Subaqueous Landslides Research Articles

Morphometric fingerprints and downslope evolution in bathymetric surveys: insights into morphodynamics of the Congo canyon-channel

Submarine canyons and channels are globally important pathways for sediment, organic carbon, nutrients and pollutants to the deep sea, and they form the largest sediment accumulations on Earth. However, studying these remote submarine systems comprehensively remains a challenge. In this study, we used the only complete-coverage and repeated bathymetric surveys yet for a very large submarine system, which is the Congo Fan off West Africa. Our aim is to understand channel-modifying features such as subaqueous landslides, meander-bend evolution, knickpoints and avulsions by analyzing their morphometric characteristics. We used a new approach to identify these channel-modifying features via morphometric fingerprints, which allows a systematic and efficient search in low-resolution bathymetry data. These observations have led us to identify three morphodynamic reaches within the Congo Canyon-Channel. The upper reach of the system is characterized by landslides that can locally block the channel, storing material for extended periods and re-excavating material through a new incised channel. The middle reach of the system is dominated by the sweep and swing of meander bends, although their importance depends on the channel’s age, and the time since the last up-channel avulsion. In the distal and youngest part of the system, an upstream migrating knickpoint is present, which causes multi-stage sediment transport and overspill through an underdeveloped channel with shallow depths. These findings complement previous less-detailed morphometric analyses of the Congo Canyon-Channel, offering a clearer understanding of how submarine canyon-channels can store sediment (due to channel-damming landslides, meander point bars, levee building due to overspill), re-excavate that sediment (via thalweg incision, meander propagation, knickpoint migration) and finally transport it to the deep sea. This improved understanding of the morphodynamics of the Congo Canyon-Channel may help to understand the evolution of other submarine canyon-channels, and assessment of hazards faced by seabed infrastructure such as telecommunication cables.

Numerical Reconstruction of Landslide Paleotsunami Using Geological Records in Alpine Lake Aiguebelette

AbstractMass movements and delta collapses are significant sources of tsunamis in lacustrine environments, impacting human societies enormously. Paleotsunamis studies play an essential role in understanding historical events and their consequences, along with their return periods. This study investigates a paleotsunami induced by a subaqueous mass movement during the Younger Dryas to Early Holocene transition, ca. 11,700 years ago in Lake Aiguebelette (NW Alps, France). Utilizing high‐resolution seismic and bathymetric surveys associated with sedimentological, geochemical, and magnetic analyses, we uncovered a paleotsunami triggered by a seismically induced mass transport deposit. Numerical simulations of mass movement have been conducted using a visco‐plastic Herschel‐Bulkley rheological model and corresponding tsunami wave modeled with dispersive and nondispersive models. Our findings reveal for the first time that dispersive effects may be negligible for subaqueous landslides in a relatively small lake. This research reconstructs a previously unreported paleotsunami event and enhances our understanding of tsunami dynamics in lacustrine environments.

Focused fluid discharge as subaqueous landsliding factor, an example of Krasnoyarskiy landslide, the Lake Baikal

There are represented results of Krasnoyarskiy subaqueous landslide researches in this paper. Landslide is located at subaqueous part of delta of the Selenga river. A multidisciplinary approach was applied to the study of the landslide, including seismo-acoustic, lithological, gas-geochemical and geotechnical studies. Obtained data from landslide and surrounding soils allowed to put forward a hypothesis, whereby a key factor to landslide origin was been high gas saturation of the soils and reason of landslide was an earthquake. The proposed approach to the studying of bottom soils in lakes and seas can be applied both in assessing their stability and in searching for focus fluid discharging zones at the bottom in areas associated with hydrocarbon deposits in the sedimentary section. Also, approach can be applied in mapping of permafrost melting in Arctic region offshore, where gases are often accumulating below it.

Subaqueous landslides associated with historical road improvements in steep glaciated terrain, Loch Lomond, western Scotland

Shorelines in steep glaciated terrain are focal points for development and can provide important natural corridors for transport (e.g. road, rail). However, the steep subaqueous slopes at nearshore sites present challenging ground conditions, and only in recent decades has the acquisition of continuous high-resolution bathymetric datasets become available to inform investigations. This study investigates a site in Loch Lomond, Scotland, where a reported displacement of 15 000 m 3 of rock fill occurred prior to completion and stabilization of an embankment for the A82 road, during improvement work undertaken in the 1980s. We revisit the area using new multibeam swath bathymetry, shallow sub-bottom seismic data and geomorphological mapping, as well as borehole logs from the original ground investigation. The bathymetric and seismic data provide strong evidence for older subaqueous landslide activity at the site. The data indicate that embankment construction was also associated with occurrence of subaqueous landslides, incorporating a total volume of up to 95 000 m 3 . The research demonstrates the value of nearshore geophysical datasets in steep glaciated terrain, both for understanding geomorphological response to past shoreline modifications and as part of investigations where future developments (e.g. transport, energy infrastructure) are planned.

Development of Chaos Terrain as Subaqueous Slide Blocks in Galilaei Crater, Mars

Chaos terrain, expressed as enigmatic blocky landscapes on Mars, has poorly understood origins. Several hypotheses have been put forward to explain chaos terrain formation, but none fully account for the morphologies observed in Galilaei crater, the focus of this study. Previously inferred to be a paleolake, Galilaei crater hosts chaos terrain composed of kilometer-scale, disorganized blocks around the southern and southeastern margin of the crater. Blocks are concentrated near the base of the crater wall, with blocks of decreasing size extending into the crater interior. The crater wall slope in regions where these chaos blocks are present is notably lower than in regions where blocks are absent. Based on the observed morphologies, we propose the chaos terrain in Galilaei crater formed by gravity-driven slope failure and down-slope transport as subaqueous landslides and mass flows, initiated at a time when the paleolake level was still high. We propose and discuss Earth analogs for the observed terrain and use mapping-constrained spatiotemporal relationships to reconstruct the sequence of landform development. Subaqueous landslides represent an uncommonly invoked mechanism to explain chaos terrain on Mars, reinforcing the idea that one mechanism cannot explain the diversity of this enigmatic terrain.

Episodic movement of a submarine landslide complex driven by dynamic loading during earthquakes

Although subaqueous slopes on active continental margins are subject to a variety of failure styles, their movement mechanisms during earthquakes remain poorly constrained. A primary explanation is that few submarine landslides have been directly sampled for detailed investigation. We have conducted a series of dynamic shear experiments on samples recovered from the base of the Tuaheni Landslide Complex, located off the east coast of the North Island of New Zealand, to explore its behaviour during earthquakes. Our experiments suggest that whilst the basal landslide sediments can be prone to liquefaction in certain conditions, this is not a likely failure mechanism at the stress states operating in the low angled shear zone at the base of this landslide system. Instead, episodic landslide movement can occur through basal sliding when pore water pressures increase sufficiently to lower the shear zone effective stress to the material failure envelope. These low effective stress conditions are most likely to be reached during earthquakes that produce large amplitude, long duration ground shaking. The observed behaviour provides a credible mechanism through which subaqueous landslides moving on low angled shear zones in similar materials may be subject to episodic movement during earthquakes without undergoing catastrophic failure.

Propagation of frontally confined subaqueous landslides: Insights from combining geophysical, sedimentological, and geotechnical analysis

Subaquatic mass movements are common in marine and lacustrine environments, but due to their barely predictable nature, direct observations of these processes are limited so that knowledge is only indirectly obtained by investigating the resulting mass-transport deposits (MTDs). Most research focuses on the most common frontally emergent slides, fast-moving events able to generate turbidity currents and tsunamis. Geohazards of frontally confined slides and mechanisms behind their typical fold-and-thrust deformation structures are however still poorly understood.We investigate frontally confined MTDs in Lake Lucerne (Switzerland) by integrating bathymetric and high-resolution seismic data with geotechnical information derived from in situ Cone Penetrometer Tests and short core analysis. Investigated MTDs consist of three units: i) a mass-slide deposit, located at the base of the slope consisting of a coherent slope sequence, ii) a fold-and-thrust system developed in basin sediments, and iii) an overrunning mass flow deposit, consisting of remolded slope sediments. The deformed and thrusted basin sediments show higher undrained shear strength compared to the undisturbed basin sequence. We propose that this strengthening is caused by lateral compression leading to fluid expulsion in the high-plasticity basin sediments by the bulldozing sliding mass. Relative kinematic indicators document that the fold-and-thrust deformation structures occur rapidly. Thus, they should be considered in tsunami hazard analysis. Furthermore, our data highlight that the slope angle of the gliding surface and basin topography are key controlling factors for slope stability and propagation of basin-plain deformations, respectively. Our integrated study supports and refines propagation models proposed in marine environments, revealing the potential of investigating smaller-scale easier-to-access MTDs in lakes.

Controlling factors for post-failure evolution of subaqueous landslides

Subaqueous slope failures can evolve in various patterns. Whereas some slides run out and further evolve into highly mobile turbidity currents, others maintain a continuum-like structure and remain frontally confined. The different failure modes impose different hazard scenarios, making an understanding of their origin crucial for reliable hazard assessments. Yet many of the factors controlling their post-failure behaviour remain not well understood. In this paper, a procedure is presented for the analysis of the post-failure evolution of subaqueous landslides, using a coupled Eulerian–Lagrangian finite-element analysis approach. The procedure is applied to analyse the St Niklausen slide in Lake Lucerne (Switzerland), providing a good prediction of observed landslide features, without back-calibration of input parameters. The approach is further applied to investigate the influence of controlling parameters, highlighting effects of different strength parameters, the surrounding water and the slope stratigraphy and geometry on the landslide dynamics. The procedure presented can be generally applied to predict the post-failure evolution of subaqueous landslides and facilitates the extraction of the moving soil–water boundary, which can serve as source input for tsunami propagation modelling.

Morphology of small-scale submarine mass movement events across the northwest United Kingdom

A review of multibeam echo sounder (MBES) survey data from five locations around the United Kingdom northwest coast has led to the identification of a total of 14 separate subaqueous mass movement scars and deposits within the fjords (sea lochs) and coastal inlets of mainland Scotland, and the channels between the islands of the Inner Hebrides. In these areas, Quaternary sediment deposition was dominated by glacial and glaciomarine processes. Analysis of the morphometric parameters of each submarine mass movement has revealed that they fall into four distinct groups of subaqueous landslides; Singular Slumps, Singular Translational, Multiple Single-Type, and Complex (translational & rotational) failures. The Singular Slump Group includes discrete, individual subaqueous slumps that exhibit no evidence of modification through the merging of several scars. The Singular Translational Group comprise a single slide that displays characteristics associated with a single translational (planar) failure with no merging of multiple events. The Multiple Single-Type Group incorporates scars and deposits that displayed morphometric features consistent with the amalgamation of several failure events of the same type (e.g. debris flows or slumps). Finally, the Complex (translational & rotational) Group comprises landslides that exhibited complex styles of failures, including both translational and rotational mechanisms controlling the same slide. The submarine mass movements that comprise this dataset are then discussed in relation to global fjordic and glaciomarine nearshore settings, and slope failure trigger mechanisms associated with these environments are described with tentative links to individual submarine landslides from the database, where appropriate. It is acknowledged that additional MBES data are needed not only to expand this database, but also in order to create a more statistically robust study. However, this initial study provides the basis for a much wider investigation of subaqueous mass movements and correlations between their morphometric parameters.

Centrifuge modelling of static liquefaction in submarine slopes: scaling law dilemma

The scaling laws for the centrifuge modelling of the initiation and propagation of static liquefaction in submerged slopes are investigated in this paper. A theoretical model is developed to analytically determine the scaling factor of fluid viscosity in simulating the onset of static liquefaction by detailed analysis of the hydromechanical processes at the grain scale. Based on this, a fluid with a viscosity of [Formula: see text]-times that of water ([Formula: see text]-fluid) is suggested, where N is the geometrical scaling factor in centrifuge modelling. A fluid with a viscosity of N-times that of water (N-fluid) was adopted for simulating dynamic events in the centrifuge; N-fluid is used and suggested by previous researchers. Centrifuge tests were designed to examine and verify the scaling factors for pore fluid viscosity in simulating the onset of static liquefaction and the post-liquefaction behaviour of subaqueous landslides. These tests were performed at 10g, 30g, and 50g conditions, with [Formula: see text]-fluid, N-fluid or water, where g is the Earth’s gravitational acceleration. Results confirm that the correct scaling factors (prototype/model) for pore fluid viscosity are [Formula: see text] and 1/N for investigating the onset of static liquefaction and the post-failure behaviour of the submarine slopes, respectively.

About this title - Subaqueous Mass Movements and their Consequences: Advances in Process Understanding, Monitoring and Hazard Assessments

This volume focuses on underwater or subaqueous landslides with the overarching goal of understanding how they affect society and the environment. The new research presented here is the result of significant advances made over recent years in directly monitoring submarine landslides, in standardizing global datasets for quantitative analysis, constructing a global database and from leading international research projects. Subaqueous Mass Movements demonstrates the breadth of investigation taking place into subaqueous landslides and shows that, while events like the recent ones in the Indonesian archipelago can be devastating, they are at the smaller end of what the Earth has experienced in the past. Understanding the spectrum of subaqueous landslide processes, and therefore the potential societal impact, requires research across all spatial and temporal scales. This volume delivers a compilation of state-of-the-art papers covering topics from regional landslide databases to advanced techniques for in situ measurements, to numerical modelling of processes and hazards.

Towards a national-scale assessment of the subaqueous mass movement hazard in Canada

Abstract Characterized by an active margin to the west, passive margins to the east and north, and numerous fjords and estuaries, the seafloor of Canada is prone to subaqueous landslides. The Geological Survey of Canada (GSC) facilitates government response in times of crisis by providing timely and concise information to Canadians, and informs the strategies to address natural hazards. Thus, the GSC is conducting a national assessment of the subaqueous landslide hazard. This paper reviews dozens of major subaqueous mass movement deposits with an emphasis on recent publications and summarizes the attempt to produce a national database. The types range from ephemeral turbidity current deposits to very large deposits (>100 km 3 ). To date, 1266 deposits are identified with many more expected as mapping progresses. This work is important as it will feed into the larger national tsunami strategy, and is a step forward for the national government to manage the risk. Canada is among the first countries to enter its entire database using the consistent morphometric characterization recommended by members of the UNESCO IGCP-640 (S4SLIDE) Community.

Subaqueous mass movements in the context of observations of contemporary slope failure

Abstract The consequences of subaqueous landslides have been at the forefront of societal conscience more than ever in the last few years, with devastating and fatal events in the Indonesian Archipelago making global news. The new research presented in this volume demonstrates the breadth of ongoing investigation into subaqueous landslides, and shows that while events like the recent ones can be devastating, they are smaller in scale than those Earth has experienced in the past. Understanding the spectrum of subaqueous landslide processes, and therefore the potential societal impact, requires research across all spatial and temporal scales. This volume delivers a compilation of state-of-the-art papers covering regional landslide databases, advanced techniques for in situ measurements, numerical modelling of processes and hazards.

A scenario-based assessment of the tsunami hazard in Palermo, northern Sicily, and the southern Tyrrhenian Sea

Abstract Palermo is a populous city situated on the northern coast of Sicily, bordered by the Tyrrhenian Sea. This central part of the Mediterranean Sea features dramatic bathymetry, numerous subaqueous landslides and is also the epicentre to many subaqueous earthquakes. As such, the region is an area prone to tsunamis. This investigation uses the Cornell Multi-Grid Coupled Tsunami (COMCOT) tsunami modelling package to simulate five near-field landslides, and five near-field earthquakes regarded as worst-case credible scenarios for Palermo. The seismic simulations produced waves on a very small scale, the largest being c. 5 cm at its maximum height, and none of the earthquake-generated tsunami waves produced any measurable inundation. The landslide simulations produced larger waves ranging from 1.9 to 12 m in maximum height, two of which resulted in inundation in areas surrounding the Port of Palermo. Sensitivity analysis identified that fault width and dislocation as well as landslide-specific gravity did have significant influence over maximum wave height, inundation and maximum run-up wave height. There are methodological issues limiting the extent to which this study forms a comprehensive tsunami hazard assessment of Palermo, such as gaps in bathymetric data, computational restrictions and lack of a probabilistic element. These issues are counteracted by the fact that this study does serve as a robust first step in identifying that landslides in the region may produce larger tsunami waves than earthquakes, and that the directionality of mass movement is critical in landslide-driven tsunami propagation in the southern Tyrrhenian region.

Deep‐water sediment transport patterns and basin floor topography in early rift basins: Plio‐Pleistocene syn‐rift of the Corinth Rift, Greece

AbstractOur current understanding on sedimentary deep‐water environments is mainly built of information obtained from tectonic settings such as passive margins and foreland basins. More observations from extensional settings are particularly needed in order to better constrain the role of active tectonics in controlling sediment pathways, depositional style and stratigraphic stacking patterns. This study focuses on the evolution of a Plio‐Pleistocene deep‐water sedimentary system (Rethi‐Dendro Formation) and its relation to structural activity in the Amphithea fault block in the Corinth Rift, Greece. The Corinth Rift is an active extensional basin in the early stages of rift evolution, providing perfect opportunities for the study of early deep‐water syn‐rift deposits that are usually eroded from the rift shoulders due to erosion in mature basins like the Red Sea, North Sea and the Atlantic rifted margin. The depocentre is located at the exit of a structurally controlled sediment fairway, approximately 15 km from its main sediment source and 12 km basinwards from the basin margin coastline. Fieldwork, augmented by digital outcrop techniques (LiDAR and photogrammetry) and clast‐count compositional analysis allowed identification of 16 stratigraphic units that are grouped into six types of depositional elements: A—mudstone‐dominated sheets, B—conglomerate‐dominated lobes, C—conglomerate channel belts and sandstone sheets, D—sandstone channel belts, E—sandstone‐dominated broad shallow lobes, F—sandstone‐dominated sheets with broad shallow channels. The formation represents an axial system sourced by a hinterland‐fed Mavro delta, with minor contributions from a transverse system of conglomerate‐dominated lobes sourced from intrabasinal highs. The results of clast compositional analysis enable precise attribution for the different sediment sources to the deep‐water system and their link to other stratigraphic units in the area. Structures in the Amphithea fault block played a major role in controlling the location and orientation of sedimentary systems by modifying basin‐floor gradients due to a combination of hangingwall tilt, displacement of faults internal to the depocentre and folding on top of blind growing faults. Fault activity also promoted large‐scale subaqueous landslides and eventual uplift of the whole fault block.

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

A granular landslide impacting a river may lead to the formation of a landslide dam blocking the streamflow, and subsequently create a barrier lake. Should a barrier lake outburst, the flood may be destructive and spell disastrous consequences downstream. The last decade or so has witnessed a number of experimental and numerical investigations on barrier lake outburst flooding, whilst studies on barrier lake formation remain rare – a physically enhanced and practically viable mathematical model is still missing. Generally, barrier lake formation is characterized by multi-physical, interactive processes between water flow, multi-sized sediment transport and morphological evolution. Here, a new double layer-averaged two-phase flow model is proposed, which is an advance on existing continuum models that involve a single-phase flow assumption and presume a single sediment size, and discrete models that preclude fine grains and assume narrow grain size distributions. The proposed model is first validated against data from previous laboratory experiments of waves due to landslides impacting reservoirs and landslide dam formation over dry valleys. Then it is applied to explore the complicated mechanism and threshold for barrier lake formation. The water and grain velocities are shown to be disparate, characterizing the primary role of grains in driving water movement during subaqueous landslide motion and also demonstrating the need for a two-phase flow approach. The grain size effects are revealed, i.e., coarse grains and grain-size uniformity favour barrier lake formation. A new threshold condition is proposed for barrier lake formation, integrating the landslide-to-river momentum ratio and grain size effects. The present work facilitates a promising modelling framework for solving barrier lake formation, thereby underpinning the assessment of flood hazards due to barrier lakes.

About this title - Subaqueous Mass Movements and Their Consequences: Assessing Geohazards, Environmental Implications and Economic Significance of Subaqueous Landslides

The challenges facing submarine mass movement researchers and engineers are plentiful and exciting. This book follows several high-profile submarine landslide disasters that have reached the world's attention over the past few years. For decades, researchers have been mapping the world's mass movements. Their significant impacts on the Earth by distributing sediment on phenomenal scales is undeniable. Their importance in the origins of buried resources has long been understood. Their hazard potential ranges from damaging to apocalyptic, frequently damaging local infrastructure and sometimes devastating whole coastlines. Moving beyond mapping advances, the subaqueous mass movement scientists and practitioners are now also focussed on assessing the consequences of mass movements, and the measurement and modelling of events, hazard analysis and mitigation. Many state-of-the-art examples are provided in this book, which is produced under the auspices of the United Nations Educational, Scientific and Cultural Organisation Program S4SLIDE (Significance of Modern and Ancient Submarine Slope LandSLIDEs).

Landslide Material Control on Tsunami Genesis—The Storegga Slide and Tsunami (8,100 Years BP)

AbstractTsunami generation from subaqueous landslides is controlled by landslide kinematics, which in turn is governed by the material properties of the slide mass. Yet the effect of the material properties on tsunami genesis is poorly understood. Geomorphological observations of landslide runout put constraints on the landslide dynamics. In addition, observations of tsunami runup heights can improve our understanding of how the landslide material transforms from initiation to final runout. The giant prehistoric Storegga Slide off the mid‐Norwegian coast caused a well‐documented ocean‐wide tsunami that offers a unique setting for coupling landslide material models to tsunami generation models. In this study we simulate the dynamics of the Storegga Slide and tsunami using the depth‐averaged landslide model BingClaw, which implements visco‐plastic rheology and remolding, and couple it to a standard tsunami propagation model. A broad sensitivity study varying the landslide material strength parameters in BingClaw shows that the initial soil yield strength and remolding rate are most important for the tsunami genesis but that the residual strength determined the final runout distance. BingClaw parameters were further optimized to obtain the observed runout distance and to minimize the relative error of the tsunami runup heights. As detailed time‐dependent three‐dimensional representations of landslide parameters cannot be determined through a field investigation of the landslide itself, these simulations of the Storegga Slide and tsunami can help in the selection of plausible parameter ranges for prognostic modeling in quantitative hazard assessments.

A two-phase SPH model for massive sediment motion in free surface flows

Massive sediment motion in water with a free surface is an important kind of geophysical flows such as hyper-concentrated sediment laden river flows discharging into estuarine delta and turbidity currents generated by subaqueous landslides. One of the key and common characteristics of such flows is that interactions between water and sediment as well as those among sediment particles are equally important in affecting the sediment motion and the fluid flow. This paper presents a numerical model that builds on and extends an earlier two-phase SPH model based on a continuum formulation of solid-liquid mixtures (Shi et al., 2017) to provide a unified description of massive sediment motion in free surface flows. In the model, a constitutive law based on the rheology of dense granular flow is introduced to express the intergranular stresses while the interphase drag force is determined by combining the Ergun equation for dense solid-fluid mixtures and the power law for dilute suspensions. The proposed model is firstly applied to the study of collapse of loosely or densely packed granular columns submerged in water. The computed surface profiles of the granular column are found to be in good agreement with the experimental data. It shows that the loosely packed and the densely packed columns behave rather differently due to the differences in water-sediment interaction processes. The model is then used to simulate a dam-break flow over a mobile sediment bed. The computed configurations of the flow and the movable bed also agree well with the measured data. The predicted position on the leading edge of the flow has a mean error of 0.8% while the mean error for the maximum bed height is 12.9%. To further identify the dynamic processes involved, effects of water-sediment interactions on the motion of bed materials are investigated by examining the spatial and temporal variations of pressure and flow velocity. As shown in the applications, the proposed two-phase SPH model can successfully represent both the gravity-driven underwater granular flows and the shear flow driven intense sediment transport, implying its potential use in practical scenarios in which the two kinds of flows exist simultaneously, such as landslides triggered by storm in shallow sea and flows resulted in barrier or dam breaks.

The subaqueous landslide cycle in south-central Chilean lakes: The role of tephra, slope gradient and repeated seismic shaking

Subaqueous landslides are common features at active and passive ocean margins, in fjords and lakes. They can develop on very gentle slope gradients (<2°) and the presence of sandy tephra layers seems to facilitate the development of translational failure. Despite numerous investigations, it remains elusive how different slope preconditioning factors act and interact over time and how different triggering mechanisms can lead to slope failure. In settings of low to moderate seismicity, stratigraphic sequences with sublacustrine mass-transport deposits (MTDs) have successfully been used for constructing prehistorical earthquake catalogs. In high seismicity areas, it is inferred that not all strong earthquakes succeed in triggering landslides on the investigated slope segments, and MTD records do not fully represent their complete recurrence pattern. Here, we present the spatio-temporal distribution of MTDs in two large glacigenic Chilean lakes (Villarrica and Calafquén) based on a detailed seismic-stratigraphic analysis and several radiocarbon-dated piston cores (up to 14 m long). We find a strong influence of slope gradient on the occurrence and volume of landslide events; i.e. most (small) landslides take place on slopes of 5–20°, whereas the few large (potentially tsunamigenic) landslides exclusively occur on slopes of <4°. Liquefaction of sandy tephra layers facilitates the development of thin (<0.5 m) in-situ deformations during earthquake shaking. When sandy tephra layers get progressively buried, liquefaction becomes unlikely, but repeated excess pore pressure transfer to overlying units facilitates the development of translational sliding. The occurrence of voluminous landslides seems to follow a “landslide cycle” which starts with the deposition of a tephra layer and the development of in-situ deformations directly on top. Once the slope sequence reaches a critical thickness, the end of the cycle is indicated by incipient scarp development, and subsequent major sliding event(s). The duration of the landslide cycle is defined by the rate of gradual sedimentation, but may be affected by sudden geological events (e.g., volcanic eruptions), expediting the end of the cycle. Despite the many methodological challenges inherent to the construction of a MTD stratigraphy, we propose that well-dated multiple MTD events can be used as positive evidence to strengthen and specify the regional paleoseismic record, concerning the largest events in a high-seismicity region. This method is most successful when targeting the base of relatively steep slopes (5–20°) with frequent, minor landsliding, and complementing this with seismic-stratigraphic analysis of fluid-escape features and correlation with distal turbidite records.