In a bizarre and relatively unheard of avalanche accident, a snowmobile trail groomer was caught in an avalanche in late February in Montana. The groomer operator was not hurt in the accident, but the groomer was badly damaged as it was carried 165 feet down the mountain.
A story about the avalanche and resulting accident is here: https://ravallirepublic.com/outdoors/article_cd7b376a-a7cb-5b66-af8f-2c4f0a5e676b.html
Here are the details from the Gallatin National Forest Avalanche Center (www.mtavlanche.com).
Elevation 7800 feet
Notes GNFAC investigation: We went and looked at the avalanche that partially buried a groomer without injury to the driver at 8:15 p.m. the night before (2/27). The slide broke on facets at the ground and was 2-3 feet deep, 100 feet wide, and ran 600 feet slope distance. It put 8 feet of debris on the road cut. The slope was west facing at 7,500 feet and averaged 38 degree steep in the starting zone. Weak snow at the ground is found throughout our advisory area.
The groomer triggered the avalanche when he was clearing a wind drift from the road.
The groomer is badly damaged.
Crown: N45.38528, W111.06487, 7802 feet
Toe of debris: N45.38554, W111.06693, 7482 feet
Alpha Angle: 30 degrees
Number of slides 1
Number caught 1
Number buried 0
Avalanche Type Soft slab avalanche
Trigger Modifier u-An unintentional release
R size 3
D size 3
Bed Surface O - Old snow
Problem Type Persistent Weak Layer
Slab Thickness 36 inches
Vertical Fall 400 feet
Slab Width 130 feet
Weak Layer Grain type Depth Hoar
Weak Layer grain size 2.00 mm
Weak Layer Hardness F
Slab Layer Grain Type Rounded Grains
Slab Layer Grain Size 1.00 mm
Slab Layer Hardness 1F