbitz C, Mangerud J, Dawson A and Svendson J (2005) The Storegga slide tsunami comparing field observations with numerical solutions. Mar Pet Geol 22:195–208. Boussinesq J (1872) Théorie des ondes et des remous que se propagent le long d’un canal rectangulaire horizontal, en communiquant au liquide contenu dans ce canal des vitesses sensiblement pareilles de la surface au fond. J Math Pures Appl 17:55–108. Di Risio M, De Girolamo P, Bellotti G, Panizzo A, Aristodemo F, Molfetta MG and Petrillo AF (2009) Landslide-generated tsunamis runup at the coast of a conical island: New physical model experiments. J Geophys Res 114: C01009, doi: 10.1029/2008JC004858. Enet F and Grilli ST (2005) Tsunami landslide generation: Modelling and experiments. Proc., 5th Int. on Ocean Wave Measurement and Analysis, WAVES 2005, Madrid, Spain, IAHR, Paper No. 88. Enet F and Grilli ST (2007) Experimental study of tsunami generation by three-dimensional rigid underwater landslides. J Waterway Port Coast Ocean Eng 133:442–454. Fine I, Rabinovich A, Bornhold B, Thomson R, Kulikov E (2005) The Grand Banks landslidegenerated tsunami of November 18, 1929: Preliminary analysis and numerical modelling. Mar Geol 215:45–47. Fritz HM, Hager WH, Minor H-E (2001) Lituya Bay case: rockslide impact and wave run-up. Sci Tsunami Hazards 19:3–22. Fritz HM (2002) Initial phase of landslide generated impulse waves. Ph.D. thesis ETH-No. 14871, Swiss Federal Institute of Technology, ETH Zürich, Switzerland. Fritz HM, Hager WH, Minor H-E (2003a) Landslide generated impulse waves: part 1: instantaneous flow fields. Exp Fluids 35:505–519, doi: 10.1007/s00348–003–0659–0. Fritz HM, Hager WH, Minor H-E (2003b) Landslide generated impulse waves: part 2: hydrodynamic impact craters. Exp Fluids 35:520–532, doi: 10.1007/s00348–003–0660–7. Fritz HM, Hager WH and Minor H-E (2004) Near field characteristic of landslide generated impulse waves. J Waterway Port Coastal Ocean Eng ASCE 130:287–302, doi: 10.1061/ (ASCE)0733–950X(2004)130:6(287). Fritz HM, Kongko W, Moore A, McAdoo B, Goff J, Harbitz C, Synolakis C, et al. (2007) Extreme runup from the 17 July 2006 Java tsunami, Geophys Res Lett 34: L12602, doi:10.1029/ 2007GL029404. Fritz HM, Mohammed F, Yoo J (2009) Lituya bay landslide impact generated megatsunami 50th anniversary. Pure Appl Geophys 166:153–175, doi:10.1007/s00024–008–0435–4. Glimsdal S, Pedersen G, Langtangen H, Shuvalov V and Dypvik H (2007) Tsunami generation and propagation from the Mjølnir asteroid impact. Meteorit Planet Sci 42:1473–1493. Glimsdal S, Pedersen G, Atakan K, Harbitz CB, Langtangen H and Løvholt F (2006) Propagation of the Dec. 26, 2004 Indian Ocean Tsunami: effects of dispersion and source characteristics. Int J Fluid Mech Res 33:15–43. Grilli ST and Watts P (2005) Tsunami generation by submarine mass failure I: Modeling, experimental validation, and sensitivity analyses. J Waterway Port Coast Ocean Eng 131:283–297. Heinrich P (1992) Nonlinear water waves generated by submarine and aerial landslides. J Waterway Port Coastal Ocean Eng 118:249–266. Liu P-F, Wu T-R, Raichlen F, Synolakis CE and Borrero JC (2005) Runup and rundown generated by three-dimensional sliding masses. J Fluid Mech 536:107–144. Loualalen M, Asavanant J, Kaewbanjak N, Grilli ST, Kirby JT and Watts P (2007) Tsunami generation by submarine mass failure: 1. Modeling of the 2004 Indian Ocean tsunami: Case study impact in Thailand. J Geophys Res 112:C07024, doi: 10.1029/2006JC003850. Müller L (1964) The rock slide in the Vajont Valley. Rock Mech Eng Geol 2:148–212. Panizzo A, De Girolamo P and Petaccia A (2005) Forecasting impulse waves generated by subaerial landslides. J Geophys Res 110:C12025, doi:10.1029/2004JC002778. Raffel M, Willert C and Kompenhans J (1998) Particle Image Velocimetry. Springer, Berlin. 718 F. Mohammed and H.M. Fritz Synolakis CE, Bardet JP, Borrero J, Davies H, Okal E, Silver E, Sweet J and Tappin D (2002) Slump origin of the 1998 Papua New Guinea tsunami, Proc Roy Soc Lond Ser. A, 458: 763–789. Tanaka M (1986) The stability of solitary waves. Phys Fluids 29:650–655. Tinti S, Manucci A, Pagnoni G, Armigliato A and Zaniboni R (2005) The 30 December 2002 landslide-induced tsunamis in Stromboli: sequence of the events reconstructed from the eyewitness accounts. Nat Hazards Earth Sys Sci 5:763–775. Tinti S, Maramai A, Armigiliato A, Graziani L, Manucci A, Pagnoni G and Zanoboni F (2006) Observations of physical effects from tsunamis of December 30, 2002 at Stromboli volcano, Southern Italy, Bull Volcanol 68:450–461. Walder JS, Watts P, Sorensen OE and Janssen K (2003) Tsunamis generated by subaerial mass flows. J Geophys Res 108(B5):2236. Watts P (2000) Tsunami features of solid block underwater landslides. J Waterway Port Coastal Ocean Eng 126:144–152. Weiss R, Fritz HM and Wuennemann K (2009) Hybrid modeling of the mega-tsunami runup in Lituya Bay after half a century. Geophys Res Lett, 36, L09602, doi:10.1029/2009GL037814.