ISLAND PARK — A snowmobiler from the Midwest was killed Sunday after a group of four riders was caught in a large avalanche in the Centennial Mountains near Island Park, authorities said.

The slide occurred around 2 p.m. in the Keg Springs area of Carrot Canyon. Three of the four riders were caught and carried by the avalanche. Two were partially buried and survived. One was completely buried and did not.

The Gallatin National Forest Avalanche Center, or GNFAC, confirmed the fatality Sunday evening.

“We are deeply saddened to report a snowmobile avalanche fatality today,” the center said in a statement on Facebook. “Our thoughts are with the family and friends of the victim during this tragic time.”

The avalanche was classified as a soft slab on an east-facing slope at roughly 8,000 feet. It measured a destructive size of D2 which means strong enough to bury or destroy a vehicle and was triggered unintentionally by a snowmobile on a buried weak layer.

Fremont County Sheriff Bart Quayle told East Idaho News his crews were simultaneously responding to two other mountain rescues in Fremont County, one in the Two Top area near Island Park and another near Hotel Creek.

Crews from Madison County and Gallatin County, Montana assisted in all three efforts. All people involved in those accidents made it out safely.

Ron Sykes, commander of Fremont County Search and Rescue, said current snow conditions are primed for avalanche danger. A dry January left weak layers on the ground, and last week’s fresh snowfall created an unstable combination.

“We went a lot of January with no snow,” Sykes said. “We get this fresh snow on top of it and it creates real bad avalanche conditions.”

“Danger is low in the Bridger Range where avalanches are unlikely. Remain alert for small wet loose avalanches or wind slabs.” The GNFAC wrote on Facebook.

It is the first avalanche involving victims that either county has responded to this year.