Avalanche Size
Avalanche size
The European avalanche warning services (EAWS) seperates avalanche sizes into five size classes.
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’ 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 slabthickness of around 50 cm. This is equivalent to a slab volume of approximately 2’000 m³ or around 400 tonnes of snow.
In the following we present the different size classes with their potential damage, run out and typical dimensions.
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
Stops within steep slopes.
Typical dimensions
Length: 10-30 m
Volume: 100 m³
Size 2: Medium avalanche
Potential damage
May bury, injure or kill a person
Size 2 corresponds to the typical skier-triggered avalanche
Run out
May reach the end of the relevant steep slope
Typical dimensions
Length: 50-200 m
Volume: 1’000 m³
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
Size 4: Very large avalanche
Potential damage
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.
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
Size 5: Extremely large avalanche
Potential damage
May devastate the landscape and has catastrophic destructive potential
Typical for danger level 5-Very High
Run out
Reaches the valley floor
Largest known avalanche
Typical dimensions
Length: > 2 km
Volume: > 100’000 m³
