After almost six months, the Dec. 5 snow crust is continuing to cause problems in the alpine as Blackcomb ski patrollers took the unusual step of closing all but two lifts this past weekend due to the risk of avalanche.
According to Tony Sittlinger, senior avalanche forecaster for Blackcomb Ski Patrol, the patrollers started to close the Lakeside area of 7 th Heaven on Tuesday, May 13 in response to avalanches that were spotted outside of the ski area boundary and patrol tests in the ski area. The risks got progressively worse, with patrol closing sections of the alpine before making the decision to close the Glacier Express and 7 th Heaven lifts, as well as the Horstman T-Bar on Sunday, leaving just the Excellerator and Crystal lifts open to the public.
Sittlinger says it might be possible to open the south runs on 7 th Heaven this week with cooler weather and sub-zero temperatures returning to the alpine, but the risk at press time is still high.
“We were already closing areas for avalanches on Tuesday (May 13), and as the temperature has risen and the warm weather persisted the closures were more and more widespread,” he said. “Inside the Blackcomb ski area there have already been four size-three avalanches, full depth avalanches or close to it, and all of those were in areas we closed.
“It’s going to take some time to calm everything down. There’s still quite a bit of momentum in the snowpack and avalanches in excess of three metres at the deepest point, which is virtually full-depth.”
Sittlinger is also warning backcountry skiers to stay out of the alpine for the time being.
“We were seeing full depth avalanches on compacted, inbounds terrain that had moguls,” he said. “We were able to predict them, close the areas, and avoid any problems in the ski area, but outside there is less compaction, uncontrolled cornices, and the potential for more deep slab activity.”
Cornice failures and snow falling off rocky areas onto slopes below have been identified as causing avalanches outside the ski area boundaries.
The Dec. 5 snow crust was formed during a period of rain in the high alpine across southern B.C. The wet surface quickly froze and was covered by snow. Although the snowpack consolidated over the next month and a half — the last in-bounds activity related to the Dec. 5 weakness was on Jan. 15 — the latest warming cycle has brought the crust into play again.
“The whole snowpack is always changing and moving depending on temperature, crystal type, density, and other variables, and with the warm temperatures we’ve seen snow turn to water… and the snowpack start to creep,” said Sittlinger. “When you get more free water into the snowpack it starts to accelerate, which led to a lot of the big events we were seeing. Any significant trigger onto a gliding snowpack, on top of that week layer, had the potential to trigger a larger slab avalanche.”
Just as it took five days for the avalanche risk to reach its highest point, Sittlinger says it could take just as long for the cooler temperatures to stabilize the snowpack.
“We’re monitoring it closely. It may seem that things developed rapidly, but it took days to get to the point where things were at their worst on Saturday night and Sunday morning. It will take days for things to settle down.”