natural avalanche on Andesite Ridge

Location Name: 
Andesite Ridge
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Fri, 03/12/2010 - 20:00
Location Map: 
United States
39° 21' 3.9276" N, 120° 21' 57.4308" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
40degrees
Trigger type: 
Natural
Crown Height: 
2 ft
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Avalanche Width: 
200ft.
Terrain: 
Near Treeline
Elevation: 
8 120ft.
Bed Surface: 
Old Snow
Avalanche Length: 
150ft.
More detailed information about the avalanche: 

Natural avalanche that occurred overnight. Debris covered by 10 cm of new snow. Slope angle at crown ranged from 35 to 48 degrees. Crown height ranged from 15 to 60 cm. 3 x ECTN with failure within the new snow and at bed surface in pit on skier's right end of crown. Slab depth 45 cm at that location. No unique crystal type of hardness difference within storm snow. Instability likely due to high precipitation intensity last night.

No evidence of continued instability while on tour in the area. Surface slabs on SE aspects near treeline and below treeline becoming increasingly harder than new snow below, but no warming instability observed at time of observations. All indications pointing to development of warming instability in wind protected areas as day progresses. Significant wind transport of snow by NE winds. Winds keeping snow surface cold on E-SE-S aspects above treeline.

Photo 1: Deepest section of crown under cornice.

Photo 2: Far crown and flank can bee seen in back upper portion of photo.

Photo 3: Far skier's left flank and crown

Avalanche Photos: 
Weather Observations
Air temperature: 
Precipitation: 
Air temperature trend: 
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: