Quick report
- Slope Angle
- 47°
Avalanche
- Slab Width
- 76 m
- Weak Layer
- Depth Hoar
- Trigger Type
- Natural
- Avalanche Type
- Hard Slab
- Trigger Detail
- Repeater
- Start Zone Aspect
- North
- Avalanche Problem
- Persistent Weak Layer
- Start Zone Elevation
- 2682 m
Several slabs failed Saturday on the Sisters sub-ridges north of Mt. Elmer in Logan Cottonwood Canyon. The most subtle was a steep, north-facing rock band that released. We skinned up across the bowl and saw a small crown. The next skin up, the crown had more than tripled in size to several hundred feet in width. We postulate that it failed on a depth hoar layer that we had identified on similar slopes/aspects near rocks and logs. It failed as a large hard slab first, running a couple hundred feet, and then failing again, as the crown propagated further along the sub-ridge. Images were poor quality as it was snowing hard. We didn't approach this avalanche or any others due to unsafe conditions.
Also apparent in Cottonwood Canyon were several repeater hard slabs that released on steep, east-facing slopes. These all failed in storm slabs over the early-season facets. Some of these extended across existing crowns, some were in steep micro-features below the initial crowns. Steep, north-facing and east-facing aspects with a touch of wind deposition were all suspect, all weekend. South and west aspects skied clean and fast, and had more complex melt-freeze and sun crusts bridging old layers to the well-bonded late-week (30-31 JAN) storm snow. Not enough loose storm snow to cause much commotion on these aspects.
With more snow or big wind, the aspects where we observed natural slide could all load up for another natural persistent slab avalanche cycle.