More Persistent Slabs

CBAC 2020-21 Observations

Zone: Northwest Mountains

Location: Elk Creek Drainage off Kebler pass

Date of Observation: 12/14/2020

Name: Jack Caprio and Zach Guy


Subject: More Persistent Slabs

Aspect: North, North East, East

Elevation: 9,800′-10,500′


We observed numerous persistent slab avalanches on NE and E aspects BTL, ranging from D1-D2 in size, most that ran this weekend and some that we triggered today. While skinning up a ridgeline, we crossed above 7 NE facing avalanche paths. Of those 7, 5 had already run naturally during our recent storm cycle. The remaining two were easily triggered by ski cutting convexities near the top of the start zones. The slab depths varied from 12-16 inches, encasing all the recent storm snow. As the slides picked up speed, they entrained some of the rotten snow at the bottom of the snowpack.  All of the slides propagated across their entire start zones and ran about 3/4 of the distance to the bottom of the avalanche path.  They were all soft slabs failing on the 12/10 interface.

Weather: Little to no wind. Overcast skies. The snowfall rate varied from S-1 to S2 from 12 pm – 2 pm, with a few inches of new snow throughout the day.

Snowpack: Traveled below treeline hoping to find improving stability but continue to get widespread collapses and triggered slides.  The top 12-16 inches of the snowpack consisted of F hard precipitation particles from our recent storm accumulations. Sitting below the storm snow is the 12/10 weak layer/ interface. On Northerly aspects, this interface consists of F hard buried near-surface facets. On Northeast through East facing aspects, this interface consists of a thin melt-freeze crust with near-surface facets sitting on top.