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Name Lesson 4 Summary Use with pp. 276–281 Lesson 4: What is erosion? Erosion is the movement of materials away from one place. It is a destructive process. Deposition is the placing of the materials in a new place. Deposition is a constructive process. Erosion and deposition together create valleys, deltas, and sand dunes. Gravity is the main force causing erosion. Gravity pulls rocks and dirt downhill. This is called a landslide. A landslide is one kind of erosion. Gravity also causes rivers to flow. Rivers pick up and carry sediment as they flow downhill. The sediment can erode riverbeds and form deep canyons. Rivers also cause deposition. A river flows much slower when it meets an ocean. This causes the river to deposit heavy sediment like gravel and sand. The sediment create a delta. Glaciers are big bodies of ice that can cause erosion. Gravity pulls glaciers down along a valley. Rocks beneath the glaciers are broken down into sediment. The glacier moves the sediment downhill. This can make the bottom of a valley more U-shaped over time. Waves are a source of erosion and deposition. Waves from storms or tides crash against rocks along the coastline. The rocks break. Sand and gravel in the waves acts like sandpaper. They wear down the rocks even more. This is how some of the sand on beaches is created. Not all parts of a shoreline are eroded at the same rate. Harbors and inlets form when some areas erode more quickly than 72 Chapter 9, Lesson 4 Summary others. A harbor is an area that is protected from ocean waves. Waves can make caves when parts of a cliff erode more quickly than other parts of the cliff. Waves push sand when they hit beaches. A spit is a narrow piece of sandy land. A baymouth bar is like a spit. But it forms across a bay. Barrier islands form along coastlines. Erosion can move barrier islands. The wind can move dust, dirt, or sand from one place to another. This dust and sand can blow against a rock. Tiny bits of the rock might break off and blow away. This is erosion. The wind deposits large, loose amounts of sand to create sand dunes. Wind pushes sand up one side. This sand will move over the edge of the dune’s top. The sand will pile up until gravity pulls it down. This creates a steeper slope than the one that faces the wind. Winds can move a sand dune. The wind will pick up sand from one side of the dune and deposit it on the other side. This causes the dune to slowly move in the direction of the wind. Wind erosion can cause problems on farms. If bare, plowed fields become very dry, the wind can blow the topsoil off the fields. Topsoil is the best kind of soil for growing crops. It cannot be quickly replaced. Farmers try to prevent wind erosion by planting trees along the edges of fields to block some of the wind. © Pearson Education, Inc. 5 Erosion and Deposition Quick Study Name Lesson 4 Checkpoint Use with pp. 276–281 Lesson 4 Checkpoint 1. Suppose sand, gravel, and clay are being carried by a river. As the water enters a lake and slows down, in what order will these sediments settle out of the water? Explain why they settle out in this order. 2. Describe how waves, currents, tides, and storms affect the geological features of the ocean shore (beaches, barrier islands, inlets, and harbors). 3. Define erosion, and tell how gravity works with water, ice, and wind to cause erosion. 4. How does a delta form? © Pearson Education, Inc. 5 5. How do sand dunes form? Why is one side of a dune different than the other side? Quick Study Chapter 9, Lesson 4 Checkpoint 73