Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Objectives Distinguish between chemical and physical weathering. Explain how chemical weathering can form underground caves in limestone. Describe the importance of water to chemical weathering. Identify three different physical elements that can cause erosion. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Bellringer 1. What features of a wave allow it to move sand as the wave rolls onto a beach? 2. The Colorado River flows through the Grand Canyon. What do you think made the Grand Canyon? 3. What are some other environmental factors that change the land? 4. How do you think potholes form in a road? Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Physical Weathering There are two types of weathering: physical and chemical. Physical (or mechanical) weathering breaks rocks into smaller pieces, but does not alter their chemical compositions. Chemical weathering breaks down rock by changing its chemical composition. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mechanical Weathering Section 4 Weathering and Erosion Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chemical Weathering Section 4 Weathering and Erosion Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Physical Weathering Ice can break rocks. A common kind of mechanical weathering is called frost wedging. Water seeps into cracks or joints in rock and then freezes. When water freezes it expands, pushing rock apart. Every time the ice thaws and refreezes, it wedges farther into the rock. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Physical Weathering, continued Plants can also break rocks. The roots of plants can also act as wedges as the roots grow into cracks in the rocks. As the plant grows, the roots exert constant pressure on the rock, eventually causing pieces to break off. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Chemical Weathering Some minerals react with oxygen, forming oxides. Carbon dioxide can cause chemical weathering. Carbon dioxide can react with water in the air to form carbonic acid. This weak acid reacts with some minerals. Minerals dissolved by carbonic acid may be washed away, leaving underground pockets, or caves. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Chemical Weathering, continued Water plays a key role in chemical weathering. Some minerals react with water, which changes their physical properties. Some minerals dissolve in water and are carried to new locations. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Chemical Weathering, continued Acid precipitation can slowly dissolve minerals. Sulfur dioxide and nitrogen oxides enter the air as a result of burning fossil fuels. These chemicals can react with water in the air, forming sulfuric acid, nitric acid, or nitrous acid. When this happens, the precipitation that results is acidic. Acid Rain Control Program required power plants to reduce the release of sulfur dioxide, which has reduced the acidity of rain. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Acid Precipitation Section 4 Weathering and Erosion Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Erosion Erosion a process in which the materials of the Earth’s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravity Deposition the process in which material such as sediment is laid down, or deposited as a result of erosion Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Erosion, continued Water erosion shapes Earth’s surface. Water is the most effective physical weathering agent. Rivers carry sediment to the ocean, and create canyons and riverbeds. The faster the water flows, the larger the sediment it can carry. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Erosion, continued Oceans also shape Earth. Waves crash onto shores, shaping the land. Ocean waves can create tall cliffs and jagged coastlines. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Erosion, continued Glaciers erode mountains. Large masses of ice can exert tremendous forces on rocks. Glaciers can carve U-shaped valleys in mountains. Moving glaciers grind rocks below them into fine powder. Glacial meltwater streams carry the sediment away from the glacier. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Erosion, continued Wind can also shape the landscape. Fast moving wind can carry fine sediment. Sediment carried by wind can smooth Earth’s surface and erode the landscape. Wind erosion can play a part in forming sandstone arches Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Weathering and Erosion Erosion, continued One theory to explain the formation of arches is shown below. Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Erosion Section 4 Weathering and Erosion Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Concept Mapping Section 4 Weathering and Erosion Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts 1. Which of these occurs where two tectonic plates move away from each other? A.convergent boundary B.divergent boundary C.ocean trench D.subduction zone Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 1. Which of these occurs where two tectonic plates move away from each other? A.convergent boundary B.divergent boundary C.ocean trench D.subduction zone Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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 Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 4. Which of the following is an example of chemical weathering of rock? F.deposition G.erosion H.frost wedging I.leaching Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 4. Which of the following is an example of chemical weathering of rock? F.deposition G.erosion H.frost wedging I.leaching Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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? Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter Why do most scientists now accept the idea of moving continents, even though earlier scientists did not?
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Reading Skills, continued 6. [See previous slide for question.] Answer: New observations provided evidence that was not available in These observations explain how continents can move and support the theory. Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 7. What type of volcano is illustrated here? A. cinder cone B. composite C. seamount D. shield Standardized Test Prep Chapter 21
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics, continued 7. What type of volcano is illustrated here? A. cinder cone B. composite C. seamount D. shield Standardized Test Prep Chapter 21