Pro Field Report
Basic Information
Observation Details
Observation Date:
January 13, 2020Submitted:
January 13, 2020Observer:
SAC - SavageZone or Region:
Soldier and Wood River Valley MtnsLocation:
Croy Canyon - Rotarun "sidecountry", 5400-5900'Signs of Unstable Snow
Recent Avalanches?
YesCracking?
WidespreadCollapsing?
WidespreadSnow Stability
Stability Rating:
PoorConfidence in Rating:
HighStability Trend:
Bottom Line
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.
Media/Attachments
Advanced Information
Weather Summary
Cloud Cover:
OvercastTemperature:
20s FWind:
CalmAbout 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.
Avalanche Observations
| # | Date | Location | Size | Type | Bed Sfc | Depth | Trigger | Comments | Photo |
|---|---|---|---|---|---|---|---|---|---|
| 20 |
Croy Canyon 6000-7000' |
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 |
Bullion Gulch - Peak 8435' E 8300' |
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 |
Kelly Mt SE 8000' |
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 |
Snowpack Observations
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.
Avalanche Problems
| Problem | Location | Distribution | Sensitivity | Size | Comments |
|---|---|---|---|---|---|
Wind Slab
|
|
Layer Depth/Date: several, see notes above Comments: Could call it a persistent slab problem or a wind slab problem: recent wind loading above a variety of weak layers. |
Terrain Use
We dabbled in about 30-32 degree terrain on small slopes with no consequences (terrain traps, trees, rocks, etc).