08/17/2026
The Avalanche Terrain Exposure Scale (ATES) classifies terrain into five categories based on slope angle, forest density, slope shape, terrain traps, avalanche frequency/magnitude, starting zone size and density, runout zone characteristics, interaction with avalanche paths, and route options for managing exposure.
• Non-avalanche (Class 0): No known exposure to avalanches. Very low angle or densely forested slopes located well away from avalanche paths, or designated trails/routes with no exposure to avalanches.
• Simple (Class 1): 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.
• Challenging (Class 2): Exposure to well-defined avalanche paths, starting zones, terrain traps or overhead hazard. Options exist to reduce or eliminate exposure with careful routefinding.
• Complex (Class 3): Exposure to multiple overlapping avalanche paths or large expanses of steep, open terrain. Sustained exposure to overhead hazard. Many avalanche starting zones and terrain traps with minimal options to reduce exposure.
• Extreme (Class 4): Exposure to very steep faces with cliffs, spines, couloirs, crevasses or sustained overhead hazard. No options to reduce exposure and even small avalanches can be fatal.
———
