Avalanches are one of the objective dangers of winter sports away from secured (ski) areas. Especially for ski tourers, avalanches pose a great danger. In order to understand the danger of avalanches, a basic knowledge of avalanches and their formation is a prerequisite. Avalanche knowledge includes, among other things, an understanding of Avalanche types, the Avalanche triggering and the various Avalanche sizes.
1. avalanche types
Every year, an average of 20 to 25 people die in Austria as a result of avalanches. This makes it all the more important to acquire a sound understanding of avalanches.
Snow slab avalanches
The most dangerous for winter sports enthusiasts are Snow slab avalanches. On the one hand, because they are difficult to predict. On the other hand, because their linear onset can extend over several hundred metres on a slope, the snow masses start sliding at lightning speed and escape from the danger zone is rarely possible. Snow slab avalanches can go off in dry or wet snow.
Loose snow avalanches
Loose snow avalanches are a different type of avalanche. In contrast to the linear avalanche of snow slab avalanches, the avalanche of a loose snow avalanche is point-shaped. As the slide progresses, loose snow avalanches become wider and wider. One also speaks of a "pear-shaped" form of the avalanche. Loose snow avalanches can consist of dry snow as well as very wet and heavy snow. Dry loose snow avalanches occur mainly after new snow falls in sunny steep terrain. Especially in steep terrain, the danger of entrainment and falling due to loose snow avalanches should not be underestimated! Wet loose snow avalanches are the result of moisture penetrating the upper snow layers, which can quickly lose their strength.
Gliding snow avalanches
Gliding snow avalanches slide on a smooth layer above the ground. The cause of the sliding is a friction loss at the transition of the snow cover to the ground. The friction loss is caused by water. Avalanches of sliding snow often occur on grassy slopes where the ground is not frozen. The warmth of the ground makes the snowpack wet, and the water causes a loss of friction between the ground and the snowpack. On the slippery, grassy ground, the entire snowpack starts to slide. Sliding snow avalanches are very difficult to predict. A sure sign are so-called fish mouths. These crevice-like cracks in the snowpack indicate that the snowpack is about to slide. Contrary to persistent opinion, they are not a sign of relaxation in the snowpack. Areas under fish mouths should be avoided or traversed quickly.
2. avalanche release
A snow slab avalanche - the most dangerous type of avalanche for winter sports enthusiasts - requires certain ingredients:
- Bound snow (drifting snow)
- A weak layer
- A steep slope (> 30°)
- An additional burden
The process of avalanche formation is very complex and therefore difficult to predict. One reason for this is the inhomogeneous structure of the snowpack. It happens that stable and unstable zones lie next to each other on a slope. In the unstable zones, so-called "Hot Spots", can Snow slab avalanches are triggered particularly easily. Unfortunately, it is not possible for winter sports enthusiasts to see where these weak zones are located on the slope. Even a snow profile only provides information about the situation at a specific position on the slope.
The basic ingredient for a snow slab avalanche is a Weak layer. Weak layers in the snowpack can consist of floating snow, snow-covered surface rime or sleet, or hard old snow. Characteristic of the weak layers is that they are only poorly connected to the surrounding snow layers. The stresses in the weak areas are greater than the strengths. Characteristics of weak layers are often large temperature differences within the snowpack, large differences in the hardness of the layers or in the size of the snow crystals.
Now lies Bound snow (e.g. brittle drifting snow that can only poorly compensate for loads) on such a weak layer, only two further ingredients are needed to trigger a snow slab avalanche: a Additional load and a Slope.
A Additional load is, for example, a single downhill skier, a group on the ascent or further snowfall. How great the additional load must be for an avalanche to be likely to be triggered depends on the current danger situation and is always a topic in the Avalanche situation report. Certain measures can be taken to protect the snowpack from excessive stress. For example, ski down individually on slopes of 35° or more, or keep your distance when ascending slopes of 30° or more.
Between the Trigger probability of an avalanche and the Slope there is a connection. As a rule, slopes above 30° are avalanche-prone. The avalanche report then speaks of "steep slopes". Therefore, if you refrain from skiing on steep slopes, the avalanche risk can be reduced.
3. avalanche sizes
The size of avalanches is determined by the European Avalanche Warning Services divided into five classes. One factor in the size assessment is, among other things, the damage potential. According to this definition, even "small" and "medium" avalanches are fatal for a skier.
potential for damage
Small Avalanche (Slide)
Comes to a standstill in the area of the steep slope
Burial is unlikely except in unfavourable run-out areas. In extreme terrain, the risk of falling outweighs the risk of burial
< 50 m
Can reach the foot of the slope
Can spill, injure or kill a person. Corresponds to the "skier's avalanche
Length 50 - 200 m
Can negotiate flat terrain (well below 30°) over a distance of up to 50 m
Can bury and destroy cars, damage heavy trucks, destroy small buildings and break individual trees. If skiers get caught in avalanches of this size, the fatality risk is very high
Several 100 m
Very large avalanche
Overcomes flatter terrain (well below 30°) over a distance of > 50 m, can reach the valley floor
Can bury and destroy heavy trucks and trains, can destroy larger buildings and small areas of forest. Very large avalanches are possible at hazard level 3, typical at hazard levels 4 and 5.
1 - 2 km
Extremely large avalanche
Reaches the valley floor, largest known avalanche
Can devastate the landscape, catastrophic destruction potential possible (Galtür). Typical for hazard level 5
> 2 km
4. avalanche courses
Building on the theoretical knowledge of avalanches and how they occur, it is essential for winter sports enthusiasts to take professional courses to further their education and learn more about strategies to avoid avalanche accidents.
One-day Fresh-Up Avalanche & Safety on the Pitztal Glacier
At the one-day Avalanche course on the Pitztal Glacier you will learn from a state-certified ski guide how to use the emergency equipment (avalanche transceiver, probe, shovel) quickly and efficiently and thus save lives. There will also be a theory lecture with an introduction to strategic avalanche awareness, interpretation of the avalanche situation report, avalanche problems and risk management on tour.
Ski touring basic course in Pitztal for beginners
For beginners to the sport of ski touring, the Basic ski touring course on. In addition to handling emergency equipment, the programme also includes snow and avalanche awareness, tour planning, ascent and descent techniques, as well as terrain selection and tracking.