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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