20-21

Cottonwood Creek Basin 46.03407, -110.35897

Date
Activity
Skiing

Toured up the Cottonwood Creek drainage in the Crazy Mountains. Observed heavy NE cornicing as well as complex wind transport. Lots of stripped N aspects. Conditions deteriorated throughout the day with high winds and graupel deposition. Our 100cm depth pit was on a 240º SW aspect at 8000 feet, a 20º slope angle, wind speeds at 1pm were 15-20 mph and the temperature was around 20º F. The sky condition was overcast. We performed an ECT and received an ECTX result. We performed a isolated column test and received a CTH - 22 RP Q2, fracturing 30cm below the top on a layer of facets.

Skied low angle treed slopes and saw no recent signs of avalanches.

Region
Out of Advisory Area
Location (from list)
Other place
Observer Name
Haylee Darby

Widespread whumpfing/collapsing and cracking above Hebgen Lake

Hebgen Lake
Lionhead Range
Code
Aspect
E
Aspect Range
N-E
Latitude
44.83810
Longitude
-111.34300
Notes

Observation 1:

Sun 1/3: Skied both north and east facing terrain on the west side of Hebgen today. The few inches of new snow that has fallen recently seemed a bit denser than what was already on the ground. Made for an EXTREMELY touchy day. Widespread whumpfing and collapsing everywhere we went. We kept our slope angles low. On one slope we had a large collapse when the first skier started which created many longitudinal cracks across the entire width and length of the slope. We measured the slope at 27 degrees - I am confident a steeper slope in this area would have easily released.

Observation 2:

Summary of observations from Sat 1/2 and Sun 1/3: -No avalanches observed -Lots of whumphing and shooting cracks on N through SE aspects between 6600' and 8900' -3" of new snow at 8900' within 24 hour period from Saturday to Sunday; snowed S1 for a few hours Sunday morning but stopped by 1 p.m. and skies went from obscured at 9:00 a.m. to broken at 3:00 p.m. -Imperceptibly calm winds on Sunday below ridgetop at 8900' and trees holding snow at all elevations; ridge at 8900' had light Westerly winds gusting at moderate; we observed blowing and drifting snow at ridgetop being deposited on NE through E slopes. Snowpit Data from E aspect at 8200' (26 degree slope) on Saturday 1/2 at 1:00 pm: HS 75cm Weakest layer found at 50 cm down; weak layer is the interface between F-hardness basal facets (2-3mm) and 4-F, smaller facets above them Test results on this layer were ECTPV, ECTP13, and PST 25/100 (end)

Number of slides
0
Number caught
0
Number buried
0
Problem Type
Persistent Weak Layer
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

Propagating cracks on wind drifts in Fisher Creek

Lulu Pass
Cooke City
Code
Aspect
N
Latitude
45.07090
Longitude
-109.95800
Notes

Found cracking/propagation on wind-loaded roll overs, 8-16’’+ fractures, while touring today. Was enough to keep us out of the gullies. North facing bench glades across from Scotch Bonnet, just below Lulu pass above the old buildings.

Number of slides
0
Number caught
0
Number buried
0
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

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 slide occurred 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

Avalanche Gulch, Hyalite

Date
Activity
Ice Climbing

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

Region
Northern Gallatin
Observer Name
Edward Angus

Hyalite/Divide Basin

Date
Activity
Skiing

Toured in Hyalite main fork today and found decent powder skiing in protected trees up high. No signs of instability observed: no recent avalanches, no cracking, no collapses.

The winds receded throughout the day and the temps gradually dropped while broken skies developed before a final wallop of snowfall around 3pm (S2+ rate) during our exit ski.

It did seem like the open upper elevation slopes all showed surface texture evidence of the the significant wind overnight/this morning. We opted to not mess with them.

Quick pit at 9050' NE aspect HS 140cm with a pronounced facet/decomposing melt freeze crust combo buried ~1m down underneath the solid seeming mid-pack. ECTP27@38cm on the facets above the decomposing crust. Looks like the upper elevation snow pack is headed in the right direction... but still has a way to go before it can actually be trusted.

Region
Northern Gallatin
Location (from list)
Divide Cirque
Observer Name
Zachary Stephen Miller

Hebgen Lake

Date
Activity
Skiing

Skied both north and east facing terrain on the west side of Hebgen today. The few inches of new snow that has fallen recently seemed a bit denser than what was already on the ground. Made for an EXTREMELY touchy day. Widespread whumpfing and collapsing everywhere we went. We kept our slope angles low. On one slope we had a large collapse when the first skier started which created many longitudinal cracks across the entire width and length of the slope. We measured the slope at 27 degrees - I am confident a steeper slope in this area would have easily released.

Region
Southern Madison
Location (from list)
Hebgen Lake
Observer Name
Chris Pierce

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
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

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

Northern Gallatin, 2021-01-03