Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2
It's no secret - the snowpack is weak, rotten, and faceted on northerly and easterly facing slopes. In general, the odds of triggering an avalanche have decreased because the snowpack hasn't been stressed by the weight of new snow. The exception is specific slopes with the additional weight of wind-blown snow where triggering a slide is more likely.
The challenge is that slopes with the best coverage are generally ones harboring this weak snow with a slab on top. What's the strategy today?
- Avoid recently wind loaded slopes. Look for evidence of this wind deposited snow because it looks round, smooth, and pillowly. It often exists under cornices. Look at the images in the next section showing patterns of wind loading.
- Ride slopes less than 30 degrees in steepness where avalanches don't happen and don't ride under steeper slopes. You could trigger an avalanche on a steep slope by just tickling the bottom of it.
- If you do ride something steeper, first ask what the consequences of triggering an avalanche will be? It could break 2 feet deep and several hundred feet wide. Where will it take you?
The graph below from students in a professional avalanche course shows the layers in the snowpack. The horizontal bars indicate the hardness of the layers. Longer bars show hard layers. Shorter bars show softer layers. Strong snow over weak snow is the recipe for an avalanche. I like to interpret it as a kindergarten student would - when you place big blocks on top of small blocks, all it takes is a bump and all the blocks fall down.
