Avalanche accident on Twin Peaks

Flint Creek Range
Butte Area

2 Snowmobilers riding into the Twin Peaks area, and one decided to sidehill a slope with patchy larch trees that is 42 degrees at the top, and consistently windloaded.  The resulting avalanche took him and his sled approximately 300 feet downhill to a patch of small diameter larch trees where the trees formed a fence that strained the rider and his sled and also piled up the debris.  It was likely one of these small trees that broke the victim's leg.  They were very familiar with the area, and all the previous accidents (one fatality occurred north of this spot by 150 yds, and several full and partial burials have occurred along this ridge) that have happened in that area.  They were carrying all rescue gear and airbags(victim did not deploy his airbag).  One of the riders was at an avalanche class I put on at the toe of the slope 5 years ago.  There was no real hazard evaluation, and the riders did not observe any signs of instability prior to triggering the avalanche. Once the rider sidehilled into the open everything fractured above him in the windslab.  My partner and I had several large collapses assessing the area, and the victim's riding partner stated that they had several collapses moving the victim to the helicopter.  The helicopter landed very close to the toe of the slope.  The snow depth at the crown was 60 inches deep, with one wind slab sitting on another on facets, and at the toe of the slope the snow depth was less than 20 inches deep.  The fracture traveled roughly 800 feet in and around the larch trees near the top of the slope and it deposited debris in 3 different run outs.

Victim was buried vertically with a boot sticking out, and his riding partner exposed his face in 2 minutes.  He extricated his whole body in 8-10.  He had a broken femur and a broken hand.  As they were digging, rescuers stated that the second leg wasn't vertical, and they found it at an oblique angle to the rest of the body.  They had an inreach and sent out a help signal that was picked up, and LifeFlight was nearby.  Lifeflight was able to land at the base of the slope and take him to St. Pete's in Missoula at 1230 pm.

Photo: https://www.mtavalanche.com/images/24/twin-peaks-avalanche

Number of slides
Number caught
Number buried
Trigger Modifier
u-An unintentional release
R size
D size
Bed Surface
O - Old snow
Slab Thickness
60.0 inches
Slab Width
Slab Thickness units
Single / Multiple / Red Flag
Single Avalanche
Advisory Year