What's climate change doing to avalanches and how we predict them?
CBC
In February, five people were killed in separate avalanches across B.C. and Alberta. That same month, more than a dozen people were killed in California and Utah, including a particularly deadly avalanche that claimed the lives of nine. In Europe, from Andorra to Slovakia, the season has recorded 125 deaths from avalanches so far.
These tragedies highlight the ever-present risk of backcountry recreation, even as some of those killed were experienced and well-equipped for avalanche dangers. But they also highlight the challenges to knowing when an avalanche will strike.
CBC News spoke with three experts to find out how avalanches form, why they're hard to predict and whether climate change will make them more dangerous.
An avalanche is "a mass of snow moving at a visible speed," said Simon Horton, research officer and forecaster at Avalanche Canada.
Ethan Greene, director of the Colorado Avalanche Information Center, adds that this movement is generally down an inclined slope and follows a basic premise: "You need a very strong layer over a very weak layer in order to produce an avalanche."
And then you need a trigger, some kind of stress on the layers to kick it off.
How and when these ingredients are added is critical — and you can see that when cutting into a mountain snowpack.
And while it may look uniform, Greene says snow and ice are very dynamic.
"The crystalline structure of the snow is always changing," Greene said. "Sometimes, it'll change to make things stronger. Sometimes, it will change to make that layer weaker."
Nicolas Eckert, a scientist who studies mountain risks with Université Grenoble Alpes and the national research organization INRAE, says the snowpack gradually transforms with each successive precipitation or temperature event.
"Each layer evolves," Eckert said. "That can create conditions which can be more or less favourable to avalanches."
Avalanche types can differ, from loose, not very cohesive sluffs to heavy, water-logged chunks, each with different triggers.
"We call them avalanche problems because there's these common patterns that form that weak structure and those patterns have similar distribution over terrain," Horton said.
Greene and Horton consider ‘slab' avalanches as the most dangerous group, which are cohesive pieces of snow that break off the hillside.
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