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Weathering, erosion, and mass wasting


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Weathering, erosion, and mass wasting

  2. 2. WEATHERING <ul><li>Two types of weathering are mechanical and chemical . </li></ul><ul><li>Mechanical weathering is the physical break up of rock exposing more surface area by: </li></ul><ul><li>Frost wedging – common in mountains and middle latitudes </li></ul><ul><li>Unloading </li></ul><ul><li>Biological activity </li></ul>
  3. 3. <ul><li>Frost Wedging </li></ul><ul><li>When water freezes it expands by about 9% and exerts tremendous force. This force breaks off rocks, tumble and pile up at the bottom of the cliff into large pies called talus. </li></ul>
  4. 4. <ul><li>Unloading </li></ul><ul><li>Exposed rock reduces pressure causing the outer layers to expand. The outer layers separate from the rest of the rock by a process called exfoliation . </li></ul>
  5. 5. <ul><li>Biological activity </li></ul><ul><li>Plant roots grow into rocks breaking rocks apart. </li></ul>
  6. 6. <ul><li>Chemical weathering is the transformation of rock into one or more new compounds. </li></ul><ul><li>Water is the most important agent of chemical weathering </li></ul><ul><li>The oxygen dissolved in water reacts with certain minerals forming oxides , such as iron oxides in soil (yellowish or red soils) </li></ul><ul><li>Water falling through the atmosphere absorbs carbon dioxide forming weak carbonic acid . This acid reacts with many minerals, for example limestone. </li></ul><ul><li>Water in the atmosphere reacts with sulfur oxides and nitrogen oxides from the burning of coal and petroleum to form acid rain . The acid rain reacts with many minerals. </li></ul>
  7. 7. <ul><li>Chemical weathering of granite forms the minerals feldspar and quartz . The feldspar reacts with the carbonic acid forming clay . The quartz is resistant to weathering and remains unchanged. </li></ul>
  8. 8. <ul><li>The rate of weathering is influenced by mechanical weathering , rock characteristics, and climate . For example </li></ul><ul><li>Granite weathers slower than marble or limestone. </li></ul><ul><li>  </li></ul><ul><li>Climate favorable to weathering have high temperatures and abundant moisture . </li></ul><ul><li>Where is chemical weathering the slowest? </li></ul>
  9. 9. EROSION <ul><li>Soil erosion is a natural part of matter recycling. </li></ul><ul><li>  </li></ul><ul><li>The rate of soil erosion depends on soil characteristics, climate , slope , and type of vegetation . </li></ul>
  10. 11. <ul><li>Types of Water Erosion </li></ul><ul><li>Sheet erosion – thin sheets of water carriers away soil particles </li></ul>
  11. 12. <ul><li>Rills – tiny streams of water </li></ul><ul><li>Gully erosion – deep trenches </li></ul>
  12. 13. <ul><li>Wind erodes soil much more slowly. However prolonged drought can remove large quantities of exposed soil. </li></ul>
  13. 14. <ul><li>Human activities that increase the rate of soil erosion are land clearing due to development and road building. Sedimentation is the number one stream pollutant in North Carolina. </li></ul>
  14. 15. MASS MOVEMENT (WASTING) <ul><li>MASS MOVEMENT (WASTING) – the down slope movement of rock and soil due to gravity </li></ul>
  15. 16. <ul><li>Triggers of mass movements </li></ul><ul><li>Water-logged soils </li></ul><ul><li>Over-steepened slopes from road building and development </li></ul><ul><li>Removal of vegetation </li></ul><ul><li>Earthquakes </li></ul>
  16. 17. <ul><li>Types of Mass Movements </li></ul><ul><li>Rock falls – rock or rock fragments fall off </li></ul>
  17. 18. <ul><li>Landslides – a block of material suddenly moves down along a flat inclined surface </li></ul>
  18. 19. <ul><li>Slump – a block of materials move down along a curved surface </li></ul>
  19. 20. <ul><li>Mudflows - contain a high amount of water, occur quickly, occur in mountainous areas </li></ul>
  20. 21. <ul><li>Earth flows move relatively slowly, form a tongue-shaped mass </li></ul>
  21. 22. <ul><li>Creep – the slowest type of mass movement, travels few millimeters to centimeters per year, freeze-thaw cycles contributes to creep. </li></ul>