TRIGGERED SLAB | INCONSISTENT SNOW DEPTH

Montana, Absaroka Range, Republic Mountain

The following report analyzes an avalanche incident one year ago in Montana. This report was included in the new backcountry avalanche section in the 2021 edition of Accidents in North American Climbing. There are some great lessons here for backcountry travelers this winter.

On the morning of January 8, 2021, a group of six skiers (one female and five males) met in Cooke City, Montana, and decided to ski the Fin on Republic Mountain. None of them had been to this particular slope or mountain before. All members carried an avalanche transceiver, shovel, and probe, and three were wearing helmets. Two carried avalanche airbag packs. All had at least some avalanche education. They had read the local avalanche forecast the day before, but not the day of this incident (the danger had not changed).

On their ascent, visibility was poor and they could not see the entire slope or the ridge line they intended to climb. As they left the trees, they dug two pits and performed [stability] tests. One later wrote, “Though we identified potential weak layers at 60 cm and a deeper one…we got minimal failure and no propagation. What we saw in the pits was a nice right-side-up snowpack. However, we knew if we skinned along the ridge to the southwest, the snowpack would change due to wind exposure. We discussed mitigating this by skinning close to the ridge and skiing back down our skin track if we saw warning signs.”

As they continued and “when those in the skin track crossed over a wind lip into a slightly more southerly aspect,” they felt the slope collapse and watched a crack propagate 250 feet upslope. The avalanche broke 1.5 to two feet deep, 200 feet wide, and ran 700 feet vertically. Skiers 1 and 2 were carried the full distance to the base of the slope. Skier 3 was carried about midway downslope. Skier 4 was at the edge of the slide and able to hold their position, and Skiers 5 and 6 were further back in the skin track.

Skier 1 deployed his airbag and was partially buried. He freed himself from the debris and began a transceiver search. He followed the signal to Skier 2, whose head was buried more than two feet deep; the skier was unconscious and not breathing. Skier 1 cleared Skier 2’s airway, and Skier 2 began breathing and regained consciousness. Skier 2 sustained injuries to his leg, but later made it out under his own power.

Skiers 4, 5, and 6 quickly skied down to help Skier 3, who was partially buried about halfway down the slide path and sustained serious injuries to his ribs and lungs. Skiers 4 and 6 had two-way radios and called for help. (There is no cell service in this region.) They were able to contact someone with a radio in Cooke City, who reported it to Park County Search and Rescue. Because Skier 3 could not move, the group eventually congregated at Skier 3’s position, where they built a fire and waited for rescuers. Skier 3 was evacuated by helicopter at about 4 p.m., and the rest of the party was able to get out under their own power with the help of rescuers.

ANALYSIS

The avalanche occurred on an east aspect at 9,700 feet. The average slope angle was 37 degrees (33 degrees at the crown). The mountains near Cooke City had received heavy snow in October and November, which formed a dense, two- to four-foot-deep snowpack on many slopes. In late November to December, minimal snowfall and cold temperatures led to the formation of weak layers of sugary facets on some slopes, especially where the snowpack was relatively shallow. These layers were buried by subsequent heavy snowfall in late December, followed by small storms through the first week of January.

The skiers dug a six-foot-deep snow pit close to where the avalanche was triggered. They found good snow structure and good stability in their pit, which investigators confirmed the next day when they dug in the same spot. Approximately 100 feet away, with a slight change in aspect, the snowpack thinned from six feet to two to three feet deep. This thin area is where they initiated a fracture in the faceted grains.

In a video produced after the investigation at the accident scene (see video below) and in comments to viewers, Doug Chabot of Gallatin National Forest Avalanche Center [and a former AAC board member] warned skiers to “be really careful and paying attention to if the snowpack is changing as you’re skinning along. As soon as [these skiers] wrapped around to a slightly different aspect, the depth and snow structure changed. A stability test is one of many pieces of info that goes into deciding whether to ski or not. A poor test result is enough to turn around, yet the absence of that is not a green light to move forward…. The bottom line is that you should know that the snow is very stable if you are considering entering large, highly consequential avalanche terrain like the Fin.” (Source: Gallatin National Forest Avalanche Center.)

AVALANCHE COVERAGE IN ANAC: WHAT DO YOU THINK?

The 2021 edition of Accidents in North American Climbing introduced a new section of reports on backcountry skiing and snowboarding avalanches. Accidents has always covered mountaineering avalanches (including some ski mountaineering incidents), but the new 15-page section expanded our coverage to backcountry ski touring and snowboarding terrain, with 10 detailed reports and photos from December 2020 to April 2021. We’d like to know what you think: Did you read the new avalanche section? Did you think it was helpful and educational? Do you think this section was an appropriate use of pages in ANAC, or should the book stick exclusively with its traditional subject matter? Please fill out the 2 minutes survey. Thank you!

BACKCOUNTRY MEDICINE ON YOUR PHONE

Wilderness Medicine Reference is an information-packed app with diagnosis and treatment recommendations for many backcountry medical situations, plus prevention and evacuation checklists and strategies. Created by Karen Lapides, a longtime Colorado-based paramedic, wilderness medicine instructor, and Outward Bound mountaineering course director, the app is aimed at backcountry travelers with little medical training up to those with wilderness EMT certification. Nothing can replace formal wilderness medical training and practice, but for just 99 cents, this app offers an inexpensive and convenient field reference or backup.

THE SHARP END: GROUND FALL NEAR LAKE TAHOE

In Episode 72 of the Sharp End Podcast, climber Kyle Broxterman describes a serious trad climbing accident near Lake Tahoe, California. His attempt on a 5.11 trad climb ended when he fell and pulled out three wired nuts he’d placed for protection. Hear why Kyle is taking a step back from letting his ego drive his climbing and how he is managing his recovery from a terrible fall.

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