This huge avalanche occurred Friday June 4, 2021 near Beartooth Basin ski area, above Twin Lakes on Beartooth Pass. Multiple days of exceptionally warm temperatures followed by rain caused a large cornice to break and trigger the nearly 10' deep wet slab.
There were three of us from Billings that took a day trip to ski Top Notch.
Late afternoon ski decent off of Top Notch Peak in Yellowstone Park - Sylvan Pass, really warm, and a three layer cake. Lots of temp variations throughout the afternoon. The weather was overcast and mostly above freezing. We had small periods of light rain and snow throughout the afternoon. After leaving the summit at 4pm we skied down the skin track to the main drainage into the gut of the northwest bowl. There was clearly new snow blown in from the previous day or so, as it was much more white than the surrounding snow. First skier descended with a ski cut and everything stayed put. At that point she committed herself to the run and made one turn and the snow let go. She was caught, and took the ride down the gut of the run. She was totally unharmed, kept her skis on, and wasn't buried. She picked herself up and made her way out of the run out zone and to safe spot. I didn't take time to really analyze the snow after the fact, and simply skied down the debris field and out of the run with the other skier. It broke at least 6" deep, and 25' wide, and ran about 40 yards, or the main gut of the ski run. If I had to guess, the snow was saturated from previous rains and then that new snow loaded up on top of it was just too much for it. It wasn't just a surface slough either, at least to my knowledge. The debris field piled up blocks of snow ranging from 1-2' in size.
I did not see any avy activity during the day, and no other slides were obvious to me. I noticed there were some bigger slides that had happened at some point in the past when some cornices broke off and left some very large car-sized blocks of snow in one of the other bowls. Our group was communicating well, and no one had "the feeling". This was a case of simply ignoring the signs and looking for the quick out back to the car. I think we got lucky that no one was hurt or broke a binding or something. It very easily could have turned into a torn ACL and a long miserable day. Many lessons learned.
I know this was awhile ago, but I remember hearing requests for reports on any and all avy activity, even outside of the normal area. I don't know if you guys want this info or not, but i'll report it regardless. Everyone learned some valuable lessons that day.
This morning I toured up Mt Blackmore to check out the new snow. I tested the snowpack on a SE aspect of the east face of Blackmore at approximately 2905m in elevation. At this location, the new snow total was around 10cm. An ECT resulted in ECT16N @ 20cm. This failure occurred at an interface below a rain/ice crust that had pencil hardness and about 7cm thickness (photos). A shear test conducted on the remaining ECT column (photo), and a handful of hand shears on the approach, resulted in Q1 shears with medium to difficult effort. The new snow was well bonded to this crust and I observed no failures or movement at this interface. I observed small and isolated collapsing on the skin track during the approach (photo). Gaining the east ridge, I observed wind loading and a wet loose release on the east face (photo). With additional snow and sun in the forecast tomorrow, I am concerned with the potential for the below crust interface to propagate.
From obs: 5/9/21: "Yesterday we went to check out the new snow in Beehive Basin.... While traversing... along the north ridge of 10602, we triggered a small wind slab that carried down into Peruvian, which then released another small wind slab on a northeast aspect of the face (photo). The crown height of this wind slab was measured at 60cm at it's deepest point, and approximately 30ft wide by 10ft long.
Looking down into the face of Peruvian, we observed a natural dry loose slide that released from the ridge. We observed an increase in wind speed throughout the morning, and a shift in wind direction from west to southwest in the early morning moving to west to north west by the late morning."
From obs: 5/9/21: "Yesterday we went to check out the new snow in Beehive Basin... Looking down into the face of Peruvian, we observed a natural dry loose slide that released from the ridge... We observed an increase in wind speed throughout the morning, and a shift in wind direction from west to southwest in the early morning moving to west to north west by the late morning. The combination of variable and high winds with the amount of new snow available for transport created a noticeable increase in the hazard of wind slabs on all aspects we observed during the morning..." Photo: E.
From obs: 5/9/21: "Yesterday... While traversing... along the north ridge of 10602 [near Beehive], we triggered a small wind slab that carried down into Peruvian, which then released another small wind slab on a northeast aspect of the face (photo). The crown height of this wind slab was measured at 60cm at it's deepest point, and approximately 30ft wide by 10ft long. Looking down into the face of Peruvian, we observed a natural dry loose slide that released from the ridge.
From obs: 5/9/21: "Yesterday... While traversing... along the north ridge of 10602 [in Beehive], we triggered a small wind slab that carried down into Peruvian, which then released another small wind slab on a northeast aspect of the face (photo). The crown height of this wind slab was measured at 60cm at it's deepest point, and approximately 30ft wide by 10ft long. Looking down into the face of Peruvian, we observed a natural dry loose slide that released from the ridge.
From obs 5/9//21: "Yesterday we went to check out the new snow in Beehive Basin. We dug a pit on the south face of Peak 10602, and conducted an ECT with results ECTN8@20, ECTN11@30, and ECTN25@60. The new snow total in this location was 30cm. Although we saw no propagation, a hand shear test (photo) and a shear conducted on the remaining ECT block (photo) resulted in a Q1 shear at the interface at the bottom of the new snow.
