The headline should be fairly obvious. Residents of the Sea to Sky region live in the shadows of mountains on either side. Squamish, Whistler and the Pemberton Meadows especially.
But nevertheless, with concerns about landslides heightened in light of the Meager incident, it’s worth reflecting on other areas of the Sea to Sky region where avalanches could pose a serious hazard to nearby residents.
Here’s a story I did about the Barrier near Squamish, which doesn’t present as much a risk as did Meager but is nevertheless serious enough to have required the uprooting of a town nearby.
The Barrier remains a concern
In the wake of the Meager landslide is the region prepared for another natural catastrophe?
By Jesse Ferreras, Pique Newsmagazine
September 1, 2010
The Meager area isn’t the only part of Sea to Sky that’s vulnerable to landslides.
The second biggest landslide in Canadian history, which fell about 60 kilometres from Pemberton last month, creating a natural dam in Meager Creek and closing the Lillooet Forest Service Road, has raised concerns in the region about the risks that landslides post to various communities.
Some concerns persist in particular about The Barrier, a natural lava dam located about halfway between Whistler and Squamish in Garibaldi Provincial Park. It’s about 300 metres thick and holding back Lesser Garibaldi Lake.
Though the lake is about two kilometres from The Barrier, there are nevertheless worries that the dam could collapse, releasing the water and causing downstream damage as far as the District of Squamish and the waters of Howe Sound.
The story of The Barrier goes back about 13,000 years to when Mount Price, one of the 13 cones in the Garibaldi volcano, erupted and sent a massive lava flow down the Rubble Creek valley.
At the time the valley was still filled with the Cordilleran ice sheet, a major sheet that covered a large part of North America including Western Montana, northern Washington and just about all of British Columbia.
The lava flow stopped at the edge of the glacier that filled the Cheakamus Valley. When the lava met the glacier it retreated, creating a crevasse-like opening against the ice that was later filled with more lava. This process took place several times and created vertical slabs of lava right across the width of the Rubble Creek valley.
The process created a natural lava dam that blocked the valley and allowed Garibaldi Lake to form behind it.
“This was identified by one of my geology profs, Bill Matthews, years and years ago,” volcanologist Jack Souther said in an interview. “He noted that the columns at the toe of The Barrier were horizontal. They’d been quenched against the ice and therefore had grown back at right angles to this vertical surface.”
Once the glacier melted, it left behind a vertical cliff of lava now known as The Barrier.
As geologist Frank Baumann tells it, the lava flows that make up The Barrier are brittle and broken, creating constant rockfalls that vary in size. The falling material builds up at the base of the Barrier Cliff and creates a “big sloping apron” of material known as talus.
In an e-mailed response, Baumann described two theories that exist regarding future landslides at The Barrier.
The late UBC Professor William Mathews advanced the first one. He said big vertical slabs of lava that make up the Barrier Cliff occasionally collapse and form massive rock avalanches that move down the valley.
The other theory suggests that water flows under the bottom of the talus slope at the base of The Barrier and over the top out of Barrier Lake during hot summers. This process saturates the deposits, causing them to collapse and form big debris flows that then flow down into the valley.
The last such flow occurred around 1856. The date was established by First Nation legends describing how the Cheakamus Valley between Squamish and Pemberton was blocked by a major landslide around that time. Also, the rings in the trees in the Rubble Creek valley suggest they’re less than 154 years old.
Asked precisely what it would take to make The Barrier fall, Baumann said, “basically a big flow of water out of Barrier Lake that saturates the talus cliffs at the base of The Barrier and mobilizes them. A big rock fall off The Barrier is triggered during periods of very wet weather or could also be triggered by an earthquake.”
Concerns around the area’s instability reached a peak in 1980. The community of Garibaldi was then situated along the Cheakamus River where Rubble Creek joins it, near the Black Tusk trailhead.
The provincial government was alerted to Mathews’s theory about a big collapse of rock at The Barrier, falling far enough to damage the town’s homes and infrastructure. The government thus began making arrangements to move the town.
Nelson Bastien was a Garibaldi resident when the provincial government decided to move the community. He said in an interview that the town had about 85 homes, as well as a couple of lodges, cabins and campground. There was also a fire hall, school and a recreation hall. It was located close to the Chance Creek bridge crossing, the log cabins and campgrounds immediately to the bridge’s right.
“The community was built around that highway from there north,” Bastien said. “Both sides of the highway had homes, I was right along the Cheakamus River.”
Prior to May of 1980, work was beginning on a subdivision called Evergreen on the east side of the highway. It was stopped when the government did a study into the stability of The Barrier but didn’t immediately release the report.
Then the eruption of Mount Saint Helens took place in Washington state, the only significant eruption on this side of the world since 1915. The government began to worry that another eruption in the Cascade chain, which the Garibaldi volcano belongs to, could stir another rockslide.
The province released the report and passed an Order-in-Council ordering that all development stop in the vicinity of The Barrier.
The government gave Garibaldi residents two choices: be bought out or they wouldn’t be able to do anything with their properties in future, including leasing, selling or repairing them.
“If a power line fell down, it was gone forever,” Bastien said of properties that weren’t sold to the government.
The government assessed all the properties at Garibaldi then met individually with owners to bargain with them about the value of their homes. The government eventually bought all of them out and allowed them to bid on properties at a new site called Black Tusk Village.
Sixty-three families took part in the “land draw” for Black Tusk Village but only about 26 of them actually moved there. Bastien, for one, got $104,000 for his property, a 1,100 square foot rancher. The payout included $8,000 for the Garibaldi lot. He bought a lot in Black Tusk Village for around $40,000.
Today, Bastien questions whether there was ever a significant risk from rockslides at The Barrier. He wonders why the town had to be kicked out when there are still power lines and a highway running through the area.
“You’ve got a highway that has hundreds of people at the same time, you’ve got a train running up and down,” he said. “There’s so many other dangers that could be created, but they chose to kick us 85 people out of there.”
Baumann conceded in his e-mail that there’s currently very little risk of a rockslide from The Barrier, but he didn’t dismiss the possibility of another major landslide down the Rubble Creek valley.
For this reason, he said, it was “probably correct” to remove the town of Garibaldi, although he also said it could have been done with less urgency.
“A future event is likely,” he said. “Hundreds, if not thousands of years away.”