At around 350 pm, March 19, 2017, a group of three skiers were taking a break near the summit of Ruby Mountain (7408 feet) which is located 3.5 miles south of the North Cascades Highway and about 3 miles east of Diablo Lake. Having already skied a long lap on the upper mountain’s north slope, they had just re-ascended their skin track and were taking in the views. 600 feet below them a party of two were descending the upper slopes. And further below that party, a group of three had already descended out of sight and into treeline. Skies were mostly sunny, skiing had been reported as good with 12 inches of recent storm snow, temps were in the upper 20’s, and winds were light out of the East.
What happened next, right in front of both of the highest groups, can best be described as a “low probability-high consequence” avalanche (LP/HC). The trigger in this case, a massive cornice collapse (estimated to be 30 feet tall at its failure point), initiated the fracture and failure of a Deep Slab - a size 3.5 avalanche with the destructive potential to destroy a car, a wood frame house, or break mature timber. It was approximately 1200 feet wide, ran 1400+ vertical feet, and had a crown depth of 7-25 feet. The avalanche narrowly missed the middle party of two, completely destroying all the ski and skin tracks from earlier in the day depositing debris well into treeline.
Photo above by Milda Tautvydas: Cornice Failure Point
Without a doubt, this was a close call. But, as local ski guide Larry Goldie likes to say: “Close calls are free lessons.” It can’t be overstated, therefore, what a gift this type of “free lesson” is for those of us who choose to recreate in avalanche terrain. We should all applaud any members of our community who step forward to share their close calls and view their experiences as “free lessons” - especially during long and complex winters like this one.
Alaskan Joe Stock writes about free lessons this way: “The fastest way to learn about avalanches is to almost get nailed by one. Not killed or hurt, just really scared. Where you can brush off the dust, thank Ullr, and analyze the shit out of what happened.”
Avalanche Canada’s, Karl Klassen, who recently wrote a timely article about low probability-high consequence avalanches, states: “Managing this problem requires discipline. But if you look closely and watch the big picture, like avalanche forecasters do, there’s a pattern.”
There is no doubt that that such a destructive avalanche as the one on Ruby fits firmly into the category of LP/HC. It is extremely unlikely, if not impossible, to human trigger such an avalanche. It takes something massive (rapid snow or wind loading, huge amounts of rain, large cornice fall) to trigger such a Deep Slab. Of the nine avalanche problems that have become the mainstay of public avalanche forecasting and education throughout North America, Cornices and Deep Slabs (as well as Glides and Wet Slabs) are among the most difficult to manage. Tests and observations are inherently unreliable. Behavior is unpredictable. Almost by definition these types of events are outliers. As Joe Stock points out, most avalanches could, in fact, be considered outliers given the fact that the snowpack is generally stable a vast majority of the time. Having an “outlier mindset” is a great tool for your toolbox, therefore, and a critical tool to wield wisely when the types of avalanches that are occurring are so large, as well as unpredictable and potentially deadly. Avalanches such as the recent one on Ruby are almost certainly un-survivable. The only trustworthy decision making tool at our disposal, therefore, is avalanche avoidance. Karl Klassen writes about this eloquently in the aforementioned article better than anyone. Situating yourself within avalanche terrain such that you minimize your exposure to very large avalanches is certainly possible, but know that if you make a mistake or have missed something, those large dice you just rolled are likely to crush you.
Photo by Milda Tautvydas: Upper avalanche debris deposit
One of first questions I asked the party who witnessed the Ruby avalanche was whether or not they observed it as a “step down” avalanche. From NWAC’s perspective, being able to identify the weak layer and bed surface of any avalanche is important. If you’ve been following the evolution of this winter’s snowpack, or have been keyed into the forecasts this season, you’ve no doubt heard a lot about the “Valentine’s Day” crust and it’s associated persistent weak layer. Being able to identify whether or not large to very large avalanches are continuing to run on this layer provides necessary context, places avalanche occurrences and cycles within an observable pattern, and speaks directly to avalanche size and destructive potential. After looking at the photos and talking to witnesses, it appears unlikely that the Ruby avalanche ran on the 2/14 crust. NWAC was not able to do a fracture line profile on this particular avalanche, therefore some level of uncertainty remains as to its bed surface and weak layer.
During the 10 days prior to the Ruby avalanche, cumulative water equivalent (WE) as measured by Mt Baker Ski Area telemetry was upwards of 15 inches. An astounding amount of water fell from the sky. While much of the west slopes of the Cascades were suffering heavy rain on snow events, it’s safe to say that above 6000 feet on Ruby, all that water fell in the form of snow. Extrapolating for its location in the range, NWAC Director Kenny Kramer thinks roughly 7-10 inches of WE fell on Ruby in the 10 days prior to 3/19. This translates roughly to 7-10 feet of storm snow. Throw in periods of intense wind loading and a Deep Slab of epic proportions is almost certain.
It also bears mentioning that peaks like Ruby, Shuksan, Hood, Rainier - all relatively achievable winter objectives with good road access - should be considered as unique “second tier” zones with respect to their elevation bands. On these peaks, motivated and fit parties can quickly access alpine terrain that has a different seasonal snowpack and weather history than what is the norm in our “above treeline” avalanche forecast band. Above the Cascade Crest, all the types of avalanche hazard and levels of uncertainty that come with increasing elevation and exposure are present (often at significantly higher levels) and this demands the requisite skill and experience to manage, not to mention a higher risk tolerance. This becomes more and more relevant as spring access to higher alpine terrain opens up, folks become more ambitious and start to stretch their legs more widely throughout the state.
Photo by Crispin Prahl: Mid-avalanche debris deposit
Looking back at the NWAC forecast for 3/19 and in the days prior, a trend is worth pointing out in light of these patterns: avalanche size trending up over time, dangers increasing with elevation and geographic location, and the lingering threat of LP/HC avalanche problems.
The Ruby 3/19 avalanche, therefore, is both a reminder that significant avalanche hazard remains, as well as a great segue into our spring season. A common question after many close calls with avalanches is to ask the question: “What did I miss?” I’d like to advocate, however, that we ask ourselves this question not at the end of our days, but perhaps more importantly, at the start of each day that involves travel in avalanche terrain...as well as along every step of our way while traveling in the snowy mountains. This mindset will always serve us well - building confidence, fostering solid group decision making, and ensuring the lessons that we all learn are free.
Note: All photos taken on 3/19/2017. Lead photo by Milda Tautvydas. Hyperlinked annotated photo of powder cloud and party of two below summit by Crispin Prahl. The original observation submitted to NWAC by the reporting party can be found here.