VOLCANO, ANOTHER POWERFUL THREAT

A volcano its to a natural disaster:

A Volcano is a vent in the earth through which hot gases and molten rock rise to the surface. A coneshaped mountain of erupted material around such a vent is also called a volcano. The name is taken from Vulcano, an island north of Sicily in the Mediterranean Sea. The island was given its name by the ancient Romans because it spewed smokelike vapor, and was thought to be the home of Vulcan, their god of fire.

A Volcano consists of a fissure in the earth's crust, above which a cone of volcanic material has accumulated. At the top of the cone is a bowl-shaped vent called a crater. The cone is formed by the deposition of molten or solid matter that flows or is ejected through the vent from the interior of the earth. The study of volcanoes and volcanic phenomena is called volcanology. Most volcanoes are composite landforms built up partly of lava flows and partly of fragmental materials. Italy's Mount Etna, in Sicily is an example of a composite cone.

In successive eruptions, the solid materials fall around the vent on the slopes of the cone, while lava streams issue from the vent and from fissures on the flanks of the cone. Thus, the cone is built up of layers of fragmental materials and flows of lava, all inclined outward away from the vent. Some enormous, craterlike basins, called calderas, at the top of long-dormant or extinct volcanoes, are eventually occupied by deep lakes, such as Crater Lake in Oregon. Some calderas are the result of cataclysmic explosions that destroy the erupting volcano. Others form when the subterranean magma chamber, emptied by repeated eruptions, can no longer support the weight of the volcanic pile above it. Therefore it collapses.

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