Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
A layer of surface hoar buried 1 to 3’ deep is still capable of creating a large avalanche. This type of weak layer is notorious for taking months to heal which is unusual to a lot of us. Usually weak layers tend to gain strength faster but this has not been the case for this layer in Turnagain Pass where many human triggered avalanches have occurred. There have been less human triggered avalanches in Lost Lake and Seward which is telling us that this layer may be harder to trigger. The truth is we are not sure exactly how dangerous this layer is because we have limited information in these zones.
You can completely avoid this probem by sticking to lower angle terrain away from overhead slopes. If you do decide to venture into steep terrain, look for slopes that fan out and do not have terrain traps such as gullies or creeks where snow can pile up. People have triggered avalanches above them from relatively flat terrain. Human-triggered avalanches on this weak layer have occurred on slopes with many tracks on them so do not assume these slopes are safe.
(3/20/2025)
Snow pit in Lost Lake showing the layer of buried surface hoar.
Photo: Andrew Schauer