Trigger:
Most avalanches are “naturally” triggered, meaning
that weather (wind, snow, rain or sun) stress the snowpack to
its breaking point. Like a tree falling in the woods, for the
most part, we only care about the ones that affect people. Luckily,
in 92 percent of avalanche accidents, the avalanche is triggered
by the victim or someone in the victim’s party. In other
words, most avalanche accidents happen by choice, not chance.
These are “human triggered” avalanches. In other
words, weather adds stress to the snowpack until it nearly equals
the strength of the snowpack. Then, the added weight of a person
provides the final thump to initiate a fracture within the buried
weak layer. (No, noise does NOT trigger avalanches. It’s
a cliché plot device in the movies, but noise is simply
not enough force to trigger an avalanche.)
| Trigger Size Required to
Initiate an Avalanche |
| Stability |
Large Cornice |
Explosive |
Human |
Natural |
| Very poor |
X |
X |
X |
X |
| Poor |
X |
X |
X |
|
| Fair |
X |
X |
|
|
| Good |
X |
|
|
|
| Very good |
|
|
|
|
We can also think of snow stability in terms of the size of
trigger required to trigger an avalanche. Notice that when natural
avalanches are occurring, the stability meter is pegged out
at the top of the scale. That’s why the best sign of avalanche
danger is another avalanche on a similar slope.
|
|
