The risk of avalanche is the major fear of the skiers who venture off-piste like it is possible to on the ridges of Puy de Sancy, in the Puy-de-Dôme department. The probability of an avalanche varies with the instability of the snowpack formed by the accumulation of constantly changing layers of snow. The ice crystals and snow strata indeed continue to transform at ground level with the inclination of the slope, the temperature, the wind, and the subsequent snowfalls.