SnowFlurry 7 2016/17 | Repetition and clarification

The powder apocalypse continues to fail to materialize and the snow pusher is amused by various internet reports flirting with a change in the weather in the crystal ball range. Time is better spent sitting back and relaxing, waiting for the onset of winter and in the meantime looking at the current situation and other interesting things. And to clarify a few things from the first SnowFlurry articles:

To repeat:

The SnowFlurry knows that this has already been mentioned in the last SnowFlurry. However, thanks to his studies with a pedagogical-didactic background, he also knows that building knowledge and developing an understanding of such processes does not happen overnight. Abstract learning in itself is a slow process that can be supported by repetition and the constant reappearance of various descriptions.

One process is still currently shaping the snow transformation: the constructive transformation. Where two weeks ago you would have encountered a load-bearing snow cover due to wind and melting crusts, the ground is breaking through more and more easily or feels more and more "powdery". The build-up transformation first forms crystals with visible edges and facets from each original crystal form, later even entire cups (like a hollowed-out pyramid) up to 1 cm in diameter. These crystals have little bond to each other and trickle through the hands like sugar. The build-up transformation starts at a temperature gradient of around 15°C/m. In simple terms: the temperature difference between the surface and the ground of a 1m thick layer of snow must be about 15°C. With a snow cover only half a meter thick, half the temperature difference between the layer close to the ground and the surface layer is enough.

On the one hand, the fragility depends on the shape of the crystals: Platelets and cups have few points of contact with each other - the framework only hangs together in a few places - whereas small, round shapes are much more tightly packed together and touch each other on a much larger surface. In contrast, fused lumps are cemented together with water ice and also hold together well despite their size.

On the other hand, the fragility depends on the current temperature of the crystals: The colder they are, the more brittle the framework is, so it breaks more easily. Slab avalanches are caused by fractures in this structure. If a particularly thick snowpack is relatively homogeneous and ideally consists only of decomposed round grains with the same degree of hardness, there is practically no possibility of a fracture.

The less pronounced temperature gradient in a thick snowpack, the probably less frequent or long periods of good weather with blasting, and the fact that the snow is less brittle, make it easier for avalanches to occur. The less pronounced temperature gradient in a thick snowpack, the probably less frequent or long periods of good weather with sunny nights during the build-up of a thick snowpack and the probability that any weak layers are so deep inside that they can no longer be disturbed, make snowy winters safer overall than winters with little snow.

Excursus: Bound snow has nothing to do with hard or soft
Here is another video from October where you can see very nicely that bound snow for a snow slab is only conditionally related to the snow hardness:

Note: Snow is porous, hot and transformable. The transformation of snow is always related to the temperature within the snowpack. Snow slabs are formed by a fracture and fracture propagation in the snow structure.