EAS 201 - 3 - The Science of Natural Disasters Natural...

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The Science of Natural Disasters Natural Disasters , 7th ed., by Patrick L. Abbott (New York: McGraw-Hill, 2009; ISBN-13: 978-0-07-337669-1). Written Assignment 3 – Due Sunday Short Answer Questions Answer the following questions as completely as possible. Describe the major types of volcanoes, and explain how the type of magma influences their form and behavior. [LO3.2, 3.4] There are 6 types of volcanoes: 1 1. Shield volcanoes – The Largest of all volcanoes (excluding flood basalt flows) built by many layers of runny lava flows. Containing a central vent or group of vents forming a sloping cone. The cone is shaped by the basaltic lava, which can't be piled up into steep mounds. Shield volcanoes may be produced by hot spots, which lay far away from the edges of tectonic plates also occurring along the mid-oceanic ridge along subduction related volcanic arcs (sea floor spread). Eruptions of shield volcanoes are characterized as low-explosivity, lava-fountaining form a cinder cone and spatter cone at the vent. Ninety percent of the volcano is lava rather than pyroclastic material. Famous shield volcanoes include; Mauna Loa and Kilauea in Hawaii. 2. Strata volcanoes (also called composite volcanoes) – Seemingly some of our tallest volcanoes, forming snow-capped peaks exceeding 2500 meters in height, 1000 square kilometers in surface, and 400 km3 in volume 2 . While the strata volcanoes are usually large, they are distinguished by a cone shape, from there they can be pyramidal, convex, concave, helmet shaped, collapsed, or even nested into multiple summits or even elongated like Hekla in Iceland. Sixty percent of the Earth’s volcanoes are strata or composite volcanoes. Usually considered extinct when dormant, then explosive upon eruption. This is because of the gas pressure building due to clogged crater pipes. Once the pressure builds enough the viscous magma is released in an explosion resulting in an eruption of half lava and the other half pyroclastic material (volcanic ash and rock, composed primarily of volcanic materials) . The lavas usually released from Strata volcanoes are andesite, dacite and rhyolite. Strata volcanoes are found along subduction zones. Famous strata & composite volcanoes include; Mount Hood, Mount Rainier, Mount Shasta, Mount Fugi, Mount Mayon, and Vesuvius. 3. Large rhyolite caldera complexes Large bowl shaped craters, formed by 1 http://facstaff.gpc.edu/~pgore/geology/geo101/volc.htm 2 http://www.sciencedaily.com
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large volume eruptions. Geologists consider these violent volcanic eruptions, blowing the tops off of the volcano and are considered the Earth’s most explosive volcano. Often rhyolite caldera complexes remain active over long periods of time with small-scale eruptions during the long reposes between big explosive events. The caldera is best described by its name cauldron, after blowing off its top,
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EAS 201 - 3 - The Science of Natural Disasters Natural...

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