Natural on Elephant's Back

Location Name: 
Elephant's Back
Region: 
Carson Pass Area
Date and time of avalanche (best estimate if unknown): 
Mon, 04/12/2010 - 11:30
Location Map: 
United States
38° 40' 46.3008" N, 119° 58' 59.1096" 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: 
dry,slab,
Slope: 
40degrees
Trigger type: 
Natural
Crown Height: 
2 ft
Aspect: 
Northeast
Weak Layer: 
Storm Snow
Avalanche Width: 
200ft.
Terrain: 
Above Treeline
Elevation: 
9 400ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
300ft.
More detailed information about the avalanche: 

This natural R1 D2 likely was triggered by a cornice drop, and within an hour of my arrival just after 12:00, judging by the still angular debris and crown during significant wind transport (photos taken during brief lull in wind).

Crown height at its largest was 50cm. Debris measured 120cm in several places. Some debris cleared the flat bench and continued downslope, with no additional fractures triggered.

Shooting cracks observed while ski cutting adjacent slope.

Note step-down, yet all of slab fractured within new storm snow - not at new snow / old crust interface.

Picture 3: Very small loose snow avalanche on nearby test slope - less wind slab thus less propagation at this site.

On nearby slopes, wind loaded but below treeline:

2x ECTP 8 Q2 at 30cm on PPs. 40cm new snow, 40 degree slope, 105 degree aspect, 8620ft.

1x ECTP 13, 1x ECTP 15 - both Q2 at 35cm on PPs. 55cm new snow, 43 degree slope, 5 degree aspect, 8670ft.

All of the above ECTs showed progressive compression near the surface before propagating on fracture layer just below subtle 4cm denser but still F hard layer. All PPs - no persistent weak layers observed.

 

 

 

Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
75% of the sky covered by clouds
Air temperature: 
Wind Speed: 
Strong
Precipitation: 
Snow
Air temperature trend: 
Warming
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

S1 precip with significant wind transport. Very light, low density snow available for wind transport up until appx 1pm, when strong solar radiation penetrated broken cloud cover and noticeably warmed snow surface on windward aspects - though moderate wind transport continued.