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10 Avalanche Danger Patterns
Based on the analysis of countless avalanche accidents, the heads of the Tyrolean Avalanche Warning Service, Rudi Mair and Patrick Nairz, formulated 10 causal, memorable hazard patterns, which could have prevented many an accident if they had been known of and taken into account.
1. deep persistent weak layer
The second snowfall is so crucial because between the first layer of snow and the second snowfall, a distinct weak layer can form which can easily be disturbed by winter sports enthusiasts. The weak layer near the ground can also have an impact on the avalanche situation later in the winter.
2. gliding avalanche
Snow glides downhill preferably on steep, smooth surfaces. This causes snow gliding snow(fish) mouths, i. e. easily visible cracks in the snow cover, some of which are several meters deep. Contrary to an old "doctrine" that is unfortunately difficult to eradicate, such gliding snow cracks are not regarded as favourable, but rather as unfavourable criteria regarding the possibility of an avalanche.
3. rain
Avalanches are guaranteed. Rain can occur in any part of winter. The big advantage: no danger pattern can be recognized more easily than rain.
4. cold after warm / warm after cold
For too long, the doctrine that a great temperature difference during snowing (whether cold on warm or vice versa) has a positive effect on the avalanche situation was argued in avalanche science. This is an insidious issue, as the weak layer does not yet exist immediately after snowing and develops over the next few days.
5. snow after long cold period
A classic avalanche event. In a very short period of time, an avalanche situation becomes very delicate for the winter sportsman. This is also the case if after a long cold period "only" strong wind blows without any snowfall. The problem: Fresh snow is deposited in lee side slopes, which can easily be disturbed by additional load.
6. cold, loose snow and wind
"Wind is the master builder of avalanches". With light, dry snow, wind always leads to transportation of snow and thus to an increase in the danger of avalanches! A pattern that can usually be seen quite well.
7. snow-poor zones in snow-rich surrounding
The phenomenon is also observed in winters with normal snow conditions, when there is little snow in a snowy environment. This is often the case for spines, but also near terrain edges.
8. surface hoar blanketed with snow
It becomes dangerous when it is covered by new, bound snow layers and is therefore rightly considered one of the most critical weak layers of snow and avalanche science.
9. graupel blanketed with snow
Graupel is often scattered over a small area and is difficult to detect even by experts without looking into the snow cover. A thoroughly insidious affair, which fortunately only leads to short-term problems.
10. springtime scenario
It is rarely the case that "safe" and "dangerous" are so close together in terms of time, which means that the range of hazard levels issued during a day is rarely so wide. Timing discipline and flexibility in route planning are more in demand than ever for winter sports enthusiasts.
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