Deep Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Unlikely
- Size
- 2–3
Recent Avalanches: Two human-triggered avalanches occurred last Thursday in Raggedtop Bowl (get the details here and here). Both natural and human-triggered loose snow avalanches were reported on Sunday related to warming and sun. Several natural wind slab avalanches occurred last week from the outflow wind event. The largest avalanches that have occurred recently happened on 2/14 during a north wind event. One of these was on a southeast slope on Fish's Breath and the other was on northeast facing slope in Ragged Bowl.
It has been almost 3 weeks since a large avalanche has occurred on the weak snow that formed in December in the Turnagain Pass area. There are a few reasons why this is still our main concern despite the lack of avalanches and low likelihood.
- Poor structure still exists in thin spots in the snowpack. A large slab is sitting on very weak snow in places. This layer has gained strength over time, but these types of layers are very hard to fully trust and the consequences could be devestating if the unlikely avalanche occurs.
- The large avalanches on the north side of the Girdwood area last week tell us that large avalanches could still occur in the right thin spot with the right load. That side of the Girdwood valley has a different snowpack than the south side of the valley and Turnagain Pass, but the thin places in Turnagain have similar structure to where those avalanches occurred.
We think it is unlikely that a person could trigger one of these avalanches, but there is always some uncertainty with this type of problem. Some things you can do to reduce your exposure and vulnerability include checking safety gear at the parking lot, choosing safe, low angle up routes, avoid riding close to rocks, and travel one at a time in steep terrain while watching partners closely.
