Wind Slabs and Loose Wet Avalanches on Andesite Peak

Location Name: 
Andesite Peak
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Mon, 03/10/2014 - 13:00
Location Map: 
United States
39° 21' 1.8828" N, 120° 21' 59.2848" 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
Rapid warming
Obvious avalanche path
Terrain Trap
Observation made by: Professional Observer
Avalanche Observations
Avalanche Type: 
Wet
Dry
Slab
More detailed information about the avalanche: 

3-4'' of new snow in the Andesite Peak area today.  Previous wind loading on the highest exposed ridgelines and peaks only with small amounts of moving snow throughout most of today, no new snow was falling after 11am.  2 natural wind slabs were observed in this area with the larger one off of the shoulder of Andesite Peak and running into the trees below, see photo.  By 1pm at snow pit location all stability tests and informal obs indicated that the wind slab was gaining strength with no test results and no signs of instability. 

The snow changed dramatically by early afternoon.  Temperatures increased and more frequent sun breaks occured.  Several natural loose wet avalanches were observed on multiple aspects and wide spread skier triggered loose wet avalanches occured on all terrain over 30 degrees.  Some of these skier triggered loose wet avalanches were large enough to injure a skier.  The existing rain crust below this storm snow is firm and smooth which is providing a great bed surface for the loose wet avalanches to run on. 

 

Photo#1:  Small natural wind slab on Andesite Ridge, 7800', East aspect.

Photo#2:  Natural wind slab avalanche off of the shoulder of Andesite Peak, 8200', NE aspect.  Crown line 8'' deep.

Photo#3:  Natural wet loose avalanche.  7800', North aspect, 35 degree gully running full path to bench area.

Photo#4and#5:  Wide spread skier triggered wet loose avalanches on all aspects and elevations at 30 degrees and steeper.  These avalanches were running full path on the firm and efficient rain crust bed surface. 

 

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
75% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Moderate
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
Southwest
More detailed information about the weather: 

Light snow in the morning before 11am then mostly cloudy with sun breaks.  Light wind loading throughout the day only observed on exposed ridges and peak.