The most common myths about snow and avalanches
Number 4: "It hasn't snowed in many days, so the snow has stabilized"
Well, it all depends on how many days it hasn't snowed, the temperature, and... the wind.
In fact, if the temperature is mild after a snowfall, the snowpack stabilizes progressively thanks to the metamorphism due to the temperature gradient (destructive metamorphism); the number of days needed to stabilize the snowpack depends on the temperature. The higher the temperature, the faster the snow transformation will be.
In simple terms, little by little snow crystals lose their initial shape (which tends to have many points) becoming progressively more rounded. The rounder and smaller crystals tend to approach each other, filling the air spaces and having more contact surface which binds them, gradually increasing the stability of the snow cover.
On the other hand, if the temperature is cold, the snow cover "freezes" and this metamorphism is slowed down or even stopped; the crystals will maintain their original shape for longer, and the metamorphism will be slowed down and therefore the consolidation of the snow cover as well.
This means that with negative temperatures, any instability of the snow cover following a snowfall (the more snow falls and the more important the presence of wind, the greater the instability tends to be) lasts for more days. How many? It depends on the temperature, of course!
Furthermore, we must remember that a snowfall at low temperatures deposits very light snow crystals, which are easily transportable by the wind. The wind can transport the crystals already during the snowfall itself, but also in the hours and days following.
The wind, carrying the crystals from the more exposed areas (where the wind is faster) to the more sheltered ones (where the wind is slower), modifies them by breaking them and reducing their size. The final result can be the formation of wind slabs, which are very dangerous, and which we will talk about in another article.
Wind transport can occur at any time, regardless of how many days ago it snowed; all that is needed is wind, more or less strong, capable of moving the snow crystals.
Therefore, the factor that makes the snow cover safe is not the calendar!
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Ernesto Bassetti
Ernesto is one of the leading snow and avalanche experts in Italy and beyond.
By passion and by profession, he has been involved in mountain safety for over 40 years, with particular attention to the avalanche issue.
He is co-founder, and until 2020 Vice President, of MND Group; important international player in the field of mountain infrastructure and world leader in controlled avalanche release systems.
He is a ski instructor, National Ski Mountaineering Instructor, former director of the Mario Righini Ski Mountaineering School.
He was promoter, co-founder and soul of the "Servizio Valanghe Italiano" (Italian Avalanche Service), of which he held the Presidency for 18 years.
