subject: What Exactly Is A Avalanche [print this page] When a tremendous mass of snow, ice, or loose rocks and earth slides down the side of a hill or mountain, it is called an avalanche. Anything tends to slide downhill, but usually snow or rocks will cling to a mountain side. When a mass of snow becomes too heavy, perhaps because of a big snowfall, or because the sun has melted a lower layer that was holding up the top layer, part of it may start sliding, which will carry all the rest along with it. Avalanches can be very dangerous. They can bury people, houses, and even whole villages.
Avalanches sometimes go faster than 100 miles an hour, and the biggest ones have contained five million tons of snow. A loud noise, such as a rifle shot or even a man shouting, can start an avalanche. The sound waves make the snow or ice shake a little, which may be just enough to loosen it. The worst places for avalanches are in the Alps, the big mountain chain in southern Europe (Switzerland, Austria, and Italy), and in Alaska. The biggest disaster ever caused by an avalanche was in the Alps in 1916, when nine thousand soldiers of the Austro- Hungarian Army were buried and died under tons of snow. There have been big avalanches of rocks breaking off the cliffs at Niagara Falls, and once (in 1935) six hundred tons broke off the Rock of Gibraltar and slid into the sea.Avalanches are classified by their morphological characteristics, and are rated by either their destructive potential, or the mass of the downward flowing snow.
