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Chapter 21 Section 2 Earthquakes and Volcanoes Objectives • Identify the causes of earthquakes. • Distinguish between primary, secondary, and surface waves in earthquakes. • Describe how earthquakes are measured and rated. • Explain how and where volcanoes occur. • Describe the different types of common volcanoes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Bellringer 1. Imagine a corked bottle of soda pop that is standing in a pan of hot water. What do you think will happen as the soda pop heats up? 2. What happens when the pressure builds up in the soda pop? 3. Molten rock in Earth’s mantle is like the soda pop. What happens when pressure builds up in Earth’s mantle? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes What are Earthquakes? • Earthquakes occur at plate boundaries. • Earthquakes are vibrations resulting from rocks sliding past each other at a fault • Seismic waves are waves of energy released during in earthquake • Focus the area along a fault at which the first motion of an earthquake occurs • Epicenter the point on Earth’s surface directly above an earthquake’s focus Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes What are Earthquakes? continued • Energy from earthquakes is transferred by waves. • Earthquakes generate three types of waves: • Longitudinal waves • Transverse waves • Surface waves • Longitudinal waves travel by compressing and stretching crust, also called primary waves (P waves) • Transverse waves travel in an up and downward movement, also called secondary waves (S waves) • Surface waves seismic waves that can move only through solids, move in a rolling circular motion Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Longitudinal Waves Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Transverse Wave Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Seismic Waves: Surface Waves Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes What are Earthquakes? continued • Waves move through Earth and along its surface. • Both P waves and S waves spread out from the focus in all directions through the earth. • Surface waves move only on Earth’s surface. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes • Seismologists detect and measure earthquakes. • Seismology the study of earthquakes including their origin, propagation, energy, and prediction • Seismologists use sensitive equipment called seismographs to record data about earthquakes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Seismographs and Mapping Earth’s Layers Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • Three seismograph stations are necessary to locate the epicenter of an earthquake. • There are more than 1000 seismograph stations across the world. • Because P waves travel faster, the difference between the arrival of P waves and the arrival of S waves allows scientists to calculate how far away the focus is. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • Geologists use seismographs to investigate Earth’s interior. • The way P and S waves travel through Earth’s interior help scientists make a model of Earth with layers of different densities. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • The Richter scale is a measure of the magnitude of earthquakes. • Richter scale a scale that expresses the magnitude of an earthquake • The intensity of an earthquake is measured by the modified Mercalli scale. Intensity depends on many factors. • Earthquakes that occur deeper below the Earth’s surface will not be as intense at the surface. • The hardness of the rock above and around an earthquake affects the intensity. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Richter Scale Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Measuring Earthquakes, continued • Scientists are trying to predict earthquakes. • Scientists are trying to measure changes in Earth’s crust that might signal an earthquake. • The ability to predict an earthquake could save thousands of lives in the future. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes • A volcano is any opening in Earth’s crust through which magma has reached Earth’s surface. • Vent an opening at the surface of Earth through which volcanic material passes • Volcanoes generally have one central vent, but they can also have several smaller vents. • Magma that reaches Earth’s surface is called lava. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Shield volcanoes have mild eruptions. • Lava from shield volcanoes is very fluid and forms a gently sloping mountain. • Shield volcanoes are some of the largest volcanoes. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Composite volcanoes have trapped gas. • Composite volcanoes are made up of alternating layers of ash, cinders, and lava. • The lave is thicker than that of shield volcanoes. • Gases are trapped in the magma, causing eruptions that alternate between flows and explosive activity that produces cinders and ash. • Composite volcanoes are typically tall with steep sides. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Cinder cones are the most abundant volcano. • Cinder cones are the smallest and most common volcanoes. • Large amounts of gas are trapped in the magma, and violent eruptions of hot ash and lava occur. • Cinder cones tend to be active for only a short time and then become dormant. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Types of Volcanoes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Most volcanoes occur at convergent plate boundaries. • 75% of the active volcanoes on Earth are located in an area known as the Ring of Fire. • The Ring of Fire is located along the edges of the Pacific ocean, where oceanic tectonic plates are colliding with continental plates. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Ring of Fire Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Underwater volcanoes occur at divergent plate boundaries. • As plates move apart at divergent boundaries, magma rises to fill the gap. • This magma creates the volcanic mountains that form ocean ridges. • Iceland is a volcanic island on the Mid-Atlantic ridge that is growing outward in opposite directions. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Volcanoes, continued • Volcanoes occur at hot spots. • Some volcanoes occur in the middle of plates. • Mantle plumes are mushroom shaped trails of hot rock that rise from deep inside the mantle, melt as they rise, and erupt from volcanoes at hot spots at the surface. • The plumes remain in the same place as the tectonic plate moves, creating a trail of volcanoes. • The Hawaiian Islands are an example of this type of volcanic activity. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Section 2 Earthquakes and Volcanoes Hot Spots and Mantle Plumes Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts 1. Which of these occurs where two tectonic plates move away from each other? A. B. C. D. convergent boundary divergent boundary ocean trench subduction zone Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 1. Which of these occurs where two tectonic plates move away from each other? A. B. C. D. convergent boundary divergent boundary ocean trench subduction zone Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 2. What causes earthquakes along the San Andreas fault in California? F. subduction of the Pacific plate by the North American plate G. collision between the Pacific plate and the North American plate H. divergent movement of the Pacific plate and the North American plate I. horizontal movement along the boundary of the Pacific plate and the North American plate Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 2. What causes earthquakes along the San Andreas fault in California? F. subduction of the Pacific plate by the North American plate G. collision between the Pacific plate and the North American plate H. divergent movement of the Pacific plate and the North American plate I. horizontal movement along the boundary of the Pacific plate and the North American plate Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 3. How can the absolute age of a layer of rock be determined? A. by the principle of superposition B. by the ratio of radioisotopes C. by the amount of weathering that has shaped the rock D. by analysis of the types of minerals that make up the rock Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 3. How can the absolute age of a layer of rock be determined? A. by the principle of superposition B. by the ratio of radioisotopes C. by the amount of weathering that has shaped the rock D. by analysis of the types of minerals that make up the rock Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 4. Which of the following is an example of chemical weathering of rock? F. G. H. I. deposition erosion frost wedging leaching Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 4. Which of the following is an example of chemical weathering of rock? F. G. H. I. deposition erosion frost wedging leaching Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 5. Both S waves and P waves travel from the site of an earthquake. How does the difference in the way these waves travel reveal information about the structure of Earth’s interior? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Understanding Concepts, continued 5. Both S waves and P waves travel from the site of an earthquake. How does the difference in the way these waves travel reveal information about the structure of Earth’s interior? Answer: S waves cannot pass through liquid. The fact that P waves can be detected on the opposite side of the planet, and S waves cannot, indicates a liquid core. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Reading Skills In 1912 Alfred Wegener first proposed the theory that all of the continents formed when one giant continent broke apart. Wegener used the shape of the continents, the distribution of fossils, and similarity of rocks at different parts of the world as evidence. Wegener’s Continental Drift theory was not immediately accepted by scientists. Some wondered about, but could not find, forces that would be strong enough to move such large masses of solid rock over great distances. In the middle of the 20th century, evidence from ocean floor exploration provided new evidence that continents move. The theory of plate tectonics, which explains how land masses move, not across the ocean floor, but across the Earth’s mantle, is now widely accepted. 6. Why do most scientists now accept the idea of moving continents, even though earlier scientists did not? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Reading Skills, continued 6. [See previous slide for question.] Answer: New observations provided evidence that was not available in 1912. These observations explain how continents can move and support the theory. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Interpreting Graphics 7. What type of volcano is illustrated here? A. cinder cone B. composite C. seamount D. shield Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 21 Standardized Test Prep Interpreting Graphics, continued 7. What type of volcano is illustrated here? A. cinder cone B. composite C. seamount D. shield Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.