Storm Slab on Facets Above the 12/15 Rain Crust

Location Name: 
Silver Peak
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of avalanche (best estimate if unknown): 
Sat, 12/24/2016 - 11:10
Location Map: 
United States
39° 13' 46.7292" N, 120° 14' 8.9916" 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: 
Skier
Crown Height: 
1 ft
Aspect: 
North
Weak Layer: 
Old Snow
Avalanche Width: 
60ft.
Terrain: 
Below Treeline
Elevation: 
7 280ft.
Bed Surface: 
Old Snow
Avalanche Length: 
250ft.
Number of similar avalanches: 
1
More detailed information about the avalanche: 

This slide was remotely triggered from a lower angle ridge about 60 ft. away. The crown measured 30 to 40 cm (12 to 16 inches) in depth and it failed on a thin 1 cm thick layer of loose old snow (near crust facets) resting on top of the 12/15 rain crust. The slope angle measured between 36 and 39 degrees and the aspect wrapped from N to NE. It ran down slope into gullies and trees.

In addition to this avalanche, we saw several shooting cracks in below, near, and above treeline terrain as well as some skier triggered loose dry sluffs in the new snow on steep test slopes. Some collapsing and whumfing also occurred on sheltered slopes between 7200 and 7800 ft. Hand pits and observations indicated that the near crust facet layer that this slide failed on was more likely to be found on northerly aspects than on the more southerly facing slopes in this area. 

Along the NE ridge of Silver Peak ski kicks near wind-loaded slopes did cause some shooting cracks but no avalanches were observed nor did we ski any of the steeper wind loaded slopes. We chose to descend on lower angle, well-anchored (tree covered) slopes.

Photo 1: This slide was triggered from this spot on the ridge above the slide. The lower angle slope below me cracked but did not slide.

Photo 2: Overview of the slide, taken from between the trigger point and the crown.

Photo 3: Looking a the skier's left side of the crown. Note the firm bed surface (the 12/15 rain crust) and the thin darker line in the crown just above the rain crust at the bottom of the new snow - the near crust facets. 

Photo 4: Skier's right side of the crown and flank as the slope become lower angle to the skier's right. 

Photo 5: Looking down the path at the debris and terrain traps below. 

Photo 6: Small skier triggered loose dry sluff and a shooting crack on a N-NE facing slope around 8000 ft. 

Avalanche Photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
75% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Calm
Precipitation: 
Snow
Air temperature trend: 
Cooling
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Light intermittent snow showers during the day with 2 to 5 cm of accumulation above 7000 ft. and less than 2 cm below 7000 ft.