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Weathering , Erosion, and Soil

Weathering , Erosion, and Soil. How does this cartoon relate to weathering and erosion?. BIG Idea:. Weathering and erosion are agents of change on Earth’s surface.

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Weathering , Erosion, and Soil

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  1. Weathering, Erosion, and Soil

  2. How does this cartoon relate to weathering and erosion?

  3. BIG Idea: • Weathering and erosion are agents of change on Earth’s surface.

  4. Weathering: the process by which rocks are broken down chemically and physically by the action of water, air, and organisms.

  5. I. WEATHERING PROCESSES • Mechanical Weathering Strictly a physical process • Rocks and minerals break into smaller pieces • No change to chemical composition

  6. Agents of MECHANICAL Weathering: • ice • plants and animals • gravity • running water • wind

  7. 1. Ice (Frost) Wedging • water seeps into rock cracks and then freezes

  8. What causes this to happen?

  9. 2. Pressure • Exfoliation: outer rock layers are stripped away (like an onion’s layers can be peeled)

  10. 3. Organic Activity

  11. Root Action: tree rootsgrow within cracks in rocks and cause the rocks to split

  12. 4. Abrasion • The collision of rocks with one another, causing them to break down • Agents of abrasion: • gravity • running water • wind

  13. wearing down or smoothing of a material due to constant collisions

  14. Wind Abrasion

  15. Water Abrasion

  16. B. Chemical Weathering • Process by which rocks and minerals undergo changes in their composition • Can cause some substances to dissolve • Some new minerals form • New minerals have properties different than those of original rock

  17. What items have you seen rusted? What could you do to such objects to prevent or reduce rusting?

  18. Agents of CHEMICAL Weathering: • Water • Oxygen • Carbon dioxide • Acid precipitation

  19. Hydrolysis: reacting with water Carbonation: carbon dioxide combines with water to produce carbonic acid (dissolves limestone) Oxidation: reacting with oxygen (rust)

  20. Carbonic acid creates caves

  21. Oxidation of the iron in the rock causes a red hue

  22. Acid precipitation (rain): sulfur dioxide, carbon dioxide and nitrogen oxides released into atmosphere by human activities; gases combine with oxygen and water to form strong acid rains Plant acids: from decaying plants

  23. II. RATES OF WEATHERING • All rocks do not weather at the same rate (speed)… • Some factors that affect the rate at which rocks weather are:

  24. A. Rock Composition • Igneous and metamorphic rocks break down more SLOWLY • Hardest minerals resist weathering (i.e. quartz) • Rocks containing calcite weather QUICKLY

  25. Which layer is MORE resistant to weathering? LEAST resistant? D A C B

  26. B. Amount of Exposure • time exposed • surface area

  27. Surface Area • Which will weather faster, solid rock or crushed rock?

  28. The crushed rock of course! the large rock is tightly packed and has less surface area exposed the crushed rock is loosely packed and has more surface area exposed

  29. Increased surface area = increased weathering

  30. C. Climate • Rocks in tropical regions weather faster than rocks in dry desert areas • More rain, humidity, wind, and temperature range = faster weathering

  31. Physical Weathering: works better in a cool and dry climate Chemical Weathering: works better in a hot and moist environment (more water = more weathering)

  32. Cleopatra’s Needle stood in Egypt (hot/dry) for 3,000 years…

  33. It was only in New York City for 100 years Rain, ice, and pollution destroyed it

  34. Compare the two tombstones in the next picture… • How do they compare in appearance? • Which appears more weathered?

  35. marble slate

  36. Which tombstone is older? marble slate

  37. This means that rocks can weather at different rates! marble slate

  38. D. Topography • Higher elevation = faster weathering (colder, more ice wedging) • Steep slopes - gravity pulls rocks down hill

  39. III. Weathering and Soil Soil: loose rock fragments and clay from weathered rock mixed with organic material.

  40. A. Soil Composition A = Humus- dark organic material B & C = Soil – mixture of minerals, gases, and dead organisms D = Regolith – layer of weathered rock fragments E = Bedrock – solid unweathered rock

  41. B. Soil Profile Soil Profile: cross section of the soil layers Horizons: layers in the soil

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