Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 3
Our persistent weak layers (PWL) are largely dormant, waiting for the next big change like additional wind, water, and snow to wake 'em up. And while we've got a lull in the action, now is exactly the time to get out on the snow, map the lay of the land, and do some homework by getting out your shovel to check out the snowpack structure, looking for strong snow over weak, sugary snow. Over the past week, steep slopes that face the north half of the compass and harbor a myriad of weak layers, came to life with the Valentines storm. Now here's the tricky part... as the snowpack adjusts and gains strength, we're not hearing obvious red flags like collapsing (whooomphing sounds) or seeing cracking that are typically associated with this problem, but digging down with your shovel or track it's easy to see the sugary facets partying underneath a cohesive, dense slab.
And now where the rubber hits the road, a conundrum wrapped up in a snow stability dogma ... I'm keeping it tight and simply avoiding shallower areas of the snowpack like steep, rocky terrain where I'm more likely to trigger an avalanche that breaks deeper and wider than I might expect.
This avalanche on a steep northwest facing slope off East Lofty Peak above Cutthroat lake at 11,100", failed in a shallower area of the snowpack. Nearly four football fields wide (that's 1,200' for everyone who seats in the upper deck), and 1-3' deep, this meaty piece of snow was triggered by a sledder mid-slope.