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Origin and Occurrence of Volcanism in the USA. Volcanism exists all over the
world. From the freezing lands of Alaska to the mountains ...
Submitted by solsburyvalley on May 4, 2006
Category: Science
Words: 1467 | Pages: 6
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Volcanism exists all over the world. From the freezing lands of Alaska to the mountains of South America, volcanism continues to help shape the land in which we live in. Our origins lie in volcanic activity which took place billions of years ago as the Earth was still forming. To this day, it continues in areas where plate tectonics meet in a convergent zone and through subduction, allow magma to reach the surface. In other areas, volcanism occurs after a plate has moved. The United States in noteworthy in that it had significant volcanism in its past that transcends into the present and will continue to do so in its future.
What exactly is volcanism? Volcanism, according to "Physical Geology," is "volcanic activity, including the eruption of lava and rock fragments and gas explosions" (3). The structures most associated with volcanism are volcanoes, which are "a hill or mountain constructed by the extrusion of lava or rock fragments from a vent" (3). In the United States, volcanoes generally fall in one of three regions; the Alaskan Region, the Hawaiian Region and the Pacific-Northwest Region (6). Each region has its own unique characteristics. The theory of plate tectonics states that the Earth's surface is broken down into little patches that continually shift, pass and collide with each other at a very slow rate of only about an inch a year. Volcanoes are created when two plates collide together, and that is called a convergent zone. Since the oceanic crust is thinner than the continental crust, it goes "under" the continental crust and the water seeps up into the holes on surface and helps the magma travel up the surface. Thus, volcanoes are only usually only found near a cost or anywhere two plates meet. Volcanoes in Hawaii are a bit different in that they are formed as the Pacific plate is moving northwest. (2)
Alaskan volcanoes are very plentiful, with over 100 areas exhibiting volcanic behavior (5). "Most of these volcanoes are...
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