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Mount Revelstoke National Park of Canada

Avalanche Terrain Classification

Mountain National Parks

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The Avalanche Terrain Exposure Scale (ATES) is a new development from Parks Canada, which offers an avalanche classification system based on the landscape – not the snow. The system presents two models: technical, and public communication.

The technical model has been designed for users trained and skilled in the subtle nuances of avalanche terrain. The public communication model is designed for communicating technical concepts to the public, who is largely unable to comprehend the technical details. Both scales represent the same thing – spoken in two languages.

The ATES can be applied at whatever scale is appropriate. Parks Canada has chosen to link with popular guidebooks, and apply ATES ratings to backcountry trips, which are well described in these books. This classification could however, be applied to any given piece of terrain – it is all a question of scale.

This is a brand new concept, and as such it is expected that this scale will evolve over time, as experience with using avalanche terrain ratings grows.

Click on Simple, Challenging or Complex below for a list of rated trips in the Mountain National Parks.

Avalanche Terrain Exposure Scale

Technical Model (v.1-04)
 1 - Simple2 - Challenging3 - Complex
Slope angle Angles generally < 30º Mostly low angle, isolated slopes >35º Variable with large % >35º
Slope shape Uniform Some convexities Convoluted
Forest density Primarily treed with some forest openings Mixed trees and open terrain Large expanses of open terrain. Isolated tree bands
Terrain traps Minimal, some creek slopes or cutbanks Some depressions, gullies and/or overhead avalanche terrain Many depressions, gullies, cliffs, hidden slopes above gullies, cornices
Avalanche frequency
1:30 ≥ size 2 1:1 for < size 2
1:3 for ≥ size 2
1:1 < size 3
1:1 ≥ size 3
Start zone density Limited open terrain Some open terrain. Isolated avalanche paths leading to valley bottom Large expanses of open terrain. Multiple avalanche paths leading to valley bottom
Runout zone
Solitary, well defined areas, smooth transitions, spread deposits Abrupt transitions or depressions with deep deposits Multiple converging runout zones, confined deposition area, steep tracks overhead
Interaction with
avalanche paths
Runout zones only Single path or paths with separation Numerous and overlapping paths
Route options Numerous, terrain allows multiple choices A selection of choices of varying exposure, options to avoid avalanche paths Limited chances to reduce exposure, avoidance not possible
Exposure time None, or limited exposure crossing runouts only Isolated exposure to start zones and tracks Frequent exposure to start zones and tracks
Glaciation None Generally smooth with isolated bands of crevasses Broken or steep sections of crevasses, icefalls or serac exposure

Using this scale:

Any given piece of mountain terrain may have elements that will fit into multiple classes. Applying a terrain exposure rating involves considering all of the variables described above, with some default priorities.

Terrain that qualifies under an italicized descriptor automatically defaults into that or a higher terrain class. Non-italicized descriptors carry less weight and will not trigger a default, but must be considered in combination with the other factors.

Backcountry Avalanche Information

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