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Es Ch  6 Weathering&Soil
 

Es Ch 6 Weathering&Soil

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    Es Ch  6 Weathering&Soil Es Ch 6 Weathering&Soil Presentation Transcript

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