Avalanche: Douglas Island

Location: Jumbo Chute

Route & General Observations

Hiked up the west shoulder of Jumbo planning on skiing something in the sun, particularly suspicious of north aspects based on all the recent avalanche activity on Stuart, Fruit Bowl, and South Douglas. Natural crown line in the Jumbo Chute observed from sea level was expected to be only in the lower runout of the chute, but when we got a better view of it found that the avalanche had started at the top entrance. Could clearly see that the entire chute had ripped out at some point in the past week, and had refilled with the most recent snowfall. Probing at the crownline at the top revealed a firm layer 135cm from the surface. A compression test adjacent to the crownline found a resistent planar shear at the same depth, 135cm from the surface. A botched extended column test (cut too thin) gave us a sudden planar propagation at this layer, but on the second attempt with proper dimensions in the ECT block, we were not able to get any results on this layer after 30 taps. Should have done a Deep ECT but moved on to try the compression test instead. Upon investigation of the CT shear interface at this 135cm layer, found 1mm near surface facets. This is the most likely candidate for the weak layer that has produced all these recent north aspect avalanches on Douglas.
Also got test results on a graupel layer 70cm deep between wind packed rounds.

Avalanche Details
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Trigger CorniceAvalanche Type Hard Slab
Aspect North NorthwestElevation 3100ft
Slope Angle 43degCrown Depth4ft
Width 100ftVertical Run 1500ft
Avalanche Details

Crownline at the top looked to be cornice triggered. Stauchwall through the chute similar depth to the crown or shallower. When the avalanche emerged into the bowl at the bottom of the chute it ripped out a deeper pocket but didn't appear to be a step down, just deeper snowpack in the bowl. Large debris pile at the bottom. The entire bowl under the Jumbo cliffs was covered in chunks from numerous wet slides but the debris from this avalanche left the biggest pile. HS-NC-R4-D3-I on 1mm NSF.

Red Flags
Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.
Obvious signs of instability
Recent Avalanches?Yes
Collapsing (Whumphing)?Yes
Cracking (Shooting cracks)?Yes
Observer Comments

Localized whumphs and cracks in the hollow windslab along the summit ridge.

Photos & Video
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