Test Slope Failure on Andesite Peak

Location Name: 
Andesite Peak
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Thu, 02/16/2017 - 11:30
Location Map: 
United States
39° 20' 58.8048" N, 120° 21' 55.746" W
See map: Google Maps
US


Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
39degrees
Trigger type: 
Snowboarder
Crown Height: 
1 ft
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Avalanche Width: 
30ft.
Terrain: 
Above Treeline
Elevation: 
8 100ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
30ft.
Number of similar avalanches: 
2
More detailed information about the avalanche: 

Kicks from a split-board released a refrigerator-sized cornice onto a wind-loaded test slope. The cornice triggered a 10 to 14 inch wind slab on the slope that did not propagate very far from the edges of the cornice drop. Ski kicks and cuts on a slightly lower angle part of this test slope did not trigger cracking unless the slope had been previously undercut. Wind-loading was continuing throughout the day in this area and large cornices had formed above wind-loaded slopes. Wind slabs measured between 8 and 14 inches in depth. 

In more sheltered areas, only ~4 inches of new snow existed and observations did not reveal signs of instability in non-wind-loaded areas.

Photo 1: Split-board kicks triggered a refrigerator-sized cornice failure onto the wind loaded test slope. This resulted in a 12-14 inch deep wind slab failure.

Photo 2: The other side of the wind slab that resulted from the cornice drop.

Photo 3: Wind slab cracking in an undercut wind-loaded slope.

Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Strong
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Clouds and snow decreasing in the afternoon.