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 Recurrent storms, floods, landslides, earthquakes and tsunamis challenge the development of resilient infrastructure and communities in coastal northwestern British Columbia. Vulnerability assessment first requires extended and improved understanding of geohazards in the Pacific Basin to constrain modelling of future events. An investigation of soils and bedrock structures in the Douglas Channel provides insight into the distribution of deposits attributed to geohazards in the region. Newly discovered marine inundation deposits corroborate numerical models and suggest that Pacific-sourced storms and earthquake-triggered tsunamis expend much of their energy in the outer coast and rarely reach far up the mainland fjords. Small-volume Folisolic slides and rockfalls do not generate tsunamis of any consequence. In contrast, marine sediments deposited beyond storm berms at the fjord head are a record of local tsunamis generated by large-volume marine slumps. Deep-fractured bedrock mapped upslope from relict submarine features would trigger damaging tsunami waves if rapid failure into the fjord were to occur. The observations above suggest only great earthquakes, large landslides and seasonal storms above a certain threshold volume and impulse energy produce geomorphically significant inundation events. However, even small submarine landslides have tsunamigenic potential in Douglas Channel since they occur in shallow water.

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 This paper presents the geohazard assessment for a proposed bridge across Bjørnafjorden in western Norway. The fjord is c. 5 km wide with a maximum depth of 550 m at the proposed bridge crossing. The main geohazards of concern are submarine slope instabilities. To identify locations of instability, their susceptibility to failure, and their potential runout distances, we performed the following analyses: (1) static and pseudo-static limit equilibrium analyses for the entire fjord crossing area; (2) 1D seismic slope stability sensitivity analyses for different slope angles and soil depths; (3) 2D static and pseudo-static finite element analyses for selected profiles; (4) back-analysis of a palaeolandslide; and (5) quasi-2D and quasi-3D landslide dynamic simulations calibrated using results from the back-analysis. The workflow progresses from simplified to more advanced analyses focusing on the most critical locations. The results show that the soils in many locations of the fjord are potentially unstable and could be the loci of landslides and debris flows. The evidence of numerous palaeosubmarine landslides identified on geophysical records reinforces this conclusion. However, the landslide triggers and timing are currently unknown. This paper demonstrates the need for comprehensive and multidisciplinary geohazard analyses for any infrastructure projects conducted in fjords.

Abstract A 6.3 m tsunami swept through Kitimat Arm, British Columbia in 1974. An even larger wave struck and damaged the Northlands Navigation dock at Kitimat and the Haisla First Nation docks at Kitamaat Village the following year. Further down the fjord, two large coastal block failures were observed on the fjord walls across from the Gitga'at village of Hartley Bay. Several large infrastructure projects have recently been proposed for the Kitimat Arm coastal areas. The Geological Survey of Canada has therefore embarked on a five-year project to understand the magnitude and frequency of submarine mass movements in this fjord system to provide information regarding the risks from these events and to propose mitigation measures that may reduce these risks. We provide here an overview and the main results to date of an ongoing multidisciplinary study, which includes palaeotsunami studies, geomorphological and sub-seabed mapping, subaerial landslide hazard assessment, tsunami modelling, in situ and laboratory geotechnical testing, and the real-time tracking of seismic activity and seafloor movement. Some of these activities are reported in greater detail elsewhere in this book. The results of this research are summarized as a list of conclusions and recommendations to the Government of Canada.

Abstract: Fjord valleys are carved during glaciation and then form local sediment sinks, which fill during retreat of the ice. Thus fjord valleys appear analogous to lower-latitude incised valleys, but they are remarkably different because fjords experience isostatic rebound during deglaciation, causing relative sea level to fall during infill. This paper explores stratigraphic architecture of fjord valley fills based on Late Quaternary deposition in Clyde Inlet, Baffin Island, Arctic Canada, as constrained by 11 cosmogenic dates and 9 accelerator mass spectrometry (AMS) 14 C datings. A major ice stream of the Laurentide Ice Sheet occupied Clyde Inlet at last glacial maximum and bulldozered through a U-shaped valley forming a lower sequence boundary. During the Early Holocene the system entered a deglacial stage; tidewater glaciers retreated rapidly (>100 km in 1000 yrs) through the fjord from 10.4 ka onward. Grounded ice lobes started retreating from the Clyde fjordhead by 9.4 ka. Then ice-contact fans (ICF) were deposited consisting of flat-topped fan deltas, covered with channels and boulder-strewn bars. Elevations of the surfaces vary between 62 and 77 m above sea level, which marks the relative sea level at the time of deposition and is considered to be the marine flooding surface. Marine muds have been draped directly onto the ICF complexes. Subsequently, coarse-grained glaciofluvial valley trains (GFVTs) prograde downstream caused by rapid base-level fall, despite possibly high sediment supply (i.e., forced regression). During the Late Holocene (3.5 ka) the last remaining lobes of the Laurentide Ice Sheet retreated from the middle parts of Clyde River basin to form the present Barnes Ice Cap. At this phase, the rate of base-level fall has decreased (~1.6 m/ka over the last 3.5 ka), still the river incises significantly, marking a reduced sediment supply. Narrow coarse sandy fluvial terraces were being deposited at the lowest level of the incised river valley. Clyde fjordhead may not have entered a postglacial stage by definition, nevertheless a strongly reduced sediment flux is apparent. Numerous upland lakes likely play a role in trapping sediment in the hinterland. In addition, we speculate that the glacial regime of the Barnes Ice Cap switched from a sediment producing regime to a nonerosive cold-based regime. In conclusion, stratigraphic patterns of valley fills in high-latitude areas display an evident signature of isostatic rebound and a strongly varying sediment supply. Rapid uplift causes ice proximal units to occur high in the infill and reverses classic fining upward valley fill sedimentary trends. The exact interplay of local sea-level change and sediment supply dictates the complexity of the valley fill, but coarsening upward trends with younger sandy fluvial deposits incising into the fill deposits ultimately have important implications for the interpretation of similar deglacial valley fill settings.