The Avalanche Terrain Exposure Scale (ATES)
About the ATES
The Avalanche Terrain Exposure Scale is a system for analyzing and rating avalanche terrain, so that skiers, hikers, climbers and others can better understand their degree of avalanche exposure while in the backcountry.
The ATES was created in Canada in 2004, in response to an avalanche that engulfed 17 students on a school outing to Glacier National Park in British Columbia, killing seven. Since then, the original three-point scale has been applied to backcountry ski terrain in Europe and New Zealand, and has begun appearing in ski touring guidebooks for Colorado and other Western states. Canada was the first to rate waterfall ice climbs using the ATES, when Parks Canada published ratings for 75 popular ice routes in 2005.
In 2023, Avalanche Canada unveiled ATES V.2, with a 5-point scale instead of three, and with an ATES model specifically for waterfall ice climbing. It is this new 5-point ATES for ice climbing that Climb Avy Aware is using to rate Colorado’s most popular ice climbs.
ATES For Waterfall Ice Climbing
Avalanche terrain generally has many distinct and complex characteristics. ATES analysis takes into account physical attributes like slope angle, slope shape, level of forestation, the presence of terrain traps like cliffs, spines and couloirs, and overhead hazard. Known avalanche history–size, frequency, and the location of avalanche paths, starting zones and runout zones–are additional data points to be considered.
The ATES system simplifies these attributes into broader classifications that are more easily communicated to the backcountry user. An ice climber who understands that her objective for the day carries an ATES rating of, for example, “3–complex” can assess whether it’s a good route choice in light of her skills, risk tolerance, and current conditions, including the daily avalanche danger forecast.
In Colorado, that forecast is issued by the Colorado Avalanche Information Center, and published on its website and mobile app. The forecast, based on the North American Public Avalanche Danger Scale, covers three elevations–at, above and below treeline–and the 5-point color-coded scale ranges from “green–low” to “black–extreme” avalanche danger. A skilled yet risk-averse climber planning to tackle a frozen waterfall with an ATES rating of “4-extreme” might opt to avoid avalanche terrain altogether if the avalanche forecast for the day is something other than “low.”
CAIC Avalanche Danger Scale
Although both employ a 5-point scale, the ATES and the avalanche danger scale are based on entirely different criteria. The ATES is about the terrain, without regard to current snowpack or weather conditions, and as such an ATES rating will generally not change. The exception would be for routes where new data comes to light about avalanche history–for example, if it were learned that more and bigger avalanches had occurred in the past than previously thought, that route might be put in a higher exposure category.
In contrast, the danger scale is based on ever-changing conditions, the snowpack and weather, so the CAIC forecast may change from day to day or week to week.
When taken together, the ATES rating for an ice route and the CAIC forecast for the area become important risk management tools for ice climbers in Colorado.