Avalanche Terrain

Most avalanches occur on mountain slopes with a steepness between 30 and 45 degrees. Avalanches only occur on slopes of less than 30 degrees if the snowpack is very unstable. Slope angles steeper than 45 degrees usually shed snow regularly as it accumulates through sluffing or shallow-depth slab avalanches, which prevents larger avalanches from occurring. This is especially true in continental and intermountain avalanche climates. In maritime climates, slab avalanches can sometimes build to greater depths on steeper slopes, between 45 and 60 degrees.

Graphical depiction showing the window of terrain steepness in which avalanches can form

Avalanche terrain is also defined by other factors, such as:

  • The aspect (direction that a tilted ground surface faces); aspect affects how wind deposits snow on a slope and the intensity of solar radiation on that slope
  • The elevation (altitude); elevation impacts the type of snow that an area gets and its temperatures and wind regime

Note that upper slopes can have different snowpack conditions, exposure to wind and sun, and vegetation than lower slopes. For more information on avalanche terrain, see the COMET module “Snowpack and Its Assessment.”