This is a sign of things to come throughout the French Alps and surrounding areas….
On the subject of off-piste and ski touring, here at Henry’s Avalanche Talk we never want to frighten people from going out into the backcountry because there’s almost always a way to do it safely. However, right now there are some really serious things to look out for.
This skier-triggered avalanche in the Queyras (French Southern Alps) on Sunday December 6th on a NE facing slope around 2700 m, was not a surprise given the recent evolution of the snowpack. It happened as a result of new snow which came down on top of a very weak layer of cohesion-less facets (which we sometimes call ‘sugar snow’ and in French is sometimes referred to as ‘goblets’ or ‘rock salt’ because of its texture). This weak layer is present throughout the French Alps in similar sorts of shaded or North’ish facing slopes. Most of the Southern French Alps has recently received more snow than the N. French Alps, which is one reason why I mention it’s a ‘sign of things to come’. There’s more snow on the way.
Thanks very much to Data Avalanche and the guys ‘sur place’ for the info. On the subject of the people who were involved with this event on site, I really appreciate you sharing your experience because all of us can benefit from the information and obvious lessons. I applaud you for doing so, especially in face of the nasty opinionated comments that I see on the Facebook page. I know that I comment a lot on ‘recent avalanche activity’ and have done so on some nasty accidents, but I always try my hardest not to make it personal, but to keep it objective with the goal of further awareness and prevention in sight. Indeed, I’ve been accused of being more of an avalanche maker than an avalanche educator more than once. (The best introduction I ever had was “Henry the poacher, turned game warden, here to talk about avalanche safety…”!).
This weak layer on North’ish facing and shaded slopes above 2400 m approx has been present for a number of weeks now. It formed due to the clear skies that dominated the month of November/early December. Clear skies create surprisingly low snow temperatures near the surface of the snowpack due to ‘radiational cooling’, which leads to a large temperature gradient in the snowpack i.e. the difference with the 0° temperature of the ground. A large temperature gradient between the ground and the layer(s) near the snow surface creates these cohesion-less snow grains called facets, especially if the total snowpack is thin – as it has been for a while now in many parts of the French Alps and surrounding areas.
This phenomenon of a weak layer forming at the beginning of the season Nov/Dec is common – it happens to a greater or lesser extent each year. This year it is not so much worse than in years past, but it will be especially problematic ‘off-piste’ and touring in and around ski areas during this early winter season because of :
- No avalanche control taking place in/around ski areas, and
- Not enough skiers to compact the weak layer by ‘skier compaction’
- These, along with rain and natural purging, are the only ways to stabilize this weak layer in the short term… aside from you or me triggering a slab and thus purging the slope like the one above!
So, my advice is for people is to be extra vigilant if they are going to go ski touring in familiar places over the next few weeks. This means basing all decisions on fact and evidence (i.e. not letting oneself get distracted by ‘gut feelings’ and what other people are up to, e.g. tracks on a slope will not be an indicator that it’s totally stable… they never are). For more on this, see my recent thoughts in this article from Snow-Forecast.com.
To understand more about how this weak layer impacts the stability of the snowpack see our HAT In Depth module on Triggering, or come to one of our Zoom talks which I’m delivering over the next few weeks. We’ve also launched a series of free Webinars / Podcasts with guest speakers that may be of interest to you too!
To achieve this goal of basing ‘decisions on fact and evidence’, our half-page HAT Safety is Freedom Risk Reduction framework helps us to apply the basic points… and it’s usually the simple points that are not followed when there’s an accident. So, if we apply the points in this framework, we’ll be much safer than just charging out onto the hill.
Safety is Freedom