SnowFlurry 6 2020/21 | Mechanical conversion

First of all, I would like to briefly explain the difference between degradative and mechanical transformation. In both cases, the crystals become smaller, move closer together and a bound layer of snow is formed. However, the process leading up to this point is different: both the degradative and the constructive transformation take place within the snow cover. So we are talking about the crystals that are already on the ground. The transformation processes depend on temperature, water vapor, pressure, etc. You can find a detailed description of degradative and constructive metamorphosis in SnowFlurry No. 6 2019/20. Mechanical transformation, on the other hand, is caused by external influences, especially wind. It is a metamorphosis process like the other two, but rather a "destruction" of the snow crystals.

If there is no wind at all, the snow crystals fall from the sky in their original, dendritic shape (hexagonal) and only begin to transform once they have reached the ground. If, on the other hand, it snows when there is wind, the snow crystals are already whirled around in the air by the wind. As a result, they collide with each other, branch out and are torn apart again. Small branches break off. This can also happen if they collide with a hard obstacle. As the snow crystal whirls around, this process is repeated several times, causing the crystal to be destroyed further and further and to take on an ever smaller and rounder shape. Finally, the crystals come to rest on the ground or snow surface as a mixture of round grains and small and larger pins (felt).

The now small and roundish shape of the crystals allows them to move close together and therefore bond well with each other. The result is a bound layer of snow that reacts strongly to stress and acts very well as the "board" of an avalanche.

Properties and interesting facts about drifting snow:

• As already mentioned, drifting snow consists of a bound layer of snow that is easily disturbed and can transfer tension well. However, bound snow does not mean that the snow layer is compact! It can certainly feel like powder fun, because powder snow can also be bound!

• Furthermore, the colder and drier the snow, the more brittle it is. The material can then be seen as a solid body that can be broken. The breaking of the crystals can even be heard as crunching and cracking. The more brittle the crystals are, the easier they break and the more sensitive they are to stress, for example from winter sports enthusiasts.

• When the snow temperature is close to the melting point (0°), the snow becomes more plastic. A drifting snow problem then becomes less relevant. The snow can be "stretched", deformed and becomes pliable without the crystals breaking. This effect is easy to observe when the snow hangs curved down from a roof, for example, and simply won't break.

• The hazard pattern 6 - loose snow and wind (drift snow) is usually only present for a rather short time. The duration depends on temperature and settlement. With one exception: when a snow surface of loose, angular crystals - a result of the build-up transformation - is transported. In this case, hard and brittle drift snow layers are formed, which can be disturbed over a longer period of time.

• Drift snow can already be formed at a wind speed of 15km/h. The snow load increases sharply as the wind speed increases.

• Floating snow can be easily recognized in comparison to other hazard patterns in the terrain by wind signs such as wind gusts, dunes, flags, anraum, etc., unless it is overlaid by fresh snow.

The Schneestöberer wish you a Merry Christmas and a Happy New Year!