Recent avalanche on Frog Lake Ridge

Location Name: 
Frog Lake Ridge
Region: 
Carson Pass Area
Date and time of avalanche (best estimate if unknown): 
Wed, 12/06/2017 - 10:00
Location Map: 
United States
38° 41' 20.6736" N, 119° 59' 1.302" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Recent loading by new snow, wind, or rain
Obvious avalanche path
Observation made by: Professional Observer
Avalanche Observations
Avalanche Type: 
Dry
Slab
Slope: 
40degrees
Trigger type: 
Human-Triggered Cornice Collapse
Crown Height: 
1 ft
Aspect: 
Northeast
Weak Layer: 
Old Snow
Avalanche Width: 
50ft.
Terrain: 
Near Treeline
Elevation: 
8 800ft.
Bed Surface: 
Old Snow
Avalanche Length: 
70ft.
More detailed information about the avalanche: 

Crown was visible while driving up Carson Pass, so I went to investigate. Although the crown looks old due to both wind erosion and deposition,  the debris and a single ski track (downslope and sheltered from the wind) look more recent - possibly 24 hours old, maybe 48. My guess for a trigger is an intentional cornice drop. This is a common slope to do this on, and the ski tracks were adjacent to the path and debris, as if someone kicked the cornice and then skied down after triggering the small (D1) avalanche.

Pic 1: Crown extends a bit beyond the frame on both sides. I later performed 2 ECTs just above the crown, about 20ft apart from each other.

Pic 2: Looker's left side of crown.

Pics 3 and 4: Although ECTs failed on 1mm facets, both surface hoar and facets were observed on the bed surface.

Pic 5: Identifying 1mm facets as the weak layer before performing an ECT. The snow immediately above was firm (pencil hard), and the surface snow was loose.

Pic 6: After performing the ECT, which propagated but took more than the standard 30 loading steps. Note how clean and planar the remaining surface is. Another ECT performed about 30ft away also propagated but took more force than the standard.

Pic 7: Still some creamy skiing in wind sheltered areas, but in many places the surface is quite wind affected.  Even under the hard snow in this picture, a quick mitt pit showed loose facets about 10" down.

Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
Clear
Air temperature: 
Above Freezing
Wind Speed: 
Moderate
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
East
Accumulation rate: 
None