Weathering, Erosion and Soil


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Weathering, Erosion and Soil

  1. 1. WEATHERING, EROSION, AND SOIL The Walker School Geology
  2. 2. Weathering vs. Erosion  Weathering the decomposition of earth rocks, soils and their minerals through direct contact with the planet's atmosphere. Weathering occurs in situ, or quot;with no movementquot;, and thus should not to be confused with erosion, which involves the movement and disintegration of rocks and minerals by agents such as water, ice, wind, and gravity.
  3. 3. Formation of the Grand Canyon Debris flows shown in this clip erode rock along the walls of the canyon.
  4. 4. Arches National Park Erosion takes place at different rates – called differential erosion Produces: hoodoos, spires, arches, and pedestals Fig. 6-CO, pp. 168-169
  5. 5. Hoodoos, Bryson Canyon National Park
  6. 6. Types of Weathering  Mechanical  Chemical  Biological Weathering of Granite Fig. 6-1a, p. 170
  8. 8. Physical Weathering  Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions such as heat, water, ice and pressure. Badlands, SD
  9. 9. Abrasion The primary process in mechanical weathering is abrasion (the process by which clasts and other particles are reduced in size). Talus at the base of Rocky Mountains in Canada
  10. 10. Physical Processes of Weathering  Frost Action  Pressure Release  Thermal Expansion and Contraction  Salt Crystal Growth  Activities of Organisms
  11. 11. Frost Action Fig. 6-3b, p. 172
  12. 12. Frost Heaving in New York City
  13. 13. Pressure Release (Unloading) Granite (igneous rock) crystallizes far below the surface, so when it is uplifted and the overlying material is eroded, its contained energy is released by outward Exfoliation at Stone Mountain, Georgia expansion.
  14. 14. Thermal Expansion (Exfoliation) Slabs of granitic rock bounded by sheet joints in the Sierra Nevada, CA Rock is a poor conductor of heat, so its outside heats up more than its inside; the surface expands more than the interior. Often occurs in areas, like deserts, where there is a large diurnal temperature range. Fig. 6-4a, p. 173
  15. 15. Salt Weathering (haloclasty)  Mechanical  Derives from an external source (capillary rising ground water, eolian origin, sea water along rocky coasts, atmospheric pollution).  Favored by dry conditions in arid climates.  The expanding salt crystals exert a pressure on the walls of the rock pores that exceeds the tensile Marine Abrasion of Granite. strength of the rock.
  17. 17. Biological Weathering from Plants Trees and other plants in Lassen Volcanic National Park, CA help break down parent material into smaller pieces and contribute to mechanical weathering. Fig. 6-6b, p. 174
  19. 19. Chemical Weathering  Chemical weathering, involves the direct effect of atmospheric chemicals, or biologically produced chemicals (also known as biological weathering), in the breakdown of rocks, soils and minerals.
  20. 20. Organisms Lichens are part fungi and part algae. They derive their nutrients from the rock and contribute to chemical weathering. Fig. 6-6a, p. 174
  21. 21. Decomposition of Earth’s Materials  Dissolution (minerals dissolve in water, limestone dissolves to form caves)  Hydrolysis (hydrogen ions in water dissociate and attack minerals in rocks, ex. forms hard water)  Oxidation (minerals react with oxygen, ex. formation of rust)
  22. 22. Factors Affecting Chemical Weathering  Presence of Fractures  Particle Size  Climate  Parent Material Granite rocks in Joshua Tree National Park, CA. Chemical weathering is more intense along fractures.
  23. 23. Mechanical and Chemical Mechanical weathering speeds chemical weathering by increasing the surface area of the rock. Fig. 6-10, p. 180
  24. 24. Temperature and Chemical Weathering Chemical processes proceed more rapidly at high temperatures and in the presence of liquids. Chemical weathering can extend to depths of 10s of meters in the tropics, but only a few inches in arid or cold climates Fig. 6-11, p. 180
  25. 25. Stability is the opposite of Bowen’s reaction series. Table 6-1, p. 180
  27. 27. Regolith A collective term for sediments.
  28. 28. Soil Production through Weathering Fig. 6-1b, p. 170
  29. 29. Soil Production through Infiltration
  30. 30. Soil Composition Fig. 6-14a, p. 183
  31. 31. Soil Profile Parent material, in soil science, means the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Fig. 6-14b, p. 183
  32. 32. Variables in Soil Production  parent material  time  climate  atmospheric composition  topography  organisms
  33. 33. Climate and Soil Formation Fig. 6-15, p. 184
  34. 34. Pedocal Fig. 6-16a, p. 185
  35. 35. Pedalfer Fig. 6-16b, p. 185
  36. 36. Laterite Fig. 6-16c, p. 185
  37. 37. Soils in the Field Shows Laterite in Madagascar, a deep red soil that forms in response to intense chemical weathering. Fig. 6-18a, p. 186
  38. 38. 12 Soil Types
  39. 39. World Soils
  40. 40. U.S. Soil Orders
  41. 41. Most of the World’s Soils are Under Threat 38% of the world’s croplands have serious topsoil erosion.
  42. 42. Activities of Organisms Churn soil; Break down nutrients; Provide pathways for gases to escape
  44. 44. Soil Expansion $6 billion in damage a year to foundations, roadways, sidewalks and other structure. Fig. 6-21b, p. 188
  45. 45. Erosion Rill Gully Fig. 6-22a, p. 189
  46. 46. Stalinization Stunts Crop Growth; Lowers Crop Yields; Eventually Kills Plants; Ruins the Land
  47. 47. Slash and Burn Agriculture Practices deplete tropical soils of nutrients for agriculture. Fig. 6-19a, p. 187
  48. 48. Desertification 70% of the world’s dry lands are suffering.
  49. 49. Causes and Consequences of Desertification
  50. 50. Soil Conservation Table 6-2, p. 190