ANCHORAGE, Alaska (AP) — An avalanche in the Alaska backcountry swept away and buried three skiers who were believed to be dead under a pile of snow nearly as deep as a 10-story building, Alaska State Troopers said Wednesday.

If the deaths are confirmed it would be the deadliest U.S. avalanche since three climbers were killed in a slide in Washington’s Cascade Mountains two years ago.

While Alaska troopers have not been able to assess the site yet, “based on the information provided by the operator, unfortunately, we do not believe that any of the three missing persons survived the avalanche,” Austin McDaniel, a spokesperson for the Alaska State Troopers, said in a text to The Associated Press.

The slide caught three heli-skiers late Tuesday afternoon near the skiing community of Girdwood, located about 40 miles south of Anchorage, said McDaniel. Heli-skiers use helicopters to reach mountains in remote backcountry areas where there are no ski lifts, and then they either ski or snowboard down the mountain.

Guides from a heli-skiing company attempted to locate the skiers using avalanche beacons and identified a probable area where the skiers were buried, at a depth of 40 feet to 100 feet, McDaniel said.

“The guides were unable to recover the three skiers due to the depth. Due to considerable avalanche risk in this area and limited daylight, no further recovery operations were conducted on March 4,” he said. “If weather and conditions allow for it, Troopers plan to assess avalanche conditions from the air and determine recovery options with individuals that have experience making avalanche recoveries.”

The heli-ski operator was Chugach Powder Guides, McDaniel said. A woman who answered the phone at the company said it had no immediate comment. Its website describes Chugach Powder Guides as one of the original heli-ski operators in Alaska

The avalanche site was 8 miles northeast of the airport in Girdwood.

Girdwood is the skiing capital of Alaska, and home to the Alyeska Resort, at the base of Mount Alyeska, where people downhill ski or snowboard amid stunning views of Turnagain Arm. At the top of the mountain is the Seven Glaciers Restaurant, named for its view.

Each winter, 25 to 30 people die in avalanches in the U.S., according to the National Avalanche Center.

Colorado experiences the most avalanche deaths, with 325 people killed since 1950. Alaska ranks second, with 172 deaths in that time period, according to the center.

In 2021, Czech billionaire Petr Kellner and four others died in a helicopter crash during a heliskiing tour near Knik Glacier, in the Chugach Mountains just north of Anchorage. A year later, a heli-ski guide scouting an area for clients died when an avalanche carried his body nearly 1500 feet down a mountain, Alaska State Troopers said at the time.

Prior to this week’s accident, 15 people had been killed across the U.S. by avalanches this winter. Among them were 10 backcountry skiers and snowboarders, four people on snow machines and a ski patroller, according to the Colorado Avalanche Information Center.

The most recent was last Friday in Washington state, where three snowmobilers were caught in a slide that buried and killed one person and injured a second in the Harts Pass area. One person was killed in an avalanche in central Colorado on Feb. 22. Authorities in Grand County responded to what they described as a skier-triggered avalanche in a steep area known as “The Fingers” above Berthoud Pass.

Elsewhere, three people died in avalanches on Feb. 17 — one person near Lake Tahoe and two backcountry skiers in Oregon’s Cascade Mountains. On Feb. 8, a well-known outdoor guide was caught in an avalanche in Utah and was killed.

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Associated Press writers Becky Bohrer in Juneau and Matthew Brown in Billings, Montana, contributed to this report.