Snowpack in the mountains around Bozeman has stayed relatively stable so far this winter, but avalanche danger is mounting in areas further south.
The Gallatin National Forest Avalanche Center has rated avalanche danger as “moderate” in the Bridgers, northern Gallatins and northern Madisons around Bozeman and Big Sky over the past five days.
That means natural avalanches are unlikely, but human-triggered slides are possible, and avalanche conditions could be heightened in specific areas. Travelers should evaluate snow features and terrain in these areas carefully, the avalanche center wrote on its website.
Avalanches occur when a weak layer of snow can’t hold any additional weight, and the layers above it fracture and fall down the slope. Heavy snow can be enough to trigger a slide, but often the additional weight from a person or snowmobile triggers them.
Doug Chabot, director of the Gallatin National Forest Avalanche Center, said a layer of snow that fell early in the season has weakened, but not much snow has accumulated on top of it in the mountains north of Big Sky.
Wind-loading on slopes has contributed to some smaller avalanches, including natural slides on Saddle Peak, but Chabot said GNFAC is fairly happy with the conditions.
“This weakness is adjusting pretty well to the load placed on it at the moment,” he said. “People are getting out and skiing has improved.”
The same weak layer of snow that is adjusting in the mountains north of Big Sky isn’t holding up as well further south.
In the southern Madisons, southern Gallatins and Lionhead area around West Yellowstone and Hebgen Lake, avalanche danger has been rated “considerable” since Christmas.
A considerable rating means natural avalanches are possible, and human-triggered avalanches are likely. The avalanche center encourages travelers to make conservative decisions on slopes in these areas.
The mountains around West Yellowstone have been hammered with snow, which is putting more weight on that weak layer, according to Chabot. In some areas, over 4 feet of snow has fallen in the past week, he said.
Avalanche danger near Cooke City is also considerable. Two Minnesota men died after they were caught in an avalanche while snowmobiling on Scotch Bonnet Mountain north of the town on Monday, the Livingston Enterprise reported.
Eight snowmobilers from Minnesota were recreating there when two in the party got stuck on a slope. Another two riders raced to help, and the avalanche triggered, according to a report from GNFAC.
The 300-foot-wide avalanche broke four to five feet deep above a weak layer of snow.
Members of the group were equipped with avalanche beacons and rescue gear. They were able to dig the two men out of the debris, but were unable to revive them.
Jesse Thelen, 43, of Paynesville, Minnesota, and Carl Thelen, 40, of St. Martin, Minnesota were the victims, Park County Coroner Al Jenkins told the Livingston Enterprise on Tuesday.
A GoFundMe with a fundraising goal of $20,000 has been organized to help Carl’s family cover the costs of his funeral and any extra expenses.
Chabot said that before venturing into high elevation terrain, travelers should always check the avalanche forecast and watch GNFAC’s daily snowpack videos. They should pack rescue gear (a beacon, shovel and probe) and know how to use it.
In addition, only one person should stay on a slope at a time. That way, if a slide occurs, someone will be free to perform a rescue. Any terrain that is on or attached to a 30 degree slope carries risk, according to Chabot.
“If you are skiing or snowboarding and you see evidence that an avalanche has happened, that is a sign that all slopes in that area are suspect and dangerous,” he said. “If you are on your skis or sled and hear a ‘whumpf,’ that’s another serious warning sign that things are unstable.”
Six people have died in avalanches nationwide so far this winter, according to data compiled by the Colorado Avalanche Information Center.