21-22

Double Avalanche Fatality, Scotch Bonnet Mountain

Scotch Bonnet
Cooke City
Code
SS-AMu-R2-D2.5-O
Elevation
10000
Aspect
SE
Latitude
45.05660
Longitude
-109.95100
Notes

On December 27, two snowmobilers were caught and killed in an avalanche on Scotch Bonnet Mountain, north of Cooke City. A group of 8 snowmobilers from Minnesota were on their second day of riding when 2 of their machines got stuck on the SE face of Scotch Bonnet Mountain. Two members of their group rode up to help them dig out and the avalanche was triggered soon after. It broke 4-5 feet deep, ran 300 feet wide and 500 feet vertical and killed 2 riders, burying them under 4-5 feet of debris. Everyone had rescue equipment and they were recovered by their party. Park County Sheriff Search and Rescue brought the victims to town. The avalanche broke on a layer of facets 1.5 feet off the ground underneath a thick slab of wind drifted snow. The avalanche is classified SS-AMu-R2-D2.5-O.

 

Number of slides
1
Number caught
2
Number buried
2
Number killed
2
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
2.5
Bed Surface
O - Old snow
Problem Type
Wind-Drifted Snow
Slab Thickness
60.0 inches
Vertical Fall
500ft
Slab Width
300.00ft
Weak Layer Grain type
Faceted Crystals
Weak Layer grain size
4.00mm
Weak Layer Hardness
4F-
Slab Layer Grain Type
Wind Broken precipitation particles
Slab Layer Grain Size
0.50mm
Slab Layer Hardness
1F+
Images
Overview of Scotch Bonnet avalanche_marked
Upper portion avalanche - Scotch Bonnet
Crown - Scotch Bonnet Fatality
GNFAC Forecasters at Crown - Scotch Bonnet
Scotch Bonnet Crown Profile
Digging Out Sleds after an avalanche on Scotch Bonnet
Ian at the crown of an avalanche that killed 2 snowmobilers
Attached Videos
Scotch Bonnet Avalanche Fatality - 27 Dec 2021
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
21-22

We are sad to report that on December 27th, two snowmobilers were caught and killed in an avalanche on Scotch Bonnet Mountain to the north of Cooke City. The avalanche broke 5’ deep and approximately 300’ wide on a southeast-facing slope.

Members of Park County Sheriff Search and Rescue arrived to assist with rescue and recovery efforts. 

Our deepest condolences go out to the victim’s friends and family, members of the group, and the search and rescue community. We will release further details as they become available.

Photo: B. Zavora

Cooke City, 2021-12-27
Access other image sizes:
  • Very Large 1200px
  • Large 480px
  • Medium 220px
  • Small 150px
  • Original

    • We are sad to report that on December 27th, two snowmobilers were caught and killed in an avalanche on Scotch Bonnet Mountain to the north of Cooke City. The avalanche broke 5’ deep and approximately 300’ wide on a southeast-facing slope.

    Members of Park County Sheriff Search and Rescue arrived to assist with rescue and recovery efforts. 

    Our deepest condolences go out to the victim’s friends and family, members of the group, and the search and rescue community. We will release further details as they become available.

    Photo: B. Zavora


    Forecast link: GNFAC Avalanche Forecast for Wed Dec 29, 2021
    Cooke City, 2021-12-27
    Access other image sizes:
  • Very Large 1200px
  • Large 480px
  • Medium 220px
  • Small 150px
  • Original

    • We are sad to report that on December 27th, two snowmobilers were caught and killed in an avalanche on Scotch Bonnet Mountain to the north of Cooke City. The avalanche broke 5’ deep and approximately 300’ wide on a southeast-facing slope.

    Members of Park County Sheriff Search and Rescue arrived to assist with rescue and recovery efforts. 

    Our deepest condolences go out to the victim’s friends and family, members of the group, and the search and rescue community. We will release further details as they become available.

    Photo: B. Zavora

    Cooke City, 2021-12-27
    Access other image sizes:
  • Very Large 1200px
  • Large 480px
  • Medium 220px
  • Small 150px
  • Original

    • We are sad to report that on December 27th, two snowmobilers were caught and killed in an avalanche on Scotch Bonnet Mountain to the north of Cooke City. The avalanche broke 5’ deep and approximately 300’ wide on a southeast-facing slope.

    Members of Park County Sheriff Search and Rescue arrived to assist with rescue and recovery efforts. 

    Our deepest condolences go out to the victim’s friends and family, members of the group, and the search and rescue community. We will release further details as they become available.

    Photo: B. Zavora


    Forecast link: GNFAC Avalanche Forecast for Tue Dec 28, 2021
    Cooke City, 2021-12-27
    Access other image sizes:
  • Very Large 1200px
  • Large 480px
  • Medium 220px
  • Small 150px
  • Original

    • Wheeler Mtn

    Date
    Activity
    Skiing

    We skied Wheeler Mountain on Sunday Dec. 26. We approached via South Cottonwood. The creek is not yet frozen so the approach requires crossing in a narrow log about 40 yards upstream of the summer crossing. Snow depth remains low for most of the approach. We used the summer trail to the last prominent avalanche path and then switchbacked in the forest adjacent to it. We dug 3 pits in the area where the funnel opens up between 8000 and 8200 feet.
    All pits had about 25 to 30 centimeters of sugary snow near the ground. All ECTs failed at the top of that sugary snow (none propagated).
    Pit 1: Snow depth 60 cm, ECTN 23
    Pit 2: Snow depth 90 cm, ECTN 18
    Pit 3: Snow depth 115 cm, ECTN 29
    Additional thoughts/info: Even though the tests suggest relatively stable conditions, we did not ski this aspect because the upper meadows that feed that avalanche path are in the “perfect” 30 to 40 degree range, the snow depth was highly variable, and those meadows feed into an ugly deep and narrow trench. Anyhow, we traversed further south and skied the large meadow at the south end of Wheeler Mountain where the steepest section is 30 degrees. The skiing was excellent and we got a great workout because it’s a long approach 😉.

    Region
    Northern Gallatin
    Location (from list)
    Wheeler Mountain
    Observer Name
    Alex Lussier

    GNFAC Avalanche Forecast for Mon Dec 27, 2021

    Snowpack and Avalanche Discussion

    <p>Consistent snowfall for the last five days brings our storm total to 31-37” equal to 2.6” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… water equivalent</a> (SWE) in the Southern Madison and Southern Gallatin Ranges and 3.5” of SWE in the mountains around West Yellowstone and Cooke City. The combination of recent snow and moderate winds from the southwest creates dangerous avalanche conditions. While the wind will ease off today, recently formed 1-4’ deep drifts will remain unstable. Avalanches failing on weaker layers of snow in the mid and lower snowpack are a possibility and would be large and dangerous. This reality kept Doug and me out of avalanche terrain yesterday at Lionhead (<a href="https://www.youtube.com/watch?v=qumV6n73pTs"><strong>video</strong></a&…;). <a href="https://www.youtube.com/watch?v=rdVk9B7UbtQ"><strong>Alex’s advice from the Taylor Fork</strong></a> and <a href="https://www.youtube.com/watch?v=4GrVPi-1FC8&amp;list=PLXu5151nmAvT1nrM2… from last week in Cooke City</strong></a> holds true today, steer clear of wind-loaded slopes and carefully assess the snowpack and terrain features in non-wind-loaded areas prior to entering any avalanche terrain.</p>

    <p>With the significant caveat that visibility is limited, we have not seen or received reports of widespread avalanche activity during this storm. We do have good indicators of instability such as large “whumphs” triggered by skiers near Bacon Rind on Friday (<a href="https://www.mtavalanche.com/node/25253"><strong>details</strong></a&gt;) and unstable snowpack tests throughout the area failing and propagating within new snow layers and on weak layers near the ground. If you see an avalanche in the mountains today, snap a photo and submit it through our <a href="https://mtavalanche.com/node/add/snow_obs"><strong>observations form</strong></a>.</p>

    <p>The avalanche danger is rated CONSIDERABLE on wind-loaded slopes where human-triggered avalanches are likely and MODERATE on non-wind-loaded slopes where avalanches are possible</p>

    <p>The mountains around Bozeman and Big Sky received 5-8” of new snow equal to 0.3-0.5” SWE during yesterday’s storm with winds from the southwest quickly forming thicker drifts. Let recent signs of instability in wind-loaded terrain such as a natural avalanche on Saddle Peak on Christmas Day guide your travel plans today (<a href="https://www.mtavalanche.com/images/21/natural-avalanche-saddle-peak-1">…;). Remain dedicated to your safe travel protocols and pay attention to changes to the snow under your feet or sled, turning around if you enter a deeper drift, see shooting cracks or the snow surface seems to stiffen. These are the areas where triggering a slab avalanche within the new snow or on deeper weak layers is possible. Human-triggered slides on non-wind-loaded terrain are unlikely today. See our recent field videos from <a href="https://www.youtube.com/watch?v=_MhpDHnH8So"><strong>Saddle Peak</strong></a>, <a href="https://youtu.be/cf-qqv2Ssjw"><strong>Buck Ridge</strong></a> and <a href="https://youtu.be/ePMCJs3qAs0"><strong>Beehive Basin</strong></a> for a further look. Today, the avalanche danger is MODERATE on wind-loaded slopes and LOW on all others.</p>

    <p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

    Upcoming Education Opportunities:

    Get your avalanche brain ready for the season at one of the many classes listed on our education calendar, and list of upcoming events below.

    Every Saturday near Cooke City, 10 a.m.-3 p.m. FREE snowpack update and transceiver/rescue training. Stop by for 20 minutes or more at the Round Lake Warming Hut.

    Dave Zinn of the GNFAC gets 3 layers breaking in his Extended Column Test. About 3 feet of snow fell in the last 4 days which got blown into wind slabs. The weight of the new snow is also creating instability on a weak layer of sugary facets near the ground. Photo: GNFAC


    Forecast link: GNFAC Avalanche Forecast for Mon Dec 27, 2021GNFAC Avalanche Forecast for Tue Dec 28, 2021
    Lionhead Range, 2021-12-26
    Access other image sizes:
  • Very Large 1200px
  • Large 480px
  • Medium 220px
  • Small 150px
  • Original
    • Subscribe to 21-22