A soaring mountain covered with a thick blanket of snow is one of nature's most spectacular settings - but it can also be one of the most dangerous.
That was the lesson to backcountry enthusiasts everywhere last weekend, when avalanches in three Western states killed five outdoorsmen and injured several others. Abroad, two avalanches struck a village in the French Alps, and rescue teams worked furiously Feb. 9 to find people thought to be buried in the snow.
While the past week has been an unusually bad one for fatal avalanche accidents, the tragedies underscore a disturbing trend: The number of avalanche deaths in the US has more than doubled in the past 10 years.
The explanation is not more naturally occurring avalanches. Rather, the steep alpine terrain of America's mountain ranges has become the winter playground of a growing number of recreationists - many of whom are ignorant of the danger or how to steer clear of it.
"The easiest thing to tell people to do - and the hardest thing for them to actually do - is to stay away from avalanche-prone areas," says Dale Atkins, an avalanche forecaster at the Colorado Avalanche Information Center in Denver. "By simply staying off of steep slopes [30 to 45 degrees], you can eliminate the risk of avalanche."
Unfortunately, the urge to be the first to lay down tracks in a pristine snowfall seems irresistible to some. In an accident in Colorado Feb.6, a slide that killed three people was likely triggered by a snowmobile traversing a steep mountainside.
That's an increasingly common scenario. "The one user-group that is producing the greatest increase in avalanche accidents is snowmobilers," says Charley Shimanski, education director for the Mountain Rescue Association, based in Golden, Colo. That's partly because snowmobiles are still rising in popularity and, more powerful than ever, can readily climb treacherous terrain.
But as avalanche season peaks between now and the end of March, it takes much less than a loud machine to trigger a huge snow slide. Just the mere whisper of a pair of skis can cause snow to thunder downhill at speeds up to 100 m.p.h., experts say.
In other accidents over the weekend, a Utah man on snowshoes died after being engulfed by a massive slide south of Salt Lake City. In the Sierra Nevada, a sledder died after being trapped under an avalanche.
Here in Colorado, which leads the nation for avalanche deaths, already this year five people have died. An average of 24 avalanche fatalities occur in the US annually.
Avalanches happen when an unstable slab of snow - often several feet thick and hundreds of feet wide - slides away from an underlying thin layer of snow. This occurs most often after a heavy snowfall, when a layer of new snow fails to bond to the old snow underneath. In essence, it creates a "house of cards" - ready to tumble down on an intrepid skier, snowmobiler, or mountain climber.
The Colorado Rockies, with their high altitude and tendency for late snows, are especially avalanche-prone - even in the absence of a recent snow, says Tad Pfeffer, a researcher at the Institute of Arctic and Alpine Research at the University of Colorado in Boulder. Because early-season snows here are dry and granular, they make a poor foundation for the heavier snows of mid-winter. "The old snow underneath becomes like a layer of ball bearings," he explains. At that point, just a slight jar from above can shake a slab loose.
Although scientists have been studying avalanche dynamics for decades, "there's still a great deal about them that's unknown," says Mr. Pfeffer. The interplay of many factors - from temperature to slope angle to snow accumulation - affects when and where an avalanche may occur.
In Colorado, the Avalanche Information Center issues warnings whenever snow-pack and weather conditions conspire to increase avalanche hazards. The trouble is, those who most favor the backcountry are least likely to heed warnings. "They tend to think the consequences don't apply to them," says Mr. Atkins.
Mr. Shimanski - who trains search-and-rescue volunteers and coordinates avalanche-awareness programs nationwide - says the backcountry can be enjoyed safely, but only with adequate education.
"The biggest tip is to take an avalanche safety course. That is key," he says. It's also important to heed the basics, he says, such as not traveling into the backcountry alone, always carrying avalanche-safety gear, and checking avalanche forecasts before heading out.
Following such advice can help high-country enthusiasts make wiser choices - and prevent avalanche deaths.
"One of the biggest misconceptions is that avalanches just happen - that you're at the wrong place at the wrong time," Atkins says. "That's not true. For the most part, people cause avalanches."