Landslide in BC triggered 100m tsunami, caused earthquake scale: study

A retreating glacier in a remote valley of British Columbia triggered a massive landslide that triggered a 100-meter tsunami, wiping out miles of salmon habitat and being detected as far as Australia, a study says.

The Nov. 28, 2020 landslide sent 18 million cubic meters of rock crashing down the side of a mountain, uprooting trees and displacing soil before plunging into Elliot Creek, according to the study published in Geophysical Research Letters.

Earthquake sensors at stations around the world, including in Germany, Japan and Australia, have detected the landslide, the study said.

The slide destroyed salmon spawn habitat about 8.5 kilometers from the creek and sent a plume of mud and organic matter more than 60 kilometers into Bute Inlet, about 150 kilometers from Vancouver, it said.

Simultaneously with the slide, a professor at Columbia University in New York measured an earthquake measuring 5 on the Richter scale in that area.

Marten Geertsema, lead author of the paper and adjunct professor at the University of Northern British Columbia, said that while the landslide wasn’t the largest in Canada, it was “very, very huge.”

“Imagine a landslide with a mass equal to that of all cars in Canada traveling at about 140 kilometers per hour and landing in a large lake,” he said in an interview.

Geertsema said that when the huge slide fell into a lake below, most of the water was drained and forced through a 10-kilometer-long canal, causing widespread erosion and loss of salmon habitat. It removed about four million cubic meters of material from the creek in 10 minutes, something that would have taken thousands of years if the stream continued to flow normally, he said.

Prof. dr. Brian Menounos, Canada Research Chair in Glacier Change at the University of Northern British Columbia, said several factors came together to cause the slope instability and the landslide.

“What we don’t know is whether the last straw that broke the camel’s back, for lack of a better expression, was a downpour or unusually wet conditions in 2020,” he said.

What scientists do know, he said, is that glaciers that once covered the slopes and held them together are melting at high rates as a result of human-induced climate change, leaving the sides of the mountains loose and exposed.

Geertsema said the biggest impact of the landslide was on fisheries habitat.

The Homalco First Nation contributed to the research, and its members co-authored the study released last month, bringing their knowledge about Elliot Creek’s salmon habitat, he said.

Menounos said landslides are not uncommon and have shaped the landscape of continents over millennia, including creating or diverting water bodies and rivers.

However, deglaciation is expected to accelerate landslides, and in some cases, scientists have the tools and data to better map the topography beneath glaciers, allowing them to estimate such events, including new lake formations, he said.

“The ability to deflate maybe half the lake volume in 10 minutes or less, I mean it was hugely powerful and disruptive,” Menounos said. “It feels very small to study things with such power.”

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