24-25

Persistent Slab Avalanches Tepee Basin

Tepee Basin
Southern Madison
Code
SS-AMu-R3-D2-O
Elevation
9000
Aspect Range
E-NE
Latitude
44.90960
Longitude
-111.19400
Notes

Snowmobile triggered avalanches that resulted in a partial burial with no injuries on Friday, Feb 21 and a second slide on Saturday, Feb 22 with no one caught.

 

Number of slides
2
Number caught
1
Number buried
1
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
3
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Slab
Slab Thickness
32.0 inches
Vertical Fall
250ft
Slab Width
100.00ft
Weak Layer Grain type
Faceted Crystals
Weak Layer grain size
1.50mm
Weak Layer Hardness
4F
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Persistent Slab Avalanches Tepee Basin

Date
Activity
Snowmobiling

We got to ride into Tepee Basin with a pair of snowmobilers who were involved in an avalanche two days ago (2/23). The pair generously offered to join us and run us through the incident. It was an incredible opportunity to learn from each other. Read details about the slide.

The avalanche failed on the weak layer of facets that formed in late January. We also spotted another avalanche in similar, mid-elevation terrain likely triggered yesterday or earlier this morning. Both of these avalanches fit the pattern we've been seeing in Lionhead and the recent slide outside the forecast area in the Black Canyon area of Island Park. Other than the Black Canyon avalanche which is uncertain because we have not visited the site, the slides are taking place in mid-elevation terrain, smaller slopes with minimal wind-loading, and a thinner snowpack. 

The snowpack in both the Tepee slides was thin relative to the average snowpack depth (129 cm). 

Take Homes:

  1. You aren't good to go if you avoid the steep, upper-elevation, wind-loaded bowls. Steep slopes at mid-elevations harbor weak snow and have the potential for an avalanche. 
  2. The persistent slab avalanche problem is alive and well. The epicenter of this problem is in the Lionhead area and the Southern Madison and Southern Gallatin Ranges. 
  3. The issue with this avalanche problem is the distribution. It's nearly impossible to tell which slopes will slide and which ones won't. On many, the weak layer isn't so weak and the likelihood of triggering one is low. On other slopes, the weak layer is very weak and the likelihood of triggering one is up there. 

 

Region
Southern Madison
Location (from list)
Tepee Basin
Observer Name
Zinn and Staples

Big Belts

Date
Activity
Skiing

Observation up in Big Belts North of Baldy, by the Hut meadow.  8600FT, 22 Deg Slope, NorthEast Slope. Open Meadow.  

46.46385, -111.24431

Snow Depth, 225Cm+ 

Windy as hell. Thur - Sunday 40-70MPH above treeline from  SW to W to South.

ECTN20 @195CM.  Slabby Conditions from wind deposition but generally right side up snow.  

Significant crowns in vicinity 2-6ft deep 200ft lengths in the steep E Facing bowls nearby.

 

Region
Out of Advisory Area
Observer Name
J Budreski