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Learn how physical and chemical weathering break down rocks and how erosion shapes the Earth's surface. Discover the forces of nature and human activities that contribute to these processes.
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Physical Weathering • How does physical weathering affect rocks? • Physical, or mechanical, weathering breaks rocks into smaller pieces but does not alter their chemical composition. • Abrasion caused by particles suspended in wind or water is an example of physical weathering.
Physical Weathering, continued • 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.
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.
Chemical Weathering • How are rocks affected by chemical weathering? • Chemical weathering can cause rocks to weaken, decompose, or dissolve, and it can affect the chemical composition of rock. • Chemical weathering occurs when a rock is broken down due to chemical reactions with the environment.
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. • When this happens, the precipitation that results is acidic. • acid precipitation: precipitation, such as rain, sleet, or snow, that contains a high concentration of acids, often because of pollution in the atmosphere
Erosion • What is erosion, and what causes it to happen? • Erosion is the removal and transportation of weathered and nonweathered materials by gravity, running water, wind, waves, ice, and underground water. • 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
Erosion, continued • Water erosion shapes Earth’s surface. • Water is the most effective physical weathering agent. • Deposition occurs if a stream has too much sediment. • Rivers carry sediment to the ocean, and create canyons and riverbeds. • The faster the water flows, the larger the sediment it can carry. • deposition: the process in which material such as sediment is laid down, or deposited as a result of erosion
Erosion, continued • Glaciers erode mountains. • Large masses of ice, known as glaciers, 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.
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 weather the landscape by abrasion. • Wind blows weathered particles away from their source.
Erosion, continued • Gravity moves weathered materials downhill. • The movement of rock fragments down a slope in large quantities is known as mass movement. • Landslides and mudflows are common types of mass movement. • Humans can also cause erosion. • Humans often create conditions that speed up erosion. • Deforestation is an example of a human created condition that speeds up the erosion process.
