A group of snowmobilers thought they were in a safe area to enjoy Idaho's Sawtooth Mountains but likely didn't fully understand the dangers, one expert said Monday.
"They just didn't understand the fundamental nature of how the landscape works and that you could trigger things from down below," said Simon Trautman, an avalanche specialist at the Sawtooth National Forest Avalanche Center in Ketchum.
Trautman, who was doing research with colleagues in the area at the time of Sunday's avalanche, said he believes the group sparked the slide when they were walking in the meadow area of Frenchman's Creek north of Ketchum. They were on foot because one of their sleds got stuck, a sheriff's official said.
The area appeared safe to the snowmobilers because it was flat and open. But Trautman said one of the reasons there aren't trees in that area is because of avalanches.
"They felt they were being safe. Unfortunately, they were at the end of the avalanche path," he said.
In its daily advisory Sunday, the avalanche center rated that area's risk as "high," a 4 on a scale of 1 to 5. Under those conditions, a natural avalanche is considered likely, and a human-triggered avalanche is very likely.
Trautman said several feet of dense snow on top of "weak snow" with faceted crystals snow that looks like sugar you can't pack into a snowball made the area ripe for an avalanche. A very long dry spell created the weak snow on the ground.
When one of the snowmobilers stepped through the top layer of snow into the underlying faceted snow, it likely initiated a fracture that traveled uphill.
Faceted snow may be to blame for some of the other recent avalanches in the West, Trautman said.
"It's been a very active week across the West, a very tragic week," he said.
It was just after 2 p.m. Sunday that the avalanche occurred in Blaine County. All four of the snowmobilers were buried by the snow and debris, which was 4 to 8 feet deep and 300 to 400 feet wide.
It ran 1,400 vertical feet and carried force great enough to destroy a wood-frame house, authorities said.
Robert Swanton, 65, and Susan Swanton, 56, both of Sutherlin, Ore., dug themselves out. They used the only snowmobile that wasn't buried by the avalanche to go to the highway to flag down help, said Holly Carter, spokeswoman for the Blaine County Sheriff's Office.
George G. Martin Jr., 64, of Bellevue, was buried for an hour and could not be revived.
Three snowmobilers summoned by the Swantons found Martin's wife, Lesley D. Martin, 70. Though buried for 90 minutes, she was conscious and breathing.
"They speculate that she had a pocket of air," Carter said.
Martin, who was transported out on a snowmobile, was listed in good condition Monday afternoon at St. Luke's Wood River Medical Center, a hospital spokeswoman said.
All of the snowmobilers were wearing beacons. That was critical in saving Lesley Martin, sheriff's officials said Monday.
Blaine County Sheriff Gene Ramsey urged those venturing into the backcountry to wear beacons, take proper equipment and stay out of avalanche-prone areas.
Trautman said the public should stay out of avalanche terrain, which he generally described as any steep slope - 30 degrees or greater.
Katy Moeller: 377-6413