Observation: Public

Observation Details

Triggered Avalanches

Signs of Unstable Snow

Observations

On April 16th, myself and two partners snowmobiled up to Harts Pass for a day of snowmobiling/skiing. We skied several runs on the lower angled south and southeast sides of Harts pass peak before deciding to ski a run on the steeper east facing slope above meadows creek campground. As we ascended the gentler slopes on the south side of this hill we noticed some wind scoured snow that clearly indicated that the wind had been at work in the area. From the top of the hill, we skied due southeast and my partner triggered a wind slab in deep, pillowy snow just below a steep rollover. He was thankfully able to stay above and eventually ski out of the debris unharmed, however there were several trees in the path of the slide that he could have been dragged into.

I made several mistakes leading up to the avalanche. My first mistake was that I misinterpreted the signs of wind activity as I neared the top of our planned run. I knew from recent weather data that the prevailing winds had generally been coming from west to east however the scouring that we observed was much lower on the east side of the hill than I would have expected and given the fact that we could not see any area where the wind had clearly deposited the scoured snow, I hypothesized that the wind may have been blowing from east to west (in reverse of previous weather data) in this spot. In retrospect, this was an extremely poor interpretation of what I was seeing. First, I allowed only a few data points to override my knowledge of the general weather patterns in the area. Second, I did not consider any alternative explanations for what I was observing. Since we were on a south facing shoulder when we observed the scouring, it would have been very difficult to see far enough down the slope to the east to observe the deposited snow that we ultimately triggered. It is clear after the fact that the wind had rolled around the south side of the hill from the southwest and cross loaded the east slope. This is evident from the faint shadows on the lookers right (north /leeward side) of the trees in the photo that we submitted. It also explains why we observed scouring on the east face far below the ridge line.

My second mistake was that I was insufficiently sensitive to the very localized nature of the avalanche problem that we were dealing with on the day (wind slab). We had observed several snowmobilers rip up and down the particular slope that we were intending to ski, and given that we were not dealing with a persistent weak layer I interpreted this to indicate that the snow on the slope was generally stable. However, none of the snowmobilers had tried the steep rollover where the avalanche ultimately triggered. Given that this is a textbook place for a wind slab, we should have immediately flagged the spot as a feature to avoid.

My biggest takeaway from this incident is that it’s extremely important to remain on high alert for localized terrain features that could increase avalanche hazard. Prior to the avalanche, we had observed multiple snowmobilers high pointing below and around the site of the wind slab. It’s possible that these folks were just getting lucky, however it’s also possible that the spots that they were choosing to ride were stable and that we managed to find an island of instability. No matter what, you have to always be on guard for locations with increased hazard, even when conditions are generally stable.