Weak snowpack, still collapsing

CBAC 2020-21 Observations

Date of Observation: 01/08/2021
Name: Zach Guy

Zone: Southeast Mountains
Location: Mount Emmons
Aspect: North East, East
Elevation: 9,000 to 11,200 ft

Avalanches: Intentionally skier triggered a few small loose dry avalanches entraining the top 6″ of faceted surface snow. They ran about 600 vertical feet.
Weather: Few clouds, calm winds, mild temps above the inversion.
Snowpack: Still getting abundant collapses while breaking trail in untrafficked terrain. Persistent slab structure was about 18″ thick on average. Below ~10,000′, the slabs are so weak and faceted that the collapses only radiating a few yards (on northeast aspects). On east aspects at these lower elevations, we got a few collapses that propagated up to 20′ or so where there is a crust at the 12/10 interface helping to drive propagation. Avalanches at this elevation would be quite small and fairly isolated.
Above about 10,000′, the slabs get stiffer (up to 1F-). Collapses require a stomp or two, but they radiate across entire clearings (which were 50 feet or less where we traveled). Moderate propagating results in stability tests.
The snow surface continues to grow weaker. Large grained surface hoar is widespread except in wind exposed features. Near surface faceting is prevalent, and shallow facet sluffs are easy to trigger. Slopes that have previously avalanched (of which there are many), have an even weaker snow surface due to their shallow depths and stronger temperature gradients. The ones we poked at have an old bedsurface crust below all of the weak junk, which will make for an even more dramatic hardness difference when these layers get buried.

 

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