Degrading metamorphosis (transformation) also known as sintering: From fresh snow to felt-like crystals to small round grains.
When a snow crystal gently falls to the ground in its original hexagonal, still whole form, it is due to nature's physical endeavor to reduce its surface area. This happens with the decomposing transformation. How quickly the process takes place depends on the temperature and pressure. The higher the pressure (snow load) and temperature, the faster the transformation progresses.
The hexagonal snow crystal with its concave (indentations, hollows) and convex (tips, ridges) shapes begins to break down its branches and tips to become small and round.
This looks like this:
As an uneven distribution of crystals and water molecules in the new snow leads to a pressure difference, molecules begin to migrate (many molecules together form a snow crystal). Other snow crystals can branch out at the indentations of the new snow crystals, while the tips of the crystals find it difficult to join together. The water vapor pressure above convex shapes is greater than with concave shapes. Due to this pressure difference, ice sublimates (transition from solid to gas) at the tips and migrates as water vapor to the indentations, where it is deposited as ice again.
This process - also known as sintering - strengthens the bond between the crystals. Sintering describes the individual crystals moving closer together and becoming smaller as a result of the degradative transformation. The pore space becomes smaller and therefore there are fewer air pockets in the snow layer. In addition, the crystal becomes smaller and rounder and the crystals can move closer together. Sintering causes the snow cover to settle and thus the snow depth decreases. Consequence: Increase in the density and strength of the snow.
During the degrading transformation, a short-term loss of strength can occur, especially at the transition from the new snow crystal to the felt crystal. The new snow crystals are well branched, but these connections are partially lost during the transition to the felted crystal, as the new snow star breaks down its branches and pins (felt) remain. These pins can no longer branch out optimally.
If the degrading transformation takes longer, the snow also gains bonding, which in turn is one of the prerequisites for a snow slab. If there is still a weak layer (in the layers below) that can be disturbed, the risk of avalanches increases. Depending on the temperature, however, this is only a few days after the snowfall.
Both fresh new snow and felted snow can form a weak layer if it snows on top of it with the influence of wind, or if they are overlaid by drifting snow.
