The society says studies done in Yosemite National Park in California show that water seeping into fractures running behind and parallel to a sheer rock face can be just as damaging during extreme heat as they are in winter, when the freeze-thaw cycle can pry sheets of rock from the mountainside.
Rocks falling from the crags of the Stawamus Chief are common, but the society says what happened Tuesday caused “catastrophic damage” to the Grand Wall and Grand Wall Boulders, which attract climbers from around the world.
“There remains significant risk of further rockfall and there are a number of downed trees in the Grand Wall Boulders,” the site says.