Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Likely
- Größe
- 2–3
The addition of new snow (15 inches), adding more stress to the snowpack, has increased the likelihood of persistent slab avalanches. Areas with a thin snowpack (<100cm) pose the largest risk for triggering a persistent avalanche, as it is easier for a traveler's weight to collapse the depth hoar at the base of the snowpack. Typically warning signs such as shooting cracks and whumphing may not occur until it is too late. Anticipate that these avalanches will grow wider and run further than you expect, yielding a high-consequence scenario that could bury, hurt, or kill a backcountry traveler.
For example, the very large natural avalanche on the NE face of Fremont in early January had a max crown height of 2 meters and destroyed 30-40-year-old trees. Additionally, a second large natural avalanche occurred in Abineau Canyon. Steep W, N, and E aspects above 10,500' should be considered most suspect, as these slopes accumulated early season snow, which has since turned into depth hoar and been buried by the season's entire snowpack.
The best way to manage the risk from persistent slab 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, making this problem difficult to manage.
(1/8/2023)
Crown average ~100cm. Max ~220cm. Toe of Debris pile stopped at the Inner Basin Trail. Numerous 30-40 year old trees destroyed. Occurred ~January 1st or 2nd. HS-N-R3-D3-O
Photo: Miguel Fernandez
