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Understanding Weathering: Mechanical and Chemical Processes Explained

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frye
37 diapositives · 651 Views · Jul 22, 2014

Explore the fascinating processes of weathering that shape our planet, including mechanical and chemical weathering. Mechanical weathering breaks down rocks through physical forces such as wind, water, and plant roots, while chemical weathering alters the mineral composition of rocks through chemical reactions. Discover how factors like rock type and climate affect the rate of weathering, and learn about real-world examples found in national parks such as the Grand Canyon and Yosemite Falls.

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Understanding Weathering: Mechanical and Chemical Processes Explained
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  1. Weathering This week we write it down if it’s in ORANGE. Photo: Grand Canyon, National Park Service

  2. Wind blows sand and other sediment against rocks. Little by little, it wears away the rock! This is an example of mechanical weathering. What do you think made the hole in this rock?

  3. Water from the river wears away the rock, over thousands of years. This is another example of weathering. Photo: Yosemite Falls, National Park Service webcam What do you think made the notch where the waterfall starts?

  4. Weathering is the process that breaks down rock and other substances on Earth’s surface.

  5. Part 1: Mechanical Weathering

  6. Mechanical Weathering

  7. Here we go again with wind and rock particles sculpting rock! Photo: Delicate Arch, Arches National Park, National Park Service. Abrasion: Sand and other rock particles carried by wind and water grind away rock like sandpaper on wood.

  8. Perhaps you have seen this on sidewalks? Photo source: Morguefile.com Plant Growth: Roots of trees and other plants grow in the cracks of rocks and pry them apart.

  9. Photo source: Morguefile.com Animal Actions: Animals dig in the soil and loosen and break apart rocks.

  10. Perhaps you have seen a frozen bottle get cracked? Or cracks in the road? Why does that happen? Ice Wedging: When water freezes it expands. Ice in the crack of a rock expands and makes the crack larger.

  11. Mechanical weathering in which rock is worn away by the grinding action of other rock particles is called • erosion. • abrasion. • ice wedging. B. abrasion Whiteboard QuestionCHECK YOUR UNDERSTANDING!

  12. Release of Pressure: When rocks reach Earth’s surface, reduced pressure can cause cracks and flakes in the rock.

  13. Your completed chart should look like this! Mechanical Weathering

  14. Ice wedging causes mechanical weathering of rock by means of: • plant growth. • animal actions. • freezing and thawing of water. C. freezing and thawing of water Whiteboard QuestionCHECK YOUR UNDERSTANDING!

  15. Chemical Weathering Write it down if it’s in ORANGE.

  16. Chemical weathering is the process that slowly breaks down rock with chemical changes, including changes in the minerals. This rusty color is caused by oxidation in a wet climate.

  17. What kind of weathering causes the mineral composition of rocks to change? • Chemical weathering. • Mechanical weathering. • General weathering. A. Chemical weathering Whiteboard Question CHECK YOUR UNDERSTANDING!

  18. Part 2: Chemical Weathering

  19. Chemical WeatheringChemical weathering is___________________________________________________________________________________________________________

  20. This limestone cave was created by water dissolving the stone. Photo source: Morguefile.com Water: Water is the most important cause of chemical weathering. When a rock dissolves in water, it mixes completely with the water.

  21. What made this old truck rusty? Photo source: Morguefile.com

  22. Rust happens to old vehicles, and to rocks. Photo source: Morguefile.com Photo source: Morguefile.com Oxygen: Iron combines with oxygen and water in a process called oxidation. The result is rust. Oxidation of a rock makes it soft, crumbly and red or brown.

  23. Limestone. Carbon dioxide: Carbon dioxide in the air dissolves in rainwater, becoming a weak acid called carbolic acid. Acids weather rocks such as limestone and marble.

  24. Lichen growing on a rock will weather it. Photo source: Morguefile.com Living organisms: Plants, and other living organisms such as lichen, release weak acids that slowly dissolve rocks.

  25. Acid rain: Burning coal, oil, and gas for energy produces pollution. This pollution combines with air and water, to create acid rain, and fast chemical weathering. Photo source: Morguefile.com

  26. A rock containing iron becomes soft and crumbly and reddish-brown in color. It probably has been weathered by: • abrasion • oxygen. • acid rain. B. oxygen Whiteboard QuestionCHECK YOUR UNDERSTANDING!

  27. Your completed chart should look like this! Chemical WeatheringChemical weathering is___________________________________________________________________________________________________________

  28. Abrasion of a rock by blowing sand is an example of __________________ weathering. • Acid rain washing away the face of a statue is an example of __________________ weathering. • True or False? Living things can cause both chemical and mechanical weathering. • A tree’s roots growing through cracks in a rock is an example of _________________ weathering. mechanical chemical True mechanical Is it Chemical or Mechanical Weathering? Final Whiteboard Questions

  29. Part 3: Rates of Weathering What makes a rock weather fastest? Photo source: Morguefile.com

  30. The most important factors for the rate (speed) of weathering are1. rock type; and 2. climate. Rate of Weathering Photo source: Morguefile.com

  31. Mechanical and Chemical Weathering Work Together • Photo source: Morguefile.com • Photo source: Morguefile.com Mechanical weathering increases the surface area available for chemical weathering. Increased surface area usually results in faster chemical reactions (chemical weathering).

  32. Mechanical and Chemical Weathering Work Together Which rock do you think will weather faster? A permeable rock weathers easily because it contains many small, connected air spaces

  33. A permeable rock weathers easily because it: • is made up of small particles. • contains many small, connected air spaces. • is made up of many minerals. B. contains many small, connected air spaces. Whiteboard QuestionCHECK YOUR UNDERSTANDING!

  34. Photo source: Morguefile.com Which of these places would have faster weathering of rock? Why? How Does Weather Affect Weathering? Photo source: Morguefile.com • Photo source: Morguefile.com

  35. Rainforests have warm, wet weather. • Photo source: Morguefile.com Wet climates with high temperatures speed up both mechanical and chemical weathering. Photo source: Morguefile.com

  36. Granite lasts a long time when it is used for building in areas where the climate: • is cool. • has lots of acid rain. • is hot and rainy. A. is cool Whiteboard QuestionCHECK YOUR UNDERSTANDING!

  37. The most important factors in determining the rate of weathering are: • carbon dioxide and acid rain. • animal actions and oxygen. • rock type and climate. • abrasion and acids from root plants. C. rock type and climate Whiteboard QuestionCHECK YOUR UNDERSTANDING!