A massive mudslide west of Banff shut down the Trans-Canada Highway for several hours on Friday (July 20), forcing the RCMP to turn visitors away from the national park tourist town.

And Parks Canada warns more heavy rainfall could trigger more mudslides, especially given the combination of record snowpack high in the mountains over winter and a very wet June.

“It’s like trying to predict an earthquake, but if we get another heavy rainfall, I wouldn’t be surprised if it did happen again,” said Douglas Kerr, Parks Canada’s operations manager for highways and roads.

“With the conditions we’ve had, the drainage channels are quite unstable. It’s up to Mother Nature, but I’m preparing for more of these kinds of events.”

A torrent of mud, trees and rocks swept down the mountainside onto the highway about two kilometres west of Banff at about 3:30 p.m., as thousands of tourists flocked to the mountains or were simply passing through.

The RCMP turned people away from Banff, except those with hotel reservations or residents, setting up a roadblock at the east gates to Banff National Park around 6 p.m.

Vehicles were backed up for 25 kilometres through the park.

“I’m just relieved that nobody was hurt,” said Banff Mayor Karen Sorensen.

“It was unfortunate for people, but I know Parks Canada and the RCMP did everything they could under the circumstances.”

The mudslide closed the highway in both directions, with about a metre of mud landing on the westbound lanes and half a metre on the eastbound lanes. Thick, soupy mud also made its way onto Vermilion Lakes road.

Parks Canada rescue specialists were quick to make sure no one was caught in the slide. A handful of people on Vermilion Lakes Road were flown to safety by helicopter, but one vacationing couple spent the night there in their RV.

“There were a couple of people stranded on Vermilion lakes, but we moved them out with a helicopter,” said Marc Ledwidge, visitor safety manager with Parks Canada.

“One couple spent the night in their motorhome and they were fine because they had food and shelter.”

Using loaders, excavators and trucks, Parks highway crews were quick to get the eastbound lanes open within a few hours, and the westbound lanes of the highway were re-opened around 1:30 a.m. on Saturday (July 21).

Kerr said the mudslide ran about 400 metres in distance, completely covering the highway, flowing over the centre barrier onto the eastbound lanes and down onto Vermilion Lakes Road below.

“When this type of debris flow comes down, it’s very soupy, but it has a lot of rock and wood and whatever else is brought down,” he said.

“This area is not a creek. I’ve seen the shoulder of the road covered there, with a bit coming out, but never anything like this here in my 29 years of working with Parks.”

In 1999, huge amounts of debris were washed down Five Mile Creek – just three kilometers west of this location – following intense rainfall. The highway was closed for several days as a result.

The Rockies and southern B.C. have been hit hard my massive mudslides this summer. Two people are dead following a slide that wiped out three cabins near Johnson’s Landing on Kootenay Lake earlier this month.

Tourists were also stranded when a slide came down near Fairmont Hot Springs in B.C., temporarily closing Highway 93 and covering the source of the springs.

A smaller mudslide also came down on the Minnewanka Loop on Friday.

Kerr said the conditions have created a “perfect storm” for mudslides, noting Friday’s slide across the highway came down following 45 minutes of intense rainfall.

“We had record snowpack, late spring runoff and in early June we had severe rainstorms,” he said, noting 122 mm fell in the valley bottoms in the national parks in two days in early June.

“That whole thing, combined with some of the biggest runoff I’ve ever seen, has de-stabilized the drainage basins and created some unusual conditions.”

The timing of Friday’s mudslide could not have been worse, as at mid-afternoon on a Friday in summer can see up to 50,000 cars a day passing through.

“The only thing that could have made it any more difficult is if it had been on a long weekend. The timing was extraordinary,” he said.

“There’s just no other route and there was a huge amount of effort by everyone – Parks, RCMP, emergency services, everyone – it really was a coordinated response to this.”

Meanwhile, Kerr said a culvert beneath the Trans-Canada Highway at Five Mile Creek that was completely blocked earlier this summer with debris following intense back-to-back storms in June – is working fine.

“In fact, when I got the call about the mudslide on Friday, I was sure it was Five Mile. That’s where I expected this incident, but Five Mile was actually fine,” he said.

The Banff townsite was extremely busy throughout the entire weekend, but Mayor Sorensen said it’s her understanding Banff was going to be busy anyway with many hotels reporting no vacancies.

“Once the RCMP got word that Banff was full, that is when they chose to start not allowing people to come in unless they had a confirmed reservation or were residents,” she said.

“I assume Banff was to full capacity on Friday night, but I also believe it would have been close to capacity anyway. Anyone who was headed to B.C. probably made the choice to get up and leave on Saturday.”

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