1. Weathering • weathering • mechanical weathering • chemical weathering • oxidation

2. Weathering and Its Effects • The mechanical and chemical processes that change objects on Earth’s surface over time are called weathering. • Over thousands of years, weathering can break rock into smaller and smaller pieces, such as sand, silt, and clay.

3. Mechanical Weathering • When physical processes naturally break rocks into smaller pieces,mechanical weatheringoccurs. • The chemical makeup of a rock stays the same during mechanical weathering. • Mechanical weathering can be caused by ice wedging, abrasion, plants, and animals.

5. Mechanical Weathering(cont.) • An example of mechanical weathering is when the intense heat of a forest fire causes nearby rocks to expand and crack. • When something is broken into smaller pieces, it has a greater surface area. • Surface area is the amount of space on the outside of an object.

6. Chemical Weathering • Chemical weatheringchanges the materials that are part of a rock into new materials. • These granite obelisks show how chemical weathering can affect some rock. Dr. Marli Miller/Getty Images

7. Chemical Weathering(cont.) • Water is important in chemical weathering because most substances dissolve in water. • The process of dissolving breaks up the minerals in the rock into small pieces. The small pieces mix with water to form a solution and are washed away from the rock. • Acids are also agents of chemical weathering and cause more chemical weathering than pure water does.

8. Chemical Weathering(cont.) • Oxidationcombines the element oxygen with other elements or molecules. • The product of oxidation is called an oxide. • When rocks that contain iron oxidize, a layer of iron oxide forms on the outside surface.

9. What affects weathering rates? • The environment helps determine the rate of weathering. • Mechanical weathering occurs fastest in locations that have a lot of temperature changes. • Chemical weathering is fastest in warm, wet places. • The type of rock being weathered also affects the rate of weathering and determines what kinds of products result.

10. The Erosion-Deposition Process • erosion • deposition

11. Reshaping Earth’s Surface • A combination of constructive processes and destructive processes produce landforms. • Constructive processes build up features on Earth’s surface. • Destructive processes tear down features on Earth’s surface.

12. The breakdown of rock—weathering—is one type of destructive process that changes Earth’s surface.

13. A Continual Process of Change • Chemical weathering alters the chemical composition of rock. • Physical weathering is the breaking of rock into pieces, called sediment, without changing the chemical composition of the rock. • Water, wind, and ice are agents, or causes, of weathering.

15. Erosion • Erosion is the removal of weathered material from one location to another. • Agents of erosion include water, wind, glaciers, and gravity. • Factors that affect the rate of erosion include weather, climate, shape of the land, and type of rock.

16. Erosion (cont.) • The presence of plants and the way humans use the land affect the rate of erosion. • The rate of erosion sometimes depends on the type of rock. • Weathering breaks some types of rock into large pieces. Other rock types easily break into smaller pieces that are more easily transported.

17. Deposition (cont.) • Deposition is the laying down or settling of eroded material. • As water or wind slows down, it has less energy and can hold less sediment, which can result in some of the sediment being deposited. • Sediment is deposited in locations called depositional environments, such as swamps, deltas, beaches, and the ocean floor.

18. Interpreting Landforms(cont.) • Landforms created by deposition are often flat and low-lying. • An apron of sediment, called an alluvial fan, often forms where a stream flows from a steep, narrow canyon onto a flat plain at the foot of a mountain.