Regional distribution of avalanche accidents in Switzerland

One explanation for this lies in the snowpack structure

The inner-Alpine areas in Valais and Graubünden are those that often have an unfavorable snowpack structure (Fig. 3). One reason for this is that the snow cover is generally less thick than on the northern slopes of the Alps, for example. An unfavorable snowpack means, for example, that the base layer of the snowpack is weak - a so-called floating snow foundation - or that other pronounced weak layers are embedded. More on the topic: "Why little snow is unfavorable".

It is known from accident evaluations that these long-lasting weak layers were the fracture surface of numerous accidental avalanches. It is typical of these weak layers that they remain unstable for longer than, for example, a weak layer that forms in fresh snow. In addition, these danger spots are difficult to recognize even for experienced ski tourers, as the weak layer is hidden in the snowpack and can often only be recognized when digging a snow profile.

Where can I find information on the snowpack and the old snow problem?

Apart from digging a snow profile yourself, you can find information on the snowpack in the current avalanche bulletin (in the hazard description, as well as in the snowpack and weather section) or on the snowpack stability map with the current snow profiles. Snow profiles for the rest of the Alps are available here

The avalanche bulletin not only provides information on the danger level, the most dangerous slope exposures and altitudes, but also provides information on the relevant danger pattern. For example, if there are long-lasting weak layers deeper in the snowpack and these are important for the current avalanche situation, this is referred to as an old snow situation. Further important information on the hazard pattern is provided in the hazard description, as the following example from an avalanche bulletin from January 2014 shows:

More information on the old snow pattern can be found here.

Recommendations

Less touring activity but more avalanche accidents in the inner alpine areas of Valais and Graubünden - this indicates the higher risk of avalanche accidents. As avalanches triggered in old snow often become dangerously large, cautious behavior is important. In addition, the potential for damage in the event of an avalanche should be reduced by maintaining distances between ski tourers and skiing very steep slopes individually.

Further evaluations can be found in the article "Fürchtet den Altschnee", as well as in the scientific publication "Analysis of avalanche risk factors in backcountry terrain based on usage frequency and accident data in Switzerland".

This article was originally published on the SLF homepage and was kindly made available to PG. The text was written by Frank Techel, SLF.