On January 10, 1962, an enormous piece of glacier【B1】______and tumbled down the side of a mountain in Peru. A mere seven minutes

On January 10, 1962, an enormous piece of glacier(26)broke away and tumbled down the side of a mountain in Peru. A mere seven minutes later, when(27)cascading ice finally came to a stop ten miles down the mountain, it had taken the lives of 4,000 people.
    This disaster is one of the most(28)devastating examples of a very common events: an avalanche of snow. Because it is overly cold at high altitudes, snow rarely melts. It just keeps(29)piling up higher and higher. Glaciers are eventually created when the weight of the snow is so great that the lower layers are pressed into solid ice. But most(30)avalanches occur long before this happens. As snow accumulates on a steep slope, it reaches a critical point at which the slightest(31)vibration will send it sliding into the valley below.
    Even an avalanche of light power can be dangerous, but the Peruvian(32)catastrophe was particularly terrible because it was caused by a heavy layer of ice. It is established that the ice(33)broke off weighed three million tons. As it crashed down the steep mountainside like a(34)gigantic snow plough, it swept up trees, boulders and tons of topsoil, and completely crushed and destroyed the six villages that lay in its path.
    At present, there is no way to predict or avoid such enormous avalanches, but, luckily, they are very rare. Scientists are(35)constantly studying the smaller, more common avalanches, to try to understand what causes them.