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The Geological Survey of Canada (GSC) undertook marine fieldwork onboard the Canadian Coast Guard Ship (CCGS) Vector to locate and map potential geohazards and geological features in the Salish Sea in the interest of public safety from August 11-18, 2021. This work was conducted under the Natural Resources Canada Marine Geoscience for Marine Spatial Planning (MGMSP) and the Public Safety Geoscience Programs. The GSC had observed multiple potential faults in existing data near Central Haro Strait, Stuart Channel, South of Hornby Island and near Cape Lazo through existing CHIRP and multibeam bathymetry data but required further data to quantify their activity and potential seismic risk (Barrie et al, 2021). In addition to fault activity, the GSC had detected numerous large underwater landslide deposits in Howe Sound and Saanich Inlet. The GSC required further data to constrain volumes and timing of slide activity. In English Bay the origin and evolution of a field of pockmarks was poorly understood. In Burrard Inlet, the survey required a better understanding of frequency of landslides as well as depth of sediment in order to understand natural sediment depositional rates. The research expedition included deep-tow system (DTS) sub-bottom surveys and multibeam water column and bathymetric surveys in each of these areas to better understand these marine geohazards and processes. Hydrographic surveys were completed by the Canadian Hydrographic Service (CHS) at night in Pylades Channel and near Point Grey to maximize use of ship time. Weather was good, seas were calm, and good quality data were collected. The data collected will be made publicly available and have the potential to contribute to building codes and to help communities in their decision-making and understanding of risks.

Based on recently collected seismic-reflection survey data, the western extent of the active Devils Mountain Fault where it meets the Leech River Fault has been mapped for the first time, just offshore of the cities of Victoria and Esquimalt, British Columbia. This combined approximately 180 km long fault has now been mapped from the interior of Washington State, USA onto southern Vancouver Island, BC, Canada. The occurrence of such an active fault zone poses a high possibility of a significant crustal earthquake occurring near the cities of Victoria and Esquimalt.

Just offshore Cape Lazo, near Comox, British Columbia, a significant seabed geological hazard occurs that has been tentatively termed the Cape Lazo Fault. Nearshore the seabed has been ripped open to form a 25 m deep, 2 km long pit, as part of the possible active faulting process. A limited sub-surface survey undertaken by the Canadian Hydrographic Service in September 2020 reveals the nature of the scarp in the ocean floor and provides new insights into the possible hazard for the Department of National Defense Comox site just inshore of the Cape.

This paper describes structurally controlled gas seeps and their influence on seafloor morphology at sites within Queen Charlotte Basin (QCB); a sedimentary basin situated offshore British Columbia, western Canada. Numerous surficial and shallow sediment features related to both ice cover and shallow gas have been identified in high-resolution multichannel seismic, Huntec deep-towed seismic, multibeam bathymetry and backscatter, and piston core data that were acquired over a 10 km by 10 km grid in an eastern part of QCB. Pockmarks, seafloor mounds and iceberg ploughmarks are visible in the multibeam data; small-scale folds, vertical blank zones and acoustic turbidity are observed in the Huntec data. The multichannel seismic data show a faulted-anticline, phase-reversed bright spots, zones of low instantaneous frequency and velocity pull-ups. One seafloor mound lies directly above a shallow fault that offsets an asymmetric fold. The remaining mounds lie either above or in close proximity to asymmetric folds that are faulted. Bright spots are observed along some fault traces and within a cut and fill sequence at two-way travel times between 0.42 and 1.0 s. Velocity pull-ups are observed in the multichannel data below gas expansion voids present in piston cores. Backscatter data show that seafloor mounds are highly reflective compared to the surrounding seafloor. These observations indicate that gas has been migrating upward through the rock column and expelled into the shallow sediments. The shallow gas has been biologically mediated to form carbonate sediments within and around seafloor mounds; shallow gas has also deformed surficial sediments into positive relief mounds and negative relief pockmarks.

The Devil's Mountain Fault Zone extends east to west from Washington state to just south of Victoria in the northern Juan de Fuca Strait. Recently collected geophysical data were used to map this fault zone in detail, which show the main trace, and associated primary and secondary (conjugate) faults that occur within a 6 km wide deformation zone west of the Canada/U.S.A. boundary. The fault zone has been active in the Holocene as seen in the offset and disrupted upper Quaternary strata, seafloor displacement, and deformation within sediment cores taken close to the axis of the faults. Based on the length and previously estimated slip rates of the fault zone in Washington state, it appears to have the potential of producing a strong earthquake adjacent to Victoria, perhaps as large as magnitude 7.0 or greater.

British Columbia hosts Canada's most rapidly developing coastal communities along the semi-enclosed waterways of the Strait of Georgia. This region also is Canada's most seismically active zone. In 1946, the Vancouver Island M7.3 earthquake caused a number of submarine failures of sand and gravel shoreline deposits, destroying coastal facilities, shearing submarine cables and causing large, destructive waves. Multibeam and sidescan sonar technologies have been used to map three submarine landslides at Goose Spit, Mapleguard Spit and Grief Point. These sites are 32–55 km from the epicentre. The data image the failures in great detail, providing important information on size and style of mass-wasting. The total combined area affected by these three failures is over 1.3 × 106 m2. Submarine cores show the spit failures consisted of well-rounded beach gravel, cobble and sand, in some cases suspended in a cohesive mud matrix, while the Grief Point failure was likely a debris flow avalanche. Cone penetr...

Outwash plains, sometimes known as sandar or valley trains, are broad, gently sloping, sheets of outwash sediment deposited by meltwater streams fed by glacier ablation (e.g. Church 1972; Church & Gilbert 1975; Benn & Evans 2010). They may be formed by coalescing outwash fans fed by streams emerging directly from a former ice margin or from proglacial braided rivers; such glacial meltwater streams usually have highly variable discharge and, especially when flow is high, transport large quantities of glacier-derived suspended sediment and bedload (Church & Gilbert 1975). An example of a drowned outwash plain exists off northern British Columbia in Hecate Strait (Fig. 1a), where rapid glacial retreat left an extensive plain that formerly stretched 150 km across the strait linking the British Columbia mainland to the islands of Haida Gwaii. Fig. 1. Multibeam bathymetry and cross-profile of an outwash plain that abruptly ends at a …

An investigation into evidence of deposits of rapidly moving landslides that may have triggered displacement waves during the post glacial period in Howe Sound, British Columbia, was initiated by the Geological Survey of Canada (GSC) in collaboration with researchers from the Department of Earth Sciences, Simon Fraser University. It consisted of two initiatives: investigation of the present stability of the western slope of Mount Gardner on the west side of Bowen Island and of post glacial sedimentation and rates of sedimentation in Howe Sound. Investigation of sedimentation rates sought to determine the age of the run-out deposits along the sea floor of Collingwood Channel (west of Bowen Island) and to determine the duration of time that rock slide deposits would remain visible to swath multibeam bathymetry (SMB) before they were buried by subsequent sedimentation. A study combining structural geological mapping with geomorphic analysis of the subaerial and submarine portions of Collingwood Channel was carried out below Mount Gardner. More than 800 structural measurements at over 400 outcrops were made. A LiDAR digital elevation model) and orthophotos of Bowen Island were studied along with a digital elevation model of the sea bottom generated from MSB data. The investigation found that deep-seated gravitational deformation appears to have occurred along parts of the western slope of Mt. Gardner (MG) due to its geological structure and topographic factors. Evidence of ongoing deep-seated deformation was not found. Over all, a likelihood of major failure was not found. As a part of the marine geology investigation, three piston cores were collect from the bottom of Collingwood Channel below MG to sample contrasting local depositional environments. Two piston cores were also collected at the same latitude west of Lions Bay in the widest part of HS. One sampled a submarine fan and the other the sea bottom protected from submarine fan sedimentation. Seismic reflection surveys were carried out in the Collingwood Channel and Lion?s Bay and a remotely operated vehicle (ROV) traversed the sea bottom in both areas and the traverses were recorded by a high definition television system. The seismic reflection profiles determined initial relief of run-out deposits on the sea floor. The cores collected from shallowest depths in Collingwood Channel (62 to 84.5 m) were entirely deposited during deglaciation. They yielded uncalibrated 14C ages of ca. 13.1 to 12.5 years before present (yBP). No Holocene sediments were present. In the Lions Bay area, one of the widest reaches of Howe Sound, a 7 m core taken from a depth of 136 m intersected mud containing scattered plant fragments and invertebrate shells. Carbon-14 ages ranged from 8450 to 5700 yBP with the lowest 4 m of the core yielding statistically indistinguishable ages ca. 8450 yBP. Virtually no sediment post-dating 5700 14C yBP was intersected. This indicates that very rapid sedimentation occurred up to the middle Holocene with virtually none after that. This is consistent with enhanced erosion and sediment transport as a result of the paraglacial effect following deglaciation. The other core from Lions Bay core was taken at a depth of 139 m from the submarine fan below debris-flow-prone Lone Tree Creek. The core site is flanked to the north and south by entrenched submarine channels presumably cut by sediment-gravity flows. The core contains sediments at least as old as the oldest 14C dated sample ca. 4250 y BP. The core displays extensively bioturbated sediments containing wood fragments as well as angular clasts of dark Gambier Group volcanic rock which underlies much of the Lone Tree Creek basin. Intertidal invertebrate tests are present in the sediments. The most striking feature of the core is the inversion of stratigraphy with: a wood fragment with a 14C age of ca. 3740 y BP lies 500 cm below a bivalve shell dated at ca. 4250 y BP. This is attributed to the high energy environment expected for a submarine fan where older sediment can be reworked by sediment gravity flows crossing the fan. Only the upper 80 cm of the core was deposited during approximately the last 4000 years. The small amount of sedimentation over the latter half of the Holocene also reflects the waning of the paraglacial effect over this period. The low sedimentation rates over the latter half of the Holocene in Howe Sound make it unlikely that the deposits of any large and rapidly moving rock slide, large enough to generate a destructive displacement wave over the approximately the past 5000 years, would escape detection by the SMB imaging that was carried out in 2007.

Le delta du fleuve Fraser est localise dans une des regions ayant les plus hauts risques sismiques au Canada et comprend pour une bonne part des sables fluviaux meubles, tres connus comme possedant un potentiel eleve de liquefaction sismique. Des etudes recentes de la rive ouest du delta du Fraser indiquent que la liquefaction cyclique durant un fort tremblement de terre est possible, engendrant potentiellement des deformations incluant des extensions laterales, un ramollissement cyclique et possiblement une coulee. L'on presente une evaluation preliminaire de la stabilite statique des pentes apres secousse, dans laquelle les analyses ont ete limitees aux valeurs estimees des resistances au cisaillement ultimes ou a l'etat d'equilibre deduites de correlations avec les donnnees du terrain, et aux contraintes de cisaillement calculees en partant de la bathymetrie du lit de mer existant. L'on a trouve que le coefficient postliquefaction de securite contre le glissement etait inferieur a l'unite pour la pente de la terrasse superieure Roberts, en supposant une limite inferieure de resistance au cisaillement ultime equivalente a 0,06 P 0 '. Les donnees pour evaluer la validite de cette hypothese sont insuffisantes, cependant, il y a abondance de depots de rupture le long de la base de la pente du delta.

An inventory of submarine slope instability features has been compiled for coastal areas of British Columbia based on morphologic analysis of regional multibeam bathymetric data. The slope instability features are classified as submarine slides, debris flows, rock avalanches and associated features including fan deltas, sediment cones and channel complexes. In addition, the study provides an initial assessment of the size and distribution of these geohazards, with a particular focus on identifying large features that are the result of a single failure event because these would have the greatest potential to generate a damaging tsunami. Submarine landslide deposits have been identified in all fjords and inlets examined including Bute, Knight, Toba and Jervis Inlets and Howe Sound. Douglas Channel, Kitimat Arm and Alberni Inlets also have significant landslide derived sediment bodies on the margin and floors of these inlets. In the Strait of Georgia extensive failures have been identified along the Fraser River delta and on slopes where sediment accretion has occurred in the Holocene, including spits and other coastal landforms. The locus of nearly all submarine slope failures in Juan de Fuca Strait has been along the edge of a terrace landform associated with sea level lowstand. Whereas the age of some features can be tentatively inferred by association with modern or postglacial morphology, the exact age of the instability features documented in this study cannot be determined from this morphologic analysis alone. The accompanying ArcGIS document allows each instability feature to be located and queried for information such as morphologic classification, surface area, possible age, and other details.

Tidal currents on the sandy, southern slope of Fraser River delta have generated dunes with heights of 0.5–3.5 m and lengths of 11–108 m. Dune geometry and migration measurements indicate net sediment transport to the northwest in the direction of flood tidal currents. Two current meters moored in the dune field showed greater frequencies of occurrence and higher mean current speeds in the flood direction compared with the ebb. Predictions from two bed-material load models indicate sediment transport is overwhelmingly dominated by flood currents. There is no obvious source of sand to replace sediment transported in the dune field, suggesting net erosion of the surface. A previous analysis of bathymetric data also shows recent erosion of the lower slope and overall slope steepening. These patterns of erosion could lead to slope failure and damage to coastal structures.

Glass sponge reefs (Hexactinellida, Hexactinosida) off the Pacific Margin of Canada are both geologically and ecologically unique and represent the only global occurrence. In order to provide protection to these unique living cold-water reefs, the Department of Fisheries and Oceans under the Oceans Act have made the four large reefs within the Pacific North Coast Integrated Management Area (PNCIMA) designates for protection as Marine Protected Areas (MPA). The federal government's process for evaluation of a MPA of Interest requires an assessment of the non-renewable resource potential, including marine minerals. Based on the limited knowledge of the offshore British Columbia surficial mineral potential, two settings that may contain mineral placers of gold and titanium include drowned beach and reworked shelf deposits at water depths of 150 m to the modern beach. In addition, extensive areas of construction aggregate and calcium carbonate occur on the shelf. The deep water sponge reefs within the Areas of Interest occur in depths below 150 m within glacial sediments and, therefore, outside the potential setting for mineral placers or industrial minerals. Consequently, the enactment of the sponge reef Marine Protected Areas will not include any surficial mineral deposits of economic potential.

High-resolution seismic and side-scan sonar surveying, combined with coring, of the Fraser Delta slope seaward of the main fluvial distributary has revealed a complex suite of morphologic units which include undisturbed delta slope sediments, shallow rotational slides, relict and active slope channels, debris accumulations and ponded turbidites. Sediment transport through the main submarine channel is thought to be primarily by debris flows, rather than by turbidity currents. Although this is a seismically active region, the instability related features described here are probably due primarily to rapid sediment deposition on the upper delta slope at the river mouth.

An elongated sea bed depression (pit), 80 by 125 m and 10 m deep located on the Grand Banks of Newfoundland was identified on high resolution surficial geophysical survey lines and investigated using a manned submersible. The pit occurs at the termination of a long (greater than 3 km) iceberg scour, 1.5 m deep, and 80 m wide in 91 m of water. It is similar to other depressions in the region that indent the sea bed up to seven times deeper than the surrounding deepest iceberg furrows. The pit is interpreted to be the sea bed response to impact and loading by a rolling and grounding iceberg. The iceberg scour and pit appear to be of recent origin.

The northwestern Canadian continental shelf, including Dixon Entrance, Hecate Strait and Queen Charlotte Sound, can be divided into four surficial geological units all overlying Tertiary bedrock within the Queen Charlotte Basin. They include: (1) glacial till, deposited primarily in the troughs between banks and considered to be late Wisconsinan in age; (2) glaciomarine mud, deposited in the troughs as ice retreated from the shelf; (3) Queen Charlotte sands and gravels, outwash deposition in the north and sublittoral sand deposition in the south during sea level low stand and subsequent reworking during transgression; and (4) Queen Charlotte muds, deposited within the troughs of the region from late Wisconsinan times until present. These units are a result of a glaciation ending 15,000–13,000 years BP followed by relative sea level lowering by approximately 100 m, that persisted until 10,500 years ago, and a subsequent transgression that occurred over approximately 1500 years in a series of steps.

Icebergs drifting in ocean currents over the Labrador continental shelf may contact and move through seabed sediments to create characteristically curvilinear features, commonly referred to as scours, which average 1–2 m in depth and about 30–40 m in width. Such scours may continue for several hundreds of metres or several kilometres. The period of seabed interaction may last from a few minutes to several months and results in modification of both the seabed sediments and the iceberg keel. When observed from submersible soon after their formation, scours exhibit morphological characteristics not seen in old, degraded scours. The scour trough, between two berm ridges, is generally flat-bottomed but is characterized by the presence of ridge-and-groove microtopography, with amplitudes up to 0.3 m developed parallel to the scour axis. These features are formed at the trailing edge of the keel by clastic material embedded in the ice and by open fissures in the ice. In places along the inner berm margins, ridges and grooves may be developed at an angle to the scour axis, reflecting lateral displacement of material towards the berm as the iceberg moves forward. Voids up to 1 m deep and 2 m wide occasionally truncate the ridges and grooves. Voids are formed following the dissolution of small (a few m 3 ) masses of debris-laden ice that are mechanically broken off from the base of the keel and pressed into the seabed by the scouring iceberg. Initially low areas within the scour trough may preserve seafloor that has not been affected by ice-seabed interaction. In these regions deposition of bulldozed sediment from the surcharge at the leading edge of the keel may partially fill the narrow spaces beneath the keel in areas of initially low seabed elevation. Scour berms consist of in situ fractured but intact blocks of material on the inner flanks, and disarticulated blocks 1–2 m high along the berm crest. The outer berm slopes generally consist of pieces of larger blocks spalled from the berm crest resting in relatively finely comminuted, reworked material. The reworked material originates in the leading edge surcharge before being displaced to either side of the keel. Scour berms have irregular topography ranging in height from a few centimetres to as much as 6 m above the seabed. Isolated irregularly-shaped mounds beyond the outer berm may represent pieces of cohesive sediment that originated at the berm crest as overhangs and which subsequently collapsed.

Bioherms dominated by hexactinellid sponges occur in the three major troughs which cross the north-central continental shelf of British Columbia, Canada. The preferred substrate of the bioherms is till, glaciomarine sediments or bedrock in 150 to 250 m water depth. These bioherms began to develop in the early Holocene and have expanded since that time to discontinuously mantle more than 700 km 2 today. The sponge colonies form mounds and sheet-like structures up to 15 m thick and several kilometres wide and accrete new material to the bioherm through the removal of silty clay from suspension by the baffling of bottom currents. The sedimentologic and morphologic characteristics of the bioherms are in part due to fused siliceous mainframe skeletons of the sponges that provide the framework for the construction of the bioherm. The locus of sponge habitation on the surface of the bioherms changes with time in response to sediment accretion and microtopographic changes which affect delivery of sediment and nutrients entrained in bottom currents.

The reef-forming scleractinian coral, Lophelia pertusa has been recovered in bottom samples and observed as a dense debris field during remote-operated vehicle transects on a terrace on the flank of a steep-sided seamount-like knoll in the central Strait of Georgia, British Columbia. The coral debris has a minimum thickness of 33 cm and extends over several hectares in water depths of 225 to 255 m, suggesting that the coral community dominated this site for several centuries. Lophelia pertusa forms extensive reefs in many regions of the world, suggesting that a cold-water coral reef existed at this site in the recent past. This site and a sample from the west coast of Vancouver Island represent the first recognized British Columbia occurrences of Lophelia pertusa. In addition, regional multibeam surveys have revealed the presence of small (< 1 square km) Hexactinellid sponge reefs in waters 100 to 140 mdeep along the eastern approaches to the Gulf Islands in the southern Strait of Georgia in areas of low-relief glacial deposits. The surfaces of these reefs are covered with large Hexactinosidan sponges, predominately Heterochone calyx and Aphrocallistes vastus, or mantled with broken sponges where anthropogenic impacts, including trawling, have occurred. Mapping of these and other sensitive habitats will allow effective ocean management measures to be undertaken by the responsible agencies.

Six acoustic and sedimentary facies have been mapped in the central and northern Strait of Georgia that reflect the late Quaternary development of the region. During the Vashon Stade of the Fraser Glaciation, a Quaternary, preglacial deposit that filled most of the basin was eroded by glacial ice moving south down the strait. Ice-proximal and ice-distal glaciomarine deposition over glacial till occurred during the rapid deglaciation of the strait with development of marine conditions by 12.4 ka BP. Sea level fell during deglaciation from a relative high stand and continued to fall after all ice had left the strait reaching a low stand sometime after 10 ka BP. Holocene deposition within the strait has been dominated by the Fraser River plume and coastal and nearshore processes. 1 Resume : Dans le centre et le nord du detroit de Georgia, on a releve six facies acoustiques et sedimentaires qui temoignent de l’histoire geologique du Quaternaire superieur dans cette region. Durant le Stade de Vashon de la Glaciation de Fraser, un depot preglaciaire du Quaternaire qui s’etendait a la plus grande partie du bassin a ete erode par la glace s’avancant vers le sud dans le detroit. Il y a eu depot de sediments glaciomarins sur le till a proximite et a distance de la glace pendant la deglaciation rapide du detroit qui a mene a l’apparition de conditions marines il y a 12 400 ans au plus tard. A partir d’une hauteur relativement elevee, le niveau de la mer s’est mis a baisser pendant la deglaciation et cette baisse s’est poursuivie meme une fois que toute la glace eut disparue du detroit jusqu’a l’atteinte du niveau le plus bas il y a un peu moins de 10 000 ans. Pendant l’Holocene, la sedimentation dans le detroit a ete conditionnee principalement par le panache de sediments du fleuve Fraser, ainsi que par des processus littoraux et cotiers.

The Fraser River delta lies in one of the most earthquake-prone regions in Canada and is composed, in part, of loose sands that have a high seismic liquefaction potential. Engineering investigations at the western margin of the Fraser delta have demonstrated that seismic liquefaction is possible on the existing delta slope. There are several areas of past and present slope instability at the delta front. Present examples include chronic retrogressive slumping and debris flows at the mouth of the Main Channel and slow downslope creep movements in adjacent areas, where sediments are accumulating on the delta slope. Prehistoric mass movements may have been triggered by liquefaction during past earthquakes or may be related to recurrent slumping at the mouths of former distributary channels. In addition, failure may be linked to leaching of metastable marine sediments at the base of the Holocene deltaic sequence. Spontaneous failures occurring at present at the river mouth are due to the combined effects of rapid sedimentation and slope over-steepening, shallow gas held within the sediment mass, and tidal loading.

The active Pacific margin of the Queen Charlotte Islands has been subject to vigourous wave and tidal energy since glacial times resulting in a continental shelf and coastal zone that are almost devoid of sediment. After minimal glaciation of the narrow shelf, the region became emergent with sea level lowering of up to, and possibly greater, than 200 m due to a glacio-isostatic forebulge ending near 10 400BP (14C date) followed by a rapid transgression that reached approximately 15 m above present sea level. This transgression effectively removed all unconsolidated sediment along the coast except in a few protected basins, such as Rennell Sound.

The Fraser River delta, south of Vancouver, is the largest delta in western Canada. It is an important agricultural and waterfowl area and a vital link in the Fraser River salmon fishery. It is also an area of rapid urban and industrial growth and lies within the most seismically active region in Canada. The delta has formed since deglaciation 11 000-13 000 (14C date) years ago. Sand and mud slope deposits constitute the bulk of the deltic sedimentary package. The delta's distributary channels are estuaries characterized by intrusion of saline water from the Strait of Georgia. Sediment transport is controlled by river and sediment discharges, tidal conditions, and the position of the salinity intrusion. Mud is accumulating on the Sturgeon Bank slope and in the adjacent Strait of Georgia at rates of

Large-scale furrows occurring in unconsolidated Quaternary sediments on the Labrador Shelf are considered to be gouge marks of bottom-dragging icebergs. Side-scan sonograph mosaics from the northern Labrador Shelf were constructed for two bathymetric interbank areas. They reveal that both relict ice bottom gouging and modern iceberg scouring have taken place at water depths greater than 180 m. The recent scours are linear to curvilinear to crater-like in form, with average widths of 30 m at a mean scour depth of 5 m and lengths in excess of 3 km. The dominant scour trend is north-south, reflecting the Labrador Current.Impedance of icebergs by bottom interaction is primarily a function of the gross iceberg size and shape, sediment encountered by the keel, and prevailing current. For modern scouring, frequencies of detectable impact decrease exponentially with increasing scour depth, and scour depth is inversely proportional to the sediment shear and compressive strengths.