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A complex submarine geomorphology was revealed from multibeam bathymetry and seismic reflection surveys conducted between 2001 and 2006 in the Lower St. Lawrence Estuary offshore Betsiamites River, Québec, Canada. In this paper, we describe the submarine morpho-sedimentology of an area of ~500 km with focus on the consequences of three mass movement events. A chronology suggesting the ages for the failures is established. A major landslide scar is characterized by two large channels on the shelf and a sediments fan in the Laurentian Channel. This landslide is dated around 7.25 kyr cal BP. Morphological observations and sediment core analyses allow us to identify a least two different recent (i.e., less than 1 kyr BP) debris flow accumulations on the shelf and in the Laurentian Channel. Two different 210Pb-dated debris flow deposits were identified and associated to two recent earthquake episodes: (1) the AD 1663 (M~7) earthquake and (2) AD 1860 (M~6) or AD 1870 (M~6.5) earthquakes. The 1663 debris flow deposit is associated with a subaerial landslide observed on shore. [ABSTRACT FROM AUTHOR]

On steep (2-6°) offshore fan deltas of Western Gulf of Corinth medium to small scale (106-107 m3) debris flows and avalanches are the prominent slope features. Loose sands, gravels and pebbles are observed in the lower fan while silty/sandy turbidites/tsunamites detected in cores, implying sediment dissociation during failure and downslope transport. These failures are associated with significant upslope retrogression that has caused coastal retreat with important human and economic impact. All the events were estimated to have occurred during the late 4-5 kyr after or during the deposition (progradation) of the HST fan delta. Recent (late 0.1-0.15 kyr) prodelta failures in the Gulf of Corinth are evidenced by the destruction of telecommunication cables, coastal collapse and the initiation of destructive tsunami waves (i.e. 1963AD). The frequency of major failure events in the Western Gulf of Corinth is estimated to 2-3 events/0.1 kyr, usually associated with strong earthquakes and tsunamis (i.e. 1817, 1861, 1917?/,1963 1995AD events) [ABSTRACT FROM AUTHOR]

A portion of the Cap de Creus canyon, situated in the Gulf of Lion, has been selected for a detailed analysis of slope instability. This sector has been chosen because of morphological evidence for slide. Three piston cores have been taken at different water depths along an axis perpendicular to the thalweg and a box core has also been taken in the thalweg. At the top of the flank, the geotechnical signature suggests that clay sedimentation has been continuous. In contrast, overconsolidated silty clay has been observed in the core taken on the flank, about 60 m below a headwall escarpment, on a failure plane. The geotechnical profile of the core taken at the toe of the flank suggests that rapid depositional events, such as debris flows and turbidity currents, occur frequently. A series of triaxial tests have been performed, and provided input parameters for analyzing the initial stability of the flank with Slope/W. The impacts of several natural processes on failure development have been tested. Drained failures initiated by axial incisions seem to correspond to the main active process of the canyon, for small shallow failures. Large failure can occur under undrained conditions during earthquakes. [ABSTRACT FROM AUTHOR]

The main cause of tsunami generation in the Mediterranean Sea is tectonic activity associated with strong earthquakes. However, tsunami waves are also generated by landslides. From a compilation of 32 reliable cases of landslide tsunamis it comes out that most of them were caused by subaerial landslides or marine slides induced mainly by earthquakes and less frequently by volcanic eruptions. Others were caused by gravitative landslides or marine slides. The most frequent events were observed in the Corinth Gulf, Greece (11 out of 32 cases). In the volcanic Aeolian islands, Italy, 7 out of 32 cases were reported. In the Hellenic arc only 3 events are known, in contrast to the abundant, large-size tsunamis of seismotectonic origin historically documented. In Cyclades, South Aegean, only 2 but large landslide tsunamis were reported. Only few events have occurred in Marmara Sea, Cyprus, East Sicily, Liguria-Côte d'Azur and Algeria. Such a pattern of geographical distribution makes possible to assess the potential for landslide tsunami generation. [ABSTRACT FROM AUTHOR]

The western Corinth Gulf, central Greece, is characterized by steep slopes and large sediment river discharge, that are factors increasing the occurrence probability of underwater landslides. Thus the generation of tsunamis from submarine movements is expected to be frequent in this region, and this is confirmed in the historical tsunami catalogues, where reports of tsunamis related to landslides exist either triggered by earthquakes or by gravitational load. In this work we concentrate on the numerical simulation of submarine landslides and of the propagation of the ensuing tsunamis. We elaborate different scenarios basing on recent swath-bathymetry and seismic profiling surveys performed by the Hellenic Centre for Marine Research (HCMR). The most prominent potentially unstable bodies are found in three different regions: one is placed in the area off the city of Aigion, the second is located close to the Psathopyrgos fault, and the third occupies an elongated area off Eratini on the northern side of the gulf. All considered landslides are characterized by relatively small volumes (in the order ranging from 105-107 m3). For each scenario, the slide motion is simulated by means of a Lagrangian block model, implemented in the numerical code UBO-BLOCK1, developed by the Tsunami Research Team (TRT) of the University of Bologna, Italy. The tsunami generation and propagation modelling is carried out through the finiteelement code UBO-TSUFE, developed by the same research team, solving the Navier- Stokes equation in the shallow water approximation on a triangular-element mesh. We will show how landslide-induced sunamis propagate inside the western Corinth Gulf, the amplitude and period of the tsunami waves at some selected coastal points, and the spatial distribution of the extreme wave heights along the coast. [ABSTRACT FROM AUTHOR]

Interest in the generation of tsunamis by submarine mass movements has warranted a reassessment of their distribution and the nature of submarine landslides offshore of the eastern U.S. The recent acquisition and analysis of multibeam bathymetric data over most of this continental slope and rise provides clearer view into the extent and style of mass movements on this margin. Debris flows appear to be the dominant type of mass movement, although some translational slides have also been identified. Areas affected by mass movements range in size from less than 9 km2 to greater than 15,200 km2 and reach measured thicknesses of up to 70 m. Failures are seen to originate on either the open-slope or in submarine canyons. Slope-sourced failures are larger than canyonsourced failures, suggesting they have a higher potential for tsunami generation although the volume of material displaced during individual failure events still needs to be refined. The slope-sourced failures are most common offshore of the northern, glaciated part of the coast, but others are found downslope of shelf-edge deltas and near salt diapirs, suggesting that several geological conditions control their distribution. [ABSTRACT FROM AUTHOR]

Recent investigations on tsunami generation from submarine mass failures show that one of the most important factors influencing the source characteristics of the wave is the initial acceleration of the failure itself. In a number of these studies, a translational slide is modeled as a rigid body sliding down an inclined plane and basal resistance is neglected. In this paper, a similar rigid body model is proposed that incorporates basal resistance, which is related to the shear strength of the soil. Initial slide kinematics were investigated under two triggering mechanisms including overpressures at depth and rapid sedimentation. The model results show that soil behavior significantly influences the acceleration time history as well as the magnitude of the peak acceleration. The slide kinematics depend largely on the initial stress state and on the undrained residual shear strength of the soil along a potential failure surface, which highlights the importance of performing detailed geotechnical site investigations when assessing these geohazards. More research is needed to determine the influence of using more realistic basal friction models on the initial wave heights generated by submarine mass failures. [ABSTRACT FROM AUTHOR]

The level of tsunami hazard to the east coast of the United States is not well understood. This information is critical for the population, emergency services, and industry of the region. Assessing this hazard is particularly difficult because of the lack of tsunamis in the historical record and the uncertainty regarding the return periods of large-scale events that have been proposed, such as a large transoceanic tsunami possibly caused by a collapse of the Cumbre Vieja volcano in the Canary Islands, or a large co-seismic tsunami initiated in the Puerto Rican subduction zone. The most significant tsunami hazard in this region, however, may be due to local submarine mass failures (SMF), which could cause concentrated damage in coastal communities located near the failures. This paper presents results of a probabilistic analysis that estimates the hazard, expressed in terms of runup (at a given probability of occurrence), of SMF tsunamis triggered by earthquakes, on the upper northeast coast of the United States. A Monte Carlo approach is employed, in which distributions of relevant parameters (seismicity, sediment properties, type and location of slide, volume of slide, water depth, etc.) are used to perform large numbers of stochastic stability analyses of underwater slopes, based on standard geotechnical methods. When slope failure occurs, initial tsunami characteristic height and runup are estimated, based on earlier numerical work, for specified return periods of seismic events. The overall hazard associated with SMF tsunamis along the coast is found to be quite low at most locations as compared, e.g., to the typical 100 year hurricane storm surge in the region (5 m). Two sites, however, located off of Long Island, New York and Atlantic City, New Jersey, show an elevated risk of higher tsunami runup (5.0-7.5 m). These two sites should be the focus of more detailed studies. [ABSTRACT FROM AUTHOR]

Submarine-mass-failure-generated tsunamis pose a significant threat to the coastal communities around the Corinth Gulf. An effort was made towards the mitigation of a potential tsunami generated in the eastern part of the gulf, due to a submarine landslide. The impact of the tsunami was assessed along the coastal segment of the summer resort town of Xylocastro. The analysis (study) of the data within a Geographical Information System revealed that a 4 m tsunami run-up will flood 12% of the town's district. One fifth of the permanent residents are expected to be affected, while one fourth of the infrastructure is likely to undergo damages. Although alarm and reaction times to a possible local tsunami are short, there is just enough time for evacuation. Therefore a more detailed hazard assessment and an emergency management plan should be undertaken, not only for Xylocastro, but also for other coastal regions in the Corinth Gulf, where extensive development is taking place. [ABSTRACT FROM AUTHOR]

The M9.2 Alaska earthquake of 1964 caused major damage to the port facilities and town of Valdez, most of it the result of submarine landslide and the consequent tsunamis. Recent bathymetric multibeam surveys, high-resolution subbottom profiles, and dated sediment cores in Port Valdez supply new information about the morphology and character of the landslide deposits. A comparison of pre- and post-earthquake bathymetry provides an estimate of the net volume of landslide debris deposited in the basin and the volume of sediment removed from the source region. Landslide features include (1) large blocks (up to 40-m high) near the location of the greatest tsunamiwave runup (~50 m), (2) two debris lobes associated with the blocks, (3) a series of gullies, channels and talus, near the fjord-head delta and badly damaged old town of Valdez, and (4) the front of a debris lobe that flowed half-way down the fjord from the east end. [ABSTRACT FROM AUTHOR]

A large-scale mass-transport deposit (MTD) called Sl6 was recognized on the upper slope of the western Nile margin, downslope from of a 30 km-long scarp located along the outer shelf. Regional mapping indicated that this MTD extends on nearly 505 km2 and involved about 14 km3 of Pleistocene-Holocene sediment. Sl6 was triggered between 10 and 9 kyr BP, during the Holocene sea-level rise and coeval pluvial period (increased river flow). The consequent enhanced sediment supply on the upper slope and the outer shelf area caused local overburdening. This factor combined with the potential accumulation of gas in the sediment and earthquake activity is thought to have been the main factor triggering the Sl6 MTD. From the estimated volume of the MTD, a potential slide-generated tsunami was numerically simulated using the GEOWAVE software. The results indicate that the ~80 km wide Egyptian continental shelf protects the main part of the coastline from a slide-induced tsunami coming from the Rosetta area. An exception is the part of the coastline around Alexandria because focussing and shoaling processes can be simulated very close to the coast. [ABSTRACT FROM AUTHOR]

The flanks of the Cape Verde Islands Fogo, Brava and Santiago show extensive evidence of past and potential slope failure. Analyses of bathymetric and subaerial datasets show debris avalanches, turbidite pathways and debris flows, with the transportation of large volumes of rock and sediment. Similarities are seen with many of the processes operating on the flanks of the Canary Islands. In this paper we show the use of different multibeam bathymetry systems for geomorphological description and quantitative analysis. Slope maps, profiles and backscatter analysis can be used to classify the bathymetric characteristics. These derivative processes delineate the size and shape of the debris avalanches and flows and identify channel systems, as well as areas of recent seafloor volcanic activity. Two distinct debris fields covering at least 2000 km2 sourced from the east coast of Fogo are thought to contain up to 250km3 of material. Large slope failures, such as those from Fogo, may result in damage to seafloor installations such as submarine cables. However, greater hazards may be posed by the consequent generation of tsunamis. [ABSTRACT FROM AUTHOR]

Earthquakes are a commonly cited mechanism for triggering submarine landslides that have the potential to generate locally damaging tsunamis. With measured runups of over 35 metres in northern Sumatra from the December 26th 2004 tsunami source, these runups might be expected to be due, in part, to local submarine landslides. Mapping of the convergent margin offshore of Sumatra using swath bathymetry, single channel seismic and seabed photography reveals that seabed failures are common, but mainly small-scale, and composed of blocky debris avalanches and sediment flows. These failures would have contributed little to local tsunami runups. Large landslides are usually formed where there is significant sediment input. In the instance of Sumatra, most sediment is derived from the oceanic plate, and there is little sediment entering the system from the adjacent land areas. Input from the oceanic source is limited because of the diversion of sediment entering the subduction system off of Sumatra, that is attributed to collision between the Ninetyeast ridge and the Sunda Trench at approximately 1.5 million years ago. [ABSTRACT FROM AUTHOR]

Examination of seismic profiles west of Milos Island (Aegean Sea) show that the north Milos slope is affected by extensive mass movements, whereas the south slope is generally stable. Conditions that promote sediment failures include late Quaternary volcanic activity and related seismic activity, tectonically oversteepened slopes and possibly hydrothermal fluid escape. Big and small depressions indicative of phreatic explosions and hydrothermal venting, respectively, have been observed in Milos shelf. Sediment coring revealed that the surficial sediments are relatively soft and thus prone to failure. The lack or presence of sapropel layers is also indicative of unstable or stable slope conditions of the surficial sedimentary cover, respectively. [ABSTRACT FROM AUTHOR]

Seismic data have been used to evaluate the extent, characteristics and importance of the sediment failures in the Santorini basin. The failures are small but abundant, occupying almost half of the areal extent of the study area, and modify the relief of the basin and the surrounding slopes. The fact that surficial mass flow deposits are the source area of younger sediment failures is evident of the high intensity and frequency of the sediment instabilities. The major factors which are responsible for the observed instabilities are seismic activity and seismicity related to modern volcanic activity, steep slopes and the open sediment structure due to the specific texture of the volcanic material. Sediment failures are believed to compose a big part of the deeper sedimentary column. [ABSTRACT FROM AUTHOR]

Recent multibeam sonar and acoustic subbottom profiler surveys and sediment coring offshore the city of Sept-Îles (NW Gulf of St. Lawrence) reveal different types of submarine mass-movements and gravity flows in glaciomarine, paraglacial and postglacial deposits. These mass-movement and gravity flow features are slumps, gullies and channel-levee systems and fans. The key results of this study include: 1) slumps involve the entire deglacial and postglacial sequence, indicating their recent triggering; 2) identification of a 57-cm thick turbidite and several sand layers in sediment cores collected in a deep and isolated basin unaffected by fluvial inputs, along with 210Pb measurements, indicate the recent activity of mass wasting events derived from slope instabilities; 3) important volumes of sediments are being transported from the coastal to the deeper marine environment by gravity flows processes on the prodelta of the Moisie River. Hypotheses for explaining the widespread occurrence of recent mass-movements due to slope instabilities in the area possibly include their possible triggering by the AD 1663 (M~7) or another large earthquake. [ABSTRACT FROM AUTHOR]

High-resolution seismic analyses on the sedimentary subsurface of the deep basin of proglacial Lake Bramant (Grandes Rousses Massif, Western French Alps) allowed the detection of a large lens-shaped body with chaotic internal reflections corresponding to a mass wasting deposit (MWD) triggered by the nearby AD 1881 Allemond earthquake (MSK intensity VII). This MWD was only retrieved at the base of a short gravity core and the top of a piston core. Sediments associated with this MWD are remoulded and laminated. Locally, blocks of sediment have preserved the original stratification. This earthquake-induced mass movement is an example of a slide that evolved into a slump. In addition, several Late Holocene turbidite and hyperpycnal deposits related to exceptional flood events were identified using highresolution sedimentological, physical and geochemical analyses. However, the identification of hyperpycnites is sometimes complicated as erosion of the basal sequence can occur during the rising limb of the flood. While the precise dating of the oldest flood event is still ongoing, two flood events are coeval with the St. Sorlin glacier retreat following the end of the "Little Ice Age", suggesting outbursts of temporary ice contact lakes or subglacial lakes during warmer periods. [ABSTRACT FROM AUTHOR]

Following the 1964 M9.2 megathrust earthquake in southern Alaska, Seward was the only town hit by tsunamis generated from both submarine landslides and tectonic sources. Within 45 seconds of the start of the earthquake, a 1.2-km-long section of waterfront began sliding seaward, and soon after, ~6-8-m high waves inundated the town. Studies soon after the earthquake concluded that submarine landslides along the Seward waterfront generated the tsunamis that occurred immediately after the earthquake. We analyze pre- and post-earthquake bathymetry data to assess the location and extent of submarine mass failures and sediment transport. New NOAA multibeam bathymetry shows the morphology of the entire fjord at 15 m resolution. We also assembled all older soundings from smooth sheets for comparison to the multibeam dataset. We gridded the sounding data, applied corrections for coseismic subsidence, post-seismic rebound, unrecovered co-seismic subsidence, sea-level rise (vertical datum shift), and measurement errors. The difference grids show changes resulting from the 1964 earthquake. We estimate the total volume of slide material to be about 211 million m3. Most of this material was transported to a deep, flat area, which we refer to as "the bathtub", about 6 to 13 km south of Seward. Sub-bottom profiling of the bathtub shows an acoustically transparent unit, which we interpret as a sediment flow deposit resulting from the submarine landslides. The scale of the submarine landslides and the distance over which sediment was transported is much larger than previously appreciated. [ABSTRACT FROM AUTHOR]

The Trondheim harbor has been the locus for many large flow slides during the last century. The most recent of these occurred in 1990 just outside the mouth of the Nidelv River and mobilized ca. 5 106 m3 of sediments. The mass movement took place as a liquefaction-induced flow slide outside the river outlet and developed into a lateral spread. The sediment mass slid along a weak layer of loose silty sand recognized by a distinct seismic reflection interpreted from high resolution seismic data. A combination of static and dynamic loading probably triggered the slide. [ABSTRACT FROM AUTHOR]

The Cape of Batumi belongs to accumulative morphological forms and mainly consists of terrigenous sediments of Rv.Chorokhi. It's location in the central part of the City of Batumi stipulates an importance of intensive research of phenomena. The natural growth of the cape towards the sea was stopped in 30-40-ties of last century, when it's frontal part closely approached the head of the Rv.Chorokhi submarine canyon. Investigation of the stability conditions of the bottom sedimentary layers deposited inside the canyon has been undertaken on the base of field observations, that repeatedly was held in 1960-2003. Sediment material from Rv.Chorokhi is a main component of the littoral cell of the Adjarian coastline of the Black Sea. The Chorokhi Canyion head locates at depth of 7-8 m at a distance of 70-140 m from the river mouth and invades the area of sediment laden currents. Its frontal area spreads along the shore line for as much as 1,5 km. More, than 90% of the river's load discharge were transported through the Chorokhi Canyon. The stability conditions of submarine sediments are disturbed by changes in the tangential reaction between soil particles or blocks, increased pore pressures, storms, instability of the underlying rocks, structural motions, tsunamis, earthquakes ( e.g. stability conditions has been violated by strong earthquake occurred in Turkey on 14-th of January,1999).Conducted research deals with the analytical considerations of dynamical processes occurring in the given area. [ABSTRACT FROM AUTHOR]

The geomorphological interpretation of the high resolution bathymetry of the Albano lake (central Italy), together with conventional geological and geomorphological investigations for the subaerial slope, allowed us to identify several subaerial and submerged morphologies due to slope failures of different size and presumably age. Two main landslide categories will be decribed in this paper: totally submerged, combined subaerial-submerged landslides. Furthermore a detailed description of two past large slope failures (volume of 106m3) and the 1997 subaerial and submerged debris flow are presented. The wave induced by the 1997 debris flow testifies also the tsunamigenic potential of these phenomena which is still more serious if the presence of coastal settlements is taken into account. [ABSTRACT FROM AUTHOR]

Seismic and multibeam data have shown the occurrence of Plesitocene large-scale Mass Transport Deposits (MTDs) and Holocene failure events in Ursa Basin at ~1000 m depth in the eastern levee of the Mississippi Canyon, northern Gulf of Mexico. During IODP Expedition 308 Sites U1322 and U1324 were drilled adjacent to the Recent failures and through several MTDs of Holocene and Pleistocene age. A complete suite of logging, sedimentological and geotechnical data were acquired to reveal the factors controlling initiation of past sediment failures and to characterize the hazard potential of future slope instabilities. Fluid overpressure estimated from a variety of direct and indirect methods indicates that the vertical effective stress is 50 to 70 % lower than if hydrostatic conditions existed. Overpressure in Ursa Basin most likely results from deposition of fine-grained sediments with rates at least 1 m ky-1 with peaks up to 25 m ky-1. The thickest and most widespread MTDs occur in periods of highest sedimentation rate. Considering the very low seismicity experienced by the margin it is most probable that the changes in sedimentation rate might be the primary driving force of slope failure. At Sites U1322 and U1324 a total of 14 MTDs were identified, which leads to a frequency of emplacement of 1 MTD/4.5 ka. Considering only the thickest MTDs the recurrence interval reduces to 1 MTD/10 ka. [ABSTRACT FROM AUTHOR]

Pore pressure and shear strength are major controlling parameters for slope stability, which can be measured in situ using CPT (cone penetration testing) instruments. This paper presents results from initial tests with two free-fall CPT probes deployed in the neotectonically active submarine slope of northern Crete, Greece. Research expedition P336 investigated landslide-prone areas in the Cretan Sea using multibeam swathmapping, seismic reflection profiling, in situ CPT measurements, and gravity coring. Several large landslide complexes at the NE Cretan Margin as well as a small, but steep landslide scarp structure further east were identified on the seismic profiles. CPT devices were deployed in undisturbed slope sediments, across the slide scar, and in the main body of the slide, and remained stuck in the sediment for ~10 minutes to monitor pore pressure dissipation upon insertion. Excess pore pressure after insertion is in a range around 60 kPa in background sediment, and exceeds 80 kPa in the slide deposits. Cone resistance of the slope sediment ranges between 300 and 500 kPa, corresponding to undrained shear strengths of up to 40 kPa. The slid sediments (specifically the headwall material with <10 kPa strength) show velocity-weakening behaviour during ring shear experiments, indicating that those sediments are unlikely to show stable creep and instead may fail catastrophically. [ABSTRACT FROM AUTHOR]

The rheological behavior of soils depends on many factors, including their mineralogy and grain size distribution. This work comprises an extensive search of data collected from the literature, an experimental work on about 17 samples. These results, along with a compilation of existing data, have been used to show that, as a first approximation, the yield strength/viscosity ratio is about 1000, 100 and less than 10 for clayey, silty and sandy fine-grained sediments mixtures, respectively. Our research results on the rheological properties of fine-grained sediments indicate that they are very sensitive to the variation in grain size, shear rate, and geometry of the system. [ABSTRACT FROM AUTHOR]

The Pointe-du-Fort submarine mass movement likely took place at the time of the February 5th 1663 earthquake as a sidewall slope failure which generated a mudflow with a run out distance of 1070m and a final flow thickness of 10-15m resting on a slope of 1.4 degrees. The slide involved about 1.95 Mm3 of clayey sediments from an original slope of 24 degrees. The slide took place in normally consolidated sediments composed of stratified low organic Laflamme Sea clay at the base overlain by progressively more organic rich recent sediments. In situ strength testing and sampling on the tidal flat, morphological analysis and remolded strength of the debris lobe can be related to rheological tests to model the mobility of the debris. For the first time, it has been possible to link the mobility of a submarine slide with the characteristics of the sediments at the time of failure with no need to consider water content increase to explain the observed mobility. [ABSTRACT FROM AUTHOR]

The in situ measurement of seafloor physical properties such as pore pressure, shear strength or compressibility poses a challenge to engineers, in particular in the marine realm. We present the design and first use of a marine, deep-water free-fall instrument for cone penetration testing (CPT). The probe can be operated in up to 4000 m water depth to measure cone resistance, sleeve friction, deceleration, temperature and tilt as well as pore pressure in u1 and u3 position. In this paper we discuss the advantages and disadvantages of the current prototype design, and dwell on the differences between quasi-static versus dynamic cone penetration testing. [ABSTRACT FROM AUTHOR]

A detailed marine survey in Antikyra Bay in the northern margin of the Gulf of Corinth graben in Greece was carried out to examine the distribution and dispersion of bauxitic "red mud" tailings. The red mud tailings have been discharged at a rate of 500 000 to 640 000 tonnes/year via submerged outfalls on the shelf at a water depth of 100 m. The red mud tailings at the mouth of the outfalls have formed three oval shaped mounds. These mounds have a maximum thickness of about 27 m and thin out radially in the downslope direction along the longitudinal axis of the bay in a south-southwestward direction forming a common depositional lobe. The "red mud" tailings are transported by turbidity currents, via channels which incise the slope, to the basin floor at a water depth of 800 m and over a distance of 17 km, where they form small sheet-like deposits. High-resolution sedimentological analysis of 30 short cores using visual inspection, Xradiography, grain size measurements, X-ray diffraction and smear slides have shown the presence of seven (7) distinct turbidity flow events which were activated on the shelf and the slope and have occurred during the 24 years of tailing discharge. Five of these have their source at the "red-mud" mounds at the mouths of the outfalls and two of them have their source at the shelf break and the upper slope. The analysis revealed that the former consist of (a) graded structureless red mud deposits and/or bioturbated red mud deposits, or (b) laminated red mud deposits, whereas the latter are mostly structureless and poorly graded. [ABSTRACT FROM AUTHOR]

Most of the parameters used in slope stability analyses, in particular the mechanical soil properties, are uncertain. Probability theory and reliability analyses can provide a rational framework for dealing with uncertainties. Different methods for doing reliability analysis for slopes are discussed in this study and applied to case studies. The results obtained from FOSM, PEM, and FORM via response surface method combined with the finite element method are compared, and the parameters which contribute most to the uncertainty in the factor of safety are identified. [ABSTRACT FROM AUTHOR]

In Hudson Bay and Hudson Strait, the rapid collapse of the Laurentide Ice Sheet (LIS) culminated in the catastrophic drainage of proglacial Lake Agassiz into the North Atlantic around 8500 cal BP. It has been suggested that this catastrophic event may have triggered the 8200 cal BP cold event recorded in Greenland ice cores. Evidence for that outburst flood was the identification of a centimeter to decimeter-thick hematiterich red layer that was observed in Hudson Strait sediments around 8000 yr BP. In this paper, we have identified a sequence of two flood-induced turbidites (i.e., hyperpycnites) in a reddish layer from two cores collected in northern Hudson Bay (core AMD0509-27bLEH) and western Hudson Strait (core AMD0509-28PC) in 2005 onboard the ice-breaker CCGS Amundsen. These two reddish layers can be correlated to a red bed previously identified as a regional isochron in Hudson Strait and associated with the final drainage of Lake Agassiz around 8500 cal BP. Regardless of the exact timing of the catastrophic drainage, the hyperpycnites described in this paper suggest that they were deposited following two pulses, which is in agreement with the one of the scenarios proposed by Clarke et al. (2003) [Science 301, 922-923] for the drainage of Lake Agassiz. Finally, this study demonstrates for the first time the turbiditic and the flood-induced nature of the Hudson Strait red bed isochron. [ABSTRACT FROM AUTHOR]

The marine environment presents various settings in which talus slopes are formed via a rock fall process similar to what exists on land. This is the case along fjords and submarine canyons in particular. Although many studies have been carried out on land, surprisingly very little is known for the submarine environment. We propose here the first kinematics analysis of underwater rockfall. It is postulated that the block have a diameter of more than one meter. As it can be expected, the main addition to the subaerial case is the consideration of the role of water (e.g. density or current). For submarine rockfall analysis, the effect of the ambient fluid cannot be neglected. Hydrodynamic constraints are controlled by the speed, shape, and size of the moving mass. Wind does not have a significant role in subaerial rockfall analysis, but currents must be considered in the subaqueous environment. In addition, coefficients of restitution are not only controlled by the elastic properties of the material, but also by impact Stokes number. This paper provides a summary of underwater rockfall kinematics in order to formulate underwater rockfall governing equations. [ABSTRACT FROM AUTHOR]

Spreading is a pervasive type of ground failure in subaerial environments, but its occurrence has hardly been documented in submarine settings. However, recent advances in seafloor imaging techniques show that repetitive extensional patterns of parallel ridges and troughs, oriented perpendicular to the direction of mass movement and typical of spreading, are widespread offshore. A spread develops via the failure of a surficial sediment unit into coherent blocks. These blocks are displaced downslope along a quasi-planar slip surface. Two modes of failure can be identified: retrogressive failure of the headwall, and slab failure and extension. Mechanical modelling indicates that loss of support and seismic loading are the main triggering mechanisms. The extent of displacement of the spreading sediment is controlled by gravitationally-induced stress, angle of internal friction of sediment, pore pressure escape and friction. The resulting block movement patterns entail an exponential increase of displacement and thinning of the failing sediment with distance downslope. A deeper insight into submarine spreading is important because of the widespread occurrence of ridge and trough morphology in numerous submarine slides, particularly in the vicinity of submarine infrastructures. [ABSTRACT FROM AUTHOR]

Deep sea turbidity currents, mud flows, and debris flows have been the subject of a number of industry and government studies over the past two decades. While evidence of these flow events are common in a wide variety of continental slope and rise locations, the mode, scale, and frequency of these events have been shown to vary widely from place to place. Based on over more than a dozen field and modeling projects, we present an overview of the controls, scale, flow type, and flow behavior. The most general controlling factors are the type and scale of the triggering event, the slope and morphology of the seafloor, and the material properties of the flow. In this overview we focus on details of the evolving flows that need to be included in quantitative analyses with numerical models. [ABSTRACT FROM AUTHOR]

A series of comparable subaerial and subaqueous debris flow experiments of sand-claywater mixtures has been performed at the St Anthony Falls Laboratory (SAFL) at University of Minnesota. Different compositions were tested and velocities measured in detail using PIV (Particle Image Velocimetry) techniques. The experimental series provides a unique data set highlighting the effects of the ambient and interstitial fluid in comparable subaerial and subaqueous debris flows. Based on our experimental data we emphasize the differences in the dynamical behaviour associated with the two environments and suggest important mechanisms to be included in numerical models. [ABSTRACT FROM AUTHOR]

The Nazaré and Setúbal Canyons of the west Iberian margin are highly complex seafloor environments, displaying a range of sedimentary features and processes that reflect the transition from erosive upper to depositional lower canyon. Upper sections are characterised by a deeply incised, narrow, V-shaped thalweg, and frequent localised intra-canyon slope failures. Lower sections have a U-shaped floor with heterogeneous sediment distribution. Two types of gravity flow are observed: thin-bedded, finegrained deposits that may be the result of frequent turbidity currents generated by high sediment supply to canyon heads, and thicker, siliciclastic coarse sandy turbidites, probably generated by larger earthquake-triggered slope failures on much longer timescales. Our results highlight the complex interplay of sedimentary processes operating within major canyon systems. [ABSTRACT FROM AUTHOR]

The 1929 Grand Banks earthquake, landslide and tsunami were pivotal in geologic history as they led to the first unequivocal recognition of a landslide-triggered tsunami and turbidity current. The event is well constrained in terms of trigger, timing, sequence of events and impact. The landslide site was surveyed in September of 2006 with a 12 kHz multibeam echosounder. Regionally, these bathymetric data show canyons, valleys and gullies, somewhat typical of the continental slope in the region. No major headscarp related to the event is recognized (cf. the Storegga Slide). Most significant are a series of shallow gullies with small headwalls about mid-slope. Upslope from these is a series of shallow escarpments that probably represent upslope retrogression of the failure. The landslide appears to have been relatively shallow (top 5-100 m) and laterally extensive. There is no evidence of a single massive submarine landslide with major headscarp and debris lobe. [ABSTRACT FROM AUTHOR]

A very high-resolution shallow-seismic survey along the central part of the faultbounded Corinth Gulf southern margin (offshore Xylocastro town) revealed that three morphological zones characterize the area: the shelf, the slope and the basin. Three E-W trending, right stepping basin bounding faults define the basin-slope contact, producing a step like configuration along the base of slope. Steep scarps, caused by mass failures, sculpt the fault plane surfaces, which act as part of the slope. The shelf and the slope are dissected by submarine canyons and numerous minor channels. The largest canyons are located immediately off the river mouths, run perpendicular to the slope and are linear. Seismic profiles across the canyons suggest that some of them are fault controlled. The head and the walls of the canyons are affected by mass failures. It is estimated that about 1.1 km3 of mass failed sediments have been removed from the canyons and transported downslope to the basin floor. [ABSTRACT FROM AUTHOR]

The Holocene Storegga Slide is one of the world's largest exposed slides and also the most studied of all the Norwegian slides. However due to its complexity it is far from being fully understood. Three-dimensional (3D) seismic combined with swath bathymetry data from the southern flank of the Storegga Slide have been used to study mass movement processes occurring in the region. The high spatial resolution provided by the 3D seismic data has allowed a detailed geomorphological analysis of sedimentary and deformational structures. The Holocene Storegga failure affected a significant part of the studied area. The predominant feature is a compression zone, comprising two lobes, where the seabed shows marked parallel ridges. Down slope it is possible to identify another compression zone. A relative chronology of events was established and it is proposed that these two compressions zones are the result of gravity-driven slope failures related to different stages of the Holocene Storegga Slide. [ABSTRACT FROM AUTHOR]

A morphometric analysis of submarine landslides on the continental slope of north Colombia - south Ecuador convergent margin provides insights into hazards, including mass movements locations, size of failures and location control. Bathymetric and seismic data acquired in 2005 revealed three distinctive types of locations with the occurrence of potentially tsunamogenic submarine landslides: 1) the erosive margin toe is characterized by three 5-6-km wide and up to 1500m high semi-circular scarps. The toe is also affected by a 35-km long area of linear scarps resulting from the imbrication of successive failures, 2) canyon walls are affected by five up to 500m high scarps, 3) the deformation front exhibits a 50x20 km potentially destabilized area characterized by intensive fracturation. All these features are controlled by active tectonics, Slope oversteepening is a key parameter facilitating the onset of slope failure for the two first types, and is associated with 1) seamount subduction, 2) subsidence related to basal erosion of upper plate, and 3) uplift along active tectonic structures. Regarding the third type, the destabilisation area is influenced by the intensive fracturing at the vicinity of a splay fault. [ABSTRACT FROM AUTHOR]

The slope along the SW Labrador Sea is a prospective exploration frontier with limited legacy data and geoscience knowledge. Newly acquired seismic reflection and multibeam bathymetry data provide a better understanding of mass failure processes. A semicontinuous seismic section along the upper slope from Flemish Pass to north of Hamilton Spur shows an alternation of major morphological elements that includes canyons and failure corridors, inter-canyon ridges, ice-outlet trough mouth fans (TMFs), and sedimentary spurs. Preliminary geohazard investigation shows a wide variety of Plio- Pleistocene mass failure products including shallow detachment faults, head-scarps, creep folds, decollement surfaces, and a preponderance of mass transport deposits (MTDs) of various origins. Particularly noteworthy are two newly identified fans outboard the Hawke Saddle and Notre Dame Channel (believed to be TMFs constructed of mass wasted material), and a large shallow buried failure complex north of the Hamilton Spur, which contains many km-scale slide blocks dispersed over thousands of square kilometers. [ABSTRACT FROM AUTHOR]

The Sahara Slide occurred approximately at 50-59 Ka offshore Western Sahara in a mid-slope setting (1900 m water-depth). The existence of several buried and stacked slide events, seen on high resolution seismic profiles, provide new insights into slide location and triggering mechanisms. Buried slide scarps coincide remarkably with scarps and boundaries of the Sahara Slide, presently exposed on the seafloor. The objectives of this work are to examine the long-term stability of this part of the margin and investigate the triggering mechanism(s) that led to these massive events. [ABSTRACT FROM AUTHOR]

The Krishna and Godavari rivers have formed the Krishna-Godavari delta where they enter the ocean. Both the rivers, which drain a significant part of the Indian peninsula, and the delta are influenced by a seasonal sediment supply controlled by the monsoon rains. The delta system receives nearly all its sediment during this annual flushing of the river system. [ABSTRACT FROM AUTHOR]

The morphology of two lower - middle Pleistocene paleo-slope surfaces within a muddy glacigenic succession was studied on 3D seismic data. The lower surface is characterised by irregular relief. It terminates upslope by an escarpment that represents the upper part of a paleo-slide scar. The slide scar morphology is relatively similar to that of modern slide scars and failure is inferred to have occurred during or after a glacial maximum when the ice reached the paleo-shelf break. A large area immediately outside the paleo-slide scar was affected by sediment creep or sliding, thus the area of unstable sediments extends beyond the paleo-slide scar. The upper surface morphology is dominated by three straight to slightly meandering paleo-channels, at least one of them formed by mass wasting. Together, the two paleo-surfaces exemplify slope morphology that may result from sediment instability on glaciated margins. [ABSTRACT FROM AUTHOR]

The statistics of submarine mass movement inventories are poorly characterised in comparison to those of subaerial mass movements. In this study we investigate the aggregate behaviour of the Storegga Slide by carrying out a statistical analysis of its constituent mass movements. By using area as a proxy for mass movement magnitude, we demonstrate that the non-cumulative frequency-magnitude distribution of mass movements within the Storegga Slide is a power law with an exponent of 1.52. The Storegga Slide has the characteristics of a dissipative system in a critical state, where the input of sediment is continuous in the form of hemipelagic sedimentation and glacial deposition, and the output is represented by mass movements that are spatially scale invariant. We conclude that the Storegga Slide may be modelled as a large-scale geomorphic system that exhibits self-organised critical (SOC) behaviour. In comparison to subaerial mass movements, the aggregate behaviour of submarine mass movements is more comparable to that of the theoretical ‘sandpile' model. The origin of SOC may be linked to the retrogressive nature of the Storegga Slide. Since SOC is an emergent feature, the large-scale behaviour of the Storegga Slide should be autonomous of the smaller-scale elements. A power law distribution also implies that incomplete submarine mass movement inventories may be extrapolated within the limits of power law behaviour, which is important in terms of hazard management. [ABSTRACT FROM AUTHOR]