Large collapses on W aspects on Andesite Ridge

Location Name: 
Andesite Ridge
Region: 
Donner Summit Area
Date and time of observation: 
Mon, 01/14/2013 - 14:00
Location Map: 
United States
39° 20' 59.1972" N, 120° 22' 0.5772" W
See map: Google Maps
US


Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Observation made by: Public
Snowpit Observations
More detailed information about the snowpack: 

Today (Jan 14) at about 1400 I initiated a deep collapse under a substantial wind slab on the lee (W) side of the low angle saddle (approx UTM 726900E 4358900N) about 200 m S of the top of Andesite Pk.  The collapse was violent, dropping the slab a cm or so and sounding like a rifle shot. Another large adjacent (mostly flat) wind slab alaso collapsed and and initiated a crack that ran 10s of meters when loaded by several people at the same time.  We all descended below and did 14 CTs across a 20 degree slope which yielded 14x CTV most at two separate and simultaneous failure planes from 10 to 30 cm below surface.  HS ranged from 140 to 180 cm.  Weak grains between a hard crust and the wind slab above is what was failing.  Deposition in this region seemed at a maximum; with about a 1.5 m deep drift at the top.  E winds were still ripping on the ridge but snow transport was much reduced.  I don’t think there was much more to move.  The E side of the ridge in this region was almost entirely stripped bare to hard crusts and ancient ski tracks.

Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
Clear
Air temperature: 
Below Freezing
Wind Speed: 
Strong
Precipitation: 
Air temperature trend: 
Warming
Wind Direction: 
Northeast
Accumulation rate: 
More detailed information about the weather: