Avalanche activity near and above treeline 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, 02/24/2010 - 13:30
Location Map: 
United States
39° 13' 24.1572" N, 120° 14' 35.7288" 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
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
37degrees
Trigger type: 
Skier
Crown Height: 
2 ft
Aspect: 
North
Weak Layer: 
Other
Avalanche Width: 
500ft.
Terrain: 
Above Treeline
Elevation: 
8 000ft.
Bed Surface: 
Old Snow
Avalanche Length: 
400ft.
Number of similar avalanches: 
2
More detailed information about the avalanche: 

 From 7200' up on the skin into Silver peak signs of instability became increasingly widespread. See this observation for more information about the shooting cracks, whumphing, snowpack collapse and test-slope failure that occurred below treeline. Near and above treeline 1-2 ft thick windslabs had formed on the N-NE aspects on Silver Peak. Large overhanging cornices had also formed along the N ridge off the N summit. No natural activity was observed in the main bowl on Silver nor on the more north facing slopes above near and above treeline. No natural activity was observed on the surrounding peaks either. A large skier-triggered avalanche did occur on the N facing, wind-loaded, 35-38 degree, near treeline slope on the north side of the ridge leading up to the peak. I triggered this slide with one ski kick while on the ridgeline near the west end of the slide. This slide started at interface between the heavy layer of new snow and the lighter layer of new snow below it. This slide quickly stepped down to the bottom of the Feb. 19th crust layer and propagated for 500 ft to the east. The slide ran about 400 ft downslope and depostied debris about 3 ft up on tree trunks. A second simmilar 150 ft wide slide released sympathetically as a result of this first slide. These two slide were connected by shooting cracks.

Photo 1: The west end of the skier-triggered slide

Photo 2: The east end of the skier triggered slide

Photo 3: The second sympathetic release slide

Avalanche Photos: 
Avalanche observation video: 

Avalanche on Silver Peak in the Tahoe area 2-24-10

Weather Observations
Blowing Snow: 
Yes
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
Air temperature trend: 
Cooling
Wind Direction: 
Northwest
Accumulation rate: 
More detailed information about the weather: 

 A brief period of N-NW winds occurred while I was on the ridgeline. There was very little evidence of long periods of snow transport by this wind. Broken clouds allowed some periods of sunshine to warm the snow surface up to 7800' on sun exposed aspects.