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Chapter 6 Volcanoes Table of Contents Chapter Preview 6.1 Volcanoes and Plate Tectonics 6.2 Volcanic Eruptions 6.3 Volcanic Landforms 6.4 California Geology Chapter 6 Volcanoes Chapter Preview Questions 1. Igneous rocks form when a. sediment is compacted and cemented. b. rocks are changed by heat and pressure. c. sediment is heated and cooled. d. lava and magma cool and harden. Chapter 6 Volcanoes Chapter Preview Questions 1. Igneous rocks form when a. sediment is compacted and cemented. b. rocks are changed by heat and pressure. c. sediment is heated and cooled. d. lava and magma cool and harden. Chapter 6 Volcanoes Chapter Preview Questions 2. Melted material that erupts from a volcano is called a. magma. b. sediment. c. lava. d. mica. Chapter 6 Volcanoes Chapter Preview Questions 2. Melted material that erupts from a volcano is called a. magma. b. sediment. c. lava. d. mica. Chapter 6 Volcanoes Chapter Preview Questions 3. Why do volcanoes erupt? a. They are hot and fiery. b. They form beneath the ocean floor. c. Gases in magma expand as it rises to the surface. d. Lava is a pure liquid. Chapter 6 Volcanoes Chapter Preview Questions 3. Why do volcanoes erupt? a. They are hot and fiery. b. They form beneath the ocean floor. c. Gases in magma expand as it rises to the surface. d. Lava is a pure liquid. Chapter 6 Volcanoes Chapter Preview Questions 4. Which of these does NOT rapidly change Earth’s land surface? a. earthquakes b. mountain building c. landslides d. volcanic eruptions Chapter 6 Volcanoes Chapter Preview Questions 4. Which of these does NOT rapidly change Earth’s land surface? a. earthquakes b. mountain building c. landslides d. volcanic eruptions Chapter 6 Volcanoes What causes volcanoes, and how do they change Earth’s surface? You know that if you want to open a bottle of soda, you must do so carefully. Otherwise, the soda might spray out of the bottle as soon as you loosen the cap. What causes the soda to rush out with such force? How is this similar to what happens when a volcano erupts? Explain. Chapter 6 Volcanoes Use Clues to Determine Meaning Unfamiliar words Some volcanoes result from hot spots in Earthís mantle. A hot spot is an area where material from within the mantle rises and then melts. A volcano forms above a hot spot when the hot material erupts through the crust and reaches the surface. A hot spot in the ocean oor can gradually form a series of volcanic mountains. For example, the Hawaiian Islands formed one by one over millions of years as the Pacific plate drifted over a hot spot. Example Hot spot is the subject of the sentence. Definition, follows boldface Explanation Chapter 6 Volcanoes Apply It! Review the clues to the meaning of hot spot. Then complete the following. 1. What clue tells you that hot spot might be followed by a definition? The term is in boldface and is the subject of the sentence. 2. What example helps you understand hot spots? The Hawaiian Islands formed one by one over millions of years as the Pacific plate drifted over a hot spot Chapter 6 Volcanoes End of Chapter Preview Describe what happens along a fault beneath Earth’s surface when an earthquake occurs? How do volcanoes change the land? Volcanoes Chapter 6 Volcanoes Section 1: Volcanoes and Plate Tectonics Where are most of Earth’s volcanoes found? How do hot spot volcanoes form? A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Magma is molten material that has not reached the surface and is still underground. Lava is molten material, or magma, that has reached the surface. Ring of Fire is a major volcanic belt that rims or circles the Pacific Ocean. Island Arc is a string of islands formed by weak spots or hot spots in the crust where magma burns through. Chapter 6 Volcanoes Volcanoes and Plate Boundaries Volcanic belts form along the boundaries of Earth’s plates. Chapter 6 Volcanoes Volcanoes and Plate Boundaries Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate. In both situations, an oceanic plate sinks through a trench. Rock above the plate melts to form magma, which then erupts to the surface as lava. Chapter 6 Volcanoes Hot Spot Volcanoes A volcano forms above a hot spot when magma erupts through the crust and reaches the surface. Chapter 6 Volcanoes More on Volcanoes Click the PHSchool.com button for an activity about volcanoes. Chapter 6 Volcanoes End of Section: Volcanoes and Plate Tectonics What causes volcanoes to form at a spreading boundary? Where are most of Earth’s volcanoes found? Explain. Describe the order of parts through which magma travels as it moves to the surface. Which is more likely to be dangerous – a volcano that erupts frequently or a volcano that has been inactive for a hundred years? Why? Chapter 6 Volcanoes Section 2: Volcanic Eruptions What happens when a volcano erupts? What are the two types of volcanic eruptions? What are a volcano’s stages of activity? Volcanic Eruptions Chapter 6 Volcanoes Magma Reaches Earth’s Surface When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Magma chamber is a pocket beneath a volcano where magma is collected or stored. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Pipe is a long tube inside a volcano that connects the magma chamber to the Earth’s surface. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Vent is an opening through which molten rock and gas leave the volcano. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Lava flow is the area covered by lava as it pours out of a vent. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Crater is a bowlshaped area that may form at the top of a volcano. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Pahoehoe is a very thin, fast moving lava. Pahoehoe contains low amounts of silica, which gives it it’s thinness. When Pahoehoe hardens, it forms wrinkle and ropelike rock formations. Pahoehoe is hotter than Aa. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Aa is a very thick, slow moving lava. Aa contains high amounts of silica, which gives it it’s thickness. When aa hardens, it forms a rough surface consisting of jagged (sharp) lava chunks. Chapter 6 Volcanoes Magma Reaches Earth’s Surface Pyroclastic flow is an explosive eruption that includes hot gases, cinders (volcanic ash), and bombs (volcanic rocks). Chapter 6 Volcanoes Composite Volcano Eruption Activity Click the Active Art button to open a browser window and access Active Art about composite volcano eruption. Chapter 6 Volcanoes Magma Composition Magma varies in composition and is classified according to the amount of silica it contains. The graphs show the average composition of the two types of magma. Use the graphs to answer the questions. Chapter 6 Volcanoes Magma Composition Reading Graphs: Study both graphs. What materials make up both types of magma? Silica, other oxides, and other solids. Chapter 6 Volcanoes Magma Composition Reading Graphs: Which type of magma has more silica? About how much silica does this type of magma contain? Rhyolite-forming magma; about 70 percent. Chapter 6 Volcanoes Magma Composition Estimating: A third type of magma has a silica content that is halfway between that of the other two types. About how much silica does this type of magma contain? About 60 percent Chapter 6 Volcanoes Magma Composition Predicting: What type of magma would have a higher viscosity? Explain. Rhyolite-forming magma would have higher viscosity because it is higher in silica. Chapter 6 Volcanoes Kinds of Volcanic Eruptions Within the last 150 years, major volcanic eruptions have greatly affected the land and people around them. Deadly Eruptions Chapter 6 Volcanoes Stages of Volcanic Activity Active volcanoes are considered “live” meaning that it is erupting, or has shown signs that it may erupt in the near future Mount Shasta Lassen Peak Chapter 6 Volcanoes Stages of Volcanic Activity Dormant volcanoes are considered “asleep” or “sleeping bears” meaning that they may become active in the future Long Valley Craters Chapter 6 Volcanoes Stages of Volcanic Activity Extinct volcanoes are considered “dead” meaning that it is unlikely that they will erupt again St. Lucia Auckland Chapter 6 Volcanoes End of Section: Volcanic Eruptions Chapter 6 Volcanoes Section 3: Volcanic Landforms What landforms do lava and ash create? How does magma that hardens beneath the surface create landforms? Types of Volcanoes Chapter 6 Volcanoes Landforms From Lava and Ash Volcanic eruptions create landforms made of lava, ash, and other materials. These landforms include composite volcanoes, shield volcanoes, cinder cone volcanoes, and lava plateaus. Chapter 6 Volcanoes Landforms From Lava and Ash Composite Volcanoes have quiet eruptions that alternate with explosive eruptions, forming layers of lava and ash. Cotopaxi, Ecuador Mayon, Philippines Chapter 6 Volcanoes Landforms From Lava and Ash Shield Volcanoes have quiet eruptions and have gentle slopes, which are not steep. Mauna Loa, Hawaii Erta Ale, Ethiopia Chapter 6 Volcanoes Landforms From Lava and Ash Cinder Cone Volcanoes have explosive eruptions of ash, cinders, and bombs that form a cone-shaped hill. Mount Etna, Italy SP Crater, Arizona Chapter 6 Volcanoes Landforms From Lava and Ash Lava Plateaus are formed from runny lava (pahoehoe) that cools in flat sheets of rock. Over time these layers form high plateaus. Steamboat Rock, Washington Hawaii Chapter 6 Volcanoes Landforms From Lava and Ash Calderas are formed when a magma chamber is emptied after an eruption and the volcano mountain collapses into the empty space creating a crater. Aniakchak, Alaska Crater Lake, Oregon Chapter 6 Volcanoes Landforms From Lava and Ash A caldera forms when an volcano’s magma chamber empties and the roof of the chamber collapses. The result is a large, bowlshaped caldera. Chapter 6 Volcanoes Landforms From Magma Features formed by magma include volcanic necks, dikes, and sills, as well as batholiths and dome mountains. Chapter 6 Volcanoes Landforms From Magma Batholiths Chapter 6 Volcanoes Landforms From Magma Volcanic Necks Chapter 6 Volcanoes Landforms From Magma Dikes Chapter 6 Volcanoes Landforms From Magma Sills Chapter 6 Volcanoes Batholiths A batholith is a mass of rock formed when a large body of magma cools inside the crust. Several large batholiths form the core of mountain ranges in western North America. Half Dome in Yosemite National Park, California, is part of the Sierra Nevada batholith. Chapter 6 Volcanoes Links on Volcanic Effects Click the SciLinks button for links on volcanic effects. Chapter 6 Volcanoes End of Section: Volcanic Landforms Chapter 6 Volcanoes Section 4: California Geology How does plate tectonics help to explain features of California’s geology? Chapter 6 Volcanoes Plate Tectonics and California The movements of three plates have shaped the geologic features of California over millions of years. Chapter 6 Volcanoes Plate Tectonics and California Many geologic processes worked together to form California’s landscape of volcanoes, faults, mountain ranges, and basins. Chapter 6 Volcanoes End of Section: California Geology Chapter 6 Volcanoes Chapter 6 Volcanoes QuickTake Quiz Click to start quiz.