A building slab isn't showing propagating results over a thick stack of facets in sheltered, north-facing middle-elevation slopes. Wind-affected slopes continue to have shooting cracks and collapsing over this weak layer. Active wind transportation and new snow were building a new generation of soft slabs in exposed middle and upper elevations.
Snowfall was steady S1 throughout the day until leaving the field at around 1600. The intensity increased to S3 before leaving but trended back down to S1. The wind was mainly light, with the occasional moderate gust blowing snow along ridgelines.
My main objective was to see how much the slab is growing in sheltered locations over the new/old interface (2/18). The snow pit locations were on a NE slope at 8400' and an N slope at 9300'. A razor-thin melt freeze crust was glued to the 2/18 interface with very weak, sugary facets below it. Stability test results showed no propagation (ECTN7,12,15) where the slab is about a foot thick (~30cm). Surface hoar (3-5mm) that formed a day ago just got buried by today's snow, but it appeared not to be standing in a semi-sheltered location at 9300'. The snowpack below this weak layer was very strong to the ground.
Problem | Location | Distribution | Sensitivity | Size | Comments |
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Layer Depth/Date: 1-2' Comments: Rose reflects where the problem was observed. |
Today's evidence supports needing wind-affected snow to add the tipping point of triggering avalanches. The slab is 25-30cm thick in this location and will likely need more of a load on top of it to become more sensitive in sheltered locations.
Solo travel. I avoided skiing in avalanche terrain but would feel comfortable skiing most middle elevation terrain that isn't wind-loaded.