Weathering and Soil - PowerPoint PPT Presentation

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Weathering and Soil

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  1. Weathering and Soil

  2. Weathering • Weathering: • breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earth's atmosphere, organisms and water. • Two basic types • Physical/mechanical • Chemical

  3. Physical/Mechanical • Frost/Ice wedging • Water seeps into open spaces and freezes. • Expansion of water wedges and cracks material • Breaks at distinct angles

  4. Physical/Mechanical • Exfoliation • also known as unloading, overlying materials (not necessarily rocks) are removed (by erosion, or other processes) • which causes underlying rocks to expand and fracture parallel to the surface

  5. Physical/Mechanical Paper beats rock  • Plant roots • seedlings sprouting in a crevice and plant roots exert physical pressure • Provide a pathway for water and chemical infiltration.


  6. Physical/Mechanical • Abrasion • mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. • moving particles dislodge loose and weak debris from the side of the rock.

  7. Clicker • Which type of Physical weathering occurred in the picture below? • Frost/ice wedging • abrasion • Exfoliation • Plant roots Times up! Timer

  8. Chemical Weathering • Oxidation: • Materials react with Oxygen from atmosphere or water (H2O) • Most common Iron (Fe) “rusting”

  9. Chemical Weathering • Hydrolysis(water): • Materials react with water to form new material • Water dissolves rock • Chemicals in water react

  10. Chemical Weathering • Dissolution: • Acid dissolved in water dissolves rock Reactions • CO2 + H2O → H2CO3carbon dioxide + water → carbonic acid • H2CO3 + CaCO3 → Ca(HCO3)2carbonic acid + calcium carbonate → calcium bicarbonate

  11. Chemical Weathering • Plant Acids: • Some plantsproduce weak acids that seep into rocks and dissolve certain minerals • Examples : Lichens and Mosses

  12. Clicker • “rusting” is an example of which type of weathering process? • exfoliation • abrasion • dissolution • oxidation Times up! Timer

  13. Factors that influence weathering Rock Composition Climate • Rocks are made of minerals • Tougher the mineral the slower the weathering • Surface area • More area exposed to weathering forces, faster the weathering • Very cold( no change) • Slow weathering • Polar regions • Dry and Hot • Slow weathering • Desert regions • Moderate (warm summer/cold winter) • Fast weathering • Temperate regions

  14. Surface area and speed of weathering

  15. pH scale

  16. Clicker • While doing a standard pH test on uncontaminated rain water, you observe a pH of 5, this result indicates that: • Rain water is slightly more basic/alkaline • Rain water is neutral • You made an error • Rain water is acidic Times up! Timer

  17. Lab Analysis • pH concentration • “power of Hydrogen” • Lower pH = more H+ ion (acidic) • Higher pH= less H+ more OH- ion (basic or alkaline) • 1 x 10 – pH =Concentration

  18. Lab analysis • 1 x 10 -2.5= .003 • 1 x 10 -6.5= .0000003 • .003/.0000003= 10000 times more concentrated • Or 6.5-2.5=4 • 104 =10000

  19. The dirt on dirt (soil) • Bedrock: • Solid un-weathered rock below the surface • Regolith: • layer of loose, weathered material covering solid rock.(bedrock)

  20. Components of Soil • Minerals • 54% weathered rock • Rocks are made of minerals • Water • 25% water • Gases • 25% Air • Humus (organic matter): • 5% organic material

  21. Weathering and soil formation • Explain the relationship between weathering and soil formation. • Weathering and erosion make soil

  22. Soil profile • Soil profile: Cross section, shows layers top to bottom O. Organic materials • Topsoil (organic material) • Subsoil minerals collect • Regolith R. bedrock

  23. Clicker • Soil is formed as a result of which of the following: • Weathering of rocks and minerals • Decaying of plants and animals • Microorganisms adding Nitrogen • All of the above Times up! Timer

  24. Activity

  25. Answers • Tropical climate: • Rain and High temperatures cause thick infertile soils to develop. • Desert: • Low precipitation causes thin soil • Arctic: • Slow weathering creates thin soil