Northern San Juan
AvalancheAnonymous · Jan 14, 2014 · Northern San Juan
Weather
Post storm that dropped >1ft of new snow. Constant strong winds mostly from NW'ly direction; on E'ly aspects and below treeline wind was much less noticeable. Significant wind scouring and loading all aspects and elevations. Clear skies with Tmax in the low/mid 20's though windchill made it feel quite a bit colder.
Snowpack
Two stories that describe the current avalanche problems (Wind Slab / Persistent Slab): 1) On ESE-S-SW observed old melt-freeze crust with small facets, buried 15-80cm down under mostly a soft slab 4F/1F. Hand tests revealed easy and clean failures at the crust/facet level. We produced some angry collapses around treeline rumbling far into the distance; dug them up to confirm failure to be at crust/facet layer. The recent avalanches we observed appear to have slid on that crust/facet layer as well. It seems that it is this snow structure most associated with the Persistent Slab problem. The few big collapses we had suggest that these Persistent Slabs can be triggered by backcountry travelers. We therefore avoided these aspects (snow quality there is marginal anyway) or at least stayed away from underneath bigger terrain or stuck to slopes 30dgr or less. 2) Strong winds predominantly from the NW created a drastically variable snowpack over short distance, especially around and above treeline. N-SE around/above treeline show lots of wind loading. On slopes steeper than 35dgr, these Wind Slabs are sensitive to skier triggering. Failure layer around/below treeline is basal dh, above treeline hard old snow.
Avalanche
1) Tricot E Ridge, NE flank, observed from across the valley: SS-N-R2D2.5-I (est. 70m wide, 300m vertical, 40dgr), SZ 12,200ft, EZ 11,400ft, within 24h. 2) Commodore Gulch, far S side, NE face below Pt 11,628, SS-N-R5D2-O(basal layer of dh), within 48h. 3) Prospect Gulch: several small hills E facing slopes (+35dgr) SS-N-R3D1-I, within 72h.