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Weathering

Weathering. Weathering is the breaking down of rocks and other materials on the earth’s surface. Two Types of Weathering. 1) Mechanical/physical weathering. No change in the rock’s chemical composition. Agents of mechanical weathering include:

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Weathering

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  1. Weathering

  2. Weathering isthe breaking down of rocks and other materials on the earth’s surface

  3. Two Types of Weathering

  4. 1) Mechanical/physical weathering No change in the rock’s chemical composition. Agents of mechanical weathering include: • Temperature: causes repeated expansion and contraction

  5. 1) Mechanical/physical weathering Ice wedging (frost action, freeze-thaw cycle): when liquid water goes into cracks and then freezes causing the cracks to get wider

  6. Organic activity (root-pry, burrowing animals, human activities)

  7. Gravity: rocks falling and colliding with other rocks

  8. Abrasion: wearing away by solid particles Wind-blown Sand

  9. Unloading: the expanding of high pressure rock when exposed to a lower pressure Classic sheeted granite along the Tioga Road, Yosemite National Park. The granite is broken into gently dipping plates by unloading joints. Unloading joints probably form as the rock is exposed by erosion. These joints, and others that are more steeply oriented, provide pathways for water to enter the rock.

  10. Exfoliation or unloading - rock breaks off into leaves or sheets along joints which parallel the ground surface; caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial

  11. Contraction due to crystallization The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallisation. This example is at Yehliu, Taiwan. Salt weathering of building stone on the island of Gozo, Malta

  12. 2) Chemical weathering The altering of the composition of minerals within a rock that results in a reduction in size. Agents of chemical weathering include: • Water: Dissolves minerals out of rocks making them weaker

  13. Chemical weathering Acid: Dissolves minerals in rocks (examples: carbonic acid, acid rain, and plant acid)

  14. Lichens such as these growing on the rocks in the picture can produce weak acids that react with the rock.

  15. 3000 year old Egyptian Obelisk after 100 years in NY 3000 year old Egyptian Obelisk

  16. The Parthenon in Greece shows discoloration and chemical weathering effects from air pollution and acid rain.

  17. Chemical weathering • Oxidation: Oxygen combines with iron minerals and sulfur minerals changing the composition of the rock Oxidation turned these rocks in Nevada's Valley of Fire red.

  18. Factors that determine the rate of weathering: • Composition • Physical conditions of rock • Cracks, holes, crevices – easier weathering • Solid, unbroken – more weather resistant

  19. In which shape will weathering occur faster?

  20. Climate: • ColdClimates– mechanical weathering breaks down rocks rapidly • Warm, wet climates – chemical weathering breaks down rocks rapidly

  21. Topography: the position of the rock • Air pollution • Exposure time • Surface area exposed Mechanical and chemical weathering work together

  22. Weathering by Brainpop • How long does the weathering process take? • What is carbonic acid a mixture of? • What kind of rocks are formed by weathering?

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