Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
Earlier this week, a large natural avalanche occurred on the NE face of Fremont Peak. The avalanche occured as wind built a slab over weak faceted snow, producing a failure near/at the ground. Steep NW, N, and NE aspects above 10,500' should be considered most suspect, especially on slopes with fine cinder substrate, with few rock anchors and depth hoar. Some westerly slopes may also have this problem, see January 2nd pit from Allison Clay.
Many easterly slopes were skiied in Humphrey's Cirque over the past few days, however this is not solid evidence that a persistent slab avalanche will not be triggered on an easterly slope. A traveler could trigger a persistent slab avalanche from thin areas on the slope, where it is easier to affect the buried weak layer.
The best way to manage the risk from persistent slabs avalanches is to make conservative terrain choices. Persistent slabs can be potentially triggered by a skier’s/boarder’s weight, even weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
(1/5/2023)
Arrow indicates smooth, rounded and pillow shapped slopes in area of Core Ridge/Snowslide Canyon. These are southeast, east and northest slopes above treeline that appear to be wind loaded.
Photo: Paul Dawson
