Human triggered soft slabs below treeline on Hidden Peak

Location Name: 
Hidden Peak
Region: 
West Shore Area
Date and time of avalanche (best estimate if unknown): 
Wed, 02/16/2011 - 15:45
Location Map: 
United States
38° 59' 18.1284" N, 120° 7' 31.332" 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
Obvious avalanche path
Observation made by: Forecaster
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
38degrees
Trigger type: 
Skier
Crown Height: 
1 ft
Aspect: 
East
Weak Layer: 
Storm Snow
Avalanche Width: 
30ft.
Terrain: 
Below Treeline
Elevation: 
8 200ft.
Bed Surface: 
Storm Snow
Avalanche Length: 
200ft.
Number of similar avalanches: 
2
More detailed information about the avalanche: 

Below treeline on Hidden Peak today, 12-16 inches of new snow existed below 8000 ft. Between 8000 ft and 8800 ft. 14-18 inches on new snow existed. I started seeing small shooting cracks at about 7600 ft that failed on a density change within the new snow. These cracks grew in size and in frequency at the higher elevations. On three adjacent 38-42 degree, east facing slopes (denoted in the google maps location), ski cuts triggered 1-1.5 ft deep soft slab avalanches in the new snow. These slides failed and ran on a density change weakness within the storm snow snow. In most areas below treeline the storm snow seemed to be bonding to the old snow surfaces below it with moderate strength.

Photo 1: Soft slab triggered by a ski cut at the top of a 38-42 degree, east facing, below treeline slope.

Photo 2: Shooting cracks noted at a slightly lower location.

Avalanche Photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Moderate
Precipitation: 
Snow
Air temperature trend: 
Cooling
Wind Direction: 
Southwest
Accumulation rate: 
Less than 1 in. per hour
More detailed information about the weather: 

Moderate to light winds in the trees between 7500 ft and 8500 ft. Some light snow transport and wind affect on the snow surface on the open areas below treeeline.