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The characteristics of a tsunami generated by a submarine landslide are mainly determined by the volume, the initial acceleration, the maximum velocity, and the possible retrogressive behaviour of the landslide. The influence of these features as well as water depth and distance from shore are discussed. Submarine landslides are often clearly sub-critical (Froude number <<1), and it is explained that the maximum tsunami elevation generally correlates with the product of the landslide volume and acceleration divided by the wave speed squared. Only a limited part of the potential energy released by the landslide is transferred to wave energy. Examples of numerical simulations with fractions of 0.1-15 % are presented. Frequency dispersion is of little importance for waves generated by large and sub-critical submarine landslides. Retrogressive landslide behaviour normally reduces associated tsunami heights, but retrogression might increase the height of the landward propagating wave for unfavourable time lags between release of individual elements of the total landslide mass. Tsunamis generated by submarine landslides often have very large run-up heights close to the source area, but have more limited far-field effects than earthquake tsunamis. It is further shown that the combination of landslides and earthquakes may be necessary to explain observed tsunami behaviour. The various aspects mentioned above are exemplified by simulations of the Holocene Storegga Slide, the 1998 Papua New Guinea, and the 2004 Indian Ocean tsunamis. Comparisons are also made to tsunamis generated by rock slides. Rock slides are most often super-critical and the resulting tsunamis are determined by the frontal area of the rock slide, the impact velocity of the rock slide on the water body, the permeability of the rock slide, and the bathymetry. [ABSTRACT FROM AUTHOR]

Abstract: Tsunami generation by submarine slides have been a major concern in the risk assessment for the Ormen Lange gas field off Western Norway. Tsunamis are analysed with a numerical model supplemented by an analytical one. Both models show how slide extensions and slide dynamics influence the tsunamigenic potential for a large region. Several combinations of slide parameters were tested, and the product of initial acceleration and the volume of the slide gave the best correlation with the maximum surface elevation for the near coastal domain. [Copyright &y& Elsevier]

Natural hazard and risk analysis are normally conducted based on a limited number of "credible worst-case scenarios", each with a corresponding probability. Such a scenario-based approach is computationally not too costly (in terms of number of simulations) and might seem more appropriate when there are few previous events in the region, giving limited opportunities to establish magnitude frequency distribution (MFD). However, uncertainties are not quantified and hazard zoning is simply made by a single line separating between no-hazard and hazard (at the best with a corresponding probability), and it is hard to relate the results to the safety classes based on a set of different probabilities of impact. An alternative to the scenario-based approach is a probabilistic approach (using event tree) where a large number of scenarios are analysed based on frequency distributions (uncertainties) included in all steps, e.g. for landslides, uncertainties in location, release, volume, configuration, etc. are included. The results of the various simulations are integrated in an event tree analysis to calculate exceedance probability maps, which are in turn adapted to various safety classes in the Norwegian Planning and Building Act.In the presented work we sketch a framework for the probabilistic approach to natural hazard analysis where both frequency distributions and uncertainties are included. In the absence of data or statistics on previous events, expert judgement is often needed to a large extent, among others to establish (discrete) frequency distributions. The approach may be used for several types of natural hazards. The framework is demonstrated by an example of rockslide hazard analysis. We also show how secondary effects (e.g. run-up of tsunami generated by subaerial rockslides) can be included in the framework. Factoring in probabilities in all stages implies that previously designated danger areas (based on a limited number of conservative scenarios) can be released. [ABSTRACT FROM AUTHOR]

Landslides are the second most frequent tsunami source worldwide. However, their complex and diverse nature of origin combined with their infrequent event records make prognostic modelling challenging. In this paper, we present a probabilistic framework for analysing uncertainties emerging from the landslide source process. This probabilistic framework employs event trees and is used to conduct tsunami uncertainty analysis as well as probabilistic tsunami hazard analysis (PTHA). An example study is presented for the Lyngen fjord in Norway. This application uses a mix of empirical landslide data combined with expert judgement to come up with probability maps for tsunami inundation. Based on this study, it is concluded that the present landslide tsunami hazard analysis is largely driven by epistemic uncertainties. These epistemic uncertainties can be incorporated in the probabilistic framework. Conducting a literature analysis, we further show examples of how landslide and tsunami data can be used to better constrain landslide uncertainties, combined with statistical and numerical analysis methods. We discuss how these methods, combined with the probabilistic framework, can be used to improve landslide tsunami hazard analysis in the future. [ABSTRACT FROM AUTHOR]

Abstract: In the aftermath of the 2004 Indian Ocean tsunami, a large increase in the activity of tsunami hazard and risk mapping is observed. Most of these are site-specific studies with detailed modelling of the run-up locally. However, fewer studies exist on the regional and global scale. Therefore, tsunamis have been omitted in previous global studies comparing different natural hazards. Here, we present a first global tsunami hazard and population exposure study. A key topic is the development of a simple and robust method for obtaining reasonable estimates of the maximum water level during tsunami inundation. This method is mainly based on plane wave linear hydrostatic transect simulations, and validation against results from a standard run-up model is given. The global hazard study is scenario based, focusing on tsunamis caused by megathrust earthquakes only, as the largest events will often contribute more to the risk than the smaller events. Tsunamis caused by non-seismic sources are omitted. Hazard maps are implemented by conducting a number of tsunami scenario simulations supplemented with findings from literature. The maps are further used to quantify the number of people exposed to tsunamis using the Landscan population data set. Because of the large geographical extents, quantifying the tsunami hazard assessment is focusing on overall trends. [Copyright &y& Elsevier]

Abstract: Tsunami generation from submarine gravity mass flows is investigated using linear two-dimensional analytical models, a simplified slide geometry, and a prescribed sub-critical slide velocity. Slide characteristics as maximum slide velocity, initial acceleration, slide length, and thickness, are all found to determine the characteristics of the tsunami. Effects of dispersion usually turn out to be of minor practical importance. Tsunamis due to retrogressive slides are generally smaller than for a similar fixed shaped slide with the same characteristics due to an increased duration of slide mass mobilisation. However, above the rear of the slide, the surface elevation can also be increased for small time lags. [Copyright &y& Elsevier]

The Black Lake rockslide is located on the east wall of an open-pit mine initially operated by LAB Chrysotile near Thetford Mines, Quebec. Movements were observed in July 2012 when a volume of 2.0 × 107 m3 was mobilized, destroying a large portion of Highway 112. Mining operations ceased in 2012, causing the complete shutdown of the pumping system whose goal was to prevent the rise of water level in the pit. As the water level increases in the pit, it is essential to determine the potential of tsunami generation by possible partially submerged rockslides and to understand the potential impacts. A series of possible scenarios have been analysed with regard to velocity and acceleration of the potential rockslide as well as the corresponding wave generation and inundation. Results from the simulation show that when the factor of safety of the global slope is less than unity, inundation would not reach the potentially vulnerable infrastructures. Maximum wave height will vary as a function of the filling of the lake, and the lower wave height relative to water depth will happen when the lake is completely filled. [ABSTRACT FROM AUTHOR]

Abstract: Applying probabilistic methods to infrequent but devastating natural events is intrinsically challenging. For tsunami analyses, a suite of geophysical assessments should be in principle evaluated because of the different causes generating tsunamis (earthquakes, landslides, volcanic activity, meteorological events, and asteroid impacts) with varying mean recurrence rates. Probabilistic Tsunami Hazard Analyses (PTHAs) are conducted in different areas of the world at global, regional, and local scales with the aim of understanding tsunami hazard to inform tsunami risk reduction activities. PTHAs enhance knowledge of the potential tsunamigenic threat by estimating the probability of exceeding specific levels of tsunami intensity metrics (e.g., run‐up or maximum inundation heights) within a certain period of time (exposure time) at given locations (target sites); these estimates can be summarized in hazard maps or hazard curves. This discussion presents a broad overview of PTHA, including (i) sources and mechanisms of tsunami generation, emphasizing the variety and complexity of the tsunami sources and their generation mechanisms, (ii) developments in modeling the propagation and impact of tsunami waves, and (iii) statistical procedures for tsunami hazard estimates that include the associated epistemic and aleatoric uncertainties. Key elements in understanding the potential tsunami hazard are discussed, in light of the rapid development of PTHA methods during the last decade and the globally distributed applications, including the importance of considering multiple sources, their relative intensities, probabilities of occurrence, and uncertainties in an integrated and consistent probabilistic framework. [ABSTRACT FROM AUTHOR]

Much remains to understand the dynamic processes during the flow of submarine landslides. A first relevant problem is to explain the extraordinary mobility of submarine landslides, which has no comparison in subaerial mass movement. Another challenging question is the apparent disparity between submarine landslides that remain compact for hundreds of kilometres and those that disintegrate during the flow, finally evolving into turbidity currents. This problem is linked to a central ongoing debate on the relative importance of turbidity currents versus submarine landslides in reshaping the continental margin. Based on three epitomic case studies and on laboratory experiments with artificial debris flows of various composition, we suggest a possible explanation for the disparity between compact and disintegrating landslides, identifying the clay-to-sand ratio as the key control parameter. [ABSTRACT FROM AUTHOR]

Abstract: Multibeam bathymetry and seismic data disclose three submarine slides in the outer Boknafjord area, SW Norway. The largest slide (Arsneset slide) has a volume of ca. 28×106 m3. The scar of this slide is 15–30 m high and it covers an area of ca. 1.4×106 m2. Seismic data on sediment thicknesses and sedimentation rate estimates from radiocarbon dating indicate that this slide occurred ca. 10000 14C yr BP. 2D and 3D simulations of the tsunami generated by the slide indicate run-up heights on the neighbouring Galta peninsula of 2.5–4 m at a slide velocity of 25 m s−1. Possible higher slide velocities would have caused waves reaching higher areas. An archaeological excavation on the Galta peninsula at Rennesøy yielded approximately 17500 flint artefacts of Late Palaeolithic/Early Mesolithic age in an up to 1 m thick beach sediment sequence. The archaeological material combined with sedimentological and shoreline displacement data limit the occupation time of the settlements to approximately 10000–9700 14C yr BP, which makes them to one of the oldest known Stone Age settlements in southern Norway. There is no evidence of transgressions between 10200 and 9500 14C yr BP, which could explain erosion of settlements and the presence of flint artefacts within the beach sediment sequence. It is thus possible that the oldest settlements were flooded and eroded away by a slide-generated tsunami. Artefacts and sediments were transported downslope into the sea and were subsequently reworked by waves during continued isostatic uplift. [Copyright &y& Elsevier]

There is an urgent need to improve the basic understanding of geohazards and our ability to deal with the risks associated with them. The International Centre for Geohazards (ICG) does research on the assessment, prevention and mitigation of geohazards, offshore as well as on land. The main focus is placed on landslides and their effects, such as tsunamis. Activities include hazard and risk assessment for slides and earthquakes, evaluation of soil and rock slopes, instrument design and monitoring, geophysical methods, field studies, application of SAR technology for monitoring of slopes, further development of GIS as a tool in geohazard assessment, tsunami research, and numerical modelling. Education is given high priority, and graduate programmes in geohazards have been established at both the University of Oslo and at NTNU in Trondheim. Over the next few years, emphasis will also be placed on monitoring, early warning systems, and mitigation measures. [ABSTRACT FROM AUTHOR]

Abstract: Several submarine debris flows show an apparently chaotic frontal part with blocks of variable size (from roughly tens to some hundreds of metres) located some distance beyond the front of the main deposits. This outrunner phenomenon was studied both in the field and in laboratory experiments. Depositional patterns in a field case (Finneidfjord, northern Norway) are classified from the outer distal part of the debris flow to the outermost outrunner block. Similar patterns were found in experimental debris flows, and we suggest that flow processes in the laboratory are applicable to the field example. Theoretical investigations are applied to assess frontal dynamics and especially the formation and motion of outrunner blocks. As the front of the debris flow pushes through ambient water, a combination of front pressure and lift force allows for intrusion of a water layer underneath the front (hydroplaning). This water layer reduces basal friction and induces tensile stresses farther behind the front, leading to a possible detachment and decoupling with respect to the main slide body. These outrunner blocks show an increased mobility compared to the main slide body and deposition of such blocks may occur far away from the main slide body. [Copyright &y& Elsevier]

Abstract: A set of laboratory experiments on subaqueous debris flows is reported where total stress as well as pore pressure transducers were mounted in the bed. Sediment texture ranging from clayey (viscoplastic) to sandy (granular) were used in the experiments, in order to investigate changes in pressure evolution. The pressure readings confirm earlier studies suggesting that the front of the subaqueous clayey debris flow is hydroplaning on a thin layer of water, which causes low bed friction. Fronts of sandy debris flows show a fluidized head where bed friction is minimal. [Copyright &y& Elsevier]