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passage three
On January 10, 1962, an enormous piece of glacier broke awayand tumbled down the side of a mountain in Peru. A mereseven minutes later, when cascading ice finally came to a stopten miles down the mountain; it had taken the lives of 4,000people.
This disaster is one of the most “devastating”examples of a verycommon event: an avalanche of snow or ice. Because it isextremely cold at very high altitudes, snow rarely melts. It justkeeps piling up higher and higher. Glaciers are eventually created when the weight of the snow isso great that the lower layers are pressed into solid ice. But most avalanches occur long beforethis happens. As snow accumulates on a steep slope, it reaches a critical point at which theslightest vibration will send it sliding into the valley below.
Even an avalanche of light power can be dangerous, but the Peruvian catastrophe was particularlyterrible because it was caused by a heavy layer of ice. It is estimated that the ice that broke offweighed three million tons. As it crashed down the steep mountainside like a gigantic snowplough, it swept up trees, boulders and tons of topsoil, and completely crushed and destroyed thesix villages that lay in its path.
At present there is no way to predict or avoid such enormous avalanches, but, luckily, they arevery rare. Scientists are constantly studying the smaller, more common avalanches, to try tounderstand what causes them. In the future, perhaps dangerous masses of snow and ice can befound and removed before they take human lives.
单选题
The first paragraph catches the reader's attention with a _____.