Volcanoes: Volcano and Eruptions Explosive Eruptions
A Look Into Volcanoes
By: BJ
E-mail: Bran18@aol.com
I. Introduction Volcano: defined is a mountain or hill formed by the accumulation of materials erupted through one or more openings (called volcanic vents) in the earth 's surface. The term volcano can also refer to the vents themselves. 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. According to the Smithsonian Institution, 1511 above-sea volcanoes have been active during the past 10,000 years, 539 of them erupting one or more times during written history. On average, 50 to 60 above-sea volcanoes worldwide are active in any given year; about half of these are continuations of eruptions from previous years, and the rest are new. Mount St. Helen Volcanic eruptions in populated regions are a significant threat to people, property, and agriculture. The danger is mostly from fast-moving, hot flows of explosively erupted materials, falling ash, and highly destructive lava flows and volcanic debris flows. In addition, explosive eruptions, even from volcanoes in unpopulated regions, can eject ash high into the atmosphere, creating drifting volcanic ash clouds that pose a serious hazard to airplanes. II. Volcano Formation All volcanoes are formed by the accumulation of magma which is molten rock that forms below the earth 's surface. Magma can erupt through one or more volcanic vents, which can be a single opening, a cluster of openings, or a long crack, called a fissure vent. It forms deep within the earth, generally within the upper part of the mantle which is one of the layers of the earth 's crust, or less commonly, within the base of the earth 's crust. High temperatures and pressures are needed to form magma. The solid mantle or
By: BJ
E-mail: Bran18@aol.com
I. Introduction Volcano: defined is a mountain or hill formed by the accumulation of materials erupted through one or more openings (called volcanic vents) in the earth 's surface. The term volcano can also refer to the vents themselves. 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. According to the Smithsonian Institution, 1511 above-sea volcanoes have been active during the past 10,000 years, 539 of them erupting one or more times during written history. On average, 50 to 60 above-sea volcanoes worldwide are active in any given year; about half of these are continuations of eruptions from previous years, and the rest are new. Mount St. Helen Volcanic eruptions in populated regions are a significant threat to people, property, and agriculture. The danger is mostly from fast-moving, hot flows of explosively erupted materials, falling ash, and highly destructive lava flows and volcanic debris flows. In addition, explosive eruptions, even from volcanoes in unpopulated regions, can eject ash high into the atmosphere, creating drifting volcanic ash clouds that pose a serious hazard to airplanes. II. Volcano Formation All volcanoes are formed by the accumulation of magma which is molten rock that forms below the earth 's surface. Magma can erupt through one or more volcanic vents, which can be a single opening, a cluster of openings, or a long crack, called a fissure vent. It forms deep within the earth, generally within the upper part of the mantle which is one of the layers of the earth 's crust, or less commonly, within the base of the earth 's crust. High temperatures and pressures are needed to form magma. The solid mantle or
Bibliography: 1999 Microsoft Encarta; Volcanoes 1980 USGS; www.vulcan.wr.usgs.gov 2000 Volcano World; http://volcano.und.nodak.edu/vwdocs/frequent-questions/grp13/question1544.html 1980-2000 USGS; www.vulcan.wr.usgs.gov/photo/volcanoes/MSH/framework.html 1993-2000 Microsoft Corporation; various volcano media 2000 FEMA; www.fema.gov/library/volcanof.htm Word Count: 2186