Higher overnight temperatures and cloudy skies have accelerated this phenomenon… a danger for those in ‘confinement’ in the higher altitude Alpine areas.
For the significant amount of people still currently living at relatively high altitude (+/- 1800 m) in the Alps, a lack of refreeze at night (meaning lack of rebonding of the snowpack) for the first time this season along with intense daytime warming, is leading to a round of natural wet snow avalanches occurring for the first time in many weeks. This trend will continue and probably intensify over the next few days due to the rain forecast up to high altitudes (over 2500 m) and overcast skies: cloudy skies keep the heat in and increases the temperature of the snow. This decreases the strength of the snowpack because it doesn’t get a chance to re-freeze at night.
This avalanche activity will occur on all slope aspects and actually may be more likely on North’ish facing slopes that have not benefited from the stabilising effect of previous melt-freeze cycles. See these photos of the aftermath of a wet snow avalanche, taken during a short walk in the valley. This natural slide happened at around 2500 m on a North’ish facing slope, reaching the river/valley bottom around 1900 m. Other releases have also been observed at similar altitudes on slopes facing all directions.
There’s now a lot less snow cover on the sunniest South facing slopes, but this is the time of year when rock falls are coming down onto paths too.
Until now there had been very little visible avalanche activity, e.g. mainly restricted to a few small releases over the last month or so. It’s now been a month since the early closure of Alpine ski resorts due to Coronavirus restrictions. Since mid-March, we’ve had a series of sunny days and cold nights. These conditions would have been ideal for ski touring (currently banned) with fantastic quality spring snow and very little avalanche risk because of good overnight refreezes consolidating the snowpack.
With the warming now becoming more pronounced (0° C at 3200 m for the next few days) and cloudy nights, we’ll be seeing more of these sort of natural wet slides/avalanches occurring. The high altitudes above 2500 m are empty of people, but walkers taking their daily exercise on paths above 1800 m or so beneath steep snow-covered slopes should be aware of the danger, particularly later in the day as things warm up (but some, mainly North’ish facing slopes can come down at any time).
It’s worth taking into account that there are no openings or closures of paths due to danger at the moment. Also worth noting is that while the vast majority of avalanche accidents are : triggered by the victim (over 90%) and happen in December, January and February (over 75%), natural wet snow avalanches do cause accidents and can be very dangerous… their relatively infrequent occurrences at times like now can easily mislead us into a false sense of safety.
All of us at Henry’s Avalanche Talk wish you the best during these trying times, wherever you are.
In the meantime, I’ll be publishing blogs and video from time to time over the next weeks about: decision making, risk and crisis management including discussions on the human factors that lead competent people to make errors that lead to avoidable accidents. Please send us any thoughts, questions and comments to firstname.lastname@example.org