A localized area with poor snowpack structure was observed. This is the first location where test results indicated that propagation of a persistent weak layer deeper in the snowpack is possible. While I think this is an isolated problem, it should not be ignored, and more observations should be made for areas with a similar snowpack structure within the range.
Warm temperatures with little wind on Sunday produced moist snow surfaces on solar aspects.
Our AIARE 1 course travelled towards the South Bowl uptrack on Sunday. The avalanche problems and their distribution on our radar for the day were 1.) Wind Slabs above treeline on NE through E through SE aspects and 2.) Wet Loose on SE through S through SW aspects at all elevations. While traveling up towards the top of south bowl along the shoulder of the old burn scar, we noted a variable surface with plenty of wind board as a result of previously strong NW winds crossing this shoulder. We targeted an area with a shallower snowpack to investigate the snowpack layering in this area. We found just over 100 cm/39" of total snow with the upper 90 cm/35" consisting of very consolidated 1F hard to P hard snow. Below this was 10 cm/4" of 4F hard snow that consisted of very weak sugary 3 mm Faceted Grains. We conducted a compression test, and observed a sudden collapse result. (CT18SC down 90cm). We followed this test up with an Extended Column Test to see if this weak layer was capable of propagation. We confirmed that propagation of this weak layer underlying this hard slab was possible. (ECTP30 down 90cm).
This is the first place that I have seen both Sudden Collapse results and Propagating ECT results within the range, and so it was a bit alarming. We descended a 28 degree slope adjacent to our pit.
My best guess as to why this area held such poor structure: We know that shallower snowpack areas often hold weaker snow- so if you are looking for the weakest snow in the area, target areas that have the least amount of snow. I think this area probably sees quite a bit of stripping and subsequent loading due to localized wind patterns. I think these well developed facets haven't had a chance to start to heal because of the shallow nature of the snowpack in this area.
We are always looking for strong consolidated snow over weak loose snow. The avalanche sandwich was completed here by putting a hard consolidated slab of snow from wind events over the last couple of weeks on top of this weak snow. We use a hand hardness scale that many of you are familiar with, but in case you are not, the scale ranges from Fist -> 4 Finger -> 1 Finger -> Pencil -> Knife. Any time you skip one of these steps in hardness from layer to layer, it should alert you to potential poor snowpack structure. See the photo below. The interface between layers at which we got our alarming results transitioned from Pencil hard snow over 4 finger hard snow (skipping the 1 Finger step).
The good news is that I think this is a localized problem based on other snowpits that have been dug in the Northern Wallowas that have not had this poor of snowpack structure. That being said, continue to look for similar poor snowpack structure in areas that have less than a meter of snow and may have hard slabs as a result of wind transported snow. Let us know what you see!