When the side of a B.C. mountain gave way on Nov. 28, 2020, crashing into a glacier fed lake and creating a 100-metre high tsunami, no one was around to see the destruction or hear the sound of rocks and trees tearing through the valley below.
But scientists say the force, which was picked up by seismographs across North America, was the equivalent of a 4.9-magnitude earthquake.
Fortunately, no one was in the slide’s path, but experts believe that a melting glacier likely contributed by making the slope less stable — and climate change means it is a growing risk.
As more of Canada’s glaciers recede, scientists say there is great interest in finding out what exactly triggered this slide, and how the rocks and sediment have impacted the salmon population of nearby Elliot Creek and Southgate River.
The mountain, which is located about 220 km north west of Vancouver, is on the traditional territory of the Homalco First Nation.
It’s an area of remote wilderness, only accessible by air or by boating 80 km up Bute Inlet.
When the slide hit last year, more than 18 million cubic meters of rock barrelled down the slope hitting the lake within 30 seconds.
“That is the equivalent of all of the cars in Canada coming down the hill at once,” said Marten Geertsema, a geomorphologist who works with the B.C. government studying landslides.
He is one of several scientists, along with members from the Homalco First Nation, who have been studying the landslide and its cascading environmental impact on the watershed and salmon habitat.
A CBC crew flew with scientists and Homalco members on June 15 as they viewed the landslide from above and collected water samples on the ground.
Onboard was Brian Menounos, a professor of geography from the University of Northern British Columbia and Canada Research Chair in Climate Change.
As the helicopter circled above the glacier, loose rocks could be seen tumbling down the slope.
WATCH | Landslides can be triggered by melting glaciers:
Scientists were looking for fractures in the mountain, as well as a flat and stable place where they could install monitoring equipment and cameras to track any further movement.
Menounous said they know how much material broke away because they had completed a surface elevation model of the icefield and the mountain before the slide. They surveyed the area again afterwards with the help of the Hakai Institute, a B.C.-based scientific research institution.
He said the slide was so destructive because it created an outburst flood which was caused by water being dramatically displaced from the glacier lake, which sits about 1.5 km below the top of the mountain.
Due to the receding glacier, Menounous said the lake has roughly doubled in size since the 1950’s.
“In this case, we were fortunate. We dodged a bullet,” Menounos said, citing the remote location of the landslide.
“But you can imagine this sort of event happening in the Whistler corridor or other locations where you have a much denser collection of people living.”
Damaged salmon habitat
While some of the research is focused on the why and how of the slide, another part of the team has been studying the impact on the watershed.
Elliot Creek, which lies downstream from the glacier lake, was pummeled with rocks and trees that were stripped from the landscape by the wave.
According to Ian Giesbrecht, an ecosystem scientist with the Hakai Institute, the creek moved 800 metres after the slide.
“Each time it moves, that’s changing the habitat that’s available in there for fish and it’s sending a pulse of sediment out into the river,” said Giesbrecht.
He, along with others from Hakai, had been doing water sampling in the area before the slide, but ramped up the testing afterwards by taking water from additional sites.
Over the winter, the team found large spikes in turbidity or cloudiness of the water — 32 times more in some cases— downstream from the slide in the Southgate River, compared to upstream.
Giesbrecht said very cloudy water can be harmful and even fatal to fish if they are exposed to it for a long period of time.
While salmon populations may try to avoid turbid areas, Giesbrech said if they can’t, the water quality can impact their ability to find food, grow and survive.
According to officials from the Homalco First Nation, the slide damaged crucial habitat for Chum and Coho salmon.
This is why Erik Blaney, the First Nation’s coordinator for landslide response, said they declared a state of emergency afterwards.
“That is a crisis for us,” he said. “It is a major blow to the food sovereignty for the nation.”
Blaney said it also threatens the Homalco’s economic development.
The salmon runs attract grizzly bears, which in turn bring tourists for the First Nation’s wildlife tours, which are held Orford Bay, a former village site on the east side of Bute Inlet.
This is where Homalco also runs a salmon hatchery.
Homalco Chief Darren Blaney said their goal has always been to expand the hatchery and help boost declining salmon stocks. He believes it’s even more pressing now because of the landslide.
“I think with all of the turbidity and stuff that’s coming out of the river now, it’s not only this year’s run that will be impacted,” he said.
“We need to figure out what we need to rebuild.”
He said the First Nation recently launched the “Homalco Guardians” program designed to monitor salmon populations through DNA samples. They hope to expand the effort in order to track which fish are returning.
Chief Blaney said that at the base of Elliot Creek there were Coho pools where the fish would rear. As those have been decimated, they are looking at the possibility of creating new channels that would serve as habitat.
However, according to Derek Ray, a coastal geomorphologist, restoration would be expensive, as it would would involve excavating a new channel and bringing all the equipment and crews up on a barge.
“The risk is that you would put a lot of effort in and it would be overwhelmed again by more sediment and more material coming down the channel,” said Ray, who works for Vancouver-based Northwest Hydraulic Consultants and spent a few hours surveying the area.
WATCH | Examining the environmental impact of Bute Inlet landslide:
Ray said these types of slides have happened throughout history and while nature gradually repairs itself, the key difference now is that many salmon runs are struggling.
“Most salmon runs are pretty heavily impacted already,” he said.
“We are talking nails in a coffin now.”