Triggering Avalanches
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Hi, I'm Dave Thurlow from the Mount Washington Observatory and this is The Weather Notebook. Each winter, over 100,000 explosions are triggered across the West. Their purpose? To get unstable snow moving before it moves itself. Today on the show, we're going to discuss some of the ways avalanches are caused, for safety's sake.

Many of these triggered avalanches take place in ski areas, always while the skiers are gone, of course. Typically, a ski patroller takes a two-pound stick of dynamite or TNT, lights the fuse, and tosses it towards a high-risk avalanche spot -- from above. The fuses have a safety margin of about two minutes, which gives the patroller time to ski out of harm's way.

Another technique for triggering slides from a distance is to use surplus military rifles and howitzers. These are good for triggering avalanches up to two or three miles away in places, that ski patrollers can't safely reach. All this may sound like a nerve-racking business, but avalanche control, along with better education and warnings, have made a big difference in ski-area safety. Since 1986 there hasn't been a single skier killed by an avalanche within the bounds of a U.S. ski area. The bad news is that avalanche deaths from snowmobiles are on the rise. So, as always, it's dangerous for skiers to venture past that "out of bounds" sign, no matter how inviting the snow may look. It's better to knock snow off the mountain sides on purpose, than to have a stray skier do it by accident.

Thanks today to contributing writer Bob Henson. Our show is underwritten by Subaru, the beauty of all wheel drive, with major support provided by the National Science Foundation.