Volcanoes Essay -- essays research papers fc

A Look Into Volcanoes 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 peo ple, 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 crustal rock must be melted under conditions typically reached at dep ths of 50 to 60 mi. (80 to 100 km) below the earth's surface. Once tiny droplets of magma are formed, they begin to rise because the magma is less dense than the solid rock surrounding it. The processes that cause the magma to rise are poorly understood, but it generally moves upward toward lower pressure regions, squeezing into spaces between minerals within the soli... ...the first blobs of melt. As melting continues other minerals start to melt as well, and the chemistry of the magma changes. From studies like this geologists have determined that the early stages of a Hawaiian volcano's life is generated by magmas derived from only small degrees of partial melting (such as only 5% of the source melting and the rest staying behind). On the other hand, when the volcano really gets going (such as at Kilauea and Mauna Loa), the percentage of source rock that melts to produce the magma is perhaps as high as 20%. There are many other ways in which chemistry is used in volcanology, including the studies of volcanic gases, crater lakes, and trying to determine the temperatures that lava had at the time they were erupted even long after the eruption has ended. Bibliography 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