Tsunamis from submarine landslides

Most tsunamis are generated by earthquakes, with secondary, less frequent, mechanisms including subaerial and submarine landslides, volcanic eruptions and (extra‐terrestrial) bolide impacts. Different mechanisms generate tsunamis with different magnitudes, travel distances and impacts. Submarine landslides had been mapped and studied for decades but records suggested that only a few had generated tsunamis, and that these were minor. It was not until 1998, when a slump on the seabed offshore of northern Papua New Guinea caused a tsunami wave up to 15 m high that killed over 2200 people, was the significance of submarine landslides in tsunami generation realised. A combination of new (multibeam) seabed mapping technology and the development of improved numerical tsunami models for tsunami generation led to the recognition of the landslide tsunami mechanism of the PNG event. As a result the hazard from submarine landslides in tsunami generation is now recognized and better understood. Extensive mapping of ocean margins reveals that submarine landslides are common. Although many of these probably generated tsunamis, few have been identified, so their hazard remains uncertain. This article describes how the hazard from submarine landslide tsunamis was first recognized, how submarine landslides generate tsunamis, why they were previously discounted as a major hazard, and their potential hazards. An important aspect of the recognition of the tsunami hazard from submarine landslides has been the significance of geology, which has contributed to a subject previously dominated by seismologists.     

Nonseismic phenomena in the generation and augmentation of tsunamis

While earthquakes generate about 90% of all tsunamis, volcanic activity, landslides, explosions, and other nonseismic phenomena can also result in tsunamis. There have been 53 000 reported deaths as a result of tsunamis generated by landslides and volcanoes. No death tolls are available for many events, but reports indicate that villages, islands, and even entire civilizations have disappeared. Some of the highest tsunami wave heights ever observed were produced by landslides. In the National Geophysical Data Center world-wide tsunami database, there are nearly 200 tsunami events in which nonseismic phenomena played a major role. In this paper, we briefly discuss a variety of nonseismic phenomena that can result in tsunamis. We discuss the magnitude of the disasters that have resulted from such events, and we discuss the potential for reducing such disasters by education and warning systems.     

3D numerical modeling of landslide-generated tsunamis around a conical island

This paper presents numerical computations of tsunamis generated by landslides falling along the flank of a conical island. The model used is the fully three-dimensional commercial code FLOW-3D, based on the VOF technique for the treatment of the free surface. The model results are compared against available experimental data that allow validation of the model, evaluation of its accuracy, and estimation of the computational costs. The main conclusion of this research is that the model is applicable at reasonable costs for a few accurate simulations that may be used for preparing precomputed inundation maps of coasts prone to the risk of tsunamis inundation.     

Effects of grain size on subaerial granular landslides and resulting impulse waves: experiment and multi-phase flow simulation

Landslides - Subaerial landslides falling into a large body of water can generate large impulse waves (tsunamis). The wave generation by subaerial landslides involves sediment, water and air, and...     

Tsunami Hazard and Risk in Canada

Tsunamis have occurred in Canada due to earthquakes, landslides, and a large chemical explosion. The Pacific coast is at greatest risk from tsunamis because of the high incidence of earthquakes and landslides in that region. The most destructive historical tsunamis, however, have been in Atlantic Canada – one in 1917 in Halifax Harbour, which was triggered by a catastrophic explosion on a munitions ship, and another in 1929 in Newfoundland, caused by an earthquake-triggered landslide at the edge of the Grand Banks. The tsunami risk along Canada's Arctic coast and along the shores of the Great Lakes is low in comparison to that of the Pacific and Atlantic coasts. Public awareness of tsunami hazard and risk in Canada is low because destructive tsunamis are rare events.     

Subaqueous landslide-triggered tsunami hazard for Lake Zurich,Switzerland

Subaqueous landslides can induce potentially damaging tsunamis. Tsunamis are not restricted to the marine environment, but have also been documented on lakes in Switzerland and worldwide. For Lake Zurich (central Switzerland), previous work documented multiple, assumedly earthquake-triggered landslides. However, no information about past tsunamis is available for Lake Zurich. In a back-analysis, we model tsunami scenarios as a consequence of the earthquake-triggered landslides in the past. Furthermore, on the basis of a recent map of the earthquake-triggered subaqueous landslide hazard, we present results of a tsunami hazard assessment. The subaqueous landslide progression, wave propagation and inundation are calculated with a combination of open source codes. Although no historic evidence of past tsunamis has been documented for Lake Zurich, a tsunami hazard exists. However, only earthquakes with long return periods are assumed to cause considerable tsunamis. An earthquake with an exceedance probability of 0.5% in 50 years (corresponding to an earthquake with a return period of 9975 years) is assumed to cause tsunamigenic landslides on most lateral slopes of Lake Zurich. A hypothetical tsunami for such an event would create damage especially along the shores of the central basin of Lake Zurich with estimated peak flow depths of up to ~?4.6 m. Our results suggest that for an earthquake with an exceedance probability of 10% in 50 years (i.e., mean return period of 475 years), no considerable tsunami hazard is estimated. Even for a worst-case scenario, the cities of Zurich and Rapperswil, located at the northern and southern ends of the lake, respectively, are assumed to experience very little damage. The presented first-order results of estimated wave heights and inundated zones provide valuable information on tsunami-prone areas that can be used for further investigations and mitigation measures.     

Spectral Characterisation of Tsunamis and Seiches Caused by Tectonism and Volcanism in Rabaul,Papua New Guinea

Tsunamis originating in Indonesia and Papua New Guinea can be locally devastating and also occasionally threaten coastal areas of northern Australia. Tsunamis may be caused by earthquakes, volcanoes or submarine landslides. In Rabaul a unique set of records exists of tsunamis and seiches generated by tectonic earthquakes, volcanic earthquakes and a volcanic eruption. Spectral analysis of the digitised waveforms has been undertaken to compare the effects of the different sources and to estimate the characteristic natural periods of Rabaul Harbour. Seiches in Rabaul Harbourhave dominant periods of 20 to 30 min, a period band that is also typical for coastal recordings of tsunamis.     

Laboratory experiments on three-dimensional deformable granular landslides on planar and conical slopes

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation.     

Hazard assessment of underwater landslide-generated tsunamis: a case study in the Padang region, Indonesia

Submarine landslides can generate local tsunamis with high run-ups, posing a hazard to human lives and coastal facilities. Both ancient (giant Storegga slide off Norwegian coast, 8200 B. P.) and recent (Papua New Guinea, 1998) events show high potential danger of tsunamigenic landslides and the importance of mitigation efforts. This contribution presents newly discovered landslides 70 km off Padang (Western Sumatra, Indonesia) based on recent bathymetry measurements. This highly populated city with over 750,000 inhabitants exhibits high tsunami vulnerability due to its very low elevation. We model tsunamis that might have been induced by the detected landslide events. Estimations of run-up heights extrapolated from offshore tsunami amplitudes for Padang and other locations in the northern Mentawai fore-arc basin yield maximum values of about 3 m. We also provide a systematic parametric study of landslide-induced tsunamis, which allows us to distinguish potentially dangerous scenarios for Padang. Inside the fore-arc basin, scenarios involving volumes of 0.5–25 km³ could endanger Padang. Apart from slide volume, the hazard distribution mainly depends on three landslide parameters: distance to Padang, water depth in the generation region, and slide direction.     

Tsunami hazard evaluation for Kuwait and Arabian Gulf due to Makran Subduction Zone and Subaerial landslides

Given the recent historical disastrous tsunamis and the knowledge that the Arabian Gulf (AG) is tectonically active, this study aimed to evaluate tsunami hazards in Kuwait from both submarine earthquakes and subaerial landslides. Despite the low or unknown tsunami risks that impose potential threats to the coastal area’s infrastructures and population of Kuwait, such an investigation is important to sustain the economy and safety of life. This study focused on tsunamis generated by submarine earthquakes with earthquake magnitudes (M _w ) of 8.3–9.0 along the Makran Subduction Zone (MSZ) and subaerial landslides with volumes of 0.75–2.0 km³ from six sources along the Iranian coast inside the AG and one source at the Gulf entrance in Oman. The level of tsunami hazards associated with these tsunamigenic sources was evaluated using numerical modeling. Tsunami model was applied to conduct a numerical tsunami simulation and predict tsunami propagation. For landslide sources, a two-layer model was proposed to solve nonlinear longwave equations within two interfacing layers with appropriate kinematic and dynamic boundary conditions. Threat level maps along the coasts of the AG and Kuwait were developed to illustrate the impacts of potential tsunamis triggered by submarine earthquakes of different scales and subaerial landslides at different sources. GEBCO 30 arc-second grid data and others were used as bathymetry and topography data for numerical modeling. Earthquakes of M _w 8.3 and M _w 8.6 along the MSZ had low and considerable impacts, respectively, at the Gulf entrance, but negligible impacts on Kuwait. An earthquake of M _w 9.0 had a remarkable impact for the entire Gulf region and generated a maximum tsunami amplitude of up to 0.5 m along the Kuwaiti coastline 12 h after the earthquake. In the case of landslides inside the AG, the majority impact occurred locally near the sources. The landslide source opposite to Kuwait Bay generated the maximum tsunami amplitudes reaching 0.3 m inside Kuwait Bay and 1.8 m along the southern coasts of Kuwait.

     

Finite element simulation of impulse wave generated by landslides using a three-phase model and the conservative level set method

A numerical model has been developed using the finite element method for the simulation of impulse waves generated by landslides. The fluid-like landslide is modeled as a generalized non-Newtonian visco-plastic fluid. A three-phase flow model based on the incompressible viscous Navier–Stokes equations is solved using the finite element method to describe the motion of the three types of fluid in landslide. The conservative level set method is expanded to n-phase flow cases and employed to capture the interface of the three phases: air, water, and the landslide. The overall performance of the approach is checked by a number of validation cases: a Rayleigh–Taylor instability problem to illustrate the capability of the proposed method to deal with interface capturing, a benchmark test of a subaerial landslide generated by an impulse wave is carried out and compared with the published experimental data and numerical results, and finally, the 1958 Lituya Bay landslide generated impulse wave, and its results are compared against a scaled-down experiment and other published numerical results. It can be noted that the current model has an excellent ability to capture the complex phenomena that occurs during the whole process of the landslide-generated impulse wave, and considering the simplified treatment of the landslide and the numerical model, fairly good agreement between computed and experimental results has been observed for all simulation cases.     

Longwave Measurements for the Coast of British Columbia and Improvements to the Tsunami Warning Capability

A few years ago the Canadian Hydrographic Service initiated a major upgrade toall tide gauges and tsunami stations on the coast of British Columbia (B.C.). Thisprogram was undertaken to address shortcomings of the earlier digital systems andwas driven by concerns about emergency response continuity in the year 2000. By1999, thirteen tide gauge stations had been installed and were operational. Three ofthese stations (Tofino, Winter Harbour, and Langara) were selected for use as tsunamiwarning stations. Several years of continuous, high quality data have now been collectedat these stations and used for analysis of long waves in the tsunami frequency band.Careful examination of these data revealed two weak tsunamis recorded by severalB.C. stations: a distant tsunami of June 23, 2001 generated by the Peru Earthquake(M_w = 8.4), and a local tsunami of October 12, 2001 induced by the Queen Charlotte Earthquake (M_w = 6.3$). Spectral characteristics of these two tsunamis are compared with the spectral characteristics of long waves generated by a strong storm (October, 2000) and of ordinary background oscillations. The topographic admittance functions (frequency responses) constructed for all stations showed that most of them (in particular, Winter Harbour, Tofino, Bamfield, Port Hardy, and Victoria) have strong resonance at periods from 2.5 to 20 min, indicating that these locations are vulnerable to relatively high-frequency tsunamis. The Winter Harbour station also has two strong resonant peaks with periods of 30 and 47 min and with amplification factors of about 7. The estimated source functions show very clear differences between long waves associated with the seismic source (typical periods 10–30 min) and those generated by a storm, which typically have shorter periods and strong energy pumping from high-frequencies due to non-linear interaction of wind waves.     

Experimental modeling of tsunamis generated by subaerial landslides: two case studies of the Three Gorges Reservoir,China

After the Gongjiafang tsunami incident, the China Geological Survey recognized the extreme importance of subaerial landslide-generated tsunamis (SLGT) in the Three Gorges Reservoir, western China. The experimental models presented in the present paper were rooted in two common failure types of high, steep slopes in the Three Gorges Reservoir. One model represents a rigid rock plunging into the water and the other is a granular cluster sliding into the water. A wide range of effective parameters were considered and studied by performing 74 laboratory tests. The effects of bed slope angle, water depth, slide impact velocity, geometry (three-dimensional size of the rigid block and grain size of the granular cluster), and volume on impulse wave characteristics were examined. Slide kinematics and impulsive wave features, such as wave shape, amplitude, run-up, and run-down, were studied and compared. Experiments showed that the failure type of the rock mass plays a key role in SLGT and strongly influences air–fluid–solid interaction. Thus, to forecast SLGT rapidly, the zone of complicated air–solid–fluid interaction can be treated as a “black box” whose output is a water wave with definable characteristics, such as amplitude. Based on the experimental results, two dimensionless equations for the estimation of primary wave maximum amplitude were developed and successfully verified for the two failure types. The study provides basic information needed to forecast tsunamis generated by slopes with the potential to fail in other reservoirs around the world. These data can also be a very useful resource for theoretical analysis or numerical model validation.     

Rainfall thresholds for rainfall-induced landslides in Slovenia

In Slovenia, rainfall-induced landslides lead to considerable damages, even causing human losses. In order to reduce the impact of this kind of landslide, several researchers analyzed rainfall-induced landslides in this country, but to date, no rainfall thresholds have been developed for a landslide warning system at national scale. In this paper, the definition of rainfall thresholds for rainfall-induced landslides in Slovenia is presented. The thresholds have been calculated by collecting approximately 900 landslide data and the relative rainfall amounts, which have been collected from 41 rain gauges. To define the thresholds, an existing procedure characterized by a high degree of objectiveness has been used. This approach is based on a software that was developed for a test site with very different characteristics (Tuscany, central Italy). At first, a single national threshold has been defined; subsequently, the country was divided into four zones, on the basis of the major river basins. The effectiveness of the thresholds has been verified by the use of several statistical parameters and it resulted in quite good performances, even if with some uncertainties, probably due to the quality of the available data. Besides the setting of a threshold system, usable for civil protection purposes at national scale, an additional outcome of this work was the possibility of applying, with good results, a methodology defined for another region, therefore testing its degree of exportability in different settings.     

Evidence of extreme wave events from boulder deposits on the south-east coast of Malta (Central Mediterranean)

Large boulder accumulations have been observed on various coasts bordering the Mediterranean and have been associated with extreme wave events such as powerful storms or tsunamis. This study provides an in-depth analysis of 430 boulder deposits, located along a 3.5 km stretch of rocky coast situated on the SE of the Maltese Islands. It includes a geomorphometric analysis of the observed boulders and use of numerical modelling to estimate wave height required to initiate boulder movement. Comparisons of aerial imagery over a period of 46 years have made it possible to identify boulder movement that could only be attributed to storm waves, given that no local tsunamigenic event has been recorded over this time period. Positioned in the central Mediterranean, the Maltese Islands are exposed to potential tsunamis generated by seismic activity associated with the Malta Escarpment, and the Calabrian and Hellenic arcs. Although imprints from historic tsunami impact cannot be excluded, results indicate that the area is exposed to strong storm waves that are capable of displacing some of the very large boulders observed on site.     

Tsunamis recorded in tide gauges at Costa Rica Pacific coast and their numerical modeling

Here we perform an inventory of tsunamis recorded by tide gauges in the Pacific coast of Costa Rica. This paper also reveals nine tsunami records that had not been published before, at Puntarenas tide gauge corresponding to the 1979 Colombia tsunami and at Quepos tide gauge corresponding to the 1985 Mexico twin tsunamis, the 2010, 2014 and 2015 Chile tsunamis, the 2006 Tonga tsunami, the 2011 Japan tsunami and the 2013 Solomon Islands tsunami. The original record of 1990 Cóbano tsunami at Quepos was digitized again at a higher resolution and re-processed. The arrival of 1979, 1985, 2006 and 2014 tsunamis to Costa Rica is not listed on tsunami catalogs. The maximum tsunami height obtained here after processing 1990, 2011 and 2013 records was higher than reported on catalogs. The opposite happened for the 2010 tsunami. Quepos gauge record for January 2007 was analyzed as it seemed to have registered the Kuril Islands tsunami, but the results were not conclusive due to the low sample rate and the small tsunami amplitude if any. All those eleven tsunamis were modeled and the results compared with the records. A good agreement was obtained for the Quepos gauge, although the modeled 2011 and 2013 tsunamis had a difference of 8 min on the arrival time. An acceptable agreement was obtained for the Puntarenas gauge for 1979 tsunami, considering at least the first 4 h of the marigram is lost.     

The hydrodynamics of landslide tsunamis: current analytical models and future research directions

Landslide-generated tsunamis are lesser-known yet equally destructive than earthquake tsunamis. Indeed, the highest tsunami wave recorded in recent history was generated by a landslide in Lituya Bay (Alaska, July 9, 1958) and produced run-up in excess of 400 m. In this paper, we review the state of the art of landslide tsunami analytical modelling. Within the framework of a linearised shallow-water theory, we illustrate the dynamics of landslide tsunami generation and propagation along beaches and around islands. Finally, we highlight some intriguing new directions in the analytical modelling of landslide tsunamis to support early warning systems.     

Evidence of extreme wave events from boulder deposits on the south-east coast of Malta (Central Mediterranean)

Large boulder accumulations have been observed on various coasts bordering the Mediterranean and have been associated with extreme wave events such as powerful storms or tsunamis. This study provides an in-depth analysis of 430 boulder deposits, located along a 3.5 km stretch of rocky coast situated on the SE of the Maltese Islands. It includes a geomorphometric analysis of the observed boulders and use of numerical modelling to estimate wave height required to initiate boulder movement. Comparisons of aerial imagery over a period of 46 years have made it possible to identify boulder movement that could only be attributed to storm waves, given that no local tsunamigenic event has been recorded over this time period. Positioned in the central Mediterranean, the Maltese Islands are exposed to potential tsunamis generated by seismic activity associated with the Malta Escarpment, and the Calabrian and Hellenic arcs. Although imprints from historic tsunami impact cannot be excluded, results indicate that the area is exposed to strong storm waves that are capable of displacing some of the very large boulders observed on site.

     

The Tsunami of August 17, 1999 in Izmit Bay,Turkey

The Kocaeli 1999 Earthquake with an Mw = 7.4 caused major hazards throughout the NW of Turkey from Tekirdag to Bolu. Historical data indicates that some of the earthquakes around Izmit Bay have caused tsunamis. In this study, tsunami research for the Kocaeli 1999 Earthquake has been made also taking into consideration historical data. In this research more than about 70 data at 35 localities have been used to determine the tsunami evidences in the bay. Coastal observations indicated runups which were ranging from 1 to 2.5 m along the shores. However, the wave runups are more complex along the south coast due to the presence of coastal landslides (Deirmendere, Halidere, Ulasli, Karamürsel) and subsided areas (Kavakli to Yeniköy) along the shore. West of Yalova, evidence of tsunami rapidly diminished. In addition, possible tectonic mechanism has been determined by using 33 single-channel high-resolution digital seismic reflection profiles which were acquired following the Kocaeli 1999 Earthquake. As a result it has been determined that the Kocaeli Earthquake has created tsunami in Izmit Bay.     

Pacific Basin tsunami hazards associated with mass flows in the Aleutian arc of Alaska

We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska using results from numerical simulation of hypothetical but plausible mass-flow sources such as submarine landslides and volcanic debris avalanches. The Aleutian arc consists of a chain of volcanic mountains, volcanic islands, and submarine canyons, surrounded by a low-relief continental shelf above about 1000–2000 m water depth. Parts of the arc are fragmented into a series of fault-bounded blocks, tens to hundreds of kilometers in length, and separated from one another by distinctive fault-controlled canyons that are roughly normal to the arc axis. The canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes. The volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large-scale sector collapse into the sea. Large scale mass-flow deposits have not been mapped on the seafloor south of the Aleutian Islands, in part because most of the area has never been examined at the resolution required to identify such features, and in part because of the complex nature of erosional and depositional processes. Extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the Aleutian Islands. Because the Aleutian arc is surrounded by deep, open ocean, mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources.To test this hypothesis we present a series of numerical simulations of submarine mass-flow initiated tsunamis from eight different source areas. We consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope. The flows have lengths that range from 40 to 80 km, maximum thicknesses of 400–800 m, and maximum widths of 10–40 km. We also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse, at four locations (Makushin, Cleveland, Seguam and Yunaska SW volcanoes), which represent large to moderate sized events in this region. We calculate tsunami sources using the numerical model TOPICS and simulate wave propagation across the Pacific using a spherical Boussinesq model, which is a modified version of the public domain code FUNWAVE. Our numerical simulations indicate that geologically plausible mass flows originating in the North Pacific near the Aleutian Islands can indeed generate large local tsunamis as well as large transoceanic tsunamis. These waves may be several meters in elevation at distal locations, such as Japan, Hawaii, and along the North and South American coastlines where they would constitute significant hazards.