The term “geohazard” refers to natural hazards created by ongoing earth processes that pose a risk to human life and infrastructure. Some, such as earthquakes, tsunamis and volcanic eruptions are governed by large-scale deep earth processes and can be inherently hazardous and damaging in their own right, while the risks posed by surface processes like rockfall, landslides, debris flows, floods, wildfire and avalanches may be created or exacerbated both by the aforementioned events and/or weather. In the latter case, abundant evidence has shown how climate change can significantly magnify these effects.
The Sea to Sky region is the most geologically active in all of Canada. Lying adjacent to actively subducting faults, it is comprised of steep, relatively young peaks—including volcanoes—all of which have been heavily glaciated and are subjected to weather extremes of temperature and precipitation. Thus, a full spectrum of geohazards not only exist, but manifest on numerous occasions throughout each year.
Living in the area of the Sea to Sky corridor covered by the Fire & Ice Aspiring Geopark requires a knowledge of potential hazards as well as the emergency plans and procedures formulated to deal with their eventuality.
During the year ending January 25, 2013, some 2,246 earthquakes occurred in British Columbia—more than six each day. While most of the seismic activity was minimal or too far offshore to have significant impact, over 50 of those earthquakes were actually felt, most in southwest coastal regions.
Of most concern in the Fire & Ice Aspiring Geopark is the undersea thrust fault lying west of Vancouver Island that extends south 1,000 kilometres to northern California and comprises the Cascadia Subduction Zone. Along this fault, the smaller oceanic Juan de Fuca plate is sliding towards—and subducting beneath—the much larger North America plate at a rate of 2–5 cm/year. Currently, the subducting plate lies ~45 km beneath the provincial capital of Victoria, and ~70 km beneath Vancouver.
This movement is neither smooth nor constant and good evidence exists that the two plates are currently locked together, causing pressure to build in the Earth’s crust. The release of pressure from this inexorable squeezing results in southwestern B.C.’s 300 or so small earthquakes annually and the less-frequent (an average of one per decade) damaging crustal earthquakes (e.g., a Vancouver Island earthquake in 1946 registered 7.3 on the Richter Scale used to measure earthquake magnitude, written as M7.3). At some point—possibly tomorrow or perhaps long into the future, it’s impossible to know—these plates will snap loose in a huge megathrust (or subduction) earthquake similar to the 1964 M9.2 Alaska earthquake or the 1960 M9.5 Chile earthquake.
Abundant geological evidence indicates such earthquakes strike the B.C. coast every 300–800 years, the last occurring 26 January 1700. This M9.0 earthquake was one of the largest in recorded history. Much of the evidence for its size, destructiveness and deadliness to humans comes from coastal First Nations oral traditions of destruction and flooding, as well as records of the enormous tsunami triggered by the quake that crossed the Pacific Ocean to Japan. The quake caused underwater slides as well as rock- and landslides on the mainland, and the ~2-metre up-thrust of the North American plate left unmistakable geological signatures in many Pacific Northwest coastal areas.
To address this potential hazard, a Tsunami Warning System is in place along the areas of Howe Sound contained within the Fire & Ice Aspiring Geopark (Tsunami Notification Zone “E”)
More information/social media links related to earthquakes:https://www.sciencedirect.com/topics/earth-and-planetary-sciences/juan-de-fuca-platehttps://earthquakescanada.nrcan.gc.ca/index-en.phphttps://earthquakescanada.nrcan.gc.ca/zones/westcan-en.php#offshore_W
The Cascade Volcanic Arc (CVA) spans the Pacific Northwest from northern California to southwestern British Columbia. Within the Canadian segment of the arc—known as the Garibaldi Volcanic Belt (GVB)—seven volcanic centres are recognized. All of these lie within the Fire & Ice Aspiring Geopark and include, from south to north, Mount Garibaldi, Mt. Cayley, Cheakamus Valley, Elaho Valley, Mt. Meager, Salal Glacier and Bridge River. Despite the chemical composition of lavas in this transect being unusual relative to more familiar CVA peaks like Mt. Shasta (California), Mt. Hood (Oregon), Mt. St. Helens (Oregon) and Mt. Baker (Washington), there is less scientific research on GVB volcanoes due to their remoteness.
The Cascade Volcanic Arc parallels the offshore Cascadia Subduction Zone. Partial melting of oceanic slabs descending under the North American plate fuels the volcanoes, depicted here by black triangles. Credit: USGS
The most recent explosive eruption in the GVB—and in British Columbia—occurred at Mt. Meager ~2,400 ya, resulting in lava and pyroclastic flows as well as an ash plume that made it all the way to Alberta.
More information on Canada’s volcanoes can be found at:https://chis.nrcan.gc.ca/volcano-volcan/can-vol-en.php
While rockfall most often refers to a quantity of rock falling freely from a cliff face, the term can also be applied to a collapse of the roof or walls of a mine or quarry. It seems like a simple process, but has been complexly defined as a rock fragment or block that detaches from, then falls along, a vertical or sub-vertical cliff either by bouncing and flying along gravity-propelled trajectories, or by rolling on talus or debris slopes. A smoother definition is that rockfall is the natural gravitational motion of a detached block or series of blocks with a small volume involving free falling, bouncing, rolling, and sliding. Clunky as they are, both definitions are attempting to establish that the mode of failure here fundamentally differs from that of a rockslide (see “Landslides” below).
Underlying geology—including the rock type and its integrity—as acted on by climate are the primary factors in rockfall (secondary factors include things like vegetation). Areas that are commonly favourable to rockfall include exposures of some types of sedimentary and heavily fractured metamorphosed rock, as well as rock cuts where integrity of the underlying rock has been compromised by blasting. Some types of rock are prone to exfoliation—the peeling away of sheets of variable thickness from a rock’s surface due to a range of weathering processes. For instance, as often seen in upland exposures of coarsely crystalline rocks like granite, the unloading or release of stress in a rock produces expansion joints. These cracks are infiltrated by water and exfoliation occurs from resultant chemical weathering and freeze-thaw cycles.
Rockfall is common in all mountainous areas of British Columbia, but particularly so in parts of the Sea to Sky corridor occupied by the Fire & Ice Aspiring Geopark.
Landslides comprise a variety of mass-wasting events (how’s that for a term to describe slope failure!). These include slumps, slides, falls, and flows of various surface materials mostly comprised of soil and loose rock. Landslides occur whenever the gravitational force on those materials exceeds the ability of the slope to resist it; anything that erodes or impedes this ability can be the cause of a landslide.
While major geologic events such as earthquakes may trigger a landslide, the majority occur due to a combination of gravitational pressure and erosional influences. Amongst the latter, water is the most effective; it can aid in the downslope movement of surface material by: a) adding weight to it, and; b) filling pores that tend to push the grains apart, decreasing overall resistance to movement in the material. While these processes may cause a slide to release, its speed and destructive potential are determined by the volume of material and the angle of the failing slope.
Photos of the north face of Joffre Peak from Highway 99. Black dashed line encompasses both scars; the red dash lines delineate sequential failures. Photographs taken on a) 1 May 2017 and b) 6 May 2019 by Ian Routley. The face partially collapsed sometime between these two dates. This collapse and the debris emanating from the wide vertical cleft on the fall-line left of it are indicative of precursor distress. c) Photo of 13 May landslide taken on 14 May by Jay Mamay. d) Photo of 16 May landslide taken on 19 May by Ian Routley. Photos are scaled the same for comparison of scars. From Friele et al. 2020.
Although Mt. Meager has recorded a litany of prehistoric and historic rock avalanches and debris flows, considerable hazard still remains due to the combination of loosely consolidated volcanic rock, a wet climate, significant freeze-thaw cycles, and potential volcanic seismicity. In addition to large fumaroles discovered steaming through the Job Glacier in 2016, geologists have identified ~20 separate weak areas in the Mt. Meager volcanic complex that include an aptly named Slope of Concern, which monitoring has shown to be creeping downward during frost-free periods at a rate of ~3cm/yr; should this slope release, it’s estimated the volume of material could be up to 10 times that of the August 2010 slide.
More on landslides in the Sea to Sky Region:https://www.for.gov.bc.ca/hfd/library/FFIP/Evans_SG1994.pdfhttps://www.researchgate.net/publication/228493250https://kids.kiddle.co/Mount_Meager_massif
Watercourses and ecosystems in the steep Coast Mountains have evolved to handle the typical high volume of rainfall and snowmelt of the region—and to rebound from occasional more powerful events such as atmospheric rivers (sustained, multi-day rainstorms in which a narrow plume of subtropical moisture funnels into a focused area of the coast). However, human activity (e.g., logging, agriculture) and the occupation of floodplains in concert with the more extreme weather of climate change have combined to exacerbate the effects of such events on the landscape, leading to periodic flooding.
In the northern part of the Fire & Ice Aspiring Geopark, the town of Pemberton is particularly vulnerable, located as it is in a narrow valley surround on all sides by steep, glaciated peaks. Here, as the Lillooet River drains icecaps and heavily glaciated mountains including the Mt. Meager volcanic complex, it is joined by Millar Creek, Ryan Creek, the Green River and the Birkenhead River before flowing into Lillooet Lake. Although the Lillooet River has seen several prehistoric outburst floods due to glacial and volcanic activity, the handful of notable historic events is largely due to a water table that lies close to the surface across the entire valley, and the diking and channeling done to accommodate the town and its agricultural base cannot accommodate the most severe events. In recent years evacuations due to flooding have become more common in Pemberton—including an unprecedented late June 2021 snow-and glacier-melt flood.
The town of Squamish, at the southern end of the Fire & Ice Aspiring Geopark, is both a target for heavy coastal rainfall and the terminus of two great glacier-fed rivers draining wildly precipitous terrain—the Squamish and the Elaho. Thus, also has to contend with the occasional threat of flooding and evacuation. Although Pemberton and Squamish have been on alert at different times for different reasons, the atmospheric river event of October 2003 saw both towns face simultaneous washouts and evacuations.
Atmospheric rivers have become more common in recent years. Between September and November 2021, no less than eight hit the B.C. coast, the first seven causing episodic flooding and minor damage in various places. So severe was the widespread damage to infrastructure following the final event of 15-18 November 2021, however, that rail lines, an oil pipeline, and all highways were shuttered between Vancouver and the rest of B.C. due to damage. This situation—no access of any sort from the Coast to the Interior for weeks—was unprecedented in B.C.’s history.
Wildfires are part of the evolutionary ecology of most coniferous forest regions of Canada, including the Interior Douglas-fir forest contained within the Fire & Ice Aspiring Geopark. These fires were traditionally cyclical, had natural causes, and tended to burn small areas. However, in recent decades the incidence of wildfire in B.C. has increased due to a combination of human fire suppression and land-use, as well as the landscape-level effects of climate change that include elevated spring/summer temperatures and changes in precipitation patterns and snow/glacier melt that result in drier forests, as well as more widespread and intense lightning events. As a result, wildfires are more frequent, and burn hotter, longer and cover larger areas—even those not usually susceptible to fire like coastal rainforest.
Volcanic eruptions can trigger wildfire both through lava contact with forests and from the lightning often generated by an eruption plume’s convective clouds. However, the more common influence of geology on wildfires can be seen in slope angles that contribute to the spread of upward-burning fires and the fact that fire-scarred hillsides are—much like those subjected to logging—more susceptible to debris flows and flooding during heavy precipitation events.
Snow avalanches are common throughout the mountains of B.C.. Most are localized and confined to high alpine areas, but longer slide paths in steeper areas can reach highways. If an avalanche is large and destructive enough, it can carry debris like rocks, mud and trees picked up along the way, posing a significant hazard to motorists and infrastructure. Several paths along the Duffey Lake Road (Hwy 99) north of Pemberton see large avalanches every winter.
Geohazard mitigation is both more necessary and widespread in the west of North America than central and eastern areas, and particularly so in geologically active areas like the Sea to Sky Corridor. This requirement significantly increases the costs of road-building and maintenance in the region. Travelling through the Fire & Ice Aspiring Geopark provides the opportunity to view and understand many types of mitigation.
Along highways and railroads, rockfall and small landslides are actively mitigated by a number of methods: retaining walls, one of the oldest forms of geo-engineering, are built to hold back the falling rocks and soil of unstable slopes; corrosion-resistant wire meshing can be installed at the crest and foot of slopes to trap falling debris; soil nailing involves drilling closely spaced steel rods into the soil to increase its cohesion through the rods’ ability to carry tensile loads, and typically reinforced through the use of welded wire mesh; rock bolting and concrete spraying are two other mitigation methods commonly in use, often in tandem.
A type of mitigation often performed prior to initiating many of the above methods is manual rock scaling—i.e., removing potentially unstable rock with hand tools. The safest and most effective way for rock-remediation technicians to do so is to rappel on ropes from the top of a slope to reach the rock that needs to be removed.
Large-scale concrete barriers and catchments have been installed in certain locations prone to catastrophic slides or flows, and there are also warning systems in place (lights, signals, signage) on some highways for avalanches, debris flows and washouts.
Avalanche paths that threaten highways can be controlled by the erection of barriers in snow accumulation zones, or bringing down the snow through the use of explosives (typically thrown from a helicopter). In some cases reinforced sheds are built where avalanche paths cross highways or railroads.
Working with private- and public-sector partners, the Centre for Natural Hazards Research at Simon Fraser University is leading a push to expand continuous monitoring of Canadian volcanoes and unstable ice-clad mountains in the Fire & Ice Aspiring Geopark, including Mt. Cayley, Mt. Currie and Mt. Meager, where seismic activity is monitored remotely through a series of transmitter, repeater and receiver stations. Rockfall on the Stawamus Chief in Squamish is also being monitored remotely via a series of small seismometers and remote cameras.
Communities in the Fire & Ice Aspiring Geopark have developed (or are developing) warning systems and evacuation plans suited to the particular hazards posed them: Pemberton (volcanic eruption, earthquake, flood, wildfire); Whistler (earthquake, wildfire); Squamish (earthquake, flooding, wildfire, tsunami). To receive notifications via email or hand-held devices, consult the websites for each community.
A physical Tsunami Warning System (signs, sirens) is in place along B.C.’s south coast (Tsunami Notification Zone “E”) including the area of Howe Sound within the Fire & Ice Aspiring Geopark. In addition, email and phone notifications can be received by signing up at https://www.emergencyinfobc.gov.bc.ca/resources/ or following @EmergencyInfoBC on Twitter.
For more information on geohazards in the Fire & Ice Aspiring Geopark and current monitoring and research being undertaken in the area: https://www.sfu.ca/cnhr.html
Squamish-Lillooet Regional District “Geohazard Risk Prioritization” document, April 2020:https://www.slrd.bc.ca/sites/default/files/reports/SLRD
On Borrowed Time: North America’s Next Big Quake, book by Gregor Craigie
Fault Lines, a podcast by Johanna Wagstaffe
“The Great Quake and the Great Drowning,” feature article by Ann Finkbeiner.
“Thunderbird and the Orphan Tsunami: Cascadia 1700,” feature article by Dana Hunter
“Washout,” feature article by Leslie Anthony and Alison Taylor
“Climbing the Occasionally Cataclysmic Cascades,” feature article by Mary Caperton Morton
Geosites of the Aspiring GeoRegion lie wholly within the unceded traditional territories of the Líl̓wat Nation and the Sk̲wx̲wú7mesh Nation. The nations have lived in—and shared parts of—these territories since time immemorial, with many landscape features and geological events woven into their cultural and oral histories. We are grateful for, and committed to, the opportunity to learn and share these perspectives of the land alongside its original stewards.
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