Mountain guide Stefan Neuhauser experienced an unusual avalanche phenomenon during a freeride tour with a group in the Aosta Valley on 21 March 2014: despite a hard-frozen blanket of snow, with only the top few centimetres of the snow having melted, he and his group triggered an avalanche. The avalanche was triggered in the Val di Rhemes, on the Cima le l'Entrelor in the Aosta Valley (Italy). The avalanche was a mixture of a snow slab and a uniform snow avalanche.
Details of the avalanche
Date and time: Friday, March 21, 2014, approx. 1:30 pm
Exposure: south
Altitude: 2400 to 2200 meters
Snowpack: stable, hard snowpack, the surface of which was 2 to 4 cm thick
Stefan's description of the avalanche triggering
While skiing the slope described above, I triggered a snow slab from a safe spot (small plateau) by remote triggering over a distance of 30 to 40 meters. The snow was about 2 to 4 cm thick and relatively hard. In the photo you can still see three people from our group on the horizon to the right. The snow slab started to move from there. You can also see small, superficial wet snow slides from the previous day and my downhill track.
The triggering of the avalanche came as a complete surprise to me, as there were no warnings beforehand. The snow on the south-facing slope was frozen concrete hard: at around 12.00 noon, there was hardly any snow at all. That's why we climbed up again to ski the slope a second time about an hour and a half later (at this time the snow was about 2 to 4 cm thick). On the second ascent, I triggered the avalanche from above by remote triggering. This phenomenon has also occurred more frequently in Switzerland recently, so it can be assumed that such avalanches are also possible in other regions. See the weekly report from the SLF, which is well worth reading...
The Swiss Federal Institute for Snow and Avalanche Research SLF in Davos recorded a number of notable avalanche triggers and avalanche accidents, all of which occurred when the snowpack was frozen on the surface. Most of these avalanches were also triggered remotely. The SLF experts explain these unusual avalanche triggers as follows: "It is rare for people to trigger avalanches when there is a load-bearing crust of melted snow on the snow surface. However, there are always such events, especially with very unfavorably built-up snowpacks. A hard frozen snow surface gives the impression of stability and safety. The examples show, however, that avalanche triggering in very weak, angular layers deep in the snowpack cannot be completely ruled out, even with a stable surface. The risk of triggering such an avalanche is probably greatest in the period of initial moistening of the snow layers near the surface." Unlike in the case of Stefan Neuhauser's avalanche, which was triggered in a rather snowy area, the avalanches recorded by the SLF all occurred in regions with little snow, where the snowpack is weak and unstable in many places in the winter of 2014.
