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Full accident report here.
This was a large or very large avalanche unintentionally triggered by a snowmobiler that produced at least enough destructive force to bury, injure, or kill a person. The avalanche likely involved a soft slab that broke into old snow layers and failed on a layer of faceted snow and/ or surface hoar (SS-AMu-R3/4-D2.5/3-O). The positions of the victims and survivors at the time of the accident suggest they were caught in a slide that broke at least 1500 vertical feet wide and ran 300 to 500 vertical feet.
The avalanche appears to have released while one rider was climbing a slope ahead of the remaining four riders, who were stopped at what they thought was a spot free safe from avalanches. All five riders were hit by the avalanche. Riders 2-4 freed themselves and their snowmachines from the debris. They found Rider 1 partially buried, with his airbag deflated. Despite recuscitation efforts, he did not survive. Search and Rescue teams recovered Rider 1 via helicopter the following day.
Our hearts and sympathies go out to the victim's family, friends, and survivors.
We will update this report if more information becomes available.
Physical characteristics estimated using Caltopo and based on recent avalanche activity nearby.
Forecast Hotline: 406.257.8402
Call or text an observation: 406.66AVYOB