Quick report
- Red Flags
- Collapsing, Poor Snowpack Structure
Today's observation is brought to you by: Spatial Variability! ("Now more variable!")
I wanted to take a look at SE, S, and W aspects today to better understand the distribution and sensitivity of the melt-freeze crust / facet interface that was the weak layer / bed surface in the recent widely propagating Reynolds avalanche, and likely a key player in the very widely propagating Raymond avalanche. I traveled up Beartrap towards 9990', dug on SE and S in that area, then moved over to the Square Top / Red Rocks area to have a look at a W and N aspect.
I was surprised to find the melt-freeze crust / facet interface unreactive in stability tests on SE, and absent on W. Notably, the only propagating stability test above the Feb 5 Pine Needle Layer (PNL) was on a S aspect, down 45 cm on decomposing fragments. Another guide in Beartrap today also got a big whumph on a due S aspect at 7700'.
In a thin snowpack location on a frequently wind-stripped W aspect, I got propagation in cupped and striated basal facets (depth hoar). I think these wind stripped W aspects are very concerning for triggering PWL avalanches. I think about areas like Hallways (recent avalanche), Greaseball, Little Giant, and West Couloir for example.
Here are the details of my pits:
Pit 1: 9990 Area, 9754', 134 degrees SE, 27 degree slope. Height of snow in thea area ranged from 175 to 230 cm, with a median of 190 cm. Height of snow at this pit was 215 cm. The Feb 10ish melt-freeze crust / facet layer was down 95 cm. I got various ECTNs in the new snow, and ECTX on the Feb 10 layer. I got a CT24 SC down 140 below the Feb 5 PNL in loose, dry facets.
Pit 2: 9990 Area, 9789', 214 degrees SSW, 28 degree slope. Height of snow in this pit was 125 cm. The Feb 5 PNL was down 95 cm, this is the depth I isolated my tests to. Below that, the "snowpack" was comprised of one big chunky layer of melt-freeze grains and ice. I got ECTP24 and ECTP30 down 45 in decomposing fragments.
Pit 3: Squaretop Area, 9604', 254 degrees W, 25 degree slope. Height of snow in this pit was 125 cm. ECTP28 down 75 cm on depth hoar. Various ECTNs above that.
Pit 4: Red Rocks Area, 9607', 36 degrees NNE, 25 degree slope. Height of snow 240 cm. Test depth 95 cm (Feb 5 PNL). Found buried surface hoar and small facets down 75 cm (distinct thin gray line in my pit). ECTX, then dramatic propagation on 5th bonus whack.