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Volcanoes. All volcanoes are formed by the accumulation of magma. Most volcanoes have steep sides, but some can be gently sloping mountains or even flat tablelands, plateaus, or plains.

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Introduction

Volcanoes According to the dictionary, a volcano is a mountain or a hill formed by the accumulation of materials erupted through one or more openings in the earth's surface. Volcanoes get their name from the Greek word Vulcano. "To the ancient Greeks, Vulcano was Hephaestus...to the ancient Romans it was the home of the forges of Vulcan; to both Vulcano was the lair of the god of fire" (Bullard 1984). Since then the myths have all gone, but the name Vulcano has remained as the symbol for all volcanoes. "A volcano is both the place and opening from which molten rock, solid rock or gas issues from a planetary interior" (Scarth 1994). It is also defined as the mountain or hill built up around the opening at the surface by an accumulation of the ejected materials. All volcanoes are formed by the accumulation of magma. Most volcanoes have steep sides, but some can be gently sloping mountains or even flat tablelands, plateaus, or plains. The volcanoes above sea level are the best known, but the vast majority of the world's volcanoes lie beneath the sea, formed along the global oceanic ridge systems that crisscross the deep ocean floor. The major types of volcanoes, roughly in order of increasing size, are cinder cones, composite volcanoes, shield volcanoes, calderas, and plateaus. Calderas and plateaus are shaped differently than traditional volcanoes---neither has a mountain-like shape. Volcanoes are wondrous and amazing but it is the dangerous natural things on Earth. Sources of molten rock below the surface of the earth is called a magma reservoir, magma being the term given to molten or semi-molten rock below ground level. ...read more.

Middle

During this period, streams enlarge and deepen their valleys. When the volcanic activity finally ceases, erosion starts to destroy the cone. After thousands of year, the great cone is stripped away to expose the hardened "volcanic plug" in the conduit. During this period of inactivity, streams broaden their valleys and dissect the lava plateau to form isolated lava-capped mesas. Continued erosion removes all traces of the cone and the land is worn down to a surface of low relief. All that remains is a projecting plug or "volcanic neck," a small lava-capped mesa, and vestiges of the once lofty volcano and its surrounding lava plateau. Although both cinder cones and composite volcanoes are mostly the results of explosive eruptions, cinder cones consist exclusively of fragmental lava. This fragmental lava is erupted explosively and made up of cinders. Cinder cones are typically much smaller than composite volcanoes for two reasons: (1) they involve only weakly explosive, small-volume eruptions of basaltic cinder that does not travel far from the vent; and (2) they usually have a short life-often only a single eruptive burst before becoming extinct. In contrast, composite volcanoes can grow much larger because they represent the accumulated products of repeated eruptions from the same vent(s) over a long time. Shield volcanoes get their name from their distinctive, gently sloping mound-like shapes that resemble the fighting shields that ancient warriors carried into battle. Shield volcanoes are built up of almost entirely of fluid lava. Flow after flow pours out in all directions from a central summit vent, or group of vents. ...read more.

Conclusion

Volcanoes are the most dangerous natural things on earth. When the volcano erupted, thousand of house, people, economic, and environmental impacts get destroy. But the volcano provides good natural resources for people to use for in their daily life, such as the roads. Volcanoes have it goods and it bad. Volcanoes help scientist to learn more about the inner Earth. Volcanoes are wondrous and amazing natural thing on Earth. Here is a list in case a volcano erupted. To prevent some of these disasters, here is a list of caution steps and facts provided by the USGS / Cascade Volcano Observatory. * Stay indoors * If you are outside, seek shelter such as a car or a building * If you cannot find shelter, breathe through a cloth, such as a handkerchief, preferably a damp cloth to filter out the ash. * When the air is full of ash, keep your eyes closed as much as possible * Heavy falls of ash seldom last more than a few hours only rarely do they last a day or more * Heavy fall of ash may cause darkness during daylight hours and may temporarily interfere with telephone, radio, and television communications * Do not try to drive a car during a heavy fall of ash-the chance of an accident will be increased by poor visibility * The thick accumulation of ash could increase the load on roofs, and saturation of ash by rain would be an additional load. Ash should be removed from flat or low-pitched roofs to prevent thick accumulation. * During an eruption move away from a volcano-NOT TOWARD IT! * Most important-DON"T PANIC KEEP CALM. ...read more.

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