22-23

A skier remotely triggered an avalanche on Mt Blackmore (11/9/22).

From email: "I ski cut the top of the face and remote triggered a hard slab from 50’ above the crown. It broke full width of the couloir feature, 150’ wide and 10-18” deep. Broke on new snow/old snow interface which was another hard wind slab. The avalanche ran the length of the East face and stopped just below the last set of cliffs."

Our group of 3 skinned into beehive basin in search of fresh snow and expecting instability. We expected the bottom old snow to be likely decomposing and facted, as well as an interface between the wind affected snow and new storm snow. We dug a pit on an E facing slope 1/4 mile south of the lake, just past where the creek concavity eases. The slope we used for our pit was 23° and we found 80 cm of snow. See SNOWPILOT data for the complete snowpack. Our pit findings were drastically more positive than what we anticipated. The snowpack showed signs of being right-side up and having low slab formation within the new snow as well as weak layers that weren't very reactive. These findings provided us with more confidence in the early season snow than we had expected. As we moved south from our pit to a less wind sheltered area we found the upper 40 cm of the snowpack to be firmer than what was encountered from our pit. While ascending we used our poles to question this change and discuss how it would affect our planned objective. We still felt confident in our plan, but made note of a wind-skin on the surface to the south of us that we wanted to avoid. We got 4 laps on an East facing 35°-38° slope accompanied by 30 of our closest friends before skinning out with no instability observations on the slope we skied. There were however obvious point releases within and slightly buried under the new snow on adjacent west and southwest slopes further south down the basin. The west side appeared thinner with less coverage and more wind rippling as observed from afar. 

Slab 4-5 inches above ground. However seemed stable. Some wind loading. 3-4 feet at summit

Small slab avalanche triggered by skier in a small chute near The John and Bronco runs in Bridger Bowl. Propagation from skier’s ski, slab slid down through the chute. Crown maybe 10 feet wide. Slab looked about 6 or 7 inches thick. Looked like a layer of new snow from today and yesterday’s storm sliding on top of an old crust layer. Nobody harmed, just spooked.

From obs: "Saw some cracking and propagation of a 6-8" storm slab on steeper terrain near the Bridger Lift. Gentle upslope winds seem to have compacted a slab near some terrain features, and I got a small propagation at the edge of the Sluice Box gully where the slope angle tipped up near 40." Photo: C. Avis

The pit depth was approx 80cm to the ground. Slope angle 19 Degrees. Air Temp 19* F. E/NE facing slope. Hardness Test/ Fist @ 64 cm, 4F @ 45 cm, 1F @ 35 cm, 4F @ 20 cm. Conducted CT (30cm x 30 cm column), Propagated at 25 (10 wrist, 10 elbow, 5 shoulder) propagation was just below the distinct layer that you can see at 35cm in the photo labeled BM5. Then conducted ECT (90 cm X 30cm) No propagation after 30 ( 10,10,10). Picture labeled BM4 is the layer that propagated on the column test.

Today I got reassuring results from a snow pit dug at 9195' on a Northeast aspect (40 degrees) in the basin between Mt. Blackmore and Elephant Peak. The area was clearly wind-loaded with an HS of 110cm. I got a CT20, Q2 @ 50cm (see image), a resistant planar failure that appeared to occur on a thin layer of decomposing fragments. In my ECT, I received no results whatsoever, so I sense that this weak layer is quite unlikely to react, though structurally the snow consisted of a hard wind slab on top of an identifiable weak layer.

I also performed an analysis and multiple ECTs on a snow wall closer to Elephant Mountain (8950'), which was a Northwestern aspect (318 degrees). The snow wasn't as deep at this location (HS 73cm), and my results were ECTN22 @ 42cm, then ECTN21 @ 44cm (see images).

I hope these results are helpful as we begin to wrap our heads around this early season snowpack.

Thanks,

Charlie

Small slab avalanche triggered by skier in a small chute near The John and Bronco runs in Bridger Bowl. Propagation from skier’s ski, slab slid down through the chute. Crown maybe 10 feet wide. Slab looked about 6 or 7 inches thick. Looked like a layer of new snow from today and yesterday’s storm sliding on top of an old crust layer. Nobody harmed, just spooked. Watch out!