Weathering And Soil Lecture


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Weathering And Soil Lecture

  1. 1. Weathering and Soil Chapter 7
  2. 2. Weathering <ul><li>Process by which rocks on or near Earth’s surface breakdown or change </li></ul><ul><li>Erosion- Removal and transport of material from one place to another </li></ul>
  3. 3. Mechanical Weathering <ul><li>Breakdown of rocks into smaller pieces- only change in size, NEVER composition </li></ul><ul><ul><li>Temperature- water freezes, expands, and breaks the rock apart  frost wedging </li></ul></ul><ul><ul><li>Pressure- when pressure is removed from a rock, it can expand and crack; layer wear away  exfoliation </li></ul></ul>
  4. 4. Chemical Weathering <ul><li>Minerals change chemical composition (rust) </li></ul><ul><ul><li>Water- dissolves minerals  hydrolysis; reaction of water and other substances </li></ul></ul><ul><ul><li>Oxygen- reaction with oxygen  oxidation </li></ul></ul><ul><ul><ul><li>Ex: Iron; 2Fe + 3O 2  2FeO 3 </li></ul></ul></ul><ul><ul><li>CO 2 - CO 2 + H 2 O  H 2 CO 3 (Carbonic Acid), dissolves carbonates (like limestone) </li></ul></ul><ul><ul><li>Acid Precipitation- oxidation of SO 2 + NO 2 by burning </li></ul></ul>
  5. 5. Rate of Weathering <ul><li>Climate- temperature and precipitation ( ↑ temp, ↑ rain, ↑ weathering), also (↓ temp, dry, rapid/frequent freezing) Remind you of anywhere?? </li></ul><ul><li>Rock Type and Composition – how resistant to breaking (igneous) </li></ul><ul><li>Surface Area- more surface, more weathering </li></ul><ul><li>Topography (shape of land) slope increases weathering/erosion </li></ul>
  6. 6. Erosion and Deposition <ul><li>Gravity- pulls materials downhill </li></ul><ul><li>Running Water- water has great power </li></ul><ul><ul><li>Rill erosion- water running in small channels down a slope </li></ul></ul><ul><ul><li>Gulley- When a channel becomes deep and wide </li></ul></ul>
  7. 7. Coastal Deposition & Erosion <ul><li>Much of what is weathered is carried to a coast </li></ul><ul><li>When a river hits the oceans, it slows down, dropping its load of sediment </li></ul><ul><li>Ocean waves, currents, and tide continue erosion </li></ul>
  8. 8. Glacial Erosion <ul><li>Currently Cover <10% of Earth </li></ul><ul><li>Very Powerful, polish grind, scratch surfaces </li></ul><ul><li>Form valleys, waterfalls, lakes </li></ul>
  9. 9. Wind Erosion <ul><li>Major forces where ↓ precipitation, ↑ temperature  no plant cover  sandblasting </li></ul>
  10. 10. Plants, Animals and People <ul><li>Move soil around </li></ul><ul><li>Buildings, highways, etc. </li></ul>
  11. 11. Formation of Soil <ul><li>Soil- loose covering of broken rock, decaying organic matter (humus) covering Earth’s surface </li></ul><ul><li>Soil Formation- </li></ul><ul><ul><li>Beginning- weathering breaks solid bedrock into smaller pieces </li></ul></ul><ul><ul><li>Organic (living) matter added; organisms die, decay and don’t forget waste products </li></ul></ul>
  12. 12. Soil Composition <ul><li>Parent Material- bedrock “gives birth to soil” </li></ul><ul><li>Residual Soil- just above parent material </li></ul><ul><li>Transported Soil- soil moved to a location far away from parent bedrock </li></ul><ul><ul><li>Think Running Water Glaciers </li></ul></ul><ul><li>What kind of soil do we have??? </li></ul>
  13. 13. Soil Profiles- a vertical sequence of layers <ul><li>Horizons- distinct layers of soil </li></ul><ul><ul><li>O- All leaf litter, top layer </li></ul></ul><ul><ul><li>A- organic mixed with rock fragments </li></ul></ul><ul><ul><li>B- Sub Soil, rich in clay </li></ul></ul><ul><ul><li>C- between B and bedrock, mostly broken pieces of rock </li></ul></ul><ul><li>Topography affects thickness of soil, hillsides loose soil to erosion </li></ul>
  14. 14. Soil Types <ul><li>Climate main factor in soil development </li></ul><ul><li>Polar- good drainage, no horizons, very shallow (cm) </li></ul><ul><li>Temperate- varies greatly, rainfall determines vegetation </li></ul><ul><li>Desert- ↓ precipitation, little or no organic matter, rich in nutrients </li></ul><ul><ul><li>Why? </li></ul></ul><ul><li>Tropical- ↑ temp, ↑ rain; very weathered soil, lots of bacteria  no humus and few nutrients, red colored (high iron and aluminum content) </li></ul>
  15. 15. Soil Textures <ul><li>Clay- smallest particles </li></ul><ul><li>Silt- slightly larger </li></ul><ul><li>Sand- larger </li></ul><ul><li>Loam- combination of the three </li></ul>
  16. 16. Soil Fertility <ul><li>How well a soil can support plant growth </li></ul><ul><li>Factors </li></ul><ul><ul><li>Mineral/ nutrients, microorganisms, precipitation, topography and acidity </li></ul></ul><ul><ul><li>Fertilizer adds nitrates, potassium, phosporus (#-#-#) </li></ul></ul><ul><ul><li>Legumes (peas and beans) add microorganisms and nitrates to soil as they grow </li></ul></ul><ul><ul><li>Limestone reduces acidity </li></ul></ul>
  17. 17. Soil Color <ul><li>Darker in color  more humus </li></ul><ul><li>Gray/Blue  poorly drained (wet), lacks oxygen </li></ul>
  18. 18. Mass Movement Chapter 8