Stability tests in crown above Crater Lake

Location Name: 
Crater Lake
Region: 
Carson Pass Area
Date and time of avalanche (best estimate if unknown): 
Wed, 01/27/2010 - 12:30
Location Map: 
United States
38° 43' 12.576" N, 119° 58' 28.956" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Obvious avalanche path
Observation made by: Professional Observer
Avalanche Observations
Avalanche Type: 
dry,slab,
Slope: 
35degrees
Trigger type: 
Natural
Crown Height: 
1 ft
Aspect: 
North
Weak Layer: 
Old Snow
Avalanche Width: 
400ft.
Elevation: 
8 875ft.
Bed Surface: 
Old Snow
Avalanche Length: 
300ft.
Number of similar avalanches: 
3
More detailed information about the avalanche: 

Photo - 24 to 48hr old crown, a different slide path to the one I tested, but same aspect, similar configuration, and appears to be the same failure layer. 3 similar crowns were seen between adjacent slide paths.

 

Video 1: I didn't notice the fracture at 22 until watching the video. Note the progressive compression and break before the fracture that propagated.

 

Video 2: Repeatable results

 

ECTs were performed just upslope and adjacent to crown from D2 R3 slab that appeared to be 24 to 48 hours old (crown partially filled-in, debris mid-slope partially filled-in, but debris and flagging on trees downslope from crown and away from wind appeared somewhat fresh). No skier tracks were visible to indicate a human trigger. Failure layer was the bottom of a fist hard DF layer (1.5mm needles still visible) above a 4 finger layer, and below a 1 finger slab, 30cm below surface. 1 other significant hand hardness change observed just below surface crust.

 

The top 30cm of the snowpack varied from breakable crust with penetrable snow underneath, to to breakable crust over supportable but hollow sounding slab on North facing lee slopes, with very little transition between the two (no breakable slab). No cracking or whumphing. Informal tests on N facing lee slopes at and above treeline showed similar stratigraphy to where I performed the ECTs.

 

T air -3

T surf -4

T10 -5

T20 -6

 

 

Avalanche Photos: 
Weather Observations
Cloud Cover: 
100% of the sky covered by clouds
Air temperature: 
Below Freezing
Precipitation: 
Air temperature trend: 
Static
Wind Direction: 
Accumulation rate: 
More detailed information about the weather: