Cracking and collapsing was widespread on fresh wind-drifts. We were in 30-32* terrain at its steepest, almost entirely on slopes not steep enough to slide - but I would have expected 35-45* wind-loaded slopes to be fairly easily triggered. Fortunately, the wind-loading patterns are obvious in this area...until they get buried. The slope above the old animal shelter alongside the road naturally cracked and moved a little bit - this area received much less wind-loading recently than all the other activity I observed.
About 8-10" of low-density new snow (20-25cm) from last night. Generally westerly winds loaded N-E-S aspects, focused on E. The wind-loading was mostly confined to at and just below ridgelines and cross-loaded gullies. There is still a fair amount of snow available for transport.
|20||Past 24 hours||
|D1.5||SS||1'||N-Natural||Many smaller slides (D1-1.5) on N-E-S aspects. The slides broke at ridgelines where the wind-drifts were largest and the slope angle was steepest.||None|
|2||Past 24 hours||
Bullion Gulch - Peak 8435'
|D2||SS||1-2' ?||N-Natural||Two slides in adjacent gullies/bowls that looked like persistent slab avalanches failing in wind-loaded terrain. Hybrid crown/flanks spanned at least 400'. Aspect was a touch south of due east, probably E/SE.|
|2||Past 24 hours||
|D2||U||N-Natural||Slides were in the W Fork of Elk Ck drainage, Red Elephant Gulch. Aspect was SE/S. They failed in adjacent gullies, cross-loaded terrain on a sub ridge of Kelly.||None|
Rotarun area observations: 12-30" wind drifts, soft to stiff in nature but not hard slabs. E-SE cracking and collapsing was on a variety of layers: a hard interface below the recent snow (wind event after New Year's), a thin crust+facet combo under the newer snow (guessing 1/10 but could have been 1/7?), trapped lower density snow/decomposing fragments, facets/depth hoar near the ground (thin areas where the "old snow" was less than a foot before the recent snowfall), and crust/facets in the lower part of the pack but off the ground. On N aspects, the thin crust+facet combo (1/10 or 1/7) produced collapsing and cracking. Slopes continued cracking and collapsing on multiple passes/tracks on E/SE aspects and on more northerly slopes.
The variability in old snow structure over short distances (less than 10') was impressive.
Layer Depth/Date: several, see notes above
Could call it a persistent slab problem or a wind slab problem: recent wind loading above a variety of weak layers.
We dabbled in about 30-32 degree terrain on small slopes with no consequences (terrain traps, trees, rocks, etc).Close