Snowmobiler involved cornice collapse, Castle Peak

Location Name: 
N. facing bowl on backside of Castle Peak
Region: 
Donner Summit Area
Date and time of avalanche (best estimate if unknown): 
Sat, 03/05/2011 - 14:00
Location Map: 
United States
39° 21' 47.6496" N, 120° 20' 43.152" W
See map: Google Maps
US


Red Flags: 
Rapid warming
Obvious avalanche path
Observation made by: Public
Avalanche Observations
Trigger type: 
Snowmobiler
Aspect: 
Northwest
Elevation: 
8 600ft.
Number of people caught: 
1
More detailed information about the avalanche: 

While on patrol with the Tahoe Backcountry Ski Patrol, we witnessed a snowmobiler dismount his machine and walk to the edge of a cornice.  He stood on it for a few minutes, and then we saw it collapse.  The cornice broke apart into chunks ranging from basketball to small car size.  The involved person fell about 10 vertical feet, and slid another 10-20 feet, with the cornice pieces sliding almost 100 feet.  There were no injuries and no burials or injuries, other than a lost cell phone.

In addition, in the main bowl on the backside of Castle Peak, there was evidence of a skiier triggered avalanche.  It appeared to have occurred on Friday, and was about 50 feet wide, with a run of 100 feet.  We did not get a look at the crown line.  This avalanche was near the top of the bowl on a NE facing aspect.  Stability today on simliar aspects appeared good, we did not see any other avalanche signs or flags.

I have included pictures of the cornice collapse, but we were not able to get close enough to the avalanche to gather meaningful data.

 

Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Air temperature: 
Above Freezing
Wind Speed: 
Moderate
Precipitation: 
None
Air temperature trend: 
Static
Wind Direction: 
Southeast
Accumulation rate: 
None
More detailed information about the weather: