Variable PS reactivity

CB Avalanche Center 2015-16 Observations

Location: Crested Butte Area
Date of Observation: 01/11/2016
Name: Zach Guy
Subject: Variable PS reactivity
Aspect: North East, East, North West
Elevation: Near treeline (11,200-11,400ft)

Avalanches: Spotted about 3 or 4 recent natural wind slab avalanches (D1 in size, estimated last 24 hours) on S and SE aspects above treeline in the northern portion of our zone. Skier triggered 2 sluffs on steep, shady terrain N/BTL on slopes that had previously avalanched. D1.5 in size, gouging to the ground. See photo.
Weather: Thin, few clouds. Cold temps. Light to Moderate north winds. Plumes off of northern portion of our zone this morning; then a lull mid day, then pluming again late this afternoon across whole zone.
Snowpack: About 3-4″ of recent new snow. No signs of wind effect except below south/southeast facing ridgelines ATL, where we saw top-heavy windloading with minor cracking a few inches deep. Dug 5 pits on NW to NE to E aspects near treeline across 3 different basins to check out reactivity of PS problem.
1.) NW aspect. HS 165, 105 cm slab (1F to 1F+) over basal facet layer (4F+ hard, 1.5mm rounding facets) ECTX and no signs of failure with additional loading steps.
2.) NW aspect. HS ~50 cm. Faceted snow throughout (4F to F). ECTX, slab crumbled.
3.) NW aspect. HS 150. 1F slab over basal facets (4F-, 2mm facets). ECTX, but SC failure with additional loading
4.) E aspect. HS 125. 1F slab over basal facets (F+, 2 mm facets). ECTX, but SC failure with additional loading
5.) NE aspect HS 115. 1F slab over basal facets (F, 2-3 mm facets) ECTP24, Q1 SC.

IMG_5500

Skier triggered sluffs on steep, shaded terrain that has avalanched previously, leaving shallow faceted snowpack.