Es Ch 6 Weathering&Soil


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Es Ch 6 Weathering&Soil

  1. 1. Chapter 6 Weathering & Soil
  2. 3. 6.1 Weathering <ul><li>WEATHERING -The breaking down of rock material into smaller pieces. </li></ul><ul><li>Two Forms of Weathering </li></ul><ul><ul><li>Mechanical </li></ul></ul><ul><ul><ul><li>Some Biological </li></ul></ul></ul><ul><ul><li>Chemical </li></ul></ul><ul><ul><ul><li>Some Biological </li></ul></ul></ul><ul><li>Weathering reduces mountains to hills & boulders to dirt </li></ul>Pgs. 148 - 155 Lichen on boulder Chemical Weathering
  3. 4. Mechanical Weathering <ul><li>Mechanical Weathering- The breaking down of rocks without changing their chemical composition. </li></ul><ul><li>Fragments formed without changing chemical composition </li></ul><ul><li>Fragments have exact characteristics as parent rock </li></ul><ul><li>Caused by many factors: </li></ul><ul><li>Tree Roots Ice Expanding </li></ul><ul><li>Crystal Growth Lightning </li></ul><ul><li>Expansion & Contraction </li></ul><ul><li>Heating & Cooling Friction </li></ul><ul><li>Wind </li></ul>
  4. 6. Plants & Animals <ul><li>Roots grow into cracks in rocks </li></ul><ul><li>Start out thin as hair, grow larger & large </li></ul><ul><li>Act as a wedge forcing rock pieces apart </li></ul><ul><li>Ex: Sidewalks buckling due to tree roots </li></ul><ul><li>Burrowing animals increase weathering as well </li></ul><ul><li>Allow water & air to act on rocks below the surface </li></ul><ul><li>Animals also bring un-weathered materials to the surface where weathering occurs </li></ul>
  5. 7. Ice Wedging <ul><li>Natural process of breaking rocks down quickly </li></ul><ul><li>Here is the process: </li></ul><ul><li>Water seeps into cracks of rocks </li></ul><ul><li>Water expands as it freezes </li></ul><ul><li>Crack widens </li></ul><ul><li>More water able to seep in & freeze </li></ul><ul><li>Crack widens even more </li></ul><ul><li>The process repeats till pieces break off the parent rock </li></ul>
  6. 8. Wind Action: <ul><li>Winds pick up dust & particles </li></ul><ul><li>These particles act as abrasives, wearing away rock surfaces </li></ul><ul><li>Equivalent to sand blasting </li></ul>
  7. 9. Chemical Weathering <ul><li>CHEMICAL WEATHERING – The process when water, air, or other chemical wear away rocks and change it’s composition. </li></ul><ul><li>Water: </li></ul><ul><li>“ The universal solvent” </li></ul><ul><li>Oxygen & hydrogen in water reacts with minerals </li></ul><ul><li>The minerals change into much different compounds </li></ul><ul><li>Ex: Rust- Oxidation of Iron only </li></ul>
  8. 11. <ul><li>Acids: </li></ul><ul><li>React with minerals, usually dissolving them over time </li></ul><ul><li>Acids from naturally in many ways: </li></ul><ul><li>Carbonic Acid: Carbon dioxide & water (Weak acid) wears away limestone to make a lot of caves. Wears away Granite to make clay. </li></ul><ul><li>Sulfuric Acid: Sulfur and water (Strong acid) wears away marble, concrete </li></ul><ul><li>Some plant roots: Mosses produce Nitric Acid (Strong acid) Breaks down rocks and causes acid rain </li></ul>
  9. 12. Oxygen: <ul><li>Oxidation: the bonding of oxygen to other elements that changes the chemical composition </li></ul><ul><li>Almost all elements oxidize </li></ul><ul><li>Iron  Iron Oxide (Rust) </li></ul><ul><li>Aluminum  Aluminum Oxide white powder on window sills </li></ul><ul><li>Sulfur  Sulfur Dioxide- Acid Rain Most comes from power plants. </li></ul><ul><li>Copper Oxide – Turns copper green (Statue of Liberty) </li></ul>
  10. 15. Effects of Climate on Weathering <ul><li>Mechanical & Chemical weathering occur everywhere </li></ul><ul><li>Climate plays a big part in how quickly they occur </li></ul><ul><li>Climate: weather patterns for a given area over long periods of time </li></ul><ul><li>Weathering by climate: </li></ul><ul><li>Cold climates: Freezing & thawing cycles allow ice wedging to break down rocks quickly </li></ul><ul><li>Warm, wet climates: Chemical weathering acts quickly </li></ul><ul><li>Dry Climates: Wind action prevalent </li></ul>
  11. 18. 6.2 Soil <ul><li>Formation of Soil: </li></ul><ul><li>Rocks breakdown into tiny fragments = DIRT </li></ul><ul><li>Dirt is not Soil </li></ul><ul><li>Soil: weathered rock material with organic matter mixed in </li></ul><ul><li>Soil Formation Process: </li></ul><ul><li>Rocks break down into dirt </li></ul><ul><li>Dirt gets some organic material added (animal waste, plant material, etc.) </li></ul><ul><li>Small grasses & weeds begin to grow </li></ul><ul><li>Insects, worms, small animals move in (adding more organic matter) </li></ul><ul><li>Larger plants begin to replace grasses & weeds </li></ul>Pgs. 156 - 163
  12. 20. Soil Maturity: <ul><li>As organic material gets mixed into soil it gets darker </li></ul><ul><li>Mature soil is called Humus </li></ul><ul><li>Humus: soil rich in decaying plant matter & other organic matter </li></ul><ul><li>Humus provides all nutrients required by plants </li></ul><ul><li>Nitrogen – Phosphorous – Potassium & Water </li></ul><ul><li>Depending on climate, soil formation takes a few months or thousands of years </li></ul><ul><li>Soil thickness ranges from a few centimeters to 60 m </li></ul>
  13. 21. Soil Profile: <ul><li>The visible difference in soil layers from the surface to bedrock </li></ul><ul><li>Each layer is called a Horizon </li></ul><ul><li>Usually there are 3 horizons (Labeled A, B, C) </li></ul><ul><li>Horizon A: Top soil layer </li></ul><ul><li>Mostly Humus & small mineral fragments </li></ul><ul><li>Horizon B: Layer below Horizon A </li></ul><ul><li>Minimal organic matter (humus) </li></ul><ul><li>Leaching- removal of soil by water </li></ul><ul><li>Larger dirt fragments </li></ul><ul><li>Horizon C: Layer below Horizon B </li></ul><ul><li>Almost totally dirt & larger rock fragments </li></ul>
  14. 23. Types of Soil <ul><li>Texture of soil is based on amounts of sand, silt, & clay </li></ul><ul><li>Depth of horizons in soil profiles also important </li></ul><ul><li>The US can be broken into 9 general types of Soil </li></ul><ul><ul><li>Arctic Desert Glacial Mountain </li></ul></ul><ul><ul><li>Prairie River Temperate Tropical </li></ul></ul><ul><ul><li>Wetlands </li></ul></ul>
  15. 26. 6.3 Land Use & Soil Loss <ul><li>Agriculture: Soil as an important Resource </li></ul><ul><li>Many resources are directly tied to the soil </li></ul><ul><li>Food, paper products, natural fibers </li></ul><ul><li>Vegetables, grains, cotton  plants </li></ul><ul><li>Cattle, sheep, pigs  feed off the land </li></ul><ul><li>When vegetation is removed… Soil directly exposed to weather </li></ul><ul><li>Erosion occurs </li></ul><ul><li>Nutrients are lost </li></ul>Pgs. 164 - 165
  16. 27. <ul><li>Plowing disrupts the soil: </li></ul><ul><li>Every year the Earth’s population increases by at least 93 million people </li></ul><ul><li>Farmers plow more fields to meet then increasing demand for food </li></ul><ul><li>Plowing is the mechanical turning & loosening of soil </li></ul><ul><li>Turns previous vegetation under, exposes underlying soil </li></ul>
  17. 28. 2 points of View: <ul><li>Soil loss is severe in tropical regions </li></ul><ul><li>Rains wash loose soil into the ocean </li></ul><ul><li>Each year 1000’s of square km of rainforests are cleared for farming & grazing </li></ul><ul><li>Tropical soil is very thin = nutrients used up quickly </li></ul><ul><li>After a few years the soil is no longer fertile  new fields need to be cleared </li></ul><ul><li>Abandoned fields become desert like areas (Begins desertification) </li></ul><ul><li>Grasslands near deserts are normally grazing areas </li></ul><ul><li>Livestock eat every bit of vegetation </li></ul><ul><li>Increases wind erosion </li></ul><ul><li>Desert grows larger = Desertification </li></ul>
  18. 29. <ul><li>Farmers Work to Minimize Soil Loss: </li></ul><ul><li>Along with using contour plowing, crop rotation, terracing, shelter belts, etc. farmers use other methods to help protect the soil </li></ul><ul><li>Chisel Plowing: </li></ul><ul><li>Instead of turning over a complete field, chisel plows cut small furrows between previously planted and harvested crops </li></ul><ul><li>Previous crop roots hold soil, decaying plants fertilize the soil </li></ul><ul><li>Newly loosened area is planted </li></ul>
  19. 30. <ul><ul><li>No Till Farming : </li></ul></ul><ul><ul><li>Special planter used to cut a very small area for seeds to be planted </li></ul></ul><ul><ul><li>Rest of field is not disturbed </li></ul></ul><ul><ul><li>Cover cropping: </li></ul></ul><ul><ul><li>Farmers plant two crops that can grow together, harvest one & leave the other to continue growing </li></ul></ul><ul><ul><li>Ex: Grains with Grasses </li></ul></ul><ul><ul><li>Grains get combined off in early summer, </li></ul></ul><ul><ul><li>Grasses continue to grow and can be cut as hay </li></ul></ul>
  20. 31. Cover Cropping with Grapes and Beans
  21. 32. Historic Tragedy: The Dust Bowl <ul><li>People moved into the Great Plains during the 1800’s </li></ul><ul><li>Plowed under the native drought resistant grasses </li></ul><ul><li>Began farming large areas </li></ul><ul><li>Corn & Wheat were planted; Cattle & Sheep were grazed </li></ul><ul><li>As the area being farmed continually increased, the natural grasses with their extensive root systems became increasingly scarce, and erosion increased drastically </li></ul>
  22. 35. <ul><li>In 1931, a drought hit the Great Plains Region </li></ul><ul><li>Lasted several years, Crops were not able to withstand the drought </li></ul><ul><li>Soil became totally unprotected, Wind began blowing the dry topsoil away </li></ul><ul><li>Dust storms raged </li></ul><ul><li>Soil was blown into the ocean, or piled up against homes </li></ul><ul><li>More than 8 cm of topsoil was lost </li></ul><ul><li>Many farmer went bankrupt and People moved elsewhere </li></ul><ul><li>1935: Federal government began regulating Agriculture </li></ul><ul><li>Crop rotation, contour plowing & terracing were required </li></ul><ul><li>In areas able to support trees, wind breaks were planted </li></ul><ul><li>Over time, the fertility of the plains was restored </li></ul>
  23. 36. Dust Bowl Videos