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QuakeImpact

The shaking

Landslides

Highway 99 runs north from Horseshoe Bay under cliffs and debris channels, and Highway 1 runs east into the Fraser Canyon. Both have been closed before by what came down on them, and both are how help reaches this region by land.

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Loose rock sits above the roads into this region

Highway 99 climbs from Horseshoe Bay to Whistler below slopes that have been rated for rock falls, rock slides and debris flows. The rating is built from the rock type, how steep the slope is, which way it faces, what the surface is made of and how far it is from a stream.

That corridor has a long record of things coming down on it. A review of 110 km of it counted 154 landslides between 1855 and 2007, on a stretch of road that accounts for “more than 18% of Canada’s total landslide related deaths (>600)”.

Closer in, the free neighbourhood maps for the western municipalities of Metro Vancouver carry a slope instability layer alongside liquefaction, drawn street by street.

Shaking sets off the same slopes that rain does

The oral traditions of the First Nations people on Vancouver Island record numerous landslides in the Cascadia earthquake of January 1700.

The province’s planning scenario for a magnitude 7.0 earthquake close to the city is set on a January afternoon, right after an atmospheric river has soaked the ground. Its account of the first minutes reads: “Landslides and rock falls are generated in many areas, cutting off transportation routes.”

The same strategy plans on large parts of the impact area being unreachable by road, from earthquake-triggered landslides, liquefaction and bridge damage.

A road cut here stays cut for weeks

After the crustal scenario the province expects the routes into the region to be damaged or only partly usable, at much reduced capacity, for weeks to months, and the rail network in the impact area to be largely unusable through the immediate response.

Where the help is makes that worse. Provincial staging areas sit outside the impact area, and resources are gathered there and pushed in. Two of the roads they would come in on run through mountains.

In November 2021 a storm closed Highway 1 through the Fraser Canyon at 18 sites between Hope and Spences Bridge, and it reopened about two months later. Highway 8 in the Nicola Valley took about a year. The same storm cut the main rail lines out of the province.

What those closures did, and how the region moves while they last, is on getting around.

What you can do

  • Look up the slopes and the soil where you live. The free neighbourhood maps for the western municipalities cover slope instability as well as liquefaction. Ground conditions says how to read them and which municipalities they do not reach yet.
  • Plan around the road in, not the road out. Help is gathered outside the impact area and pushed in over roads that run through mountains. At home that means enough water, food and medicine to last while the roads are being cleared.

A slope that comes down on Highway 99 lands on the road that help arrives by, and clearing it is measured in weeks.

The full preparedness plan

Sources on this page

Numbered in the order they are cited. Each entry links back to where it is used.

  1. [1]ReportLandslide susceptibility maps of the Sea to Sky Corridor, British Columbia — a qualitative approachGeological Survey of Canada · 2009Blais-Stevens, A. & Kung, R., GSC Open File 6169; DOI 10.4095/247994. Terrain-and-rainfall conditioned by design; no seismic parameter in either index equationOpen the document ↗
  2. [2]ReportBlais-Stevens & Hungr, "Landslide hazards and their mitigation along the Sea to Sky corridor, British Columbia", 4th Canadian Conference on GeohazardsCanadian Geotechnical Society · 2008154 events 1855–2007. The paper mentions neither "earthquake" nor "seismic" anywhere in its text, so it records no earthquake-triggered landslide on the corridorOpen the document ↗
  3. [3]DatasetMetro Vancouver Seismic Microzonation Mapping ProjectWestern University / ICLR, with BC EMCR · 201729 Phase 1 maps published 2024; Phase II (Pitt Meadows, Maple Ridge, Langley) to late 2026Open the document ↗
  4. [4]ReportThe M9 Cascadia Megathrust Earthquake of January 26, 1700NRCan / Earthquakes CanadaThe magnitude appears in the title only, and the page credits Japanese records and subsidence, not tree ringsOpen the document ↗
  5. [5]ReportProvincial Earthquake Immediate Response StrategyMinistry of Emergency Management and Climate Readiness, Province of BC · 2022Rev. 1.1, 135 pp: the crustal M7.0 Greater Vancouver planning scenario, its impacts, the planning assumptions, the formal mutual-aid instruments, and the two-weeks-versus-72-hours pair on p. 42Open the document ↗
  6. [6]ReportBC Highway Flood RecoveryProvince of BC · 2026Highway 1 Fraser Canyon. Rainfall-triggered, November 2021, not an earthquakeOpen the document ↗
  7. [7]ReportBC Highway Flood RecoveryProvince of BC · 2026Highway 8. Rainfall-triggered, November 2021, not an earthquakeOpen the document ↗
  8. [8]ReportFrom Flood Risk to Resilience: a B.C. Flood Strategy to 2035Province of BC · 2024Open the document ↗