20-21

Ice Climber triggered avalanche in Avalanche Gulch, Hyalite

Hyalite - main fork
Northern Gallatin
Code
SS-AFu
Elevation
9200
Aspect
W
Latitude
45.44720
Longitude
-110.96200
Notes

A first person account: "Human triggered avalanche at (estimate) 1:30pm from upper 'Avalanche Gulch' by one party descending from 'Dribbles'. Climber on second moderate pitch of 'Avalanche Gulch' swept but saved by screw placement from going over pitch 1 of Avalanche Gulch. No injuries, no burials, and both parties reconvened at base of Avalanche Gulch to assess the event. All parties descended at 3pm."

More info:

We were looking around for 'Responsible Family Men' and caused the avalanche crossing the gully perhaps ~200+ ft up from the snow ramp on AG. We immediately hoofed it downslope after the slslideccurred to see if there were folks caught up in it, and assist if at all possible. Thankfully it went as it did. I would estimate that the wind around Dribbles was 5-10, gusting 20-25. 
 
Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Foot penetration
Trigger Modifier
u-An unintentional release
Problem Type
Wind-Drifted Snow
Vertical Fall
400ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
20-21

Natural cornice fall, collapses, Mt Blackmore

Mt Blackmore
Northern Gallatin
Code
C-NC-R1-D1.5
Elevation
10000
Aspect
N
Latitude
45.44440
Longitude
-111.00400
Notes

From obs: "Skied Mt Blackmore this morning. Very windy up in the basin, but calm along the ridgeline. Lots of signs of wind-loading and drifting on most slopes. I felt/heard 3 collapses while ascending the trees up to the east ridge. Saw a debris pile on the N face, likely from a cornice fall in the last 24hrs."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Cornice fall
Trigger
Cornice fall
R size
1
D size
1.5
Images
Blackmore cornice fall
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
20-21

From obs: "Skied Mt Blackmore this morning. Very windy up in the basin, but calm along the ridgeline. Lots of signs of wind-loading and drifting on most slopes. I felt/heard 3 collapses while ascending the trees up to the east ridge. Saw a debris pile on the N face, likely from a cornice fall in the last 24hrs." Photo: M. Lavery

Avalanche Details: Natural cornice fall, collapses, Mt Blackmore
Forecast link: GNFAC Avalanche Forecast for Mon Jan 4, 2021
Northern Gallatin, 2021-01-03
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    • GNFAC Avalanche Forecast for Sun Jan 3, 2021

    Snowpack and Avalanche Discussion

    <p>Today strong wind creates dangerous avalanche conditions on wind-loaded slopes in the mountains near Bozeman, Big Sky and West Yellowstone. The snowpack has widespread buried layers of weak, sugary facets which have struggled to hold the weight of overlying slabs. Yesterday I saw this unstable snowpack in the Bridger Range near two recent skier triggered avalanches on Saddle Peak (<strong><a href="https://www.youtube.com/watch?v=1ihnOqeMkLc&amp;list=PLXu5151nmAvQDzKmH…;). These avalanches and reports of large collapses in Hyalite, near Big Sky, West Yellowstone and everywhere in-between (<strong><a href="https://www.mtavalanche.com/avalanche-activity">activity log</a></strong>) are warning us that large avalanches are possible to trigger on steep slopes. Strong southwest-west wind will grow fresh drifts and push these weak layers closer to breaking today. Today avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on non-wind loaded slopes. Avoid steep wind-loaded slopes, and carefully assess the snowpack for buried weak layers before riding or crossing any steep slope.</p>

    <p>Near Cooke City, today the main concern is where moderate to strong southwest-west winds drifted snow into fresh slabs. Yesterday on Abiathar Peak, adjacent to our advisory area, skiers triggered a couple wind slabs that caught them off guard and they felt lucky to escape (<strong><a href="https://www.mtavalanche.com/node/23512">photo and details</a></strong>). Today these slabs will grow thicker and are large enough to be harmful or deadly.</p>

    <p>The snowpack near Cooke City is deeper and generally lacks widespread buried weak layers compared to the rest of our advisory area. However, weak snow exists in isolated areas. A skier triggered avalanche yesterday in Yellowstone National Park (immediately outside the advisory area) (<strong><a href="https://www.mtavalanche.com/node/23505">photo and details</a></strong>) and a snowmobile triggered avalanche last Wednesday on Crown Butte are examples of these instabilities (<a href="https://youtu.be/UEY5A4YXibg"><strong>video</strong></a&gt;).</p>

    <p>Today, freshly drifted snow makes avalanches possible on wind-loaded slopes where avalanche danger is MODERATE. Avalanche danger is LOW on non-wind loaded slopes. Be extra cautious of steep wind loaded slopes, and dig down a few feet to assess the snowpack for buried weak layers.</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>

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    Skier triggered 2 wind slabs on Abiathar

    Abiathar Peak
    Out of Advisory Area
    Code
    SS-ASu-R2-D1.5-I
    Elevation
    10500
    Aspect
    N
    Latitude
    44.97560
    Longitude
    -110.03100
    Notes

    Skiers triggered a wind slab while ascending the north couloir on Abiathar Peak on 1/2/21. On their descent they triggered another similar sized slab. They were not caught or injured, and felt lucky to "dodge a bullet". 

    From email: "We approached Abiathar north cirque intending to climb and ski the north ccouloir Two extended column tests were performed and it was determined that the main threat was new snow on shallow facets... At approx 10,500' the first member of our party released the first sslab so we pulled the plug and began to prepare for descent. Upon descent, I dropped first and faded left to eddy out behind a rock outcrop and released the second slslabwhich broke just upslope of me. I was able to edge into the bedbed surfaced the slaslabn past without incident."

    Number of slides
    2
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Soft slab avalanche
    Trigger
    Skier
    Trigger Modifier
    u-An unintentional release
    R size
    2
    D size
    1.5
    Bed Surface
    I - Interface between new and old snow
    Problem Type
    Wind-Drifted Snow
    Slab Thickness
    10.0 inches
    Slab Width
    15.00ft
    Images
    Skier triggered wind slab on Abiathar, second
    Skier triggered wind slab on Abiathar
    Slab Thickness units
    inches
    Single / Multiple / Red Flag
    Multiple Avalanches
    Advisory Year
    20-21

    Skiers triggered this slab while ascending the north couloir on Abiathar Peak on 1/2/21. On their descent they triggered another similar sized slab. They were not caught or injured, and felt lucky to dodge a bullet. 

    Avalanche Details: Skier triggered 2 wind slabs on Abiathar
    Forecast link: GNFAC Avalanche Forecast for Sun Jan 3, 2021GNFAC Avalanche Forecast for Mon Jan 4, 2021
    Out of Advisory Area, 2021-01-02
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