Northern Gallatin

Cornice triggered avalanche in Hourglass, Bridgers

Hourglass Chute
Bridger Range
Code
HS-NC-R3-D2.5-O
Elevation
8300
Aspect
E
Latitude
45.83300
Longitude
-110.93800
Notes

HS-R3-D3

3-4’ crown skiers left usual wind loaded side appeared to be started by a natural cornice drop.
 
There was a 4-5’ crown lower below the pinch on the skiers right wall. The toe of the debris stopped just short of the low meadow. It appeared that it ran on the November rain crust. 
 
3 people who did not witness anything but skied up on the crown at 3:40ish performed a transceiver search with no results. It appeared that the avalanche was a few hours old. 
 
Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Cornice fall
R size
3
D size
2.5
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
48.0 inches
Vertical Fall
800ft
Slab Width
100.00ft
Weak Layer Grain type
Depth Hoar
Images
Hourglass Chute Crown
Looking up the Hourglass gully
Top of the Hourglass avalanche
Debris from the Hourglass avalanche
Looking up at the Hourglass avalanche
Hourglass avalanche crown_from the top
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year
19-20

Photo is from the ridgeline. This avalanche was triggered midday Wednesday (2/26) north of Bridger Bowl ski above Wolverine Bowl.  The slide is east facing and broke 3-4 feet deep from a natural cornice fall. It broke 4-5 feet wide mid-slope and broke on the facets near the bottom of the snowpack. No one was caught. Photo: BBSP

Avalanche Details: Cornice triggered avalanche in Hourglass, Bridgers
Bridger Range, 2020-02-27
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    • Naturals in Storm Castle Creek

    Storm Castle
    Northern Gallatin
    Code
    SS-N-R3-D2-O
    Elevation
    8500
    Aspect Range
    E, W
    Latitude
    45.45040
    Longitude
    -111.22400
    Notes

    On Saturday 2/22/20 riders saw natural slides on east and west aspects 10 miles up Storm Castle creek. 

    Number of slides
    2
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Soft slab avalanche
    Trigger
    Natural trigger
    R size
    3
    D size
    2
    Bed Surface
    O - Old snow
    Problem Type
    Persistent Weak Layer
    Images
    Naturals up Storm Castle Creek 2
    Naturals up Storm Castle Creek
    Slab Thickness units
    centimeters
    Single / Multiple / Red Flag
    Multiple Avalanches
    Advisory Year
    19-20

    Small natural wet loose and wind slab in S. Gallatins

    Specimen Creek
    Southern Gallatin
    Code
    WL-N-R1-D1
    Elevation
    8500
    Aspect
    S
    Latitude
    45.02650
    Longitude
    -111.04800
    Notes

    From an obs on 2/23/20: "...today toured up above 9000 ft on Meldrum and some surrounding hills.... No cracking, collapsing, or naturals observed aside from some small wet loose that occurred yesterday in steep S rocky terrain at 8500 ft.... HS 150+ with depth hoar 130 down. The new snow will be falling on a variety of snow surfaces from crusts (E-S-W) to wind board (ridgelines) to NSFs (N). Temperatures warmed to above freezing today to at least 9000 ft. Winds increased to moderate out of the west by 1400 with some wind transport occurring at ridgelines."

    From another group on Electric Peak on 2/23/20: "One recent natural avalanche near the ridgeline roughly 30 cm deep probably due to wind loading (D1) and a handful of natural loose wet (D1) avalanches on southerly aspects. Dug a quick pit on the face (10700’ NE 30 degree slope HS 190cm) and got an ECTP23 @ 35 below the surface on a hardness change below a 1F fresh windslab... Also, bulletproof windboard below the first roll (@10200’) and cranking winds!"

     

    Number caught
    0
    Number buried
    0
    Avalanche Type
    Wet loose-snow avalanche
    Trigger
    Natural trigger
    R size
    1
    D size
    1
    Problem Type
    Wet Snow
    Slab Thickness units
    centimeters
    Single / Multiple / Red Flag
    Multiple Avalanches
    Advisory Year
    19-20

    Many large, destructive slides on Emigrant Peak

    Emigrant Peak
    Out of Advisory Area
    Code
    HS-N-R4-D3-O
    Elevation
    9800
    Aspect Range
    All
    Latitude
    45.26300
    Longitude
    -110.70700
    Notes

    [date of activity roughly estimated] From email on 2/22/2020: "The mountains around Emigrant Peak have certainly reached their tipping point. Skinning up in the morning we witnessed the debris of more than a dozen avalanches on all aspects, more than I have ever seen in a single day. Many of these avalanches were extremely large and powerful deep slabs that broke towards the ground, likely to have released within the past week. Slides were running to the end of their runout zones and carried with them many trees that were torn to shreds."

    Number of slides
    7
    Number caught
    0
    Number buried
    0
    Avalanche Type
    Hard slab avalanche
    Trigger
    Natural trigger
    R size
    4
    D size
    3
    Bed Surface
    O - Old snow
    Problem Type
    Persistent Weak Layer
    Slab Thickness
    60.0 inches
    Vertical Fall
    1000ft
    Slab Width
    1000.00ft
    Images
    Avalanche debris on road to Emigrant
    Another Deep Slab on Emigrant 2
    Another deep slab on Emigrant
    Big Deep Slab on Emigrant close-up
    Big Deep Slab on Emigrant
    Slab Thickness units
    inches
    Single / Multiple / Red Flag
    Multiple Avalanches
    Advisory Year
    19-20
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