Test slope failure- small slab avalanche on Andesite Ridge

Submitted by brandon on Tue, 04/20/2010 - 4:31pm
Location Name: 
Andesite Ridge
Region: 
Donner Summit Area

Location

United States
39° 21' 1.1808" N, 120° 21' 55.7316" W
See map: Google Maps
Position: 
Forecaster
Date and time of avalanche (best estimate if unknown): 
Tue, 04/20/2010 - 3:51pm
Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Avalanche Observations
Avalanche Type: 
Dry
Avalanche Type: 
Slab
Trigger type: 
Skier
Slope: 
38degrees
Aspect: 
East
Elevation: 
8080ft.
Bed Surface: 
Storm Snow
Weak Layer: 
Storm Snow
Crown Height: 
1 ft
Avalanche Width: 
30ft.
Avalanche Length: 
40ft.
Terrain: 
Near Treeline
Avalanche Photos: 
Snowpit or crown profile photo or graph: 
Avalanche observation video: 
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.

Weather Observations
Blowing Snow: 
Yes
Wind Speed: 
Strong
Wind Direction: 
Southwest
Air temperature: 
Below Freezing
Air temperature trend: 
Cooling
Cloud Cover: 
100% of the sky covered by clouds
Precipitation: 
Snow
Accumulation rate: 
Less than 1 in. per hour