Chapter 21.4

1. Chapter 21.4 Weathering and Erosion Objectives: You will be able to… Explain how physical weathering affects rocks Explain how chemical weathering affects rocks Define erosion and what causes it to happen Key terms: Acid precipitation, erosion, deposition

2. Physical, or mechanical weathering breaks rocks into smaller pieces but does not change their chemical compositions Abrasion can cause mechanical weathering in the same way sand paper smoothes rough areas Ice can play a major role as well, due to the fact that frozen water expands up to 10% of its size As something freezes and thaws, preexisting cracks can grow in size

4. Root systems from plants can also cause weathering by betting into cracks and growing

5. See Demo… Chemical weathering can cause rocks to weaken, decompose, or even dissolve the chemical composition of the rock Chemicals can cause minerals to break down into its constituent elements or react and form new minerals Gasses can react with water to form acids For example SO2 or sulfur dioxide can react with water to form H2SO4 or sulfuric acid http://dsc.discovery.com/videos/earth-acid-rain-eating-washington-dc.html

6. Water plays a vital role in chemical weathering Hydrolysis can occur in a couple ways, minerals can be dissolved in the water and transported somewhere else and deposited (like in a geode) Minerals can also dissolve and be transported to lower layers in a process known as leaching

7. Rain has a pH of roughly 5.7 because gas like carbon dioxide (CO2) are dissolved in it This makes the water slightly acidic The US Government has passed laws in order to reduce the amounts of gasses emitted to prevent larger amounts of acid rain from forming

8. Erosion is another process that can change the appearance of landscapes Erosion is the removal and transport of weathered and non-weathered materials by gravity, running water, wind, waves, and ice Water is an extremely powerful entity that can move large amounts of earth http://www.history.com/video.do?name=How_the_Earth_Was_Made&bcpid=9787674001&bclid=15202215001&bctid=15346374001

9. Varying rates of flow and different amounts of sediment can cause deposition to occur These sediments can pile up and redirect the way water flows

10. Glaciers are large masses of ice that can exert a tremendous force and carry away, scour, and deposit landscape Wind scrapes the surface of the Earth in a similar way Gravity moves weathered materials to lower positions Mudflows, landslides, rock falls, and avalanches are all examples

11. Humans are the animals that change the Earth’s landscape to the greatest extent Over farming and exhausting the soil can allow dirt and soil to be transported by the wind Roots from plants help hold soil firmly to the ground preventing erosion from the wind