SnowFlurry 2 2016/17 | Substitution

"If it snows on warm ground, winter is lost."

The ground temperature during snowfall primarily affects the sliding snow avalanche activity. The influence on other avalanche-forming factors can be neglected in practice. Frozen ground thaws again shortly after snowing and releases heat to the snowpack. This is why the snowpack near the ground always has a temperature of 0°C or just below.

"An avalanche slides down"

"Sliding" describes the process of an avalanche when the friction is lower in relation to the forces driving down the slope. Sliding snow avalanches therefore slide and can therefore never be triggered by an additional load or impulse. Snow slabs also slide off in the end, but they can be triggered because a break first paves the way for sliding off. The snow structure breaks at one point (trigger point) and the break propagates further in the event of an avalanche. For the imagination: you throw a stone into a calm lake, the fracture spreads out in several directions like a wave. Dominoes also help with abstraction in the mind. Once the stuff has broken apart, sliding comes into play: If the friction that now arises between the snow slab and the ground is greater than the downhill force (usually on slopes below +/- 30° inclination), the snow slab that has broken away from the structure will stay put. If the friction is less than the force driving down the slope (from an inclination of approx. 30°), the snow slab moves downwards. The fracture (and its propagation) is therefore the main cause of the slab avalanche. We generate fractures almost every step we take in the snow structure. Without fracture propagation over long distances and the required steepness, there is no avalanche. For this reason, stability tests that only work out the weak layers but not the fracture propagation tendency (e.g. the CT compression test) are only suitable for estimating the avalanche risk to a limited extent.

"Experience is everything"

Pure drift snow problems can be managed quite well with experience, as can wet snow situations to a large extent. If you don't have the necessary theoretical background, you will reach your limits, especially with old snow problems. Depending on their severity, old snow problems can be recognized by settling noises, crack formation and spontaneous avalanches, but they can also not be visible/feelable/audible in the terrain at all - and thus elude empirical values. The only thing that helps here is to study the avalanche situation report and realize that not all dangers are helpful and give us their signs in the terrain (without looking into the snowpack). The completely "hidden" old snow problem is not known for nothing to take the lives of particularly experienced winter sports enthusiasts. A liaison of sound knowledge and correctly interpreted experience remains the be-all and end-all.

"Snow does not hold on steep glacier ice or rock slabs"

The highly irregular structure of glacier ice and the equally irregular structure of rock slabs when viewed up close are perfectly sufficient to give the snowpack "grip". In the vast majority of cases, slab avalanches that occur on such smooth-looking surfaces are based on weak layers close to the ground. The snow crystals of the weak layer slide down on the so-called sliding surface, in this case the subsoil. However, the problem lies with the weak layer and not with the boundary between the subsoil and the snowpack (with the exception of sliding snow avalanches). An underlying, harder layer of snow can also serve as a sliding surface. However, the problem arises from a break in the weak layer above, not from the sliding surface. The snow slab and the weak layer then slide off on the sliding surface.

"Lots of snow - high avalanche danger"

The avalanche danger is increased when there is a lot of fresh snow. However, the general rule is: thick layer of old snow - lower avalanche danger. Weak layers form less frequently due to less pronounced temperature differences in a thick snowpack.

"Rain has a positive/negative effect on the avalanche risk"

This depends on the general conditions. Mostly negative, however: on the one hand because of the short-term loss of strength - on the other hand because of the favored formation of weak layers due to significant temperature jumps in the snowpack.

"Snow reflects radiation"

Yes, but only the visible part of the radiation. Long-wave radiation, which contributes a considerable amount of energy ("thermal radiation"), is almost completely absorbed by snow. This is why the snow settles better on sunny slopes, can firn up and soaks through even in diffuse light conditions.

"Bound snow is hard"

No, bound snow (necessary for a snow slab) can be so soft that you can live out your obscene powder dreams in it. Bound ? hard or soft.

"Do not exceed 30° at danger level 4, 35° at 3 and 40° at 2."

If you combine this with good route planning and risk assessment, you will be even safer. Anyone who uses this as their sole premise will sooner or later sign their death warrant.

Note: Knowledge does not replace experience and experience does not replace knowledge.

Even our current image of snow and avalanches is only a construct of reality. Some of it could turn out to be wrong in the future or will be explained differently.