Test slope failure and small, soft-slab avalanches on Carpenter Ridge

Location Name: 
Carpenter Ridge
Region: 
Independence Lake Area
Date and time of avalanche (best estimate if unknown): 
Mon, 01/18/2010 - 12:00
Location Map: 
United States
39° 24' 44.0424" N, 120° 18' 49.2876" 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: 
37degrees
Trigger type: 
Skier
Crown Height: 
1 ft
Aspect: 
North
Weak Layer: 
Storm Snow
Avalanche Width: 
50ft.
Terrain: 
Above Treeline
Elevation: 
8 520ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
100ft.
Number of similar avalanches: 
5
More detailed information about the avalanche: 

 4-6 inches of new snow above 8000' on Carpenter Ridge. Near treeline we triggered several small, soft-slab avalanches on test-slopes and small slide paths. These slides were all similar to the slide in the attached movie and photos. They all released wit a few small kicks on the wind-loaded part of the slope. The slab layer was a newly formed wind slab due to wind-loading from the south winds. All of the slabs that released failed about 6-12 inches down within the new snow. North facing slopes seemed to be the most tender while NW and NE slopes required slightly more force for the wind-slabs to fail. All of these slabs were relatively small around 12 pm today. However with more wind and snow forecasted tonight these slabs will become larger and more widespread.

Photo 1: A N-NW-facing, wind-loaded, 36-38 degree slope near treeline at 8400'. 3 skier triggered failures occurred on this slope.

Photo 2. Another N-facing, wind-loaded test-slope near treeline that failed due to skier triggering.

Avalanche Photos: 
Avalanche observation video: 

Skier Triggered test-slope failure on Carpenter Ridge (small soft-slab avalanche)

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

 Snow started to intensify around 11:30. By 2pm snowfall rates were approaching 2 in/ hr.