How to Read the Avalanche Terrain Exposure Scale (ATES)
The Avalanche Terrain Exposure Scale (ATES) is a system of rating backcountry terrain by its potential to produce avalanches. It will help you know if the terrain in the area you’re planning to ride is Risk City or Chill-ville.
While weather and snowpack stability are always changing, terrain is the constant factor in your calculations to minimize avalanche risk. The ability to evaluate terrain can help mitigate the influence of the two other variables, and help you stay safe in the backcountry.
For the purpose of helping to illustrate how this terrain rating system works, we’ll use the example of the Blue Lake riding area, near Sicamous, BC.
Undertstanding the Avalanche Terrain Exposure Scale (ATES)
ATES divides terrain into three categories:
SIMPLE - GREEN
Exposure to low angle or primarily forested terrain. Some forest openings may involve the runout zones of infrequent avalanches. Many options to reduce or eliminate exposure. No glacier travel.
What This Means
Under most conditions you can move confidently through simple terrain. It is still important to watch out for small slopes with terrain traps, openings in forests and exposure to avalanche paths from above.
CHALLENGING - BLUE
Exposure to well-defined avalanche paths, starting zones or terrain traps; options exist to reduce or eliminate exposure with careful route-finding. Glacier travel is straightforward but crevasse hazards may exist.
What This Means
Travel in challenging terrain requires a more thoughtful approach, including a thorough assessment of conditions. Big slopes with serious consequences exist, so you will need good travel techniques to travel through them, and under some conditions they should be avoided entirely. There will be frequent points at which travel decisions will need to be made to manage risk based on the current conditions and options available.
COMPLEX - BLACK
Exposure to multiple overlapping avalanche paths or large expanses of steep, open terrain; multiple avalanche starting zones and terrain traps below; minimal options to reduce exposure. Complicated glacier travel with extensive crevasse bands or icefalls.
What This Means
Travel in complex terrain requires a thorough assessment of conditions, advanced route-finding and terrain-assessment skills, and a diligent approach to all aspects of avalanche risk management. If you lack experience or are unsure of your skills, it is best to stay out of complex terrain unless conditions are entirely favourable. If this is the type of terrain you seek out, be patient and wait for the right conditions.
Depending on the area, ATES maps may also show critical decision points, major avalanche paths, main access trails, select destinations, backcountry shelter and parking lots.
What Snowmobile Areas Are Rated?
Avalanche Canada has rated all managed snowmobile riding areas in BC, several in BC provincial parks and a few other popular backcountry zones in Western Canada. Some riding areas in the Chic-Choc Mountains of Quebec and the mountainous areas of western Newfoundland have also been rated.
Where can I find ATES ratings?
ATES ratings can be found in several places, including the Avalanche Canada and Parks Canada websites, and on snowmobile club trail maps and trailhead signage. The Trip Planner on the Avalanche Canada website is a great place to get started.
If you are planning a trip where there is no ATES rating, you will need advanced training to make your own judgment regarding how exposed the terrain is to avalanche hazard.
How to Read the Avalanche Terrain Exposure Scale
Remember that Avalanche Terrain Exposure Scale zoning alone is not adequate for assessing avalanche risk. ATES must be combined with avalanche hazard information (such as provided by avalanche forecasts), local weather, snowpack and avalanche conditions to devise a complete risk treatment.
Using ATES in conjunction with all the other data required to travel safety in avalanche terrain requires training.