INNOVATION January-February 2016

R ockfalls and snow avalanches go hand in hand with British Columbia’s mountainous terrain. Most cause no trouble, because they happen far from humans and their habitats. But, as more and more people find their way into steep-sloped country, the result can be an unequal match-up between man and mountain. For example, just before noon on Sunday, April 19, 2015, an estimated 1,600 cubic metres of rock fell from the north wall of the Stawamus Chief, the 350-metre-high granite cliff by Squamish on the Sea-to-Sky Highway. The rock landed close to the Angel’s Crest trail and near the base of a popular rock-climbing route within Stawamus Chief Provincial Park. At the time, no one knew if climbers were on the trail or possibly buried at the route’s base, or if more rock would come crashing down. The District of Squamish called in GeoPacific Consultants Ltd. GeoPacific’s engineers arrived by helicopter within 45 minutes of the rockfall, and determined it was not yet safe to send in a search and rescue team or to open the forest service road at the base of the North Wall. They recommended further expert evaluation as soon as possible—that's when they called in Duncan Wyllie, P.Eng., of Wyllie & Norrish Rock Engineers, and Paul Schlotfeldt, P.Eng., of Golder Associates Ltd. Wyllie and Schlotfeldt viewed the rock face from a helicopter at about 4:00 p.m., then ground-reconnoitered the downslope edge of the rockfall. “Climbers like crevices,” says Wyllie, “and Angel’s Crest has lots of them, so it’s a good place to climb, but also dangerous—there could well have been climbers underneath the rockfall.” Together, the group of rock engineers agreed that the risk of more large boulders coming down was slim, and that a ground search could be carried out. They also recommended opening the forest service road to regular traffic, but temporarily closing the Angel’s Crest trail and the climbing route. Fortunately, rescuers found no one under the rockfall, but a few people had been climbing routes above the place where the cliff failed. The rockfall could easily have caused casualties. “The Angel’s Crest rockfall was a completely natural phenomenon,” says Schlotfeldt, “something that happens a lot in the Squamish and Sea-to-Sky Highway area. This time, there were some very fortunate and lucky people on that trail who had left the area or were high enough on the climbing route to be out of harm’s way.” Lucky this time—rockfalls can and do kill people. They can also close highways and railways for long periods, wreaking havoc on communities and economies. Europe and Japan, with their long histories of populations pushing into mountainous areas, are far ahead of Canada in their development of both rockfall and avalanche protection measures.

Rockfalls not only can kill people, they can close highways and rail lines for long periods, cutting off communities and causing economic losses. P hoto : BC M inistry of T ransportation and I nfrastructure , via CC BY-NC-ND 2.0 F acing page : Just before noon, Sunday, April 19, 2015, an estimated 1,600 cubic metres of rock broke off the north wall of the Stawamus Chief, along the Sea-to-Sky Highway. It landed near a hiking trail and the base of a popular rock-climbing route. P hoto : P aul S chlotfeldt , P.E ng .

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