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Weathering

Weathering. Earth Science – Ms. Bray. Weathering and Soil Formation. Objectives Define mechanical and chemical weathering. Discuss agents of weathering. Give examples of each type of weathering. . Two Important Types of Weathering. C hemical weathering

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Weathering

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  1. Weathering Earth Science – Ms. Bray

  2. Weathering and Soil Formation Objectives • Define mechanical and chemical weathering. • Discuss agents of weathering. • Give examples of each type of weathering.

  3. Two Important Types of Weathering Chemical weathering • Rock changes composition and becomes a different type of rock. Mechanical weathering • Breaks rock into smaller pieces by using physical processes

  4. Chemical Weathering • Rocks are decomposed, dissolved or loosened by chemical processes to form residual materials • Chemical reactions break down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces.

  5. Chemical Weathering • The most common types of chemical weathering are: • Oxidation • Hydrolysis • Carbonation

  6. Oxidation • Oxidation takes place when oxygen combines with other elements in rocks to form new types of rock. • These new substances are usually much softer, and thus easier for other forces to break apart.

  7. Oxidation • In this image you can see rust starting to form on the left side of the rock. • This is due to oxidation, which is when the iron in rocks mixes with oxygen and creates rust.

  8. Hydrolysis • Hydrolysis occurs whenwater combines with the substances in rocksto form new types of substances, which are softer than the original rock types. • HYDRO means WATER • So, just think: water and other elements are breaking down the rock. In this photo, you can see how water flowed continuously and over time it created a hole in this rock.

  9. Carbonation • Carbonation takes place when carbon dioxide reacts with certain types of rocks forming a solution, that can easily be carried away by water.

  10. Carbonation • White carbonate veins where carbon dioxide has been transformed into rock show in a dark deposit.

  11. Let’s review all of that real quick… • What is chemical weathering? • Chemical reactions break down the bonds holding the rocks together, causing them to fall apart • Oxidation • Oxygen mixes with rock to make a new type of rock • Hydrolysis • Water breaks down rock • Carbonation • Carbon dioxide reacts and breaks down rock

  12. Mechanical Weathering (This is also called Physical Weathering!) • Breaks rock into smaller pieces. • These smaller pieces are just like the bigger rock, just smaller. • That means,the rock has changed physically without changing its composition. • The smaller pieces have the same minerals, in just the same proportions as the original rock.

  13. Hang on a sec… This is the MAIN difference between chemical and mechanical weathering! • In chemical weathering, the composition of the rock changes and a NEW type of rock is formed. • In mechanical weathering, the rock is broken down, but the type of rock is NEVER changed.

  14. Ok, we can talk more about mechanical weathering now! • There are two types of mechanical weathering: • Ice wedging • Abrasion

  15. Ice Wedging • Ice wedging is mechanical weathering where rocks are broken by water expanding as it is frozen. • When water flows into a crack and freezes itexpands and breaks the rock. In this picture, millions of years ago there was a glacier covering this rock. Water got into it, froze, expanded, and cracked the rock.

  16. Ice Wedging or Frost Wedging(They mean the same thing )

  17. Another example of frost wedging:

  18. Abrasion • Rocks break into pieces by bumping into or rubbing againsteach other. • Gravity causes abrasion as a rock tumbles down a mountainside or cliff. • Moving water causes abrasion as particles in the water collide and bump against one another. • Strong winds carrying pieces of sand can sandblast surfaces. • Ice in glaciers carries many bits and pieces of rock. Rocks embedded at the bottom of the glacier scrape against the rocks below.

  19. Abrasion: What does it look like? • Abrasion makes rocks with sharp or jagged edges smooth and round. • Like when you find pebbles at the beach! This one is abrasion from water causing the rocks to rub against and bump into each other. This one is abrasion from a glacier running over the rock and smoothing it out over time.

  20. What now? • You need some practice! • Go to the VOISE Earth Science homework page and click on the weathering review activity.

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