Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Very Likely
- Size
- 2–3
Recent avalanches: We observed a widespread natural avalanche cycle on Friday, including very wide-propagating avalanches on Fresno, Raven, Butch, Tri-Tip, Templeton, and Summit Peak. There were multiple very large human-triggered avalanches in Girdwood, Turnagain Pass, and Seward, but none that we have heard of so far in the Summit Lake zone.
This is the third day since the major storm ended, and we still have the avalanche danger at high because the chances of a very large human-triggered avalanche that could bury a person are high. Our current snowpack setup is incredibly dangerous, with a buried weak layer of facets causing avalanches 2 to 4' deep that can be triggered remotely from low-angle terrain below steeper slopes. These avalanches could easily be triggered on slopes that are typically safe a few days after a storm. This type of snowpack setup may allow several tracks on a slope before someone finds the weak spot and triggers an avalanche.
This type of persistent slab setup takes time to heal and requires patience to safely manage. The only reliable way to avoid triggering a very large avalanche is to stick to simple terrain. Which means travelling in areas where the slope angle is below 30°, there is no steep terrain above that is connected and could be triggered from below, and avoiding terrain traps like gullies and cliffs where triggering even a small avalanche could have severe consequences. Don't get fooled by the quiet weather—conditions are primed for an avalanche accident.
Special Avalanche Bulletin messaging the high likelihood of very large human-triggered avalanches.
Photo: NWS Anchorage
