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Observation: East Mineral

Observation Date
1/8/2022
Observer Name
Gagne/Pease/Johnston
Region
Salt Lake » Big Cottonwood Canyon » Mineral Fork » East Mineral
Location Name or Route
Mineral Fork - East Mineral Trees and Highline
Weather
Sky
Obscured
Precipitation
Light Snowfall
Weather Comments
Mid-day snow flurries added one cm. No wind. Clearing by early afternoon.
Snow Characteristics
New Snow Depth
4"
New Snow Density
Medium
Snow Surface Conditions
Powder
Snow Characteristics Comments
5-10 cms new. Storm snow is dense and is perfect for the dense and supportable old snow surface.
Red Flags
Red Flags
Poor Snowpack Structure
Red Flags Comments
Poor snowpack structure, but showing signs of healing.
Avalanche Problem #1
Problem
Persistent Weak Layer
Trend
Decreasing Danger
Problem #1 Comments
Lots of probing down into the snowpack looking where the facets are. Overall they only seem to be present above about 8,500' in Mineral. We were constantly digging down performing quick pits, inverted ski poles, and probes determing the strength of the faceted layer. Above 9,000' on E and NE aspects in Lower East Facing Mineral, HS is about 1 meter with 10-15 cms of damp facets and 4F hardness. In other words, the facets are gaining strength.
On the next ridge to the south (Highline) the snowpack was deeper. On N aspect at 9,100' HS 160 cms with 30-40 cm layer of dry facets at the ground. But the facets also seem to be gaining strength, with hand hardness approaching 4F (4 fingers). All season long the PWL has been F (fist) hard and dropping out of the pit wall so this indicates the facets are slowly gaining strength.
On this North aspect at 9,100', pit results were ECTX (no collapse or propagation) but no surprise given the strong 1.2 meter slab on top. We also performed a PST which is a better tool for assessing deeper slabs and results were 80/120 END. Because we were able to proceed more than 50% up the weak layer before it fractured (80/120 = 67%) this is a positive indication the weak layer is gaining strength and adjusting to the weight of the strong slab above.
Comments
The biggest question right now is when will the PWL become dormant? Over the past few days the signs I have seen are the facets down near the ground are gaining strength - they are moving from soft, F-hardness towards stronger 4F in places. The weight of the slab is also helping sinter this layer.
On slopes with a 1.5 to 2m slab on top of the facets, I don't think the weight of a human can affect the faceted layer down near the ground.
I think places where the faceted layer could fail is triggering it from a thinner spot on the slope or on a repeater slope where the snowpack is thinner.
Clearing skies by mid day allowed for a look into Broads Fork where we saw no evidence of any recent natural avalanches. After the late-week storm that deposited up to 3' of water weight and wind, the lack of natural avalanches is another good sign the PWL is closer to becoming dormant.
Really difficult right now assigning a danger rating for the PWL problem. We are in the low-likelihood/high-consequence phase. Likelihood is Moderate but avalanche size and distirbution is Considerable.
Today's Observed Danger Rating
Considerable
Tomorrows Estimated Danger Rating
Considerable