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It’s time to stick to simple terrain

 | March 26, 2013
Skier-triggered slab avalanche on the February 12 sun crust layer. This slide was triggered by the eigth skier on the slope. Photo: Aaron Cooperman
Skier-triggered slab avalanche on the February 12 sun crust layer. This slide was triggered by the eigth skier on the slope. Photo: Aaron Cooperman

March can be a tricky time when it comes to avalanches. Dry periods in February often form isolated weak layers of surface hoar and facets on north-facing slopes and sun crusts on south slopes. This was the case this February, with weak layers buried by a light snowfall on February 12. Small, incremental snowfalls began to form a cohesive slab — initially not reactive to skiers. This is a common scenario for March.

March is also tricky as mixed weather of alternating cold and warm temperatures with brief sunny periods form isolated layers of crusts and surface hoar. As these layers become deeper, consequences increase and they’re no longer safe to test with ski cutting.

This is a complex snowpack situation requiring constant technical evaluation.

A “Pineapple Express” arrived March 1, bringing heavy precipitation, wind, and warm temperatures — all the right ingredients for large slab avalanches on the February 12 weak layer. The Public Avalanche Bulletin issued by the Canadian Avalanche Centre forecast high to extreme danger ratings for March 1 — which proved true with a large destructive avalanche cycle.

At the time of writing this report a more recent weak layer is being rapidly loaded by 60 millimetre water equivalency producing widespread natural and skier triggered avalanches to size two. With more snow and warm temps on the way it’s a time to stick to simple terrain and stay well away from overhead avalanche slopes until this layer begins to bond.

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