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Chapter 2: Landforms of Georgia Lesson 2: What Causes Changes To Landforms? S5E1a: Student will identify features caused by constructive processes. S5E1b: Student will identify and find examples of surface features caused by destructive processes. Vocabulary Preview Weathering: the process of wearing away rocks by natural means Erosion: the process of moving sediment by wind, moving water, or ice Delta: an area of new land at the mouth of a river, formed from sediments carried by the river Sinkhole: a large hole formed when the roof of a cave collapses Changes Caused By Wind Imagine yourself standing on a beach with your face to the wind. Sand hits your face so hard that is begins to sting. Now imagine this blowing sand hitting a rock. Over time, the sand wears away the rock by breaking it into smaller pieces. The process of wearing away rocks by natural means is known as weathering. Changes Caused By Wind The weathered pieces of rock, some as large as sand grains, are carried away by the wind. The pieces keep moving as long as the wind is blowing. But when the wind slows down, the large pieces fall to the ground. Over a long time, the wind leaves small piles of sand in an area. These piles grow as more sand is blown into the pile. Slowly, they become sand dunes. A mushroom rock like all of these, have this shape because the wind blew sand around the bottom of the rock, wearing it away. Changes Caused By Wind Sand dunes are found in many places such as in deserts, at beaches, and on lakeshores. Some deserts dunes are as high as a 30story building! Many beaches along the Atlantic Coast have long lines of dunes. These dunes help protect the land during storms. But they can also damage nearby building and roads as the move inland, pushed by winds from the ocean. Changes Caused by Moving Water Suppose your hands are dirty after working in the garden Rinsing your hands removes most of the soil. The water flows over your hands, picks up the soil, and carries it away. In a similar way, moving water can change Earth’s surface by carrying soil and small pieces of rock away from landforms. Changes Caused by Moving Water The process of moving sediment by wind, water, or ice is called erosion. Water is an important cause of change for Earth’s landforms. Moving water can dig a mile-deep canyon or change the path of a river. Ex: A rapidly flowing river erodes its banks and its bottom. Eroding the banks makes the river wider and eroding the bottom makes the river deeper. These canyons are examples of changes made by moving water. For millions of years, the river has been wearing away rocks and carrying sediment downstream. The river has carved deeper and deeper into the landforms. Changes Caused by Moving Water The moving water then carries sediment downstream. When the flow of water slows down, sediment is deposited. Deposits on a river’s banks make it narrower. Deposits on the bottom make the river shallower. Erosion and Deposition Moving wind or water has energy, which enable it to move sediment. The faster the wind or water moves, the more energy it has. Fast water, with a lot of energy, can erode a lot of sediment. Slow water, with litter energy, can erode only a small amount of sediment. But all moving water, even a gentle rain, can erode some sediment. Crashing waves can change the face of a cliff. Erosion and Deposition Rain doesn’t seem very powerful, but it can still cause erosion. When rain falls on a bare hill or mountain, it splashes away soil. As it runs downhill, the water increases its speed and gains energy. The moving water carries away sediment. Over time, water erosion may leave gullies, or ditches in the ground. Erosion and Deposition Ocean waves also cause erosion. Constant wave action can cause changing sloping shorelines into cliffs. Waves crashing against the shore carry away broken bits of rock. Piece by piece, the cliffs get steeper. In many places, there is so much erosion that the top of a cliff overhangs the bottom. When this happens, the entire cliff can collapse into the ocean. Then waves begin eroding the collapsed rock and form new cliffs. Erosion and Deposition Ocean waves change landforms in another way, too. If you stand on a beach and watch the waves, you see that each wave brings more sand onto the beach. The process by which sediment is carried in water as long as the water flows fast. Fast-flowing water has a lot of energy. When water slows down, it loses energy. Larger pieces of sediment drop out of the water first and settle to the bottom. Floods deposit nutrient-rich soil on the flood plain. When the Mississippi River enters the Gulf of Mexico, the water slows down. Sediment is deposited, and the delta grows. Erosion and Deposition As the water slows down more, smaller and smaller particles sink to the bottom. A river often deposits sediment at its mouth, the place where it empties into the ocean. The flow of water slows as a river reaches the ocean. As a result, much of the sediment the river carries is deposited, forming a delta. A delta is an area of new land at the mouth of a river. Delta Pictures: A area of new land formed at the mouth of a river. Erosion and Deposition Flooding can deposit sediment near a river. During heavy rains, a flooding river sends water over its banks. When the rains end, the water slowly returns to the river, but the sediment it carried is deposited on the land. This sediment is rich in nutrients that plants need. As a result, flood plains, as these areas are called, are usually good for farming. Sinkholes and Landslides Water can change not only landforms on Earth’s surface but also features underground. Ex: Groundwater can weather and erode soft rocks. Underground erosion causes caves to form. Often the roof of a cave collapses due to the weight of material above it. If the cave is near the surface, a large hole, called a sinkhole, may suddenly open. Most sinkholes are found where limestone is common, such as Florida. Sinkholes Sinkholes and Landslides Water isn’t the only factor that cause erosion and deposition. Gravity can also cause these landchanging process to happen. Gravity can make soil, mud, and rocks move quickly down a slope. This form of erosion is called a landslide. Landslides can happen suddenly, especially after heavy rains or earthquakes. Landslides Plants Plants can also cause weathering and The growth of plant erosion. roots can weather rock. When a seed germinates on a rocky slope, it sends roots into tiny cracks or holes in the rock. The roots grow and may eventually become large enough to break the rock into smaller pieces. Plants Plants don’t just weather rock. They also preserve and protect Earth’s landforms. Plant roots hold soil and sand into place. This helps prevent erosion by wind and water. Providence Canyon formed when plants were removed and runoff from nearby farms eroded the land. Plants Farmers often plant clover or other cover crops in fields they are using to grow food crops. Cover crops help return nutrients to the soil and help prevent erosion. In some areas, farmers plant rows of trees to slow wind erosion of nearby fields. This protection works naturally as well. Cover Crops Plants Along many beaches, plants grow on dunes. The roots of these plants help hold the sand in place when the wind blows. That’s why people should always use beach crossovers instead of walking across sand dunes and damaging the plants.