Multiple Avalanches on well anchored forested slope

Location Name: 
Tressider Peak
Region: 
Outside of the Forecast Area
Date and time of avalanche (best estimate if unknown): 
Wed, 06/15/2011 - 13:32
Location Map: 
United States
37° 49' 51.744" N, 119° 25' 12.8532" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Observation made by: Public
Avalanche Observations
Avalanche Type: 
dry,loose,
Slope: 
35degrees
Trigger type: 
Natural
Crown Height: 
5 ft
Aspect: 
East
Weak Layer: 
Storm Snow
Avalanche Width: 
200ft.
Terrain: 
Near Treeline
Elevation: 
10 000ft.
Bed Surface: 
Old Snow
Avalanche Length: 
1 000ft.
Number of similar avalanches: 
5
More detailed information about the avalanche: 

The dimensions and details are all estimated.  The date and time of the avalanches is completely unknown.  The author is a civil engineer hiking in the area July 7, 2011.

A series of small and large avalanches occurred along the east slopes of Tressider Peak near Cathedral Pass in Yosemite along the John Muir Trail.  These slides ocurred on well-anchored forested slopes with large boulders and mature pine trees.  The depth and sliding planes are difficult to determine but scarring on the trunks of standing trees and branches stuck in trees indicate the height of the runnout was about 6-8 ft above ground.  Several feet of snow has melted since the avalanches occurred.  The debris fields do not have a lot of boulders or rocks, so the weak plane was probably a significant height above ground.   The scale, quantity and size of broken trees is very impressive.  It looks like tornado damage.

 

Snowpit or crown profile photo or graph: 
Avalanche Photos: 
Weather Observations
Air temperature: 
Precipitation: 
Air temperature trend: 
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: 

It was a beautiful day in the mountains when we stumbled upon this, but who knows what it was like when this occurred several weeks prior.