A survivor of an avalanche that killed seven people, including snowboard pioneer Craig Kelly and three other Americans, said Tuesday he was awed by the incredible power of the snow slide.

"It was like swimming down the roughest river I've ever been in and trying to keep my head above water," John Seibert of Wasilla, Alaska, said of getting caught in the avalanche that thundered 300 feet down the mountainside.

The seven victims were buried under 15 feet of snow. They were part of a group of skiers and snowboarders who flew in by helicopter to a mountain chalet with access to untouched, wild glaciers and slopes.

"If you get caught in one of those things, you can't flex a muscle, let alone breathe," said Ian Stratham of the Revelstoke ambulance service, who arrived at the scene about two hours after the snowslide.

The dead were identified as Kelly, 36, who lived in Nelson, British Columbia; Ralph Lunsford, 49, of Littleton, Colo.; Dennis Yates, 50, of Los Angeles; and Kathleen Kessler, 39, of Truckee, Calif.

Three others were from Canada, including Naomi Heffler, 25, of Calgary and Dave Finnery, 30, of New Westminster, British Columbia. The name of a 50-year-old man from Canmore, Alberta, was not release pending notification of relatives.

Fourteen others in the group survived, some of them -- including Seibert -- digging themselves out of the snow.

Seibert, a geophysicist, described the weeklong backcountry ski trip that began Saturday as dedicated to safety, with a seminar on using the avalanche beacon each member carried the first order of business.

He said his three decades of experience in mountains and skiing gave him no warning of the avalanche that began with a loud crack.

"A few seconds later, the moving snow swept me off my skis and I started down the slope," he said. "I came to rest with my head and left hand exposed. The remainder of my body was locked in concrete-hard snow."

The other survivors were in a kind of shock after the avalanche, Seibert said, but some stayed up on the mountain Tuesday instead of coming down when weather cleared enough for a helicopter to reach the chalet where they spent the night.

Sgt. Randy Brown of the Royal Canadian Mounted Police said investigators were looking at what caused the avalanche as the skiers, divided into two groups, made their way up a slope.

To Seibert, the adventure involved no undue risk.

"There was nothing in my mind that was a warning sign we should not be on that slope on that day," he said, calling the tragedy "a fluke of nature."

Kelly, who also lived in Mount Vernon, Washington, helped pioneer snowboard riding in the late 1980s and was a four-time world champ and three-time U.S. Open champion.

Tim O'Mara of mountainzone.com in Seattle said Kelly was a legendary figure in snowboarding who was greatly involved in the growth of the sport.

"In recent years had gotten extremely interested and involved in backcountry snowboards. Unfortunately, that appears to be what he was doing on this trip," O'Mara said.

The remoteness of the area contributed to confusion in the hours following Monday's avalanche.

Initial reports said eight skiers died, all of them American, out of a group of 11. Later, Brown said seven people died from a group of 21 skiers that split into two groups on the mountain.

He modified the total number of skiers to 24 at Tuesday's news conference, but Seibert said the total number in the two groups was 21.

Both Brown and Clair Israelson, director of the Canadian Avalanche Association in Revelstoke, said the skiers were well-organized and properly equipped, but neither would speculate on the cause of the avalanche and whether the group proceeded despite an inappropriate risk.

Israelson noted that only one other avalanche was recorded Monday in the Selkirk Range, which he called an unusually low number. Asked if the skiers triggered the avalanche, he said: "We don't know that."

All the deaths were caused by asphyxiation, said Chuck Purse, the British Columbia coroner. He said none of the victims suffered traumatic injuries.

Avalanche safety became a national issue after former Prime Minister Pierre Trudeau's son, Michel, was killed in a 1998 avalanche. Michel's brother, Justin, started an avalanche awareness group.

To Seibert, the danger is part of the experience.

"I think the risk is well worth the reward," he said. "I've skied 35 years and this is the first time I've been caught in something like this."

Asked what the reward was, Seibert said: "It's better than sitting at home dying of boredom watching CNN."