History and Current Tools

The Avalanche Terrain Exposure Scale (ATES) is a terrain severity classification system resulting from collaborative efforts born from the aftermath of an avalanche incident in Connaught Creek, British Columbia during the winter of 2003. The British Columbia Coroner's report following the accident noted that a better system of communicating exposure to avalanche terrain was one way accidents like this could be prevented in the future. ATES was originally  introduced at the 2006 International Snow Science Workshop to explain the system and illustrate how it could be used as a communication tool for visitors on public land in Canada. Now in it’s second version, ATES is widely adapted across the globe. 

Avalanche Canada and Parks Canada have employed the ATES for 17 years as a framework to classify, describe and communicate the nuances of terrain zones  across the country. It can be used as a linear classification for individual routes, or as a zone classification for large areas. 

In the United States, ATES usage has been adopted as a communication tool in guiding and educational contexts. AIARE has adapted the tool for use in its recreational curriculum and merged it with the idea of choosing a mindset for selecting terrain. It is also being widely employed in guidebooks and mapping products, particularly those created by Beacon Guidebooks and On X Backcountry. Professionals may find the tool useful in their own operations and its potential has been realized by organizations across the country as it is widely used by professional organizations in Canada, New Zealand, Norway, and Spain. 

Applying ATES to Risk Management in the Workplace

The Technical Model can also serve as a checklist to develop consensus ratings. Skiers, climbers, and snowmobilers can all utilize this toolset as a basis for terrain classifications.  A ski area, guiding operation, or avalanche education provider may find it useful to begin classifying and building a terrain atlas that utilizes ATES and knowledge of feature history.

ATES is routinely applied to a fixed spatial scale;  ie mountain or drainage, because by applying at a finer scale (slope and feature), the more definite the rating will be and it is more likely that exposure to an avalanche increases. The categories of Exposure and Route Options are a few key drivers to understanding how terrain choice increases or decreases how much exposure is in a given piece of terrain.

When applying to a drainage or range scale there will be a mixture of terrain, making a general rating for the entire zone difficult and reducing accuracy. There will be multiple polygons likely to match the range of exposure and zones may be rated to the highest ATES Polygon with the run/route list capturing the shifts in exposure.

Exposure to low-angle or primarily forested terrain. Some forest openings may involve the runout zones of infrequent avalanches and terrain traps may exist. Many options to reduce or eliminate exposure.

Think generally sheltered terrain, a place without overhead hazard. Note the structure of the description for the Public model; ‘Exposure to…; options to reduce exposure.’ The intent of the language is to direct recreationalists to recognize where in the terrain exposure to avalanches increases and what features they can seek to reduce that exposure. Simple Terrain experiences small/D1 Avalanches so exposure to larger avalanches is unlikely and easily avoidable. The Technical Model cites a return rate of more than 30 years for a D2 which means when historic avalanche cycles happen that increase in exposure may occur in Simple Terrain without previous history.  

Exposure to multiple overlapping avalanche paths or large expanses of steep, open terrain. Frequent exposure to overhead hazard. Many avalanche starting zones and terrain traps with minimal options to reduce exposure.

One way to consistently identify Complex Terrain, look for the letter "U" or "V" in terrain photos or maps. Cirques, deep valleys, Headwalls above drainages present with a visible "V" or "U" which typically signifies convergence. This separates the exposure from Challenging with the lack of safe travel options. Identifying the transition to increased exposure in your intended run/route will help develop decision making points and marking boundaries for open and closed runs/climbs. 

Within Complex terrain polygons, it is common to have areas of Extreme terrain. These might be terminal gullies, steep rockbound chutes/couloirs, or cliffbands.  The next sub section will illustrate this clearly.

In addition to using numbers and signal words, using color for communicating ATES ratings was adopted to aid in comprehension. Colored polygons provide a unique way to overlay information on a topographic map, 3D satellite rendering, or photographs. The chosen method, linear or spatial, can show terrain ratings quickly. However, the user must be able to perceive the colors and if they have any color vision deficiency (CVD), it will inhibit their ability to assess terrain accurately.  Research is being performed to determine if a different color standard can be adopted. In the meantime, discretion is necessary when using ATES color codes to communicate a rating. When applying ATES, using a combination of numbers, signal words, and colors is advised. 

• Note: European ATES mapping uses white, green, blue, red, and purple for each respective rating. This is in line with their piste difficulty rating system.

In the image of the terrain above, ATES spatial is used to show the rating of popular ski touring areas in the San Juan Mountains of Colorado. Mapping software such as On X Backcountry has created overlays that are a combination of Auto-ATES algorithms vetted by local experts familiar with the terrain. Discretion by the user is critical, and as with slope angle shading for steepness, it is a starting point for assessment, rather than a definitive measure for managing exposure.