Observation: Public

Observation Details

Signs of Unstable Snow

Observations

Party of 3 triggered a wind slab avalanche while skinning up a west-facing slope just below the col at the top of Entrance Exam in the Baker Backcountry. The trigger location was about 20 feet below the col, and the slab broke ~5 feet above our party and ~20-30 feet across. Two people were caught - one was able to stay upright on the slope, and the other was carried ~100 feet and partially buried. The two unburied skiers were able to assist immediately and all were uninjured. We estimated the slab depth at 14" and the slope angle at the trigger point at 35-40 degrees.

Snow directly below the col was much deeper and more wind-loaded than nearby areas on the same face. We evaluated the snow as we went up - it was generally wind-affected, but cracking from the tip of a ski was minimal. The snow was alternately scoured and deep as we moved up and across the slope. We stopped to dig a quick hand pit when the snow suddenly switched from scoured to much deeper than it had been up to that point. From the pit we found a shallow (~3") reactive layer on top and another reactive layer ~14" deep. The lead skier took one additional step onto the slope, triggering the avalanche.

We were aware of the avalanche forecast and strong winds the day before. Wind was consistently out of the east rather than the south (as forecasted) while we were out during the day. In retrospect, our party should have been more spread out as the slope steepened and we should have been more cautious around the rapidly deepening snow right below a clearly wind-affected col.