Test slope failure- small slab avalanche on Andesite Ridge

Location Name: 
Andesite Ridge
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Tue, 04/20/2010 - 15:51
Location Map: 
United States
39° 21' 1.1808" N, 120° 21' 55.7316" W
See map: Google Maps
US


Red Flags: 
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: 
East
Weak Layer: 
Storm Snow
Avalanche Width: 
30ft.
Terrain: 
Near Treeline
Elevation: 
8 080ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
40ft.
More detailed information about the avalanche: 

Test slope failure in wind loaded near treeline terrain at 8,080', 77 deg aspect, slope angle ranged from 35 to 41 deg. New snow in the area measured 7cm with this test slope wind loaded to 31cm. Slab failed 25 cm deep in lower density portion of new snow at the bottom of the slab. Lightly rimed new snow crystals were noted as the weak layer. Good bonding at the old/new snow interface. Wet old snow still wet and in melt state beyond the bottom of the snowpit at 150cm.

Photo 1: Initial shooting crack cause by stepping on the top of the slope. One addition jump triggered the avalanche seen in the video.

Photo 2: Lower portion of new snow (bed surface) brushed away to reveal the wet old snow surface.

Photo 3: Old/new snow interface easily seen in the crown profile snowpit.

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

20100420 Andesite Ridge Avalanche.MOV

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: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: