May 2, 2008

Unstable Alberta mountain slope leads to building bylaw restrictions

FRANK, ALTA.

Exactly 105 years after the top of Turtle Mountain came thundering down upon the valley below in Alberta’s worst natural disaster, provincial officials fully expect history will repeat itself.

At least 70 people died that day when more than 30 million cubic metres of rock — some pieces the size of large trucks — crashed into the small mining town of Frank nestled in the Crowsnest Pass in the southern Rocky Mountains.

And with the mountain still moving, another slide is almost inevitable. It’s just a matter of when.

Corey Froese, who leads the province’s geological hazards program for the Alberta Geological Survey, says a chunk of the mountain about one-sixth the size of the original slide is currently moving downwards at millimetres per year. But that is expected to speed up as time goes on.

“As the thing starts accelerating, we would expect days to weeks of warning prior to the catastrophic collapse,” Froese said recently atop Turtle Mountain.

“That is unless you have a sudden seismic event. Conceivably, if you had a large enough seismic event, it could come down with no warning.”

In the name of early warning, the province plans to double the number of state-of-the-art monitoring systems scattered on top of the mountain this year.

They include laser sightings which measure the exact distances on the other side of the valley.

While there might be other mountains within the Rockies which are as unstable as Turtle, none pose such an imminent threat.

Cut through the nearly eight kilometres of rock fall from the original slide is the busy highway which connects southern Alberta to British Columbia’s Kootenay valley. There’s also a busy Canadian Pacific Railway line.

Even more disconcerting is the dozen or so homes nestled under Turtle’s shadow right within the so-called “splash zone.”

John Irwin, mayor of the municipal district of Crowsnest Pass, said a new bylaw is expected to be passed early next month that will forbid any further construction or subdivision in the path of the next slide.

“It would be irresponsible for us to put anyone else in harm’s way when we’re aware of the risk,” Irwin said.

“We don’t know when the mountain will fall again but we know that it will some day — it could be next week, could be a thousand years from now.”

Canadian Press

Print | Email | Comment