A mudslide covers Highway 1 east of Chilliwack, B.C., Wednesday, June 29, 2011.JONATHAN HAYWARD/The Canadian Press
A massive mudslide that hit one car and a CN Rail train on the Trans-Canada Highway on Wednesday could not have been prevented, even though the area is vulnerable to debris flows every couple of years, the Ministry of Transportation says.
Heavy rainfall and snow melt are suspected to have triggered the slide, which started at around 1,070 metres up the hills just east of Mount Cheam between Chilliwack and Hope. As the slide thundered down the slopes, it ripped up trees and boulders and grew in volume. Within minutes, four to six thousand cubic metres of mud and debris spilled onto the eastbound lanes of the road.
According to Kurt Edmunds, operations manager at the Ministry of Transportation, remedial measures are put in place only after a slide has occurred. In 2002, a similar mudslide came down about 40 metres from Wednesday's flow and half-buried five cars and damaged several houses. Crews widened the bottom of the creek and stacked heavy rocks along the sides to contain any debris that comes down.
The area that was hit by Wednesday's slide did not have such measures.
"How would we know when a situation is going to let loose?" Mr. Edmunds said. "I appreciate proactivity is something we aim for, but we don't always have that luxury given the location where it came down from. It was so far back and so high up that there would be no indication that this would be happening."
Barry Penner, B.C's attorney-general and MLA for the Chilliwack-Hope riding, said the area's topography and weather make it vulnerable to landslides. The highways are monitored frequently for hazards coming down from the mountains, but often debris flows cannot be predicted.
"Most of the year those creeks look very non-threatening and they're small and, in fact, some of them don't even flow all year round," he said. "Yesterday they were raging, and you could see some of the waterfalls were running absolutely chocolate brown, but you can't prevent something of that magnitude. If the mountain's coming down, it's going to be on its way."
The mudslide, which measured 40 metres wide and 15 metres high, slammed into a car and pushed it off the road. The female driver had stomped on the brakes, but the mud wall hit and flipped the car over. She escaped with only a bruised knee, according to the Fraser Valley Regional District. No other vehicles or people were affected.
"That woman was very lucky," said Brent Ward, a geologist at Simon Fraser University, who added that the slide would have been a terrifying sight. "It would probably have been going at 60 kilometres an hour, maybe more. It would have sounded like a train was coming down the mountainside, and sometimes there's a bit of water that's in front of it, but if you were in your car, you wouldn't hear it."
Mr. Ward also said that it would be difficult to anticipate when a slide would occur. The Sea-to-Sky Highway that leads up to Whistler, for example, is protected by debris-retention structures, but if a "much bigger than average" flow comes down, it can overwhelm the retention walls.
"That's about all they can do, put in something to catch the debris when it comes down and hopefully stop it from getting to the highway," he said.
The mess on the Trans-Canada Highway was cleared early Thursday morning. The creeks are running clear, indicating that no more material is coming down, Mr. Edmunds said. However, with the weather starting to warm up, more slides could occur, and engineers will be assessing the location over the long weekend to see if any remedial work needs to be done.