Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
You can trigger an avalanche on steep slopes where cohesive slab sit above weaker snow. The most dangerous slopes are at upper elevations where winds drifted snow into deeper cohesive slabs. Avoid trigger points on rocky slopes at upper elevations where variable snow depths mean buried weak layers could be closer to the surface. You may not observe any obvious signs of instability, such as cracking or collapsing, before triggering a dangerous avalanche.
Warm temperatures and strong sunshine increase the chances of wet avalanches. Small pinwheels and rollerballs are an early warning sign to move towards shadier terrain. Avoid traveling on or under steep sunny slopes, especially later in the day when warming reaches its peak.
On February 20, a backcountry snowboarder was caught and killed in an avalanche on a terrain feature locally known as The Nose in the Middle Fork of Mineral Creek drainage, west of the town of Silverton. The avalanche occurred near treeline on a northeast-facing slope in the San Juan Mountains. You can read the preliminary accident report here.