OLYMPIC VALLEY, Calif. - One week before Christmas, backcountry skier Toni Piva cheated death in an avalanche.
Caught in a snow slide while skiing with friends in an Idaho wilderness area near the Wyoming state line, Piva was buried for 12 minutes until his friends dug him out.
Preparation and experience along with quick action by his friends saved Piva's life. Many others aren't so lucky.
Last year - the worst on record in the United States - slides killed 35 skiers, climbers, boarders and snowmobilers. This year's total so far is 12, including four U.S. skiers killed in a Canadian avalanche this month.
It's estimated that 100,000 avalanches occur each year in the United States, according to Knox Williams, director of the Colorado Avalanche Information Center.
While most avalanches are unobserved and occur away from developed areas, Williams preaches that being aware can prevent a backcountry outing from becoming a disaster.
"If you do not pay attention to the clues, you're guaranteed to have an avalanche adventure," he said at this month's Operation Sierra Storm 2003 weather seminar held in the heart of Sierra ski country at Squaw Valley.
Piva, 32, of Driggs, Idaho, concedes he overlooked avalanche-prone conditions on Dec. 19.
"Instead of evaluating this season, we were going on past knowledge," he said.
Nobody who plays in mountain snow is safe from avalanche. But Williams said there are avoidable conditions:
For more on avalanche safety, check out these Web sites:
Southeast Alaska Avalanche Center, click on the Southeast Alaska link
Westwide Avalanche Network
Colorado Avalanche Information Center
Virtually all avalanches occur away from developed ski areas. Resorts trigger avalanches with explosives after storms to eliminate the threat from cornices and unstable areas.
More than 80 percent of all avalanches develop during or immediately after heavy snowstorms.
More than 90 percent happen on steep slopes - 30 to 45 degrees - about the pitch of a black diamond ski run.
"Snow is a lot like people. It doesn't like rapid change. Snow is very sensitive to the rate at which it is loaded or stressed," said Bruce Tremper, director of the Forest Service Utah Avalanche Center.
"Two feet of snow added over two weeks is not a problem. Two feet of snow in two days is a much bigger problem. Two feet of snow in two hours is a huge problem."
While storms seldom dump 2 feet of snow in two hours, wind piles it up 10 times faster, creating deadly cornices that loom from ledges. And it doesn't take an entire mountainside to kill. People can die under snow slides from roofs, Williams said.
Heavy fresh snow may bond safely with the existing layer. But if there has been crusting or a dusting of granular snow, there is a weak layer that produces prime avalanche conditions. It's believed that a freeze-and-thaw weather pattern created layers of ice and snow before this month's deadly avalanche in British Columbia.
"Dry slab avalanches account for almost all avalanche fatalities," Tremper said. "A slab avalanche is like a dinner plate sliding off the table. The slab shatters like a pane of glass with the victim in the middle of the slab, and usually there's no escape."
Tremper, himself an avalanche survivor, describes the experience as "skiing on tumbling cardboard boxes."
In "Staying Alive in Avalanche Terrain" (Mountaineers Books), he writes, "My hat and mittens were quickly ripped off along with both my skis. Snow went everywhere; down my neck, up my sleeves, down my underwear, even under my eyelids. ... every time I opened my mouth to breathe, the avalanche kind of injection-molded my mouth and throat full of snow again. Just when I needed to breathe the most, I couldn't."
Outrunning an avalanche is unlikely. Snow slides can build up to 80 mph. They usually are triggered by the victim or a member of his party, putting them in the middle of the danger, not down the slope observing it.
Three things contributed to Piva's survival: He was with friends, he had a locator beacon and the veteran surfer was able to "swim" in the crashing wave of snow to keep his head above the debris. Tremper also swam for his life and ended up chipping himself out of his icy, waist-deep trap.
One-third of all avalanche fatalities don't survive the first terrible minutes. They are beaten to death by tumbling snow, ice, rocks and trees.
Once a person is buried, survival is usually up to the companions. The victim is locked in an icy cell that allows no movement and provides minimal oxygen. Even with a little breathing space, exhaled carbon dioxide soon accumulates to a deadly level.
Data show that 93 percent of buried victims survive if they are rescued within 15 minutes. After that, the rate plummets to 50 percent after 30 minutes and 30 percent after 40 minutes, then levels off to 20 percent survival after two hours.
Experts advise companions to search relentlessly for 30 minutes before taking the time to seek help. If the victim doesn't have an avalanche beacon, the options are the needle-in-a-haystack approach of probes and, finally, search dogs.
"Dogs are great at finding people who are already dead," Williams said. "If you're buried in an avalanche, the prospect of survival is not good."
Williams said that as the popularity of snowmobiling has increased, so has the number of avalanche deaths.
"In the decade of the '90s, that is the recreational group that is dying most often in avalanches," he said.
Of 194 U.S. avalanche deaths from 1995 through 2001, snowmobilers accounted for one-third, skiers for 22 percent, climbers for 15 percent, snowboarders for 13 percent and various recreationists for 11 percent with residents, ski patrollers and workers accounting for the rest.
While 35 people died last year in avalanches, Williams estimated at least 10 times that number survived.
"Education is the key," he said. "Know what to look for. Avalanches aren't going to come looking for you."