Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Possible
- Größe
- 1.5–2.5
It's possible to trigger wide, 1-2' thick avalanches. They are most likely to fail on crust + facet combinations on slopes that face W-S-E. Wednesday, riders near Banner Summit remotely triggered a large avalanche from a meadow 50 yds to the side of the slope. The slide broke over 1,000' wide and 2' deep (report). Tuesday, on Mushroom Ridge, SAC staff experienced multiple large collapses and received poor snowpack test scores on slopes with a crust + facet weak layer.
We're faced with a mid-winter-style snowpack that boasts a complex mix of weak layers. Due to the variable weather in March, the distribution of these weak layers varies greatly from slope to slope and across the zone. Persistent Slab problems are tough to manage. You may or may not see obvious signs of instability on unstable slopes. Multiple skiers or riders might play on a slope before it avalanches. You can reduce your risk by staying off (and out from beneath) slopes steeper than about 35 degrees.
ADDITIONAL DISCUSSION: While it would take a dose of bad luck, triggering a massive 3-5' thick avalanche on older, deeply buried weak layers can't be completely ruled out. While triggering one of these beasts is far less likely than the slides described above, the consequences would be devastating.
(3/31/2023) Crown of a very large avalanche that was remotely triggered by riders from at least 500 feet away on the ridgeline above. It broke 4-5 feet deep and 800+ feet wide. This slope faces W at 9,300' in the Frenchman's drainage near Smiley Creek. You can clearly see the two sets of persistent weak layers in our snowpack in this photo.