Avalanche terrain ratings
Mountain safety
Know Your Exposure | Terrain Classification | Avalanche Terrain Exposure Scale
Avalanches are an integral part of the natural cycle in the mountain environment. The potential for avalanches exists on steep and even moderately steep snow slopes throughout the Mountain National Parks Visitors to the Mountain Parks who travel into backcountry terrain that is exposed to avalanches must accept the risk associated with making that choice. The Avalanche Terrain Exposure Scale (ATES) was developed to help you understand the risks that are an inherent element of travelling in avalanche terrain.
Know Your Exposure
While the snowpack changes continuously throughout the winter season, the terrain the snowpack sits on generally does not change. Avalanches don’t happen on flat ground, but they do cascade down steep slopes that run out onto flat and low-angle terrain, so the risk of being in even those places must be understood. The risk that is associated with being in places where an avalanche has the potential to bury you is called exposure.
The ATES is designed to categorize avalanche exposure based on the configuration of the terrain. By using the ATES, backcountry travellers, including skiers, boarders and waterfall ice and mixed ice climbers, will improved their understanding of the type of avalanche terrain that threatens their proposed outing. The ATES works by applying the information provided in the Public Avalanche Forecasts for the park you plan to visit, in combination with Avalanche Terrain Ratings that have been configured for many of the most popular trails and routes in that park. You can then use that information to help you evaluate the avalanche hazard of your intended route, and also to help you select appropriate trip routes and destinations based on the terrain ratings and current conditions. Avalanche Terrain Ratings have been applied to the most commonly travelled destinations located in the Mountain Parks by categorizing them as Simple, Challenging or Complex.
An Avalanche Skills Training course will also help you learn how to identify what types of slopes can produce avalanches under which conditions, and how to travel safely through that terrain.
Avalanche Terrain Classification
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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.
Avalanche Terrain Exposure Scale
| 1 - Simple | 2 - Challenging | 3 - Complex | |
|---|---|---|---|
| Slope angle | Angles generally < 30º | Mostly low angle, isolated slopes >35º | Variable with large % >35º |
| Slope shape | Angles generally < 30º | Mostly low angle, isolated slopes >35º | Variable with large % >35º |
| 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 (events:years) |
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 characteristics |
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.
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