searsc mod 4

• Weathering


  Physical, chemical, and biological processes that break up or crumble solid rock
• Erosion


  Removal of rock and mineral fragments, clays, and solutions that have been produced from solid rock by weathering
• Soils


  Mixture of the products of weathering—sand, silt, and clay—and humus
• Agents of erosion


  • Gravity
  • Running water
  • Glaciers
  • Wind
• Weathering, Erosion, and Transportation

  1. Weathering breaks down rocks

  2. Erosion removes weathered materials

  3. Transportation moves eroded materials
• Mechanical weathering


  • Physical breaking up of rocks without changes in chemical composition
• Mechanical weathering


  • Frost wedging
  • Exfoliation
• Chemical weathering


  • Alteration of minerals by chemical reactions with water, gases of the atmosphere, or solutions
• Chemical weathering


  • Oxidation
  • Carbonation
  • Hydration
• Mechanical weathering and chemical weathering are interrelated, working together in breaking up and decomposing solid rocks
• Mechanical weathering creates cracks and coarse fragments, while chemical weathering creates finely pulverized materials and ions in solution
• Granite is made up of feldspars, quartz, and ferromagnesian minerals
• Weathering of granite


  1. Mechanical weathering creates cracks

  2. Chemical weathering reacts with minerals to form soluble carbonates, metal oxides, and clay minerals

  
• Silica


  Silicon dioxide (SiO2), may appear as a suspension of finely divided particles or in solution
• Mechanical weathering and chemical weathering

  Interrelated, working together in breaking up and decomposing solid rocks of Earth's surface
• Mechanical weathering


  Results in cracks in solid rocks and broken-off coarse fragments
• Chemical weathering


  Results in finely pulverized materials and ions in solution, the ultimate decomposition of a solid rock
• Granite is made up of 65 percent feldspars, 25 percent quartz, and about 10 percent ferromagnesian minerals
• Mechanical weathering of granite


  Exfoliation and frost wedging create cracks in the solid mass

  
• Chemical weathering of granite

  1. Rainwater, with dissolved oxygen and carbon dioxide, flows and seeps into the cracks and reacts with ferromagnesian minerals to form soluble carbonates and metal oxides

  2. Feldspars undergo carbonation and hydration, forming clay minerals and soluble salts, which are washed away

  3. Quartz is less susceptible to chemical weathering and remains mostly unchanged to form sand grains
• The end products of the complete weathering of granite are quartz sand, clay minerals, metal oxides, and soluble salts
• Soil


  Accumulations of the products of weathering—sand, silt, and clay—plus humus, which is altered, decay-resistant organic matter
• Mature, fertile soil


  • Result of centuries of mechanical and chemical weathering of rock, combined with years of accumulated decayed plants and other organic matter
• Factors affecting soil types

  • Parent rock type
  • Climate
  • Time of accumulation
  • Topographic relief
  • Elevation
  • Rainfall
  • Percentage of clay, sand, or silt
  • Amount of humus
  • Other environmental variables
• Soils formed in cold and dry climates

  Shallower with less humus than soils produced in wet and warm climates
• Chemical reactions occur at a faster pace in warmer, wetter soil than they do in dry, cooler soil
• Wet and warm climate would be more conducive to plant growth, which would provide more organic matter for the formation of humus
• Loam


  Easily crumbled soil that has approximately equal proportions of sand, silt, and clay
• Topsoil


  The uppermost, more fertile layers of soil, closer to the source of humus
• Subsoil


  The soil beneath the topsoil, often containing more rocks and mineral accumulations and lacking humus
• Sand grains


  • Help keep the soil loose and aerated, allowing good water drainage
• Clay minerals


  • Help hold water in a soil
• A good, fertile loam contains some clay and some sand
• The balanced mixture of clay minerals and sand provides plants with both the air and the water that they need for optimum root growth
• Weathering has prepared the way for erosion and for some agent of transportation to move or carry away the fragments, clays, and solutions that have been produced from solid rock
• Mass movement


  Erosion caused by gravity acting directly on individual rock fragments and on large amounts of surface materials, pulling them to a lower elevation
• Mass movement


  • Creep
  • Landslide
• Gravity constantly acts on every mass of materials on the surface of Earth


  Pulling parts of elevated regions toward lower levels
• Gravity acts directly on individual rock fragments and on large amounts of surface materials as a mass, pulling all to a lower elevation
• Mass movement can be so slow that it is practically imperceptible, or as sudden and swift as a single rock bounding and clattering down a slope from a cliff