Snowpit and test slope failures in Deep Creek

Location Name: 
Deep Creek
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of avalanche (best estimate if unknown): 
Fri, 12/17/2010 - 12:30
Location Map: 
United States
39° 14' 44.484" N, 120° 14' 16.6812" 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
Terrain Trap
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
33degrees
Trigger type: 
Skier
Aspect: 
North
Weak Layer: 
Other
Avalanche Width: 
40ft.
Terrain: 
Near Treeline
Elevation: 
7 680ft.
Bed Surface: 
Other - explain below
Avalanche Length: 
20ft.
Number of similar avalanches: 
2
More detailed information about the avalanche: 

Buried surface hoar exists in this area. During the morning not enough snow had accumulated to start causing problems on this layer. Ski cuts on test slopes only resulted in loose sluffs. By midday skier triggered shooting cracks and small soft slabs started to occur on slopes as low as 30 degrees. These failed on the buried surface hoar layer. This change from sluffs to soft slabs indicates that enough snow has fallen to start overloading the buried surface hoar, and that the new snow has gained enough cohesion to break as a slab rather than a sluff.

Photo 1: The first of 2 test slope failures that failed on the buried surface hoar on a 33 degree rollover.

Photo 2: Skier triggered shooting cracks resulting from failure of the surface hoar on a 30 degree slope.

Video shows a propagation saw test indicating that fracture propgation and slab failure are becoming likely.

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

MVI 0798

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