In winter, the fresh, light snow is subject to the action of winds which shape and concentrate it in dunes (drifts) or in ledges on the mountainous ridges (photo). In spring, the snow, saturated in water, more compact, melts in place. The melting metamorphosis caused by rain or warmth leads to the appearance of water in the heart of the snowpack, and the formation of agglomerates resembling coarse salt. These make the snowpack very unstable.