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 Submarine slope failures in the nearshore waters of SE Baffin Island, eastern Canadian Arctic, present a challenge to coastal and seabed development. Submarine slope failures are a known geohazard in fjords in Norway, Chile, Alaska, British Columbia and elsewhere, but have received little attention in the coastal waters of Arctic Canada. Over the past 6 years, there has been a rapid expansion of multibeam echosounder (MBES) mapping in Canadian Arctic fjords, leading to the discovery of many submarine slope failures. One area that has been mapped in detail is inner Frobisher Bay. This macrotidal, seasonally ice-covered, semi-enclosed embayment has a glacially scoured bed, ice-contact deposits, including recessional moraines, and stratified glaciomarine and post-glacial silts and clays with abundant dropstones. The prevalence of submarine slope failures in the inner bay (one per 20 km 2 ) appears to be anomalous. To date, MBES mapping has imaged at least 246 failures, ranging in size from 0.007 to 2.1 km 2 and all within the glaciomarine and post-glacial succession. Morphometric analysis of these features based on high-resolution MBES bathymetry provides an insight into their spatial distribution, relative chronology, triggers and flow characteristics; factors essential to understanding the mechanisms underlying their abundance in this Canadian Arctic fjord.

Abstract The Laurentian Fan is one of the largest submarine fans on the western margin of the North Atlantic. Recently acquired high-resolution multibeam bathymetric data (60 m horizontal resolution) reveal a major mass-transport deposit (MTD) on the Western Levee of Western Valley (WLWV), covering >14 000 km 2 in water depths from 3900 to >5000 m. Typical submarine landslide features are observed such as headscarps that in places reach the crest of the levee, crown cracks, extensional ridges, blocky debris and flow lineations. Multiple headwalls are observed on 3.5 kHz sub-bottom profiles, indicating that the landslide retrogressed upslope. While the upper parts of the MTD consist of intact blocks that were displaced downslope as ridges and troughs, the lower parts exhibit a c. 30 m thick incoherent to transparent acoustic facies, typical of debris flows. Landslide geomorphology therefore suggests that it was generated as a retrogressive spread and that slide blocks disintegrated downslope to become a blocky landslide with a surficial debris flow. The blocky landslide/debris flow extends downslope c. 90 km and partially fills a submarine channel. The superposition of the MTD filling the channel and its location at the top of the stratigraphic succession in the levee suggests that it is late Quaternary in age, possibly Holocene. Deeper seismic reflection data also show that this is a rare event during the Quaternary; it is the largest MTD observed in the upper c. 375 m of the levee succession and among the largest and deepest in the western North Atlantic.

Abstract The seismic geomorphology of a succession of alternating gravity-flow-dominated and bottom-current-dominated deposits along the continental slope and rise off western Nova Scotia demonstrates the importance of inherited geomorphology on subsequent deposition patterns in mixed turbidite and contourite depositional systems. In the study area, widespread mass wasting and channel incision during the Miocene created a steep ramp with a complex geomorphology along the lower continental slope. In the Late Miocene and Pliocene, a sediment drift was constructed on the continental rise, forming a 50-km-wide terrace that onlapped the steeper slope. The location, style, and evolution of sediment waves associated with this sediment drift appear strongly linked to the morphology of the underlying surface. The orientation and extent of wave crests show strong correspondence to underlying geomorphic elements, with the most prominent sediment waves forming downcurrent of seafloor perturbations like failure escarpments and salt diapirs. The erosional and constructional morphology of the contour-current-swept seafloor in turn strongly influenced the trajectory and response of subsequent down-slope-oriented submarine sediment gravity flows later in the Pliocene. Preferential accumulation took place above a regional terrace constructed as the sediment drift evolved, promoting deposition from sediment gravity flows that may have otherwise been transported into deeper water. The positive relief of wave crests guided sediment gravity flows down the slope, with erosion and deposition focused along wave troughs. This study highlights the complex feedback that exists between along-slope and down-slope constructional and degradational processes.

Abstract A large submarine-slide deposit from the western Scotian Slope off eastern Canada was imaged on a 3D seismic reflection dataset in the Barrington exploration block. The mass-transport deposit (MTD) forms a tongue-shaped body that is 25 km long and 8 km wide, with a run-out distance from the headscarp of 41.5 km and a total volume of 12.5 km 3 . In profile, it consists of a chaotic seismic facies. This facies forms a highly rugose top surface morphology, suggesting that the flow consisted of an abundance of intact angular blocks. Its base reveals evidence of erosion typical of submarine MTDs, with linear downslope-trending gouges and excavation of a pit 50-m-deep. The source area and headscarp of the Barrington MTD are somewhat obscured by postdepositional erosion. Additionally, high-resolution seismic profiles show that the deposit is draped by approximately 30 m of late Pleistocene and Holocene sediment, providing an age estimate of 30 ka for the failure. Despite this drape, the modern seafloor above the MTD still has a highly rugose morphology, echoing the top surface of the deposit. Seismic profile data show a series of stacked MTDs underlying the Barrington MTD, suggesting that mass-failure recurrence is common on geologic time scales. Although it is difficult to attribute mass-failure triggering mechanisms, high sedimentation rates due to proximal shelf glaciers and intense erosion causing oversteepening, and likely established preconditions for instability. Local seismicity, possibly a result of glacial rebound, is the most probable initiating factor.