24-25

Snowmobile triggered slide in Airplane Bowl

Airplane Bowl
Lionhead Range
Code
HS-AMu-R2-D2-O
Elevation
9100
Aspect
SE
Latitude
44.72500
Longitude
-111.32200
Notes

Also, on our way out we saw an avalanche in Airplane Bowl that had been triggered during the day today. This slide also broke on the persistent weak layers, 2-3' deep, 150' wide.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Slab
Slab Thickness
30.0 inches
Vertical Fall
200ft
Slab Width
150.00ft
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Snowmobile triggered 3-5' deep hard slab at Lionhead

Targhee Creek
Lionhead Range
Code
HS-AMu-R4-D3-O
Elevation
9200
Aspect
N
Latitude
44.74130
Longitude
-111.37400
Notes

A rider triggered a huge avalanche in the uppermost reaches of Targhee creek. We discovered it on our way out. The best we could tell looking at their tracks was that they had no idea they triggered it, even though part of their tracks were swept away. 

 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
4
D size
3
Bed Surface
O - Old snow
Problem Type
Persistent Slab
Slab Thickness
48.0 inches
Vertical Fall
200ft
Slab Width
200.00ft
Weak Layer Grain type
Faceted Crystals
Weak Layer grain size
2.50mm
Attached Videos
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Avalanches at Lionhead

Date
Activity
Snowmobiling

We rode throughout most of the Lionhead area looking for and assessing a weak layer from late January. This layer produced avalanches last week that we saw. It also buried a rider last Sunday in Teepee Creek. It caught a ride yesterday in Cabin Creek.

  • In most of our snowpits, the layer was gaining hardness
  • In most of our snowpits, the layer was either not breaking in stability tests or was very stubborn. 

We were scratching our heads because the layer seemed active but we could find any evidence that it was still a major problem, UNTIL

A rider triggered a huge avalanche in the uppermost reaches of Targhee creek. We discovered it on our way out. The best we could tell looking at their tracks was that they had no idea they triggered it, even though part of their tracks were swept away. 

Also, on our way out we saw an avalanche in Airplane Bowl that had been triggered during the day today. This slide also broke on the persistent weak layers, 2-3' deep, 150' wide.

HERE'S THE DIMEMMA - On many slopes, the likelihood of triggering an avalanche on this weak layer is low. On some slopes, the likelihood of triggering one is high. Because the distribution of this problem is spotty, the damage is Moderate but that rating is deceiving. 
 

HERE'S THE OTHER CHALLENGE - You won't see any obvious signs of unstable snow like cracking or collapsing. You probably won't see any red flags in a snow pit. There will be no warning until an avalanche happens. 
 

TRAVEL ADVICE - We haven't been able to find a clear pattern for where these avalanches will happen and where they won't. It's a scary and tricky situation and these things are like booby traps. There are three options:

  • Roll the dice and hope for the best, OR
  • If getting onto steeper slopes, choose ones with a clean runout with no trees, rocks, or gullies and make sure your partners are watching you from a safe location, OR
  • Ride only on slopes less than 30 degrees in steepness where most avalanches do not happen.

Wet snow - south facing slopes were getting very wet. We saw a few wet loose slides from yesterday near Targhee Peak. One south facing slope we crossed was wet for at least a foot or two into the snowpack. 

Region
Lionhead Range
Location (from list)
Targhee Creek
Observer Name
Staples & Marienthal