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Danger levels avalanches

Avalanches rank among the greatest natural hazards in the Alpine region. They can affect houses, settlements and transportation routes, as well as people engaging in winter sports.

Avalanches are sliding or falling snow masses. They are caused by instabilities in the snowpack. Avalanches occur mostly in steep terrain. The formation of avalanches is facilitated by heavy snowfall, strong wind or a significant rise in temperature. Avalanches can be released naturally (without human intervention) or by people. In 90 percent of cases, avalanches are triggered by the victims. In settlements and on transportation routes, the local authorities ensure the safety of the population. Those who engage in winter sports beyond the boundaries of marked and open pistes, or cross-country ski or hiking trails, are responsible for their own safety.

Danger level 1 (low danger)

Characteristics

Generally favourable avalanche situation

No warning signs present. Avalanches can only be triggered in isolated cases, in particular on extremely steep slopes.

Recommendations for back-country recreationists

Travel extremely steep slopes one person at a time and be alert to the danger of falling.

Implications and recommendations for transportation routes and settlements

No danger.

Danger level 2 (moderate danger)

Characteristics

Mostly favourable avalanche situation

Warning signs can occur in isolated cases. Avalanches can be triggered in particular on very steep slopes with the aspect and elevation indicated in the avalanche bulletin. Large natural avalanches are unlikely.

Recommendations for backcountry recreationists

Routes should be selected carefully, especially on slopes with the aspect and elevation indicated in the avalanche bulletin. Travel very steep slopes one person at a time. Pay attention to unfavourable snowpack structure (persistent weak layers, old snow problem).

Implications and recommendations for transportation routes and settlements

Very little danger.

Danger level 3 (considerable danger)

Characteristics

Critical avalanche situation

Whumpf sounds and shooting cracks are typical. Avalanches can easily be triggered, particularly on steep slopes with the aspect and elevation indicated in the avalanche bulletin. Natural avalanches and re-mote triggering can occur.

Recommendations for back-country recreationists

The most critical situation for backcountry recreationists. Select best possible route and take action to reduce risks. Avoid very steep slopes with the aspect and elevation indicated in the avalanche bulletin. Unexperienced persons are advised to remain on open ski runs and trails.

Implications and recommendations for transportation routes and settlements

In individual cases exposed objects (mostly sections of transportation routes) can be endangered. Here, consideration should be given to taking safety measures.

Danger level 4 (high danger)

Characteristics

Very critical avalanche situation

Natural and often very large avalanches are likely. Avalanches can easily be triggered on many steep slopes. Remote triggering is typical. Whumpf sounds and shooting cracks occur frequently.

Recommendations for backcountry recreationists

Stay on moderately steep terrain. Heed runout zones of very large avalanches. Unexperienced persons should remain on open ski runs and trails.

Implications and recommendations for transportation routes and settlements

Avalanches can travel large distances, in particular within familiar paths. Exposed objects (mostly sections of transportation routes, but in isolated cases also buildings) can be endangered. Consider taking safety measures.

Danger level 5 (very high danger)

Characteristics

Extraordinary avalanche situation

Numerous very large and extremely large natural avalanches can be expected. These can reach roads and settlements in the valley.

Recommendations for backcountry recreationists

You are advised not to engage in winter sports beyond open ski runs and trails. Respect closures.

Implications and recommendations for transportation routes and settlements

Avalanches can travel large distances, including beyond the extent of familiar paths. Transportation routes and settlements can be seriously endangered. Extensive safety measures are usually required.

Additional information and definitions:

  • The avalanche bulletin usually describes areas where the danger is most significant in greater detail (e.g. elevation zone, aspect, topography, etc.).
  • Slope angles:
    • very steep, extreme terrain is especially unfavourable as regards the slope angle, topography, proximity to ridgelines or ground conditions
    • extremely steep: steeper than 40°
    • very steep: steeper than 35°
    • steep: steeper than 30°
    • moderately steep: less than 30°
  • Additional load (artificial triggering):
    • high (e.g. group of skiers without spacing, snowmobile/groomer, avalanche blasting)
    • low (e.g. single skier, snowboarder or snowshoe hiker)
  • Natural: without human influence
  • For avalanche sizes, see https://www.slf.ch/en/avalanche-bulletin-and-snow-situation/about-the-avalanche-bulletin/avalanche-sizes.html
  • Aspect: the compass direction which a downward slope faces
  • Ski runs: marked pistes and descents
  • Trails: marked snowshoe and winter hiking trails
  • Experience: experience in assessing avalanche danger means the ability to obtain and correctly interpret external sources of information, e.g. the avalanche bulletin, and one’s own observations with regard to avalanche danger, and to respond correctly in accordance with the situation.
  • For warning signs (recent avalanches, whumpf sounds, shooting cracks), see https://www.whiterisk.ch/en/explore#u=05-02-05-01
  • For critical amount of new snow, see https://www.whiterisk.ch/en/explore#u=01-05
  • Exposed: especially exposed to danger, e.g. section of road in steep terrain within range of even medium avalanches