Looking at an unstable March backcountry — by Aaron Cooperman

It’s hard to not keep talking about avalanches this year. The past month has provided a strong lesson on persistent deep slab instabilities, so many eye-opening, destructive avalanches propagating wide across terrain features and running far. And, unfortunately, there have been fatalities across B.C. Three of these occurred in lower elevation cutblocks, including one recently near Blue River.

Check out the Canadian Avalanche Centres (CAC) incident data base.

This Size 1 slab avalanche in Sun Peaks’ backcountry was skier triggered from above while the skier was checking a drop. Photo submitted to avalanche.ca by the avalanche reporter.

This Size 1 slab avalanche in Sun Peaks’ backcountry was skier triggered from above while the skier was checking a drop.
Photo submitted to avalanche.ca by the avalanche reporter.

Locally, there was a skier triggered avalanche in the commonly used Gil’s area outside of the Sun Peaks ski area boundary. The party didn’t have avalanche safety gear, luckily they all skied away. Close calls like this are a strong reminder that anyone using the backcountry should have the right gear, training, and an understanding of the hazards.

The current snowpack problem started back in the dry spell of late January, which formed a thick weak layer of facets, surface hoar, and crusts on south aspects.  This weak layer was buried on February 10.  Rapid storm loading followed and produced a widespread cycle of naturally and human triggered avalanches to size 3.  But this “flushing” didn’t make the problem go away, it only got bigger with the next storm loading event in early March This warm storm added up to an additional meter of snow, burying the weak layer up to 2 m in some areas, and another weak layer of crusts and surface hoar from March 1.

Natural storm avalanches sliding on the March 1 layer triggered deeper slabs on the February 10 layer, producing large avalanches up to size 4.5 on Mt Cartier in Revelstoke. Throughout this period many avalanches were triggered remotely by skiers, snowmobilers, snowcats, and helicopters, indicating the touchy nature of the slab.

During this type of deep instability, extra caution is required, not only avoiding using avalanche terrain but considering the potential for avalanches to exceed normal run outs.  Professionals have been diligently, and patiently, running a tight conservative program and continue to be cautious with additional storm loading and rapid changes in weather that includes increased spring warming and sun affect. Cornices are very large out there, and have the potential to trigger deep slabs when they drop.

The CAC forecaster blog speaks well to the current deep slab avalanche problem.