Today, these rules still apply to the banned woods and are still strict, especially in breakaway zones, where avalanches are most likely to start. A thick grove of trees can keep a layer of snow from slipping and triggering an avalanche. However, once a snow slide starts, the largest trees cannot stand against hundreds of thousands of tons of snow and ice that move downhill at 200 miles an hour.
Trees are the best natural defense against avalanches, but human-caused pollution is stripping away forests. They are being killed by acid rain, insect damage, and disease. Cold, windy winters can also leave nothing but bare rock clearings, which then become permanent avalanche paths. Without a natural fence of trees, the only way to deflect an avalanche is to build a wall or barrier of some kind.
Engineers have made new barriers out of metal anchored in concrete. These are placed in breakaway zones above the first fence of trees. These avalanche snow fences can be made up to 12 feet high. However, it would be too expensive to make barriers on every slope.
Another good way to prevent avalanches is to break up heavy masses of snow. The Canadian army patrols between towns each winter, armed with 105mm howitzer cannons. They use an average of 423 rounds of ammunition to guard the 91-mile-long stretch of the Trans-Canada Highway, breaking up snow before it can avalanche and cover the road.
In many areas, ski rangers and patrol teams test ski runs and hiking areas before opening them to the public. These rangers often work in pairs, one testing the snow while the other watches from a safe spot. The tester will zigzag back and forth across a slope, bouncing up and down, always looking for signs of instability. Obviously, these patrollers have very dangerous occupations. Both people will carry electronic transceivers to keep in touch, as well as anchor themselves to a tree or boulder before venturing into untested territory.
Large slopes, overhanging waves, and unstable slopes are sometimes blown up. Rangers call this process shooting the slopes. In the Alps, mortar and cannons have sometimes been used to break up snow. Today 75mm and 105mm recoilless rifles, 75mm howitzers, and avalaunchers (cannons powered by compressed nitrogen gas) that can shoot objects 2,000 yards away are used to dislodge snow.
As long as these methods are followed, many avalanches can be prevented each year. Of course, it is always important to know that none of nature’s disasters can be wholly prevented. Therefore, it is best to be prepared for what may someday come.
Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/avalanches/prevention.shtml
Although there’s no way to stop an avalanche, some can be prevented or turned aside. Forests and trees are a good line of defense because they hold back snow like a giant fence. However, trees are often cut down to be used for fuel or lumber. When forests are gone, their roots no longer hold topsoil in place. Open clearings like these are the best pathways for avalanches. To remedy this growing problem, forest inspectors in 14th century Switzerland set aside Bannwalders, or banned woods, where citizens could “remove nothing, growing or dead, green or withered, lying or standing, small or big, nor remove bark, berries or cones.” Punishment for breaking these rules was sometimes death.