Widespread Deep Slab Activity 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): 
Sat, 03/17/2012 - 04:00
Location Map: 
United States
39° 13' 23.592" N, 120° 14' 36.8412" 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: 
6 ft
Aspect: 
Northeast
Weak Layer: 
Old Snow
Avalanche Width: 
1 300ft.
Terrain: 
Near Treeline
Elevation: 
8 000ft.
Bed Surface: 
Old Snow
Avalanche Length: 
1 000ft.
Number of similar avalanches: 
5
More detailed information about the avalanche: 

Most of the N-NE facing avalanche paths on the north side of Silver Peak had large natural avalanches on them this morning. 1-2 inches of new snow had accumulated on top of the debris and bed surface of these slides indicating that they likely occurred in the predawn hours on March 17th. These slides all failed on the crust/facet weak layer that is now buried 3-10 ft below the surface with a dense slab on top of it. The average crown depth was close to 6 feet deep. Slides like this occurred in below treeline, near treeline, and above treeline terrain (7300 ft to 8100 ft). These slides occurred on slopes between 35 and 45 degrees in steepness.

Snowpit tests near one of these crowns indicated that if a fracture starts in the deeply buried weak layer, it can travel very long distances.

Photo 1: Overview of the near treeline slides

Photo 2: Large shooting cracks that existed on the lower angle slopes that did not slide.

Photo 3, 4, and 5: Near and above treeline crown photos. All of these slides were connected by shooting cracks and likely occurred as one event. The slide in the video also was connected to the slides in these photos.

Photo 6: Below treeline (7300 ft) deep slab avalanche that failed on the same layer.

Snowpit: Crown profile near one of the slides at 8000 ft (the one in the video)

Video: PST and avalanche overview

 

 

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

Large avalanches on Silver Peak and propagation on a PST

Weather Observations
Blowing Snow: 
No
Air temperature: 
Below Freezing
Wind Speed: 
Light
Precipitation: 
Snow
Air temperature trend: 
Static
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: