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.
People for thousands of years have been fascinated by the spectacle of volcanic eruptions and terrified of their power. Some of these eruptions have caused some of the worst disasters in history, by wiping out entire towns and killing thousands of people. The word volcano comes from the term Vulcan, which was a name the ancient Romans gave their god of fire.
Volcanoes played a role in the religious life of some of these people, and they believed that god lived beneath a volcanic island off the Italian coast.
Powerful forces within in the earth's surface cause the formation of volcanoes. Volcanoes begin as magma, deep inside the earth, which is caused by the extreme heat within the earth's interior. Magma develops from 15 to 100 miles beneath the earth's surface, where it is melted and releases gas. Gradually the magma rises toward the earth's surface because it is lighter than the solid rock around it. As the magma rises, it melts gaps in the surrounding rock and forms a large chamber two miles from the surface.
An eruption takes place when the gas-filled magma under ground is under great pressure from the solid rock around it and this pressure causes the...