Northern San Juan
AvalancheJeff Dobronyi · Jan 12, 2025 · Northern San Juan
Weather
Clear, cold, light winds, no blowing snow.
Snowpack
6" HN on south side of RMP, 10-12" HN on north side of RMP. HN felt like it was faceting already. HS in Sam's Trees was 120cm NTL at 11,700', down to 70cm at 10,000'. NTL snowpack has a distinct slab over the DDL (December drought layer), including SE aspect. Below treeline the slab is weak but still present. We observed collapsing at 11,800' and 10,200'. Shooting cracks observed at 11,200' SE aspect 30-degree slope angle but no release. Localized collapsing and cracking BTL at 10,500 E aspect, but no release on 38-degree slope. However, BTL ski track isolation produced cracking and release of slab on DDL (see photo). BTL slab was 50cm thick, F+ hardness where we traveled, seems like it would have needed 40-degree terrain without support to release, but the soft slab was present. No obs on NTL slab other than avy obs.
Avalanche
HS-ASr-R1D2-O in Riley Boy (Imogene path). Seemed like it was triggered by second person on slope from about 400' below. Crown was ~1m thick, bed surface seemed like the December wind event surface with facets above. Crown was 100m wide and debris flowed 200m vertical downhill. Crown connected rocks at top of path. Also observed a HS-N-R2D1.5-I small wind slab on the S aspect of US Basin peak below a small cornice. Another D1 soft slab BTL in the middle of one of the Brooklyn's gullies (very steep) which released mid-slope W-facing.