City and Borough of Juneau
155 S. Seward Street
Juneau, Alaska 99801
tel. 907-586-5240
fax 907-586-5385

Urban Avalanche Advisory

Avalanche Size or Avalanche Class

In the US, the five-level scale is:

  1. Sluff: any slide running less than 50 meter slope distance regardless of other dimensions
  2. Small: relative to the path
  3. Medium: relative to the path
  4. Large: relative to the path
  5. Major or Maximum: relative to the path

These categories are in relation to path size, so a size or class number is not so meaningful without information on, or familiarity with, the path. A reporting system used in Canada has the following size classifications:

Size Description Typical Mass Typical Length Typical Impact Pressure
1 Relatively Harmless > 10 tons 10 meters 1 kPa
2 Could bury, injure or kill a person 100 tons 100 meters 10 kPa
3 Could bury a car, destroy a small building, or break trees 1,000 tons 1,000 meters 100 kPa
4 Could destroy a rail car 10,000 tons 2,000 meters 500 kPa
5 Largest known 100,000 tons 3,000 meters 1000 kPa

CBJ Image