3 Erosion and Deposition by Ice

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CHAPTER 12 3 Erosion and Deposition by Ice SECTION Agents of Erosion and Deposition BEFORE YOU READ After you read this section, you should be able to answer these questions: What are glaciers?

1 CHAPTER 12 3 Erosion and Deposition by Ice SECTION Agents of Erosion and Deposition BEFORE YOU READ After you read this section, you should be able to answer these questions: What are glaciers? How do glaciers affect the landscape? National Science Education Standards ES 1c, 2a What Are Glaciers? A glacier is a huge piece of moving ice. The ice in glaciers contains most of the fresh water on Earth. Glaciers are found on every continent except Australia. There are two kinds of glaciers: continental and alpine. Continental glaciers are ice sheets that can spread across entire continents. Alpine glaciers are found on the tops of mountains. Both continental and alpine glaciers can greatly affect the landscape. Glaciers form in areas that are so cold that snow stays on the ground all year round. For example, glaciers are common in polar areas and on top of high mountains. In these areas, layers of snow build up year after year. Over time, the weight of the top layers pushes down on the lower layers. The lower layers change from snow to ice. STUDY TIP Compare As you read, make a table comparing the landforms that glaciers can produce. 1. Identify What are the two kinds of glaciers? HOW GLACIERS MOVE Glaciers can move in two ways: by sliding and by flowing. As more ice builds up on a slope, the glacier becomes heavier. The glacier can start to slide downhill, the way a skier slides downhill. Glaciers can also move by flowing. The solid ice in glaciers can move slowly, like soft putty or chewing gum. Thick glaciers move faster than thin glaciers. Glaciers on steep slopes move faster than those on gentler slopes. TAKE A LOOK 2. Define What is a glacier? This is McBride Glacier in Alaska. Interactive Textbook 221 Agents of Erosion and Deposition

SECTION 3 Erosion and Deposition by Ice continued Critical Thinking 3. Identify Relationships How is erosion by glaciers an example of water shaping the landscape?

2 SECTION 3 Erosion and Deposition by Ice continued Critical Thinking 3. Identify Relationships How is erosion by glaciers an example of water shaping the landscape? How Do Glaciers Affect the Landscape? Glaciers can produce many different features as they move over Earth s surface. As a glacier moves, it can pick up and carry the rocks in its path. Glaciers can carry rocks of many different sizes, from dust all the way up to boulders. These rocks can scrape grooves into the land below the glacier as the glacier moves. Continental glaciers tend to flatten the land that they pass over. However, alpine glaciers can produce sharp, rugged landscapes. The figure below shows some of the features that alpine glaciers can form. Horns are sharp, pyramid-shaped peaks that form when three or more cirque glaciers erode a mountain. Cirques are bowl-shaped depressions where glacial ice cuts back into the mountain walls. Arêtes are jagged ridges that form between two or more cirques that cut into the same mountain. TAKE A LOOK 4. Explain How are horns, cirques, and arêtes related? Hanging valleys are smaller glacial valleys that join the deeper main valley. Many hanging valleys form waterfalls after the ice is gone. U-shaped valleys form when a glacier erodes a river valley. The valley changes from its original V shape to a U shape. GLACIAL DEPOSITS As a glacier melts, it drops all of the material that it is carrying. The material that is carried and deposited by glaciers is called glacial drift. There are two kinds of glacial drift: till and stratified drift. Interactive Textbook 222 Agents of Erosion and Deposition

3 SECTION 3 Erosion and Deposition by Ice continued TILL DEPOSITS Till is unsorted rock material that is deposited by melting glacial ice. It is called unsorted because the rocks are of all different sizes. Till contains fine sediment as well as large boulders. When the ice melts, it deposits this material onto the ground. The most common till deposits are moraines. Moraines form ridges along the edges of glaciers. There are many types of moraines. They are shown in the figure below. 5. Explain Why is till considered unsorted? Lateral moraines form along each side of a glacier. Medial moraines form when valley glaciers that have lateral moraines meet. Ground moraines form from unsorted materials left beneath a glacier. Terminal moraines form when sediment is dropped at the front of the glacier. STRATIFIED DRIFT When a glacier melts, the water forms streams that carry rock material away from the glacier. The streams deposit the rocks in different places depending on their size. Larger rocks are deposited closer to the glacier. The rocks form a sorted deposit called stratified drift. The large area where the stratified drift is deposited is called an outwash plain. In some cases, a block of ice is left in the outwash plain as the glacier melts. As the ice melts, sediment builds up around it. The sediment forms a bowl-shaped feature called a kettle. Kettles can fill with water and become ponds or lakes. Say It Learn New Words Look up the words lateral, medial, and terminal in a dictionary. In a group, talk about why these words are used to describe different kinds of moraines. 6. Define Write your own definition for stratified drift. Interactive Textbook 223 Agents of Erosion and Deposition

4 Section 3 Review NSES ES 1c, 2a SECTION VOCABULARY glacial drift the rock material carried and deposited by glaciers glacier a large mass of moving ice stratified drift a glacial deposit that has been sorted and layered by the action of streams or meltwater till unsorted rock material that is deposited directly by a melting glacier 1. List Give two kinds of glacial drift. 2. Identify What are four kinds of moraines? 3. Compare How are continental glaciers different from alpine glaciers? 4. Explain How do glaciers form? 5. Describe How does a kettle form? 6. Infer How can a glacier deposit both unsorted and sorted material? Interactive Textbook 224 Agents of Erosion and Deposition

CHAPTER 12 4 The Effect of Gravity on Erosion and Deposition SECTION Agents of Erosion and Deposition BEFORE YOU READ After you read this section, you should be able to answer these questions: What

5 CHAPTER 12 4 The Effect of Gravity on Erosion and Deposition SECTION Agents of Erosion and Deposition BEFORE YOU READ After you read this section, you should be able to answer these questions: What is mass movement? How does mass movement shape Earth s surface? How can mass movement affect living things? National Science Education Standards ES 1c, 2a What Is Mass Movement? Gravity can cause erosion and deposition. Gravity makes water and ice move. It also causes rock, soil, snow, or other material to move downhill in a process called mass movement. ANGLE OF REPOSE Particles in a steep sand pile move downhill. They stop when the slope of the pile becomes stable. The angle of repose is the steepest angle, or slope, at which the loose material no longer moves downhill. If the slope of a pile of material is larger than the angle of repose, mass movement happens. The slope of this pile of sand is equal to the sand s angle of repose. The sand pile is stable. The sand particles are not moving. 35 STUDY TIP Ask Questions As you read this section, write down any questions you have. Talk about your questions in a small group. 1. Define What is the angle of repose? The slope of this pile of sand is larger than the angle of repose. Therefore, particles of sand move down the slope of the pile. 60 TAKE A LOOK 2. Explain Why are sand particles moving downhill in the bottom picture? The angle of repose can be different in different situations. The composition, size, weight, and shape of the particles in a material affect its angle of repose. The amount of water in a material can also change the material s angle of repose. Interactive Textbook 225 Agents of Erosion and Deposition

6 SECTION 4 The Effect of Gravity on Erosion and Deposition continued What Are the Kinds of Mass Movement? Mass movement can happen suddenly and quickly. Rapid mass movement can be very dangerous. It can destroy or bury everything in its path. 3. Describe How can landslides affect wildlife habitats? 4. Identify Give three factors that can make landslides more likely. LANDSLIDES A landslide happens when a large amount of rock and soil moves suddenly and rapidly downhill. Landslides can carry away or bury plants and animals and destroy their habitats. Several factors can make landslides more likely. Heavy rains can make soil wet and heavy, which makes the soil more likely to move downhill. Tree roots help to keep land from moving. Therefore, deforestation, or cutting down trees, can make landslides more likely. Earthquakes can cause rock and soil to start moving. People may build houses and other buildings on unstable hillsides. The extra weight of the buildings can cause a landslide. The most common kind of landslide is a slump. Slumps happen when a block of material moves downhill along a curved surface. ROCK FALLS A rock fall happens when loose rocks fall down a steep slope. Many such slopes are found on the sides of roads that run through mountains. Gravity can cause the loose and broken rocks above the road to fall. The rocks in a rock fall may be many different sizes. Critical Thinking 5. Infer Does water probably increase or decrease the angle of repose of soil? Explain your answer. MUDFLOWS A mudflow is a rapid movement of a large amount of mud. Mudflows can happen when a lot of water mixes with soil and rock. The water makes the slippery mud flow downhill very quickly. A mudflow can carry away cars, trees, houses, and other objects that are in its path. Mudflows are common in mountain regions when a long dry season is followed by heavy rain. Mudflows may also happen when trees and other plants are cut down. Without plant roots to hold soil in place and help water drain away, large amounts of mud can quickly form. Interactive Textbook 226 Agents of Erosion and Deposition

7 SECTION 4 The Effect of Gravity on Erosion and Deposition continued LAHARS Volcanic eruptions can produce dangerous mudflows called lahars. A volcanic eruption on a snowy peak can suddenly melt a great amount of snow and ice. The water mixes with soil and ash to produce a hot flow that rushes downhill. Lahars can travel faster than 80 km/h. CREEP Not all mass movement is fast. In fact, very slow mass movement is happening on almost all slopes. Creep is the name given to this very slow movement of material downhill. Even though creep happens very slowly, it can move large amounts of material over a long period of time. Many factors can affect creep. Water can loosen soil and rock so that they move more easily. Plant roots can cause rocks to crack and can push soil particles apart. Burrowing animals, such as moles and gophers, can loosen rock and soil particles. All of these factors may make creep more likely. 6. Compare How is creep different from the other kinds of mass movement that are discussed in this section? Type of Mass Movement Landslide Description Material moves suddenly and rapidly down a slope. Rock fall Mudflow Water mixes with volcanic ash to produce a fast-moving, dangerous mudflow. Material moves downhill very slowly. TAKE A LOOK 7. Describe Fill in the blank spaces in the table. Interactive Textbook 227 Agents of Erosion and Deposition

8 Section 4 Review NSES ES 1c, 2a SECTION VOCABULARY creep the slow downhill movement of weathered rock material landslide the sudden movement of rock and soil down a slope mass movement the movement of a large mass of sediment or a section of land down a slope mudflow the flow of a mass of mud or rock and soil mixed with a large amount of water rock fall the rapid mass movement of rock down a steep slope or cliff 1. List What are four kinds of mass movement? 2. Infer Why is it important for people to think about mass movement when they decide how to use land? 3. Identify Relationships How is mass movement related to the angle of repose? 4. Identify What force causes mass movements? 5. Compare How are landslides different from mudflows? 6. List Give four things that can affect a material s angle of repose. Interactive Textbook 228 Agents of Erosion and Deposition

Mass Movements, Wind, and Glaciers

Mass Movements, Wind, and Glaciers Mass Movements,, and Glaciers SECTION 8.1 Mass Movement at Earth s Surface In your textbook, read about mass movement. Use each of the terms below just once to complete the passage. avalanche creep landslide