5 people were killed in B.C.'s backcountry this year. Experts say this deadly season started months ago
CBC
Five people have been killed in avalanches across B.C. in the past month, including experienced skiiers and brothers on a guided heli-skiing trip in B.C.'s Interior.
Forecasters have compared this season's snowpack with conditions seen two decades ago, during one of the province's worst years on record for avalanches fatalities.
Experts have an explanation for what's making this season so deadly — and they say it started months ago.
This year's snowpack, with a weak layer of sugar-like crystals buried near the bottom, is being described as similar to that of 2003, when avalanches in Western Canada killed 29 people. Most of them were in B.C.
Avalanche Canada said conditions are particularly dangerous throughout the Interior, but more typical on B.C.'s South Coast.
Snow that falls onto the ground and does not melt until warmer temperatures in the spring is called snowpack. Snowpack can consist of multiple layers of snow, each one from a different snowfall, that become compacted — or pressed firmly together — under the weight of the layers falling on top.
A weak snowpack happens when one of the middle layers doesn't bond well to those around it. This fragile layer can collapse under the weight of topside snow and slip away. This leads to a slide called a slab avalanche.
This year's snowpack has a one major weak layer closer to the base and various other bad layers too.
A large part of B.C.'s problem this year began in the fall.
A shallow amount of snow near the ground was frozen by long spells of Arctic air in November and December.
When a thin snowpack is exposed to cold temperatures for a long period of time, snow grains get bigger and sharper. That means less overall surface area, which means fewer spots for the crystal-like snow to bond with layers of powder on top.
It's left the B.C. Interior with a weak foundation holding up the rest of the deep snowpack.
"It's just a perfect combination of things to build a weak base," said Ryan Buhler, Avalanche Canada's forecast program supervisor.
There are multiple warning signs a snowpack isn't stable, though clues aren't popping up as often this year because the weak layer is so deep.