A perfect day for spring snowmachining turned deadly Saturday afternoon when a crevasse swallowed a 28-year-old Anchorage man on Spencer Glacier.

Karl Jabas plunged 50 feet down an open crevasse at the top of the glacier, according to troopers and friends who were riding with Jabas.

Pat Kuckertz, one of seven people in the riding party, said no one in the group saw the hole in the snow.

"No one said they saw the crevasse and went around it," he said. "Riding on glaciers is inherently dangerous, and personally I''m not going back up there. Frankly, it wasn''t like this guy was taking a bigger risk at that place. He''s a skilled, advanced rider. He was pushing limits, but at that point anyone could have gone into the hole.

"He may not have even known what happened."

Kuckertz said the party had split into two groups and had met up about half a mile from the crevasse when they noticed Jabas was missing.

They initially thought their friend was stuck in deep snow. Kuckertz and another rider followed Jabas'' snowmachine tracks to where they ended at the edge of the crevasse.

"We called for him," Kuckertz said, "and heard nothing."

Forty feet down in the hole, they could see Jabas'' snowmachine. Kuckertz used a GPS to get the coordinates for the spot and then rode for 20 minutes until he found a place where he could get a cell phone signal and call for help.

The Alaska State Troopers responded with a helicopter and a three-man crew from the Alaska Mountain Rescue Group. Stan Olsen, a member of the rescue group who was lowered by ropes into the crevasse to retrieve Jabas, said the snowmachine and the crevasse were visible from the air.

"There were a lot of open crevasses as well as a lot that have snow bridges on them," Olsen said. "There was no bridge where he went in."

Olsen said no snow ramp led to the crevasse, so he doubts that Jabas tried to jump over the gap.

Troopers said Jabas, a 1998 Valdez High graduate, fell 50 feet into the hole, 10 feet farther than his snowmachine.

John Scudder of the Anchorage Snowmobile Club said avalanche danger may have subsided for the winter, but riders should be cautious of soft snow and unstable snow bridges.

"The snow bridges are pretty much starting to break up because they don''t have a good, cold freeze at night," he said.

In Jabas'' case, however, there was no collapsing snow bridge. Just a big hole in a wide-open snow field.

"There was a snow bridge off to the side," Kuckertz said, "but we believe it was open where he went into it."

Kuckertz, an experienced rider, said Saturday marked his first snowmachining trip to Spencer Glacier. The day was gorgeous -- clear blue skies, mild temperature and 6 feet of snow at the trail head in Whittier.

"Conditions were absolutely perfect," he said. "It would have been the crowning jewel of the season if this had not happened.

"It was the first time I ever rode there -- and probably my last."