Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Unlikely
- Größe
- 2–3
Layers of weak snow (sugary facets and crust+facet combinations) are buried beneath very dense, 2-4+ foot thick slabs. Triggering an avalanche on these layers is not likely, but the outcome of doing so would be catastrophic. Watch the video to the right/above to get a better feel for this problem.
These weak layers produced a set of historic avalanches just 10 days ago. Aside from the crowns from these older avalanches, you aren't likely to encounter signs of instability in your travels today. If you don't dig down, the snow will "feel good". But trust me, that weak snow is down there. Don't trust me? Grab your shovel and start digging.
Tracks on a slope are not an indication of stability. Avalanches may be triggered after many skiers or riders have traversed a slope. The first sign of instability may be the large, destructive avalanche you trigger. These slides may break much wider and much further above you on the slope than you expect. They can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.
The only way to eliminate your risk of encountering one of these beasts completely is to avoid avalanche terrain and terrain exposed to hazard from above. You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide.
ADDITIONAL DISCUSSION: Be on the lookout for sensitive slabs of wind-drifted snow at upper elevations. 6-8" of snow have fallen here in the past two days, but winds have remained light. Steer clear of smooth pillows of windblown snow near ridgelines and mid-slope gullies. Loose snow avalanches are possible during periods of sunshine, especially in very steep, rocky terrain.