GoPro video: See an avalanche dog ski
TORONTO – Recently, a skier in Banff National Park accidentally triggered an avalanche and was lucky enough to ride it out safely. But he was lucky. Each year an average of 14 people are killed in avalanches across Canada.
But what causes them?
“Snow hates rapid change,” said Ilya Storm, forecast coordinator for Avalanche Canada.
The winter snow pack is made up of layers, all of which reflect the weather over time, Storm said. The weight of the snow can change the snow that is at the bottom.
Some of that change can be in snowfall, temperature, wind, or even humans.
Though people can trigger avalanches — as seen in a recent YouTube video — most of them occur naturally. They are most likely to occur within 24 hours of a snowfall of 30 cm or more.
“It’s kind of like you putting out your arms, and me loading you up with sacks of flour…so it’s a lot of extra weight. And that extra weight, the snowpack needs time to adjust. So in the long term it can accommodate that, but in the short term, it’s like, whoa, I can’t handle that, and it releases.”
But there are other factors. Take temperature difference, for example.
Rapid warming can be another big contributor, especially if the temperature gets above 0 C.
“There’s a real change in snow when it turns from solid to liquid and it loses all strength,” Storm said.
As for humans, they act as a rapid load on what may already be an unstable snowpack.
“Somewhere around 90 per cent of people who die in avalanches have triggered the avalanche themselves, or someone in their party,” Storm said.
Types of avalanches
There are two types of avalanches: sluff and slab.
Sluff, or loose, avalanches are most common. Powdery snow moves as a mass down a mountainside. They are dangerous, but not as dangerous as slab avalanches.
Slab avalanches are just what they sound like: large slabs of snow break loose and speed down a mountainside at a speed of 130 km/h within seconds. The YouTube video of the skier in Banff, triggered a slab avalanche.
According to the National Snow and Ice Data Center in Colorado, a large avalanche could release up to 230,000 cubic metres of snow. That could fill 20 football fields with snow three metres high.
That fresh snow can cause the snow beneath it to become unstable, fracturing a slab.
Being caught in an avalanches is scary and dangerous. When the snow settles, it’s like concrete. And most deaths occur due to suffocation.