Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Possible
- Größe
- 2–3
What is it? 1-3 foot thick slabs overlie persistent weak layers (sugary facets, surface hoar, and/or crusts), predominantly at middle and upper elevations. Wind-loaded slopes are the most dangerous.
Where is it? Several natural and human-triggered avalanches occurred above 9000' in neighboring zones in the past 3 days. The recent activity occurred on several aspects. Wind-exposed bowls and slopes near ridgelines, prominent gullies, and chutes are most likely to produce avalanches.
How can you recognize it? Assume this problem exists until proven otherwise. You may or may not experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. Wind-loaded areas feel stiffer under your skis or sled and keep you from easily sinking into the snowpack.
How can you manage it? Unfortunately, avoiding slopes steep enough to slide is the only surefire way to manage this problem. Persistent slab avalanches are tricky. If you're playing near steep slopes, you may be able to trigger slides remotely (from gentler terrain above, below, and to the sides of steep slopes—explanatory video here). These avalanches may break wider than expected or higher on the slope above you.
ADDITIONAL DISCUSSION - OLD, SUGARY, FACETED SNOW NEAR THE GROUND: Faceted snow exists near the base of the snowpack. This layer has produced hundreds of avalanches this season and is buried beneath a thick, dense slab. Impacting deeply buried weak layers with your weight is difficult in this zone, but the consequences could be severe. While not likely, it may be possible to trigger a very large slide on this layer in steep, rocky, wind-affected alpine terrain where snowpack depths are variable. Here, skiers and riders can inadvertently find spots with a thinner snowpack where triggering an avalanche is possible. Digging down to this layer with the track of your sled is another "great" way to impact this deep weak layer.
(1/1/2023) Debris from a very large avalanche that was remotely triggered above Hyndman Creek in the Pioneer Mountains. This slide failed in a heavily wind loaded area and very likely involved a persistent weak layer. It covered the summer trail with a pile of debris that was 100-150' wide and 4' deep.
