Volcanoes Essay Research Paper VolcanoesA volcano is

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Volcanoes Essay, Research Paper Volcanoes A volcano is a vent in the earth s crust through which magma (molten rock) and gas are released. The magma, once it reaches the surface, is called lava. The lava forms a hill around the vent or opening. The lava can flow out as a viscous liquid, or it may explode from the vent as solid or liquid particles. Types of Volcanoes There are three different types of volcanoes that can be formed around a vent. The ways to identify each type are what it is composed of and what into what shape it is formed. The shield volcano, which takes its name form its resemblance to the shields of early Germanic warriors, is a quietly erupting flow that forms gently slopping mountains. The dome that is formed over a period of time involving multiple one to

ten meter thick lava flows. This type of volcano is found mostly in Hawaii and Iceland. The second type of volcano dome formation is the cinder-cone. This volcano has high gas content and high viscosity (the thickness of the lava), therefore producing a much more explosive eruption than that of the shield volcano. These volcanoes blew volcanic bombs and cinders into the air which land beside the vent to form a step-sided cone. Since these volcanoes consist of loose materials they do not grow as large as other volcanoes. Most cinder-cone volcanoes are formed by a single eruption. The third type of volcano is the composite volcano. It is the tallest of all the different types. It is a combination of shield and cinder-cone volcanoes. It goes through a cycle of quiet eruptions

followed by an explosive eruption of extremely viscous lava. The fluid lava forms an erosion resistant shell over the existing debris forming a strong, deep-sided volcanic cone. A volcano can also be classified by how active it is or has been in the past. Geologist use the terms: active, dormant, and extinct to classify how active it is. If a volcano has erupted within the past fifty years it is referred to as active. A volcano that erupted many years ago but now has no sign of life is called dormant. If scientist feel that a particular volcano will not ever erupt again they term it extinct. Volcanic Structure There are four main parts of a volcano. The vent is the channel that gas, ash and Rock is ejected. Secondly, the magma chamber that hold the magma. Thirdly, the cone is

simply the mountain that is formed around the vent. Finally, the crater is a bowl shaped depression surrounding the vent. There are many unseen forces beneath a volcano that alter rock below the crust to cause a volcano, and completely change the landscape of the earth. A volcano effects the earth in many different ways. Of course, the most obvious is the mountain formed on the surface. One of the most dramatic changes to the geological features of the earth is a caldera. A caldera is a huge bowl-shaped crater in the ground at least 2 miles in diameter. Scientists assume that these massive craters are formed at the end of a volcanoes life once the magma chamber is emptied. This causes the volcano to collapse under its own weight. The second deepest lake in the United States,

Crater Lake, was formed in a caldera. It is approximately six miles across and two thousand feet at the deepest point. An interesting formation underneath a volcano is a lava tunnel. Lava tunnels start out as horizontal lava channels which form when the surface of a large lava flow hardens but the lava beneath remains molten and continues to flow. At the end of the eruption the lava channel is empty and then referred to as a lava tunnel. The tunnels can be anywhere from a few inches to several yards in diameter. The Kasamura tunnel is the largest known lava tunnel. It is near the Kilauea volcano in Hawaii, and it twists for more than six miles beneath the surface. An igneous intrusion is formed when the intense pressure of the rocks above a magma chamber force some of the magma