'Big boom' of rockfall near Canmore startles residents

A huge chunk of rock broke off a mountain Monday with a boom so loud that people in nearby Canmore, Alta., thought a bomb had gone off — and it's just the latest in a year that has seen more rockfalls than most in the Bow Valley, says a local climber.

Alberta Environment and Parks says no one was injured and no trails were affected; however, the commotion did create a buzz on social media.

Andrea Edgar from Canmore says she was nearby when it happened.

"All of a sudden, my friend and I heard a big boom and we thought it was thunder. And then we looked up to where we kind of heard the sound and then we saw this big dust cloud," she said.

Edgar says the dust was coming down the mountain and rocks were falling down the side.

"We just watched it for a few minutes and it just turned into like basically a big dust cloud," she said.

Environment and Parks says this type of avalanche is common this time of year as the snow melts. 

However, Brandon Pullan, a Canmore-based climber and the editor of Gripped, Canada's climbing magazine, says it's not unique to the Bow Valley and that incidents like this happen all over the world.

"Well, I guess some people are calling it an avalanche. In the world of rock climbing, you call it a big rockfall," he said.

"What happened was just a big piece of rock … fell off, probably because of something called freeze-thaw."

Pullan, who has a degree in geology, says rock walls like Ship's Prow Mountain have cracks and chimneys that fill up with ice and snow, and that once it melts, the cracks expand and big rocks fall off.

"This thing has probably been slowly wedged off this mountain for centuries and it finally gave in to gravity and fell," he said.

He says rockfalls have been more common this year in the Bow Valley region, and that may have to do with an earthquake that happened near Banff in February, but it's hard to know for sure.

"You would need a lot of people doing a lot of tests to figure out exactly why this is happening, but it is happening more this year."

At Tunnel Mountain, which is near the Banff townsite and popular with hikers, a rock the size of five fridges recently broke off, Pullan said.

"Some mountain guides had to go in there and inspect it, clean it, make sure it was safe and then reopen it back up." 

However, the rockfall at Ship's Prow wasn't as big. The mountain lost a couple tons of rock from around 450 metres up.

"It's not a very popular mountain with rock climbers, but they do sometimes go up there," he said. "It will have left a lot of debris down below in a very big scree field." 

While people shouldn't be too concerned, Pullan does recommend bringing a helmet if you are traveling under cliffs.

"A lot of trails have been closed … a lot of other trails kind of skirt underneath cliff bans, and so everything has potential of being an objective hazard. People just have to watch out above," he said.

With files from The Homestretch.