Test slope failure, shooting cracks, and whumphing below 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 - 11:30
Location Map: 
United States
39° 13' 33.492" N, 120° 14' 18.7368" 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
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
38degrees
Trigger type: 
Skier
Crown Height: 
1 ft
Aspect: 
Northeast
Weak Layer: 
Other
Avalanche Width: 
20ft.
Terrain: 
Below Treeline
Elevation: 
7 400ft.
Bed Surface: 
Old Snow
Avalanche Length: 
30ft.
Number of similar avalanches: 
3
More detailed information about the avalanche: 

 Several signs of instability in the Silver Peak area today. In below treeline terrain between 7300' and 8000', widespread skier-triggered shooting cracks, whumphing, and snowpack collapse occured as a result of poor bonding both within the new snow and at the base of the new snow on the Feb 19th snow surface. The weak layer in the new snow was a density inversion (heavy snow over light snow). The Feb 19th snow surface in this area was a thin crust.

Photo 1: Skier-triggered slab on a NE facing, 38 degree, test slope at 7400'. This slide started as a sluff in the new snow then stepped down to the top of the Feb. 19th crust.

Photo 2: 30ft skier-triggered shooting crack on a NE facing slope.

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Weather Observations
Air temperature: 
Above Freezing
Wind Speed: 
Calm
Precipitation: 
Air temperature trend: 
Warming
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: 

 Broken clouds allowed some periods of sunshine to warm the snow surface up to 7800' on sun exposed aspects. Below 7500' the snow became wet and sticky. Below 7000' runnels and free water became present in the upper 3-4 inches of new snow.