Some simple observations and tests can give early warnings of potential danger. The following list was developed by Ian McCammon in 2006 and is arranged to form the mnemonic ALPTRUTh.
The presence of three or more of these clues indicates that any further decisions need to be made carefully. This threshold drops to two clues when persistent or deep, weak layers of snow are present.
- Avalanche activity within the previous 48 hours – this is the greatest clue that the slopes are dangerous
- Loading – new snow, rain, or wind-blown deposits rapidly add weight to buried weaker layers, making them more prone to collapse, the first step in slab (large blocks of snow) avalanche release
- Path – open slopes with steepness of 30 degrees or greater and a history of prior avalanches, usually indicated by absence of trees, or trees that are much younger than those on either side of the slope
- Terrain trap – features that can amplify consequences if caught (gullies, trees, cliffs, etc.)
- Rating – “considerable” or above on the North American Public Avalanche Danger Scale
- Unstable snowpack – condition in which a buried weak layer is bearing so much weight that even the small additional weight load of a person can cause it to collapse
- Thaw instability – melting due to warm temperatures and/or rain on snow. This also may include rapid warming, even if temperatures are still below freezing. Thaw weakens the snowpack, which, in turn, can become unstable as described above.
It’s about staying alive!