Innovation Winter 2025/26

Rockslide on Highway 93, 2019, near Fairmont Hot Springs. P hoto : C ourtesy of the M inistry of T ransportation and T ransit

Why are rockslides so hard to predict? Rockslides are a subset of landslides. The latter is a catch-all term encompassing rock falls, earth slides and avalanches, to name a few events. But rockslides differ fundamentally from other landslide types. “A rockslide is when a portion of rock mass detaches from its origin and moves down a slope,” explained Dr. Mehdi Amini, P.Eng., a senior rock mechanics engineer with Thurber Engineering. Unlike soil slides, which occur in more uniform materials, rockslides involve the downslope movement of rock masses and are “governed by fractures and discontinuities in the rock mass,” Amini said. These fractures are often invisible or buried, making it difficult to model or anticipate behaviour without extensive subsurface data. Another issue complicating rockslide forecasting is the unpredictability of their triggers. Dr. John Clague, P.Geo., a professor of earth sciences at Simon

Fraser University (SFU) and one of Canada’s leading authorities in quaternary and environmental earth sciences, stressed the importance of understanding the difference between what causes a rockslide, and what triggers one. “A cause is the set up that ultimately makes that rock mass susceptible to failure,” Clague said. “The trigger can be something trivial. It’s the old butterfly-on-the slope argument; sometimes, that’s all it takes to send it over the edge.” While geoscientists understand the mechanics of slopes and their strain on rock over time, the proverbial straw (or straws) that broke the camel’s back is tougher to identify amid the rubble. “All sorts of things trigger rockfalls,” said John Whittall, P.Eng., a senior geological engineer with BGC Engineering. “It could be freeze-thaw cycles; it could be roots just getting into one of these fractures and jacking it open over time; it could be vibrations; it could be that that rock found its time to go.” Therein lies another difference between rockslides and

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Winter 2025/26

Innovation