A volcano is an opening in the earth's surface through which lava, hot gases, and rock fragments erupt. These openings are formed when melted rock from deep in the earth build up around the opening, and form mountains. When these openings erupt they shoot out huge fiery clouds over the mountain, and spew glowing rivers of melted lava down their sides. In some eruptions, red-hot ash and cinders shoot out the mountaintop, and large chunks of hot rock are blasted high into the air. Only a few spectacular eruptions are so violent that they blown the mountain apart.
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