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A volcano is a hole in the earth's surface that forms when tectonic plates move and magma rises from the earth's core as lava. Volcanic eruptions can be gentle or violent, with violent eruptions spreading hot lava, smoke, and ash through towns and destroying everything in their path, as seen with the 1980 eruption of Mount St. Helens that caused an avalanche killing 57 people and the 2004 Indonesian tsunami caused by an underwater volcanic eruption.