Northwest Avalanche Center

Observation: Public

All Observations

Observation Details

Name:
Matt Primomo
Observation Date:
January 8, 2021
Submitted:
January 9, 2021
Zone or Region:
East Central
Activity:
Skiing/Snowboarding
Location:
Marion Lake

Observed Avalanches

Did you observe any avalanches? 
Yes
Avalanche Type:
Hard Slab
Size:
Size 3: Could bury and destroy a car, damage a truck, destroy a wood frame house, or break a few trees
Elevation:
6480ft
Aspect:
N
Comments:
Recent explosive triggered slide, roughly 100m wide x 75cm deep. See attached profile below.
Photo:

Signs of Unstable Snow

Did you see shooting cracks? 
No
Did you experience collapsing or whumpfing? 
Yes, Isolated

Observations

Snowing about 1cm/hr in the morning, amounting to about 5cm by afternoon. Calm to light winds, no blowing snow save for a few spin drifts off cliffs observed.

Beneath the 5cm of new snow we found some small buried surface hoar in open, NTL locations, avg 5mm. Soft snow was above and below it.

Observed a handful of recent, wide D2s and two D3s. A natural D2 below a cornice, and the rest from control activity on a previously untouched snowpack on NW-E facing slopes NTL/ATL. These were on inter-storm layers, and basal crust/facets.

Throughout the day we got 4 collapses, (without cracks) on weak snow near the ground. These were smaller in nature, though still startling. Estimated up to 10ft around and often in shallow locations on the edge of a slab.

A profile at 5,900ft on an East aspect above Marion Lake with an average snowpack depth for the highly variable zone showed HS of 89cm. 1F to P hard slab over December crust/facet layers down 45cm to 55cm from the surface. 4F hardness 2mm+ basal facets beneath this to the ground. ECTP, 14 down 55cm on this layer. PST 35/100 (End) here, and the block slid right off on a 33deg slope.

Overall, got the feeling it is becoming more difficult to trigger a persistent slab on weak snow near the ground, but still totally possible if you hit the wrong spot or have a large trigger (a few people grouped up or a snowmobile). We were careful to stay well away from large, steep features at upper elevations and went out of our way to do so.

Media

Crown profile of above mentioned hard slab. Roughly 100m wide x 75cm deep.
Photo of crown profile above
Location of a collapse, shallow snowpack with very weak snow on the ground at 6,600ft, SE aspect
Large grained basal facets from the profile at 5,900ft
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