Standards

Avalanche Size

The European avalanche warning services seperates avalanche sizes into five size classes (based on the Canadian classification). The avalanche size class is defined, among other factors, by the potential damage caused, especially to infrastructure.

Under this definition, fatal ‘skier-triggered avalanches’ are often classified as ‘medium’ or (barely) as ‘large’ avalanches despite their considerable relative size, they are typically 150 m in length with dimensions of some 50 m by 80 m with 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.

Avalanche Size 1

Small Avalanche (Sluff)

Potential damage
  • 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.
Run out
Typical dimensions
  • Length: 10-30 m
  • Volume: 100 m³
Avalanche Size 2

Medium Avalanche

Potential damage
  • May bury, injure or kill a person
  • Size 2 corresponds to the typical skier-triggered avalanche
Run out
Typical dimensions
  • Length: 50-200 m
  • Volume: 1’000 m³
Avalanche Size 3

Large Avalanche

Potential damage
  • 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.
Run out
  • May cross flat terrain (well below 30°) over a distance of less than 50 m
Typical dimensions
  • Length: several 100 m
  • Volume: 10’000 m³
Avalanche Size 4

Very large Avalanche

Potential damage
Run out
  • Crosses flat terrain (well below 30°) over a distance of more than 50 m
  • May reach the valley floor
Typical dimensions
  • Length: 1-2 km
  • Volume: 100’000 m³
Avalanche Size 5

Extremely large Avalanche

Potential damage
Run out
  • Reaches the valley floor
  • Largest known avalanche
Typical dimensions
  • Length: > 2 km
  • Volume: > 100’000 m³

PICTURES: © LWD | EAWS; © N. N. | EAWS (Avalanche Size 5)