"Avalanche!" is the most frightening alert a mountain traveler can hear. Uncontrollable snow slides in the world's mountainous regions -- from the Himalayas to the Alps to North America's Rocky Mountains -- claim many lives annually. Over the past 100 years, the overall death toll from snow avalanches may be well over 50,000 lives. Not only skiers, but those who live in mountainous areas or travel through them can be at risk. VOA's Paul Sisco set out to find what causes avalanches and what you should do if you are caught in one.
The most common and most dangerous types of avalanches look like an enormous "slab" of snow sliding down a mountainside. There can be many thousands of tons of snow -- enough to rip large trees from the ground, shift boulders and crush homes and cars.
The amount of snow resting on a mountainside, the angle of a slope and the weather are some of the factors that combine to trigger an avalanche. Scientists know the most dangerous slopes are inclined between 35 and 45 degrees, but beyond that there is no precise formula to decide when the risk is greatest. Almost anything can set the snow mass in motion -- a loud sound or the weight of a single person crossing a snowfield.
In the United States, there are about 100,000 snowslides every year.
A few days ago an enormous avalanche in the western state of Colorado swept two cars off a road. Those inside lived to tell about it.
Dave Boon, is one such avalanche survivor. He said, "It's just amazing the force we were hit with, and that we are even alive today."
Dave Boon, his wife and a young friend survived.
Boon describes what happened. "So I pushed my hand out through the window and found daylight and started, started digging out at that point, ... asked June if she was with me and okay, ... asked Gary if he was with me, and they both answered, so I said we got air. We're going to be all right."
Gary adds, "When we got out of the car and looked at it, an Aspen branch of a tree or something was through the windshield, and right next to the passenger seat, and I was sitting right behind the passenger seat, so I just knew that I was lucky and somebody was watching over me."
These Americans were lucky. Experts say for every one killed in an avalanche, five survive.
At many ski resorts, crews trigger small snowslides deliberately, before conditions become dangerous.
But if a large avalanche develops, anyone caught in the snow's path should know it is impossible to outrun an avalanche. If you are caught up by a rolling wave of snow, the best tactic is to create space around you, by "swimming" through the snow.
Ethan Green of the Colorado Avalanche Information Center explains that the largest-volume objects in an avalanche -- cars, or people flailing their arms -- almost always wind up near the surface when the snow comes to a stop. "An avalanche rolling down the hill is going through a lot of motion, and the small particles tend to fall down into the cracks and that motion pushes the largest particles up onto the surface."
No one died in this week's near disaster in Colorado, and control teams are out on the slopes working hard to keep conditions safe for skiers.