Two big snowmobile triggered on Henderson Mtn., Cooke City

Henderson Mountain
Cooke City
Code
HS-AMu-R4-D2.5-O
Elevation
10000
Aspect Range
SE-NE
Latitude
45.04480
Longitude
-109.93300
Notes

Two big avalanches were triggered on Henderson Mountain near Cooke City on 1/16/20. One was huge. The other was still big enough to bury or kill somebody. Nobody was reported caught or injured. Report and photos from a third party that did not witness the slides occur, but were in the area earlier this day and saw the slopes had not slid.

From forecaster site visit: "We parked near the bottom of the debris on the Henderson slide and climbed to the crown. Knife hard wind slab; failed on facets at the ground that were 1F+ hardness (2-4mm). The crown was 5 meters deep (measured) and tapered to 16". There are lots of rocky and thin zones on this slope that were likely the trigger point. Vertical distance was 600', 1000 feet wide, debris was 10' deep."

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
4
D size
2.5
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
80.0 inches
Vertical Fall
350ft
Slab Width
1000.00ft
Weak Layer Grain type
Faceted Crystals
Weak Layer grain size
3.00mm
Weak Layer Hardness
1F+
Slab Layer Grain Type
Wind packed
Slab Layer Hardness
K
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year