Lecture_13_Volcanoes

Lecture_13_Volcanoes - Lecture 14 Chapter 6 Sept 28 2011 Volcano Geology and Hazards You will learn What volcanoes are where they occur and why

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9/30/2011 1 Lecture 14, Chapter 6 Sept. 28, 2011 Volcano Geology and Hazards You will learn What volcanoes are, where they occur, and why they form The different types of volcanoes and the hazards associated with each type How scientists study volcanoes and come to understand and predict their eruptions How people can lower the risks posed by volcanoes Figure 6-2 Over the Volcano If you fly over the Pacific rim, you will probably find yourself looking down on volcanoes. This erupting volcano, in the Aleutian Islands of Alaska, is on the main flight path between Asia and North America. Over the Volcano
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9/30/2011 2 What Volcanoes Are Magma: (molten rock underground) rises from great depths to the upper level of the crust and erupts (as lava) onto the surface. hot and less dense (more buoyant) than surrounding solid rock quickly cools and solidifies on the surface or at relatively shallow depths in the crust magma contains dissolved gases (e.g. H 2 O vapor, CO 2 , SO 2 ) As magma rises: confining pressure of the overlying rocks decreases dissolved gases bubble out of solution and release the pressure the more dissolved gas, the more explosive the magma Figure 6-3 Volcanoes Are Rock Factories Magma quickly cools and solidifies into igneous rock. The surface of this lava flow in Hawaii is changing to a gray color as it solidifies. Lava Flow How many volcanoes have been active in the last 10,000 years? • 1300–1500 volcanoes on land with probable eruptions • only about 550 volcanic eruptions eyewitness accounts • 50–70 volcanoes erupt on land in an average year • many more volcanic eruptions occur in the deep oceans Numbers of Volcanic Eruptions
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9/30/2011 3 Figure 6-4 Many people do not realize that even in the continental United States there are several potentially active volcanoes dangerously close to large population centers. Potentially Active Volcanoes of the Western U.S. • Eruptions range from spectacular explosions to oozing red-hot lava flows. • This difference reflects the fact that not all magmas are the same. • different temperatures • compositions • dissolved-gas contents Types of Magmas Viscosity = resistance to flow , depends on temperature, composition • Composition (e.g, SiO 2 content) has greatest influence on magma viscosity • high SiO 2 = more viscous • magmas with high SiO 2 solidify at lower temperatures • their viscosity increases even more Types of Magmas (cont.)
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9/30/2011 4 Gas Content in Lavas H 2 O most abundant gas dissolved in magma, along with CO 2 , SO 2 , and others lowers viscosity (by reducing the tendency of SiO 4 ions to combine) Gases may separate from magma during ascent due to: the magma may partially crystallize (and thus hold less liquid) temperature may go down being trapped, accumulating in more viscous magmas decrease in the confining pressure gas (vapor) pressure increases Explosive eruptions! • Kilauea is the currently
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This note was uploaded on 10/12/2011 for the course GEOL 1014 taught by Professor Aufill during the Spring '08 term at Oklahoma State.

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Lecture_13_Volcanoes - Lecture 14 Chapter 6 Sept 28 2011 Volcano Geology and Hazards You will learn What volcanoes are where they occur and why

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