Chilcotin River Landslide

On July 30th, 2024, a massive landslide occurred along the Chilcotin River, approximately 50 km southeast of Williams Lake and 30 km upstream from its confluence with the Fraser River (Government of Canada (GOC), 2024). The landslide deposited substantial material into the river consisting of trees, sand, silt, and till, forming a debris field about 1,000 meters long, 600 meters wide, and 30 meters deep (NASA, 2024). This dammed the Chilcotin’s water flow completely for six days, forming a lake that extended upstream (Figure 1) (GOC, 2024). The blocked water posed a significant flash flooding risk to downstream communities, with the worst-case scenario modeling a sudden dam collapse resulting in water flows exceeding spring flood levels (District of Lillooet, 2024). Subsequently, flood and evacuation warnings were issued throughout the province.

On August 5th, 2024, water gradually breached the landslide over a 20-hour period, reducing the potential for catastrophic damage (Figure 2) (NASA, 2024). University of Northern British Columbia remote-sensing scientist Brian Menounos observed that the presence of till throughout the deposit played a crucial role in slowing the process, as its compact and erosion-resistant properties helped prevent a sudden, abrupt failure (NASA, 2024). Despite this, the flooding caused damage to the Farwell Canyon Bridge and several Indigenous cultural sites, while the increased sediment loads created barriers for migrating fish, including Chinook, Sockeye, and Coho salmon, as well as Steelhead trout (NASA, 2024; GOC, 2024).

Causal Factors A combination of complex factors drove this landslide. Although the 2017 wildfires played a role by removing vegetation and weakening the soil, geotechnical expert Dwayne Tannant from UBC Okanagan identifies that the primary causes are the area’s steep topography, ongoing river erosion, fine sand and silt layers in the valley walls, and a history of slope movement dating back to 1964 (Lompe & Lobe, 2024). Tannant also highlighted the unusual nature of the event, noting that a river-blocking landslide of this magnitude is relatively rare. Additionally, Geologist Dan Shugar from the University of Calgary emphasized that it’s tempting to link the landslide directly to wildfires or climate change, but it reflects the region’s inherent susceptibility more accurately. However, as the climate warms, the frequency of landslides, drought, and heavy rainfall is expected to rise throughout BC (Lompe & Lobe, 2024).

References CTV News Vancouver. (2024). No one knows what will happen with “devastating” landslide blocking B.C. river: chief. https://bc.ctvnews.ca/no-one-knows-what-will-happen-with-devastating-landslide-blocking-b-c-river-chief-1.6987305 Dale, A., Ling, C., & Newman, L. (2008). Does place matter? Sustainable community development in three Canadian communities. Ethics, Place and Environment: A Journal of Philosophy and Geography, 11(3), 267-281. District of Lillooet. (2024). Chilcotin River landslide Information. https://www.lillooet.ca/news-1/chilcotin-river-landslide-information Farley, J., & Voinov, A.(2016). Economics, socio-ecological-resilience, and ecosystem services. Journal of Environmental Management, 183(2), 389-398. Government of Canada. (2024). Chilcotin River landslide response. Department of Fisheries and Oceans Canada. https://www.pac.dfo-mpo.gc.ca/pacific-smon-pacifique/chilcotin-landslide-glissement-terrain/index-eng.html Lompe, H., & Lobe, S. (2024). Fire probably not the cause of Chilcotin landslide: experts. Canada’s National Observer. https://www.nationalobserver.com/2024/08/02/news/fire-probably-not-cause-chilcotin-landslide-experts Mulrennan, M.E., & Bussieres, V. (2018). Social-ecological resilience in indigenous coastal edge contexts. Ecology & Society, 23(3), 18 pp. NASA. (2024). Chilcotin River’s Landslide Lake Begins Draining. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/153195/chilcotin-rivers-landslide-lake-begins-draining