Watching for the persistent slab to wake up below treeline

CB Avalanche Center 2020-21 Observations

Date of Observation: 01/29/2021
Name: Jared Berman and Zach Guy

Zone: Southeast Mountains
Location: Coon Basin / Climax chutes
Aspect: North East, South East
Elevation: 9200′ – 11300′

Avalanches: Nothing new
Weather: Warm temps all day. Snow showers early in the morning before skies opened up and the sun popped out for a while. The afternoon brought cloudy skies again and strong winds above treeline from the southwest with visible plumes off of the high peaks.
Snowpack: Traveling through wind-sheltered terrain near and below the treeline, we found slab structures ranging from 30-40cm on southeast and northeast aspects.

On southeast aspects, slabs from new snow were not as deep averaging about 30-35cm resting on top of a melt-freeze crust that varied in thickness depending on aspect and slope angle. One snowpit dug at 11,000′ on a southeast aspect and 28-degree slope revealed a Fist-4 Finger hard slab resting on top of a thick 4.5cm pencil hard crust. The crust is resting on top of weak facets 1mm in size. This was the only pit we dug that showed propagating results (ECTP21). We also got one collapse on a SE slope where the crust was thinner

On northeast aspects near treeline, the slab was slightly larger ranging from 35-40cm which is resting on top of 60cm of completely faceted snow. Slabs on these colder aspects are also Fist-4 Finger minus in hand hardness. Two test pits did not show propagating results. However, once we added additional load to the slab, extended column tests showed full propagation (see video below). We skied steeper terrain on northeast aspects with no signs of instability, but steered clear of possible crossloaded terrain.

As we moved lower in elevation below treeline on northeast aspects, the slab steadily became softer and softer until we reached 9500′ where snowpack structure is essentially all facets to the ground, with only 15cm of recent snow on top.