A group of skiers triggered a wind-slab avalanche Sunday just northwest of Mount McDonell in the Haines Pass, killing one person and injuring another, according to a preliminary report released by Avalanche Canada.
The avalanche triggered as a group of five descended a slope northwest of Mount McDonell. The fourth person to descend triggered it during the descent at just above 4,400 feet in elevation.
One person was fully buried in nearly 5 feet of snow, and another was partially buried, according to Avalanche Canada’s report.
Someone in the group sent out a Garmin SOS alert about 3:26 p.m., and, according to a media release, Atlin Royal Canadian Mountain Police received it about 310 miles away.
When emergency officials got the call, one person was reported unconscious and receiving CPR.
Atlin Search and Rescue responded with a helicopter and flew out all five people, including the deceased group member. No identities were released.
On an avalanche scale of 1-5, Avalanche Canada rated this one has been rated as a 4, which can destroy large trucks, buildings or railway cars. It began as a wind slab, formed when snow is picked up from the upwind side of an area and deposited into thick drifts on the downwind side.
According to Avalanche Canada, as the avalanche slid, it broke deeper into a weak layer, causing an even larger slope failure toward the bottom. It slid nearly 2,300 feet and spread more than 1,300 feet wide at its base, according to preliminary reports.
Haines Avalanche Center director Jeff Moskowitz warns of deeply cold temperatures that create weak layers in the snowpack, which gett buried with each successive snowfall. One in particular is a persistent weak layer that formed about Feb. 14, he said, and has been called the Valentine’s layer. As the snow piles up on top of it, danger signs are more difficult to see.
The area where the avalanche happened, also known as Rainy Hollow, Moskowitz said has a unique snow climate – particularly when compared with nearby Chilkat or Haines Pass, which is a popular destination for backcountry recreation.
“Basically, we’ve had these really strong northerly outflows for months, and a lot of the upper pass has been totally windhammered. The snow has been stripped,” he said. “Rainy Hollow has been wind protected, so it was protecting these weak layers as they were getting buried. It’s a unique spot that has overlapping maritime and continental snow characteristics.”
Avalanche Canada rated the area’s danger at “considerable,” which Moskowitz reaffirmed saying that human-triggered avalanches are likely.
Moskowitz said he has seen shooting cracks — a visible fracture in the top of the snowpack — while out in the backcountry. Shooting cracks occur because of weight from above, often caused by skiers traveling on the surface. He has also gotten reports of human-triggered whumpfing sounds, or collapsing, which occurs when the snowpack drops with weight from above.
Moskowitz said that the strong-over-weak layering is “fairly widespread.” This occurs when a cohesive slab, essentially snow layers that are densely packed together either because of settling or to the wind adding load, lies on top of weak, sugary-faceted snow, creating poor bonds between layers.
Such layering occurs when stiff snow, often from snow drifts, sits on top of a layer of sugary snow – or snowflakes that don’t stick together well.
For those traveling into the backcountry, Moskowitz advises to “make conservative terrain choices while the snowpack adjusts, and that could include sticking to slopes less than 30 degrees.” Additionally, he said skiers should carefully assess conditions and layers before committing to steeper slopes and be aware of the high degree of uncertainty.
Since 2012, eight people have died because of avalanches around Haines, in addition to an avalanche partially burying one person.
Elsewhere in British Columbia, three heli-skiers died north of Terrace in the northwestern part of the province. At least nine people have died in avalanches since December, according to the Canadian Broadcasting Corporation.
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