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.

Abstract Marine geological and geophysical data from Alpha Ridge in the Arctic Ocean are sparse because of thick perennial sea-ice cover, which prevents access by most surface vessels. Rare seismic data in this area, acquired largely from drifting ice-camps, had shown the hemipelagic drape that covers most of the ridge is highly disrupted within a large (>90 000 km 2 ) south central region. Here, evidence of pronounced seafloor erosion and debris flows infilling seafloor lows was previously interpreted to be the result of a possible bolide impact. In recent years, several icebreaker expeditions have successfully acquired multibeam bathymetry and sub-bottom profiler data in the western segment of this region. Analysis of these data reveals a complex seafloor morphology characterized by ridges and troughs, angular blocks and escarpments as well as seismic facies characterized by hyperbolic seafloor reflections, and convoluted to incoherent and transparent sub-bottom reflectivity. These features are interpreted as evidence of sediment mass movement with varying degrees of lateral transport deformation. At least two episodes of failure are interpreted based on the presence of both buried and surficial mass-transport features. As multiple events are interpreted, seismicity is the most plausible trigger mechanism rather than bolide impact.

Abstract Marine turbidite records have been used to infer palaeoseismicity and estimate recurrence intervals for large (>M w 7) earthquakes along the Cascadia Subduction Zone. Conventional models propose that upper slope failures are funneled into submarine canyons and develop into turbidity flows that are routed down-canyon to deep-water channel and fan systems. However, the sources and pathways of these turbidity flows are poorly constrained, leading to uncertainties in the connections between ground shaking, slope failure and deep-water turbidites. We examine the spatial distribution of submarine landslides along the southern Cascadia margin to identify source regions for slope failures that may have developed into turbidity flows. Using multibeam bathymetry, sparker multichannel seismic and chirp sub-bottom data, we observe relatively few canyon head slope failures and limited evidence of large landslides on the upper and middle slope. Most of the submarine canyons are draped with sediment infill in the upper reaches and do not appear to be active sediment conduits during the recent sea-level highstand. In contrast, there is evidence of extensive mass wasting of the lower slope and non-channelized downslope flows. Contrary to previous studies, we propose that failures along the lower slope are the primary sources for deep-sea seismoturbidites in southern Cascadia.

Abstract New, high-resolution multi-beam bathymetric data from RV Sonne cruise SO251 show a widely variable surface morphology along the southern Kumano Basin and Nankai accretionary prism off SW Japan. Combined with a three-dimensional seismic volume, these data provide insight into the ubiquitous and varied nature of faulting typical of accretionary prism settings, a high number of submarine landslides across the entire study area that vary both spatially and temporally, a pronounced absence of slide deposit bathymetric manifestations, widely varied slope angles and a potential subducted seamount scar. We have mapped scars of 442 primary and 184 secondary landslides and have measured the areas evacuated by these slides. Most of the slides are completely disintegrative, so surficial landslide deposits are almost absent. The incidence with which temporally sequential slope failures and fault structures cross-cut themselves and one another provides evidence of potential failure pre-conditioning such as gas hydrates, pore fluid overpressures and bottom current activity. Seismic loading and slope over-steepening are then the most likely final trigger mechanisms to slope failure. The majority of observed landslides (64%) occur seawards of the outer ridge, providing insight into the relationship between surficial landsliding and subsurface tectonic processes along this accretionary prism.

Abstract Multibeam echosounder (MBES) images, 3.5 kHz seismic-reflection profiles and piston cores obtained along the southern Queen Charlotte Fault Zone are used to map and date mass-wasting events at this transform margin – a seismically active boundary that separates the Pacific Plate from the North American Plate. Whereas the upper continental slope adjacent to and east (upslope) of the fault zone offshore of the Haida Gwaii is heavily gullied, few large-sized submarine landslides in this area are observed in the MBES images. However, smaller submarine seafloor slides exist locally in areas where fluid flow appears to be occurring and large seafloor slides have recently been detected at the base of the steep continental slope just above its contact with the abyssal plain on the Queen Charlotte Terrace. In addition, along the subtle slope re-entrant area offshore of the Dixon Entrance shelf bathymetric data suggest that extensive mass wasting has occurred in the vicinity of an active mud volcano venting gas. We surmise that the relative lack of submarine slides along the upper slope in close proximity to the Queen Charlotte Fault Zone may be the result of seismic strengthening (compaction and cohesion) of a sediment-starved shelf and slope through multiple seismic events.

Abstract Submarine landslides represent a major, previously little recognized, geological hazard to the coastal communities. This study investigates the size, depth and degree of submarine landslides along the margins of the Ulleung Basin and examines how the shelf morphology and sediment supply affect the style and occurrence of slope failures. The slopes have experienced at least 38 episodes of submarine failures, which have left clear arcuate-shaped scarps that initiate at water depths of 150–1120 m. Individual landslides comprise volumes over the range 0.1–340 km 3 , cover 20–800 km 2 on the seafloor and have runout distances of up to 50 km from the source. The headwall scarps are observed as being in excess of 500 m high. The height of scarps in the southern margin is significantly larger than in the western margin. Moreover, the volume of mass-transport deposits in the southern margin is also much higher compared to those from the western margin. The occurrence of the broad shelf (30–150 km wide) and high sedimentation rates in the southern margin might have led to large-scale slope failures. In contrast, the narrow shelf (<20 km) and low sedimentation rates in the western margin would only have promoted small-scale mass-wasting events.

Abstract Radiocarbon isotopic ages and sedimentological data are presented for material recovered from three adjacent translational submarine landslides (YS1, YS2 and YS3) identified on the upper-continental slope offshore Yamba, New South Wales, Australia. The age data indicate that these three co-located upper-slope slides probably occurred independently of each other and not in a single, widespread regional-scale failure event. Numerical estimates of the likely runout distances for slide blocks corresponding to the entire landslide scar volumes range between 10 and 27 km, and represent a ‘runout zone’ in which landslide blocks or debris might reasonably be expected to be located. There is no morphological evidence for large blocks or debris fields derived from two of the Yamba landslide scars within their identified runout zones (YS1 and YS2), suggesting these two failures involved complete disintegration of large slide blocks after failure or the removal of sediment from the landslide sites as grainflows or turbidites. In contrast, the third runout zone (YS3) presents good evidence of at least 12 slide blocks between 100 and 200 m in diameter, suggesting that they were shed as relatively small individual blocks or they were generated due to the dismemberment of a larger slab.