SnowFlurry 3 2021/22 | Learning from avalanches

Questions upon questions, but that's exactly what's important: to think about it and not go off without thinking. I also like to call such questions my "life insurance".

At the outset, you should of course avoid triggering an avalanche at all costs. However, in the event that one does happen, regardless of whether you or someone else triggered it or it happened spontaneously, you can learn a few things from it. The best way to do this is to review the whole process, from tour planning to decision-making.

To illustrate this, let's take a closer look at an avalanche that occurred last week, on December 1, 2021, in the western Tux Alps.

The key data on the avalanche

Size 2 slab avalanche: classic ski touring avalanche

Exposure north at approx. 2450m

The slab avalanche was triggered around midday by a ski tourer who was on a descent.

Avalanche problem: Old snow problem coupled with a drift snow problem, easily recognizable in the snow profile (ECTP2).

The avalanche situation:

According to the avalanche report, danger level 3, considerable, has been issued for 1.12.2021. The reason for this is the widespread old snow problem (for a more detailed description, see Gestöber 2), which is predominantly prevalent on shaded slopes (NW over N to E) above the tree line. In addition, with the increase in wind, accumulations of drift snow prone to disruption could form in all exposures above the tree line.

In the central part of the snowpack, there are angular crystals (due to the build-up transformation) that act as a weak layer. These layers are particularly present and relevant where a closed snow cover already prevailed before the snowfall at the end of November. The snow surface at that time cooled down considerably due to radiation during the two periods of fine weather in November with cold temperatures, dry air and clear nights. The resulting large difference in temperature allowed the accumulating transformation to take full effect, sometimes throughout the entire snowpack!

Due to the lack of snow, only a few off-piste tours were feasible, so it can be assumed that there are no or few slopes that were used so much that the weak layer would have been destroyed. Where the weak layer is present, it is therefore also extensive and relatively uniform, which in turn promotes the spread of fractures. The thin snow slab above the weak layer also favors good fracture initiation: the weight of a single person is enough to produce a fracture. The snow surface of angular crystals was overlaid by the snowfall at the end of November up to and including December 1 (snowfall still in the morning).

The wind, which picked up and was stormy in some areas, also intensively displaced old and new snow. The resulting drift snow packs are ideally suited as the "board" of an avalanche. With this mixture, it is highly likely that avalanches can be triggered easily. So the motto is to be defensive when out and about.

For December 1, the forecast is for fine weather with rising temperatures and strong to stormy winds. We are therefore assuming that further fresh and disruptive snow packs will form over the course of the day. However, with good visibility and a little experience, it is usually easy to recognize drift snow in the terrain.

The first slope towards the summit is therefore questionable. However, people have already skied up without an avalanche occurring.

"Hm, is it safe after all?"

Ascent and descent tracks do not tell you whether a slope is safe or unsafe! Even the twentieth ski tourer can hit a so-called hotspot (trouble spot) and only then will an avalanche start.

With safety distances and a little more risk, you could possibly dare to do it. Nevertheless, I quickly come to the decision to skip the summit. Why? The first slope already poses an increased risk, the wind on the ridge blows horribly around your ears, the summit snack would also be uncomfortable, plus the descent is definitely only an option for me via the ascent route (ridge, back) and is therefore anything but worthwhile.

In the other descent variants, the old snow problem prevails everywhere, the steepness for an avalanche is sufficiently great and there is also drift snow. Of course, the snow would be good there and the descent would be fun - the existing tracks look good. But the winter is still long, there are still lots of great powder turns waiting for us!

So I prepare for the descent and dig another snow profile. As I stick my nose into the snow and take a closer look at the layers, there's a good rustle and a slab avalanche breaks loose on the steeper summit slopes. Avoiding the summit slope was clearly the right decision today!

Luckily, the person involved escaped with a scare. The avalanche was triggered on the descent in an area with little snow. The avalanche was a perfect match for the avalanche problems described in the avalanche report and already mentioned here several times.

Comparison of theory and practice

For me, the avalanche I witnessed confirms my thoughts, but I still take it as an opportunity to review exactly how my tour went today. We don't usually get such direct feedback on our decisions. This makes it all the more important to be self-critical even if nothing happens and to question whether you have correctly assessed the conditions, whether you might have skied a certain slope, whether you have recognized and noticed the problem and the danger signs at all, whether you have exceeded your own risk tolerance or not.

The debriefing after (or even during) the tour with the group, or even on your own, is important. But even before the tour, it is worth consciously thinking about what conditions we expect (snow depth, snow conditions, is there even enough snow for the chosen tour, ....). We can then compare these expectations with reality in the terrain. Even if you are completely wrong, it will stay in your memory!

Because you learn by combining and comparing theory and practice in the terrain. Perceive, see, feel, compare and memorize snow and conditions!