20-21

Huge wet slab on Beartooth Pass

Beartooth Pass
Out of Advisory Area
Code
WS-N-R3-D3-O
Elevation
10000
Aspect
N
Latitude
44.96910
Longitude
-109.47200
Notes

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

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Wet slab avalanche
Trigger
Natural trigger
R size
3
D size
3
Bed Surface
O - Old snow
Problem Type
Wet Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Top Notch Peak

Date
Activity
Skiing

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.

Region
Out of Advisory Area
Observer Name
Andrew Wilson

Mt Blackmore

Date

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.

Region
Northern Gallatin
Location (from list)
Mt Blackmore
Observer Name
Erich Schreier

Skier triggered and natural new snow avalanches in Beehive

Beehive Basin
Northern Madison
Code
SS-AS-R1-D1.5-I
Elevation
10000
Aspect
NE
Latitude
45.34070
Longitude
-111.39100
Notes

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."

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
R size
1
D size
1.5
Bed Surface
I - Interface between new and old snow
Problem Type
Wind-Drifted Snow
Slab Thickness
60.0 centimeters
Slab Width
30.00ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

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.

Northern Madison, 2021-05-10

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.

Northern Madison, 2021-05-10

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.

Northern Madison, 2021-05-10

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.

Northern Madison, 2021-05-10

Wet snow slides, natural and skier triggered

Taylor Fork
Southern Madison
Code
WS-N-R2-D2-O
Elevation
9500
Aspect
NW
Latitude
45.06070
Longitude
-111.27200
Notes

Multiple wet slides were reported in southern Madison and Tobacco Roots over the week 5/3-5/7.

Number caught
0
Number buried
0
Avalanche Type
Wet slab avalanche
Trigger
Natural trigger
R size
2
D size
2
Bed Surface
O - Old snow
Problem Type
Wet Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year