22-23

Snowmobile triggered avalanche

Date

Sun, 03/12/2023 - 12:25

Activity

Snowmobiling

I triggered a avalanche on the way back down the mountain. I'm unsure of the exact location but a buddy said it was under bear tooth butte. I was able to outrun the avalanche and there was no injuries.

Location (from list)

Beartooth Pass

Large recent avalanches near Cooke City

Date

Sun, 03/12/2023 - 16:20

Activity

Snowmobiling

Today we rode north of Cooke City and looked at recent natural and Human-triggered avalanches. The slide on Fisher Mtn. was very large and appeared up to 10 feet deep. It had much more volume in the debris than the slide that was triggered on this same path in December.

We also looked at the slide on Crown Butte that was triggered by a snowmobiler yesterday. This was on a SW aspect at 9,600'. It was 1-3 feet deep and broke on a layer of surface hoar and large facets below a hard slab of wind-drifted snow.

We saw two slides that had not been reported previously. One natural on the east side of Sheep Mtn. that was a hard slab of wind-drifted snow on a heavily wind loaded slope near the high ridgeline at 10,500'. The second was snowmobile triggered on a path called "Marty's" above Daisy Pass road. This was similar aspect as the slide on Crown Butte yesterday, and likely had a similar snowpack structure. We checked the debris for a beacon signal to be sure no one was caught, and did not find one. This may have been triggered today (3/12).

This recent activity is a clear sign the snowpack remained unstable with the recent loading event. Due to these slides breaking on persistent weak layers, I think similar human-triggered avalanches remain likely.

Region

Cooke City

Location (from list)

COOKE CITY

Observer Name

Alex Marienthal

Big Avalanches near Cooke City - 12 Mar 2023

Read more about Big Avalanches near Cooke City - 12 Mar 2023

Large slab avalanche near Lake Abundance

Date

Sat, 03/11/2023 - 13:00

Large avalanche with small tree and branch debris. Located on the lower NE bench face of Mt Abundance, near Lake Abundance. There were snowmobile tracks near the slide but could not determine if that was the cause. Approx 2000 feet across. Possibly 4-6 feet deep but couldn't tell from the bottom of the hill.

Region

Cooke City

Location (from list)

COOKE CITY

Observer Name

Dave Green

Mill Creek Obs

Date

Fri, 03/10/2023 - 00:00

Activity

Snowmobiling

Did a day of field work in the Absarokas up Mill Creek via snowmobile and ski. We got to approximately 8500 ft, and the snowpack there was ~150cm deep on a S aspect, with 2-3 inches of surface snow over a crust. Moderate to intense wind transport at treeline and above treeline. Snowed S-1 to S2 all day, and was raining below ~6000 ft when we sledded out.

Region

Out of Advisory Area

Observer Name

N. de Leeuw

GNFAC Avalanche Forecast for Sun Mar 12, 2023

Snowpack and Avalanche Discussion

On Thursday and Friday, the mountains near Cooke City, West Yellowstone and Big Sky received 10-14” of snow (1.0-1.5” of snow water equivalent) which was accompanied by strong to extreme westerly winds on Friday. Yesterday we received reports of over a dozen large natural avalanches that broke during or shortly after the storm (<a href="https://www.mtavalanche.com/avalanche-activity"><stro… activity list</a>). Some were up to 6 feet deep and destructive enough to break small trees (<a href="https://www.mtavalanche.com/node/28566"><span… Mtn. near Cooke</a>, <a href="https://www.mtavalanche.com/node/28558"><span… Ridge</a>). A snowmobiler triggered a large slide on Crown Butte yesterday. The rider was not caught, and the slide appeared a couple feet deep and involved the recent snow (<a href="https://www.mtavalanche.com/images/23/snowmobile-triggered-slide-crown-…;).

Today people can easily trigger large avalanches of wind-drifted snow, and slides could break deeper and wider on buried weak layers. Extreme winds affected most slopes and drifted snow into unusual places. The threat of avalanches on deeply buried persistent weak layers makes the situation more complex. Last week avalanches were triggered on weak layers that were buried in early January (<a href="https://youtu.be/nZFM_QZxG3Q">… City video</a>), and the added weight of recent snow and drifts makes similar sized slides likely today. Keep your terrain choices simple and avoid travel on and underneath slopes steeper than 30 degrees. Large, human triggered avalanches are likely and the avalanche danger is CONSIDERABLE.

The mountains near Bozeman got less snow, but strong winds created fresh drifts. Last week, skiers triggered a deep slab avalanche after a similar wind-loading event (<a href="https://youtu.be/42Zk3eLEMvE">… video</a>, <a href="https://www.mtavalanche.com/images/23/large-skier-triggered-avalanche-n…;). Avalanches breaking deep on buried weak layers are possible today. Deep slab avalanches are tricky because signs of instability are scarce, and snowpits and stability tests may not provide clear information about instability. The best strategy is to choose smaller, simple terrain with minimal wind-loading and minimal consequences, or avoid slopes steeper than 30 degrees altogether. If you choose to ski or ride steep slopes, it is still worth digging to check for buried weak layers just in case.

Additionally, fresh drifts can avalanche under the weight of a person. On Friday, skiers in the northern Bridger Range saw a natural avalanche as the new snow was being drifted into fresh slabs (<a href="https://www.mtavalanche.com/node/28568"><span… and details</a>). Fresh wind slabs may be large enough to bury a person, but even a small slide will be harmful if it carries you into rocks, trees or over a cliff. Cracks shooting out in front of your skis or sled are clear signs that you’ve found an unstable drift that would avalanche on a steep slope. Today, avalanches are possible to trigger and avalanche danger is MODERATE.

Please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs">…; website</a>, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Recent heavy snowfall and strong winds created dangerous avalanche conditions which still exist today. Freshly formed drifts can break at least 1-2 feet deep, and slides could break deeper in the snowpack. Avoid steep slopes and give them a wide berth if you’re traveling beneath them. See <a href="https://www.youtube.com/watch?v=SL1_7YZjWKI&list=PLXu5151nmAvTi1DBS…’s video update</a> from Friday for more travel advice.