Deep Slab Avalanches on Silver Peak

Location Name: 
Silver Peak
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of avalanche (best estimate if unknown): 
Wed, 01/04/2017 - 15:00
Location Map: 
United States
39° 13' 46.4304" N, 120° 14' 8.5308" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Obvious avalanche path
Terrain Trap
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
38degrees
Trigger type: 
Natural
Crown Height: 
4 ft
Aspect: 
North
Weak Layer: 
Old Snow
Avalanche Width: 
100ft.
Terrain: 
Below Treeline
Elevation: 
7 300ft.
Bed Surface: 
Old Snow
Avalanche Length: 
250ft.
Number of similar avalanches: 
3
More detailed information about the avalanche: 

Multiple deep slab and wind slab avalanches occurred in this area on 1/4/17. The facets near the 12/15 rain crust were the weak layer. Avalanches were noted in wind loaded near and above treeline terrain as well as in below treeline terrain. In the last 24 hours many of the avalanches had already refilled. A small cornice dropped onto one of the slopes that had already slid and refilled triggered an avalanche in the refilled snow on 1/5/17. Long, deep, and widespread shooting cracks existed near the avalanches. The persistent weak layer is now buried 100 to 150cm below the surface. Snowpit data and tests and observations on 1/5/17 showed multiple weaknesses remaining in the snow in the form of density changes in the upper storm snow and below wind slabs as well as the deeply buried facets. We stuck to low-angle, well-anchored slopes while collecting data. 

Photos 1 and 2: Natural deep slab avalanche that reloaded. Snowpit is from adjacent to this slope. The newer looking debris is from dropping a small cornice onto the reloaded slope. 

Photo 3: The filled in crown of a natural wind slab / deep slab from along the ridge of Silver Peak at 8000 ft. 

Photos 4: Debris from the natural wind slab / deep slab avalanche on a N aspect at 8000 ft. The debris piled against the tree is a 4+ foot block. Other trees showed snow plastered 3-4 ft above the snow surface on their trunks. The slope had already reloaded since yesterday. 

Videos: ECT and PST tests adjacent to the avalanche at 7300 ft. 

 

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Avalanche observation video: 

PST 2/130 END on Silver Peak

ECTP's on Silver Peak

Weather Observations
Blowing Snow: 
No
Cloud Cover: 
25% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Light
Air temperature trend: 
Static
Wind Direction: 
Southwest