Submarine landslides, commonly triggered by earthquakes, significantly affect tsunami wave heights. Subaerial landslides can also generate tsunamis (if the land flows into a body of water) and may be catastrophic in nature, causing human casualties and direct property damage. This work focuses on landslides associated with shear band that develops beneath the slipping mass. Accordingly, we consider a landslide as a dynamic process when a shear band emerges along the potential failure surface. Within this band, the shear strength decreases due to the softening behaviour of the particulate material. Material above the band moves downwards, causing the band to propagate dynamically. This already produces a landslide velocity before the slide reaches the post-failure stage and begins separating from the substrata and generating tsunami. However, existing models of tsunamigenic landslides assume zero initial slide velocity. Previous analyses of the catastrophic shear band propagation in slopes of normally- and over-consolidated sediments have shown that a relatively short initial failure zone is sufficient to cause a full-scale landslide. For the shear band to propagate, the energy produced in the body by an incremental propagation of the shear band must exceed the energy required for the propagation. This consideration separates the shear band growth into progressive (stable) and catastrophic (dynamic) stages and treats the band growth as a true physical process rather than an instantaneously appearing discontinuity. This work considers a dynamic shear band problem formulated within the framework of the Palmer and Rice’s [1973] approach. We obtain the exact, closed-form solution for the shear band and landslide velocities as well as for the spatial and temporal distributions of strain and material velocity. This solution assesses when the slide fails due to the limiting condition near the propagating tip of the shear band. We also obtain a simple asymptotic solution, which is compared to the exact solution. In the case of submerged slopes, the obtained solutions are used in landslide and tsunami height analyses. Our results suggest that the conventional static approach to the slope stability analysis leads to a significant underestimation of the slide size (volume). In most cases, the volumes of catastrophic slides are roughly twice the volumes of progressive slides. For submerged slides, this dynamic effect further manifests itself in increasing the tsunami magnitude compared to the static case.

This dissertation investigates the nature of submarine landslides along the deformation front of the northern Cascadia subduction zone. As the first slope stability analysis on the west coast of Vancouver Island, this study covers a variety of large-scale tectonic to small-scale, site-specific factors to investigate the nature of slope failure. Slope failure occurred mainly on the steep slopes of frontal ridges that were formed by compressive forces due to the subduction of the Juan de Fuca plate. Multi-beam swath bathymetry data are used to study the morphology of the whole margin and the geometry of two Holocene landslides that serve as representative examples. The overall margin stability is estimated using the critical taper theory, and a first-order limit equilibrium slope stability analysis provides threshold values for external forces to cause slope failure. The present-day pore pressure regime at different sites of the Cascadia margin is estimated from log-density data and expected ground accelerations are calculated via ground motion attenuation relationships. A comparison to threshold values derived from the limit equilibrium analysis suggests that, at present, slope stability is more sensitive to overpressure than to earthquake shaking. Differences in power spectral density derived from OBS-velocity data imply a slightly amplified ground response at the ridge crest compared to sites along the continental shelf and abyssal plain. Apart from estimating the trigger mechanisms of submarine landslides offshore Vancouver Island, a particular consideration is given to the potential link between slope failure and methane hydrate occurrence. The history of the gas hydrate stability zone (GHSZ) boundaries is investigated using information on regional sea-level history. Assuming colder ocean-bottom temperatures during the Holocene, a gradual shoaling of the BSR is inferred, which potentially could have caused hydrate melting. Pore pressure due to hydrate dissociation, as estimated by a previously developed method, varies over several orders of magnitude. Depending on sediment permeability, overpressure ratios can be comparable to threshold values. The two Holocene landslides are modeled numerically using a two-dimensional finite difference code in order to recreate the along-strike variability in ridge geometry and slide morphology observed along the northern Cascadia margin. Geometry and morphology correlate with the two prevalent slide mechanisms and model results suggest that sediment yield strength and average slide thickness are associated with the slide mechanism as well. / Graduate / 0373 / nscholz@uvic.ca

The development and activity of submarine canyons on continental margins is strongly influenced by temporal and spatial changes in sediment distribution associated with orbitally-forced sea-level cyclicity. On active margins, canyons are also strongly influenced by tectonic processes such as faulting, uplift and earthquakes. Within this framework the role of mass-wasting processes, including sediment failures, bedrock landslides and sediment gravity flows, are to: 1) transport material across the slope; 2) act as intra-slope sediment sources; and 3) shape seafloor morphology. In this project the seafloor-landscape signatures of tectonic and geomorphic processes are analysed to interpret the development of submarine canyon morphology on active margins. Datasets include high-resolution bathymetry data (Simrad EM300), multichannel seismic reflection data (MCS), high-resolution 3.5 kHz seismic reflection data, sediment cores, and dated seafloor samples. High-resolution bathymetric grids are analysed using techniques developed for terrain-roughness analysis in terrestrial landscapes to objectively map and interpret features related to seafloor mass-wasting processes. The Hikurangi subduction margin of New Zealand provides world-class examples of the control of tectonic and sedimentary processes on margin development, hosting multiple examples of deeply-incised canyon systems across a range of scales. Two main study sites, in Poverty Bay and Cook Strait, provide examples of canyon formation. From these examples conceptual and representative models are developed for the spatial and temporal relationships between active tectonic structures, geology, sediment supply, slope- and shelf-incised canyons, slope gully systems, and bedrock mass failures. The Poverty Bay site occurs on the subduction-dominated northern Hikurangi Margin, where the ~3000 km² Poverty re-entrant hosts the large Poverty Canyon system, the only shelf-break-to-subduction-trough canyon on the northern margin. The geomorphic development of the re-entrant is affected by gully development on the upper slope, and multi-cubic-kilometre-scale submarine landslides. From this site the study focuses on the initiation and development of upper-slope gullies and the role of deep-seated slope failure in upper-slope evolution. The Cook Strait site occurs on the southern Hikurangi Margin in the subduction-to-strike-slip transition zone. The 1800 km² Cook Strait Canyon incises almost 50 km into the continental shelf, with a multi-branching canyon head converging to a deeply slope-incised meandering main channel fed by multiple contributing slope canyons. Other medium-sized canyons are incised into the adjacent continental slope. Fluvial sediment supply to the coast is relatively low on the southern margin, but Cook Strait is subject to large diurnal tidal currents that mobilise sediment through the main strait area. Prior to the morphostructural analysis of the Cook Strait and Poverty study sites a revision of the tectonic structure was undertaken. In Cook Strait a revision of the available fault maps was undertaken as part of a wider, related tectonic study of the central New Zealand region. In Poverty Bay very limited prior information was available, and as part of this study the structure and stratigraphy of the entire shelf and upper slope has been interpreted. On active tectonic margins submarine canyons respond to tectonics at: 1) margin-setting scales relating to their ability to become shelf incised; 2) regional scales relating to canyon-incision response to base-level perturbations; and 3) local scales relating to propagating structures affecting canyon location and geometry. Interpretation of the spatial distribution of fluid vent sites, gully development and landslide scars leads to the conclusion that seepage-driven failure is not a primary control on the widespread instances of gully formation and landslide erosion affecting structurally-generated relief across the margin. Rather, the erosion of tectonic ridges is dominated by tectonics by: slope oversteepening; weakening of the rockmass in fault-damage zones; and triggering of slope failure by earthquake-generated cyclic loading. Deep-seated mass failures affect numerous aspects of submarine landscapes and play a major role in the enlargement of canyon systems. They enable the development of slope gully systems and represent a major intra-slope sediment source. Quantitative morphometric analysis together with MCS data indicate that landslides may evolve to be active complexes where landslide debris is remobilized repeatedly, analogous to terrestrial-earthflow processes. This process has not previously been documented on submarine slopes. A model is presented for the evolution of active margin canyons that contrasts highstand and lowstand canyon activity in terms of channel incision, sedimentary processes and slope-erosion processes. During sea-level highstand intervals, canyons become decoupled from their terrestrial/coastal sediment-supply source areas, while during sea-level lowstand intervals, canyons are coupled to fluvial and littoral sediment-supply sources, and top-down (i.e. shelf-to-lower-slope) sediment transport and channel incision is active. Canyon-head areas are incision dominated during the lowstand while mid to lower canyon reaches experience both a transient increase in sediment in storage and canyon-fill degradation and incision into bedrock. Tectonics influences the canyon landscape through both uplift-controlled perturbations to canyon base-levels and earthquake-triggering of mass movement. Following sea-level rise the sediment supply to canyon heads will be switched off at a certain threshold sea level. From this point canyon heads become aggradational. Mid to lower canyon reaches continue to incise due to continuing tectonic uplift and earthquake-triggered slope instability. Knickpoints are propagated up channel and excavate canyon and sub-canyon channels from the bottom up. Thus, while top-down infilling of non-coupled canyons occurs during sea-level highstands, the lower reaches of active margin canyons continue to incise due the influence of tectonic processes.

The development and activity of submarine canyons on continental margins is strongly influenced by temporal and spatial changes in sediment distribution associated with orbitally-forced sea-level cyclicity. On active margins, canyons are also strongly influenced by tectonic processes such as faulting, uplift and earthquakes. Within this framework the role of mass-wasting processes, including sediment failures, bedrock landslides and sediment gravity flows, are to: 1) transport material across the slope; 2) act as intra-slope sediment sources; and 3) shape seafloor morphology. In this project the seafloor-landscape signatures of tectonic and geomorphic processes are analysed to interpret the development of submarine canyon morphology on active margins. Datasets include high-resolution bathymetry data (Simrad EM300), multichannel seismic reflection data (MCS), high-resolution 3.5 kHz seismic reflection data, sediment cores, and dated seafloor samples. High-resolution bathymetric grids are analysed using techniques developed for terrain-roughness analysis in terrestrial landscapes to objectively map and interpret features related to seafloor mass-wasting processes. The Hikurangi subduction margin of New Zealand provides world-class examples of the control of tectonic and sedimentary processes on margin development, hosting multiple examples of deeply-incised canyon systems across a range of scales. Two main study sites, in Poverty Bay and Cook Strait, provide examples of canyon formation. From these examples conceptual and representative models are developed for the spatial and temporal relationships between active tectonic structures, geology, sediment supply, slope- and shelf-incised canyons, slope gully systems, and bedrock mass failures. The Poverty Bay site occurs on the subduction-dominated northern Hikurangi Margin, where the ~3000 km² Poverty re-entrant hosts the large Poverty Canyon system, the only shelf-break-to-subduction-trough canyon on the northern margin. The geomorphic development of the re-entrant is affected by gully development on the upper slope, and multi-cubic-kilometre-scale submarine landslides. From this site the study focuses on the initiation and development of upper-slope gullies and the role of deep-seated slope failure in upper-slope evolution. The Cook Strait site occurs on the southern Hikurangi Margin in the subduction-to-strike-slip transition zone. The 1800 km² Cook Strait Canyon incises almost 50 km into the continental shelf, with a multi-branching canyon head converging to a deeply slope-incised meandering main channel fed by multiple contributing slope canyons. Other medium-sized canyons are incised into the adjacent continental slope. Fluvial sediment supply to the coast is relatively low on the southern margin, but Cook Strait is subject to large diurnal tidal currents that mobilise sediment through the main strait area. Prior to the morphostructural analysis of the Cook Strait and Poverty study sites a revision of the tectonic structure was undertaken. In Cook Strait a revision of the available fault maps was undertaken as part of a wider, related tectonic study of the central New Zealand region. In Poverty Bay very limited prior information was available, and as part of this study the structure and stratigraphy of the entire shelf and upper slope has been interpreted. On active tectonic margins submarine canyons respond to tectonics at: 1) margin-setting scales relating to their ability to become shelf incised; 2) regional scales relating to canyon-incision response to base-level perturbations; and 3) local scales relating to propagating structures affecting canyon location and geometry. Interpretation of the spatial distribution of fluid vent sites, gully development and landslide scars leads to the conclusion that seepage-driven failure is not a primary control on the widespread instances of gully formation and landslide erosion affecting structurally-generated relief across the margin. Rather, the erosion of tectonic ridges is dominated by tectonics by: slope oversteepening; weakening of the rockmass in fault-damage zones; and triggering of slope failure by earthquake-generated cyclic loading. Deep-seated mass failures affect numerous aspects of submarine landscapes and play a major role in the enlargement of canyon systems. They enable the development of slope gully systems and represent a major intra-slope sediment source. Quantitative morphometric analysis together with MCS data indicate that landslides may evolve to be active complexes where landslide debris is remobilized repeatedly, analogous to terrestrial-earthflow processes. This process has not previously been documented on submarine slopes. A model is presented for the evolution of active margin canyons that contrasts highstand and lowstand canyon activity in terms of channel incision, sedimentary processes and slope-erosion processes. During sea-level highstand intervals, canyons become decoupled from their terrestrial/coastal sediment-supply source areas, while during sea-level lowstand intervals, canyons are coupled to fluvial and littoral sediment-supply sources, and top-down (i.e. shelf-to-lower-slope) sediment transport and channel incision is active. Canyon-head areas are incision dominated during the lowstand while mid to lower canyon reaches experience both a transient increase in sediment in storage and canyon-fill degradation and incision into bedrock. Tectonics influences the canyon landscape through both uplift-controlled perturbations to canyon base-levels and earthquake-triggering of mass movement. Following sea-level rise the sediment supply to canyon heads will be switched off at a certain threshold sea level. From this point canyon heads become aggradational. Mid to lower canyon reaches continue to incise due to continuing tectonic uplift and earthquake-triggered slope instability. Knickpoints are propagated up channel and excavate canyon and sub-canyon channels from the bottom up. Thus, while top-down infilling of non-coupled canyons occurs during sea-level highstands, the lower reaches of active margin canyons continue to incise due the influence of tectonic processes.

No description available.

This study aims at providing results for the analysis of the stratigraphy underlying contaminated sediments in Ångermanälven. The contaminated sediments, containing heavy metals and persistent organic pollutants, are derived from wastewater discharged into Ångermanälven from nearby paper and pulp industries. These sediments consist of cellulose fibres deposited as fibrebanks, or as fibre-rich sediments in the case where fibres are mixed with natural sediments. The importance of the underlying geology is enhanced since the contaminated sediments are deposited in an area where submarine landslides and slope movements occur frequently. In this study two sediment cores from a fibrebank in Ångermanälven are analysed. This is done in order to assess the risk of contaminants being dispersed in the ecosystem as a result of mass movements. Stratigraphic correlation with results from previous sediment core analysis in the middle of the estuary (International Ocean Discovery Program expedition #347) is achieved through magnetic susceptibility and density measurements of the sediment. Results show that silt layers and clay units situated throughout the estuary are potentially weak and geotechnical investigations are necessary to assess the risk of slope movements over these units. With further analysis of fibrebanks and the use of a vibro-corer, the contact between the fibrebanks and underlying sediment could be captured and further correlation establishing the stratigraphy of the estuary achieved. / Denna studie syftar till att tillhandahålla resultat och tolkningar för analys av den underliggande stratigrafin i Ångermanälven, som överlagrats av förorenade antropogena sediment. De förorenade sedimenten, vilka innehåller tungmetaller samt organiska föroreningar, härrör från avfallsvatten som släppts ut i älven från pappers- och massaindustrin. Sedimenten består av cellulosafibrer och har deponerats som fiberbankar eller fiberrika sediment, varav det sistnämnda består av cellulosa uppblandat med naturliga sediment. Eftersom fiberbankarna och de fiberrika sedimenten är avsatta i ett område där jordskred är vanligt förekommande, är den underliggande geologin som de miljöfarliga sedimenten är avsatta på av avsevärd betydelse. I studien ingår analys av två sedimentborrkärnor från en fiberbank i Ångermanälven. Syftet är att ta fram underlag för att möjliggöra riskbedömning kring spridning av föroreningarna som följd av potentiella jordskred, där de förorenade sedimenten är inblandade. Stratigrafisk korrelation med resultat från tidigare studier i den djupare delen av älven (International Ocean Discovery Program expedition #347) har uppnåtts genom jämförelse av två sedimentegenskaper: sedimentens respons av magnetisk susceptibilitet och densitet. Resultaten visar att silt- och lerlager som återfinns genom hela älven är potentiellt svaga. Vidare är geotekniska undersökningar nödvändiga för att bedöma risken för skred över dessa lager. Analys av fler fiberbankar och användning av ”vibro-corer” istället för kolvbaserad borrmetod, skulle möjliggöra analys av kontakten mellan fiberavsättningarna och den underliggande geologin, samt ytterligare tydliggöra stratigrafin i Ångermanälven.

No description available.

Cette thèse étudie les contrôles des processus gravitaires transférant la production carbonatée des plateformes vers les bassins. Ces travaux consistent en 1) une synthèse géologique de la sédimentation gravitaire dans les systèmes carbonatés et une typologie des configurations favorables pour le transfert distal de la production grossière 2) une méthodologie de modélisation numérique innovante combinant la modélisation stratigraphique forward et le calcul de la stratigraphie mécanique. Elle évalue les mécanismes d’instabilités au cours de l’évolution d’un système. Ces travaux s’appuient sur deux cas d’analogues Plio-Quaternaire: La pente occidentale sous-le-vent du Great Bahama Bank (GBB) et le système d’Exuma Sound/San Salvador, qui constitue une voie exceptionnelle de transport distal de sables carbonatés vers la plaine abyssale. Une caractérisation commune des processus de transferts gravitaires a été établie pour ces deux zones. Des essais œdométriques et de cisaillement triaxial ont été conduits pour obtenir les paramètres géomécaniques des sédiments. La méthodologie de modélisation numérique a été appliquée à un transect 2D de la pente occidentale du GBB sur l’intervalle 1,7-0 Ma. Elle précise le mécanisme de progradation de la marge sous-le-vent, liée au développement de prismes marginaux cimentés de bas-niveaux. La modélisation de la stratigraphie mécanique souligne le contrôle des instabilités gravitaires par la géométrie des dépôts et les surpressions de fluides. Celles-ci se développent sous l’effet des charges piézométriques transitoires dans la plate-forme émergée, favorisant la déstabilisation de la marge de la plate-forme. / This PhD thesis focuses on the controls of the gravitational processes transferring the carbonate production of the platform towards the basins. This work consists in 1) a geological synthesis of the gravity-driven sedimentation in carbonate systems and a typology of favorable configurations for the distal transfer of coarse material 2) an innovative numerical modeling workflow combining the forward stratigraphic modeling and the computation of the mechanical stratigraphy. It estimates the instability mechanisms during the evolution of the system. This work is based on two Plio-Quaternary analog cases: The Great Bahama Bank (GBB) Western leeward slope and the Exuma Sound/San Salvador deep basin and major canyon system, which constitutes an exceptional conduit of distal transport of carbonate sands to the abyssal plain. A common characterization of gravitational transfer processes was established for these two zones. Oedometer and triaxial tests were conducted for the determination of geomechanical parameters of the sediments. The numerical modeling workflow was applied to a 2D transect of the western slope of the GBB over the 1.7-0 Ma interval. It precises the progradation mechanism of the leeward margin related to the development of marginal cemented lowstand wedges. The modeling of the mechanical stratigraphy underlines the control of the gravitational instabilities by the geometry of the platform and fluid overpressures. The latter develop under the effect of transient piezometric head in the emerged platform, promoting the destabilization of the platform margin.

In this thesis study / mechanism and modeling of tsunamis generated by landslides are investigated. Landslide parameters affecting the surface wave characterisics are studied. In order to understand occurance of this kind of tsunamis, among many historical tsunamis, the ones that are triggered by landslides are detected and studied. The generation of the landslide generated tsunamis are modeled using TWO-LAYER model, which solves nonlinear long wave equations simultaneously within two interfacing layers with necessary boundary conditions at the sea bed, interface and water surface. The model is applied to one of the possible landslides at offshore Yalova in the Sea of Marmara. Two of the controlling parameters, which are the density and the thickness of the slid material, are analysed and a sensitivity analysis is performed to determine the level of their effects on the evolution and amplitude of the tsunami source. Furthermore, the propagation and coastal amplification of the landslide generated waves are investigated using the tsunami simulation and visualization code NAMI DANCE. The results are presented, compared and discussed.

Along with being one of the most populated regions of the world, Indonesia has one of the highest natural disaster rates worldwide. One such natural disaster that Indonesia is particularly prone to are tsunamis. Tsunamis are primarily caused by earthquakes, volcanoes, landslides and debris flows. To effectively allocate resources and create emergency plans we need an understanding of the risk factors of the region. Understanding the source events of destructive tsunamis of the past are critical to understanding the these risk factors. We expand upon previous work focusing on earthquake-generated tsunamis to consider landslide-generated tsunamis. Using Bayesian inference and modern scientific computing we construct a posterior distribution of potential landslide sources based on anecdotal data of historically observed tsunamis. After collecting 30,000 samples we find a landslide source event provides a reasonable match to our anecdotal accounts. However, viable landslides may be on the edge of what is physically possible. Future work creating a coupled landslide-earthquake model may account for the weaknesses with having a solely landslide or earthquake source event.