The Earthquake Threat in Southwestern British Columbia: A Geologic Perspective

Ten moderate to large (magnitude 6–7) earthquakes have occurred in southwestern British Columbia and northwestern Washington in the last 130 years. A future large earthquake close to Vancouver, Victoria, or Seattle would cause tens of billions of dollars damage and would seriously impact the economies of Canada and the United States. An improved understanding of seismic hazards and risk in the region has been gained in recent years by using geologic data to extend the short period of instrumented seismicity. Geologic studies have demonstrated that historically unprecedented, magnitude 8 to 9 earthquakes have struck the coastal Pacific Northwest on average once every 500 years over the last several thousand years; another earthquake of this size can be expected in the future. Geologic data also provide insights into the likely damaging effects of future large earthquakes in the region. Much of the earthquake damage will result directly from ground shaking, but damage can also be expected from secondary phenomena, including liquefaction, landslides, and tsunamis. Vancouver is at great risk from earthquakes because important infrastructure, including energy and transportation lifelines, probably would be damaged or destroyed by landslides and liquefaction-induced ground failure.     

Record of recent river channel instability, Cheakamus Valley, British Columbia

Rivers flowing from glacier-clad Quaternary volcanoes in southwestern British Columbia have high sediment loads and anabranching and braided planforms. Their floodplains aggrade in response to recurrent large landslides on the volcanoes and to advance of glaciers during periods of climate cooling. In this paper, we document channel instability and aggradation during the last 200 years in lower Cheakamus River valley. Cheakamus River derives much of its flow and nearly all of its sediment from the Mount Garibaldi massif, which includes a number of volcanic centres dominated by Mount Garibaldi volcano. Stratigraphic analysis and radiocarbon and dendrochronological dating of recent floodplain sediments at North Vancouver Outdoor School in Cheakamus Valley show that Cheakamus River aggraded its floodplain about 1–2 m and buried a valley-floor forest in the early or mid 1800s. The aggradation was probably caused by a large (ca. 15–25×10⁶ m³) landslide from the flank of Mount Garibaldi, 15 km north of our study site, in 1855 or 1856. Examination of historical aerial photographs dating back to 1947 indicates that channel instability triggered by this event persisted until the river was dyked in the late 1950s. Our observations are consistent with data from many other mountain areas that suggest rivers with large, but highly variable sediment loads may rapidly aggrade their floodplains following a large spike in sediment supply. Channel instability may persist for decades to centuries after the triggering event.     

Combining dissolved, suspended and bed load stream geochemistry to explore for volcanic massive sulfide deposits: Big Salmon Complex, northern British Columbia

Exploration successes for volcanogenic massive sulfide (VMS) deposits, such as Kudz Ze Kayah, Wolverine and Fyre Lake in the Yukon–Tanana Terrane and Slide Mountain Terrane (southern Yukon Territory) have spurred interest in the correlative rocks in the Big Salmon Complex in northern British Columbia. In an effort to further the utility of multi-media stream geochemistry in exploration frontiers that are forested, heavily drift covered, or buried, the primary streams of 19 watersheds from the East Teslin Lake (National Topographic System (NTS): 104N/9, 16) and Teh Creek areas (NTS: 104O/11, 12, 13, 14) of the Big Salmon Complex were analyzed for Cu, Pb, and Zn and other parameters in the dissolved load, suspended load and bed load. Traditionally, exploration based on stream geochemistry has employed the bed load and more recently the dissolved load chemistry, but almost never the suspended load despite strong differences in the geochemical signatures of the three media. Here, we document that copper, lead, and zinc partition into the dissolved, suspended, and bed loads differently and that the magnitude of anomalies is different for each media. The adsorbing capacity of the suspended load may make it a more sensitive indicator of mineral deposits on a regional basis than either the trace-element-poor dissolved load or the bulk-rock-diluted bed load which are likely better indicators of local mineralization. It is clear that each phase contributes unique information about the distribution of elements in the watershed that could be considered in exploration models.We also show that summing standardized element concentrations and summing the sums across media appears to be an effective method to reduce the data without loss of important information. We likewise investigated the utility of calculating major element normalized enrichments for exploration and find that it is a promising approach.     

A multi-proxy holocene record of environmental change fromthe sediments of Skinny Lake, Iskut region, northern British Columbia,Canada

A stratigraphic record from a lake in the Central Plateau Regionof northern British Columbia reveals changes in environment and inferredclimate during the Holocene. Upon deglaciation (ca. 11500 BP), Skinny Lakebecame an embayment of an ice-dammed lake. High clastic sedimentationrates, an unstable landscape, and cool, possibly wet conditions likelypersisted until the early Holocene (ca. 9000 BP). From ca. 9000–8300 BPdeclining lake levels coupled with warm and dry conditions resulted in theformation of a prominent marl bed. A colonizing shrub and herb assemblagepersisted from 9000 BP until about 8300 BP when it was replaced by a spruce(Picea) and subalpine fir (Abieslasiocarpa) forest under slightly cooler and moister conditions. Themiddle Holocene was warmer-than-present, however, decreasingtemperature and increasing precipitation trends characterize the period fromca. 6000 BP–3000 BP. The transition to modern climate at 3000 BP isevident primarily in the lithostratigraphic record and corresponds with theinitiation of the Tiedemann glacial advance (ca. 3300 BP) in thesouth-coastal mountains of British Columbia. A significant change infossil pollen occurs at ca. 2400 BP and is characterised by an increase in pinepollen accompanied by decreases in alder (Alnus), spruceand fir. This also coincides with an increase in west-sourced exoticwestern hemlock (Tsuga heterophylla) and cedar type(Cupressaceae) pollen possibly transported by regional changes in air masscirculation patterns associated with Aleutian Low dynamics. This studydemonstrates that both lithostratigraphic and biotic proxies are helpful inreconstructing the timing and nature of climate change and that each may havevarying sensitivities to a particular type of change.     

Geostatistical analyses of interactions between killer whales (Orcinus orca) and recreational whale-watching boats

Johnstone Strait in coastal British Columbia, Canada, is a core habitat for seasonal concentrations of killer whales (Orcinus orca), which have attracted considerable attention from commercial whale-watching operators and recreational boaters. Within the Strait lies the Robson Bight–Michael Bigg Ecological Reserve, a marine reserve set aside as critical habitat for killer whales and closed to recreational boat traffic. The geography of encounters between killer whales and seven types of whale-watching vessels (including kayaks, charter and pleasure craft) in and near this reserve was analysed with a suite of geostatistics in a geographic information system (GIS) vector environment. Reserve boundary violation was high among most user groups, with kayakers being the most frequent offenders. Motorized vessels had significantly longer contact times with whales compared to kayaks and sailboats. Motorized vessels showed the travel characteristic of deliberate tracking of whales. The movements of killer whales also appear to be affected by boats. These results have important implications for killer whale conservation and management in areas where they are subject to intensive whale-watching activities, and possible chronic disturbance.     

Example of a debris-flow risk analysis from Vancouver Island,British Columbia,Canada

In July 2005, a debris flow and a water flood occurred on two adjacent gullies in the White River area, on northern Vancouver Island in British Columbia, Canada. The 16,000 m³ debris flow buried approximately 7.5 ha of second-growth trees, buried approximately 500 m of a forestry road, and reached two fish-bearing streams. The water flood eroded approximately 240 m of the same forestry road and plugged four culverts before overtopping and inundating the road. To better plan for future events, risk analyses of debris flows, debris floods, and water floods were carried out for the two gullies involved, plus a third adjacent gully. The elements at risk that were analyzed included, in order of priority: users of the forestry road, the fish-bearing streams, the forestry road itself, and a timber bridge. Using a series of qualitative, but defined, relative-risk matrices, the following components of specific risk were estimated for each of the three types of events on each of the three gullies for each of the four elements at risk: probability of occurrence, probability that the event will reach or otherwise affect the site of the element at risk, the probability that the element at risk will be at the site when the event occurs, and the probability of loss or damage resulting from the element being at the site when the event occurs.     

Petrology and petrogenesis of a tertiary bimodal dolerite-peralkaline/subalkaline trachyte/rhyolite dyke association from Lundy,Bristol Channel,UK

The island of Lundy forms the southernmost igneous complex of the British Tertiary Volcanic Province (BTVP) and consists of granite (≈ 90%) emplaced into deformed Devonian sedimentary rocks (Pilton Shale) and associated with a swarm of dykes of dolerite/basalt, minor trachyte and rhyolite composition. The dolerites are of varied olivine basalt composition and are associated with peralkaline trachyte and subalkaline/peralkaline rhyolite with alkali feldspar and quartz ± alkali amphibole ± pyroxene mineralogy. The dyke swarm is therefore an anorogenic bimodal dolerite/basalt–trachyte/rhyolite BTVP association. Although the dyke association is bimodal in major element terms between dolerite/basalt and minor trachyte/rhyolite, the mineralogy and trace element geochemistry indicate that the dykes may be regarded as a cogenetic dolerite—peralkaline trachyte/rhyolite association with minor subalkaline rhyolites. Sr and Nd isotope data indicate derivation of these magmas from a similar BTVP mantle source (with or without minor contamination by Pilton Shale, or possibly Lundy granite). The petrogenesis of the Lundy dyke association is therefore interpreted in terms of extensive fractional crystallization of basaltic magma in a magma chamber of complex geometry below the (exposed) Lundy granite. Fractional crystallization of a representative dolerite magma (olivine ± clinopyroxene ± plagioclase) yields trachyte magma from which the crystallization of alkali feldspar (anorthoclase) ± plagioclase (oligoclase) + Fe–Ti oxide + apatite results in peralkaline rhyolite. Rarer subalkaline rhyolites result from fractionation from a similar dolerite source which did not achieve a peralkaline composition so allowing the crystallization and fractionation of zircon. The basalt–(minor trachyte)/rhyolite bimodality reflects rapid crystallization of basalt magma to trachyte (and rhyolite) over a relatively small temperature interval (mass fraction of melt, F = ≈ 0.15). The rapid high level emplacement of basalt, trachyte and rhyolite dyke magmas is likely to have been associated with the development of a substantial composite bimodal basalt–(minor trachytel)/rhyolite volcano above the BTVP Lundy granite in the Bristol Channel.     

‘Detachment’ of icefield outlet glaciers: catastrophic thinning and retreat of the Columbia Glacier (Canada)

We present an investigation of changes taking place on the Columbia Glacier, a lake-terminating outlet of the Columbia Icefield in the Canadian Rockies. The Columbia Icefield is the largest, and one of the most important, ice bodies in the Canadian Rockies. Like other ice masses, it stores water as snow and ice during the winter and releases it during warmer summer months, sustaining river flows and the ecosystems that rely on them. However, the Columbia Glacier and Icefield is shrinking. We use Landsat and Sentinel-2 imagery to show that the Columbia Glacier has retreated increasingly rapidly in recent years, and suggest that this looks set to continue. Importantly, we identify a previously undocumented process that appears to be playing an important role in the retreat of this glacier. This process involves the ‘detachment’ of the glacier tongue from its accumulation area in the Columbia Icefield. This process is important because the tongue is cut off from the accumulation area and there is no replenishment of ice that melts in the glacier's ablation area by flow from upglacier. As a consequence, for a given rate of ablation, the ice in the tongue will disappear much faster than it would if the local mass loss by melting/calving was partly offset by mass input by glacier flow. Such a change would alter the relationship between rates of surface melting and rates of glacier frontal retreat. We provide evidence that detachment has already occurred elsewhere on the Columbia Icefield and that it is likely to affect other outlet glaciers in the future. Modelling studies forecast this detachment activity, which ultimately results in a smaller ‘perched’ icefield without active outlets. © 2019 John Wiley & Sons, Ltd.     

Public Support for Land Acquisition: A Key Instrument for Successful Land Conservation,Governance and Management

While it is recognized that protected areas are important for biodiversity conservation and human wellbeing, governments struggle to establish and/or enlarge protected areas. Land acquisition and the challenges encountered by governing institutions in funding protected area systems expansion is discussed in this paper using the Capital Regional District (CRD) Land Acquisition Fund as a case study. We briefly discuss land acquisition in British Columbia and in the CRD, and offer an overview of the CRD Land Acquisition Fund and the public participation process that led to its establishment. We emphasize the importance of developing political and citizen support, and a shared vision about expanding protected areas systems - a key element for nearly doubling the parkland base of CRD Regional Parks in less than 20?years. We conclude by offering the lessons learned through the case study and provide guidance for policy and governance directions with regard to land acquisition.     

Dissolved and particulate aluminum in the Columbia River and coastal waters of Oregon and Washington: Behavior in near-field and far-field plumes

The distribution of dissolved (soluble and total) and particulate (leachable and total) aluminum was examined in the Columbia River and estuary, in near-field and far-field river plumes, and in adjacent coastal waters of Washington and Oregon during the River Influence on Shelf Ecosystems (RISE) cruise of May/June 2006. Dissolved and particulate aluminum (Al) concentrations were significantly greater in the river than in the coastal waters that mixed to form the plume. Dissolved Al concentrations in the Columbia River (∼80 nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000 nM and 18,000 nM, respectively. Dissolved Al within the Columbia River estuary showed a significant removal (∼60%) at salinities between 0 and 10 with salt-induced flocculation of colloidal Al complexes and enhanced particle scavenging being probable explanations for aluminum removal. Dissolved and particulate Al concentrations were significantly greater in near-field plumes relative to surrounding coastal waters. As the plume advected from near-field to far-field away from the river mouth, dilution of the plume with lower dissolved Al surface waters as well as particle scavenging along the flow path appeared to be controlling dissolved Al distributions. Particle settling as well as dilution with lower particle-load waters led to observed decreases in particulate Al as the plume moved from near-field to far-field. However, the percent-leachable particulate aluminum in both near-field and far-field plumes was remarkably constant at ∼7%. Dissolved and particulate Al in a far-field plume over 100 km southwest of the Columbia River mouth were over an order-of-magnitude greater than surrounding waters, illustrating the importance of the Columbia River plume as a mechanism for transporting Al offshore. Aluminum could be used to trace the input of biologically-required elements such as iron into waters off the shelf.