Essay on Volcanoes

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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…show more content…
The larger the rising blob of magma, the easier it moves. Rising magma does not reach the surface in a steady manner but tends to accumulate in one or more underground storage regions, called magma reservoirs, before it erupts onto the surface. With each eruption, whether explosive or nonexplosive, the material erupted adds another layer to the growing volcano. After many eruptions, the volcanic materials pile up around the vent or vents. These piles form a topographic feature, such as a hill, mountain, plateau, or crater, that we recognize as a volcano. Most of the earth's volcanoes are formed beneath the oceans, and their locations have been documented in recent decades by mapping of the ocean floor III. Volcanic Materials Three different types of materials may erupt from an active volcano. These materials are lava, tephra which are rock fragments, and gases. The type and amount of the material that erupts from an active volcano depends on the composition of the magma inside the volcano. A. Lava Lava is magma that breaks the surface and erupts from a volcano. If the magma is very fluid, it flows rapidly down the volcano's slopes. Lava that is more sticky and less fluid moves slower. Lava flows that have a continuous, smooth, ropy, or billowy surface are called pahoehoe (pronounced pah HOH ee hoh ee) flows, while aa (pronounced ah ah) flows have a jagged surface composed of loose, irregularly shaped lava chunks. Once cooled, pahoehoe forms smooth rocks, while

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