The European avalanche warning services divide avalanche sizes into five size classes (based on the Canadian classification). The avalanche size class is defined, among other things, by the potential damage caused.
Under this definition, fatal ‘skier-triggered avalanches’ are often classified as ‘small’ or (barely) as ‘medium’ avalanches despite their considerable dimensions, being typically 150 m in length and having a slab size of some 50 m by 80 m and an average slab thickness of around 50 cm. This is equivalent to a slab volume of approximately 2’000 m³ or around 400 tonnes.
In the following we present the different size classes with their potential damage, run out and typical dimensions.
- Unlikely to bury a person, except in run out zones with unfavourable terrain features (e.g. terrain traps)
- In extremely steep terrain, the danger of deep falls prevails the danger of burials.
- Stops within steep slopes.
- Length: < 50 m
- Volume: 100 m³
- May bury, injure or kill a person
- Size 2 corresponds to the typical skier-triggered avalanche
- May reach the end of the relevant steep slope
- Length: 50-200 m
- Volume: 1’000 m³
- May bury and destroy cars, damage trucks, destroy small buildings and break a few trees.
- When skiers are caught by avalanches of this size, probability for severe consequences are very high.
- May cross flat terrain (well below 30°) over a distance of less than 50 m
- Length: several 100 m
- Volume: 10’000 m³
- May bury and destroy trucks and trains
- May destroy fairly large buildings and small areas of forest.
- Very large avalanches may occur at danger level 3-Considerable and are typical during periods with danger levels 4-High and 5-Very High.
- Crosses flat terrain (well below 30°) over a distance of more than 50 m
- May reach the valley floor
- Length: 1-2 km
- Volume: 100’000 m³
- May devastate the landscape and has catastrophic destructive potential
- Typical for danger level 5-Very High
- Reaches the valley floor
- Largest known avalanche
- Length: > 2 km
- Volume: > 100’000 m³