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Changes on the earth’s surface. 1-3. I. Weathering. Weathering – breakdown of rock at or near the earth’s surface into smaller and smaller pieces Mechanical Weathering – occurs when rock is actually broken or weakened physically

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i weathering
I. Weathering
  • Weathering – breakdown of rock at or near the earth’s surface into smaller and smaller pieces
  • MechanicalWeathering – occurs when rock is actually broken or weakened physically
          • 1. breaks large masses of rock into smaller pieces (boulders,
          • stones, pebbles, sand, silt, and dust)
slide3

C. ChemicalWeathering – alters a rock’s chemical makeup by changing the minerals that form the rock or combining them with new chemicals

  • 1. can change one rock into a completely different type of rock
  • 2. many caves are formed when acidic water seeps into cracks of
  • rocks
  • 3. acid rain – chemicals in the polluted air combine with water
  • vapor and fall back to earth (destroys forests, pollutes water, eats away at stone buildings)
examples
examples

Mechanical Weathering

Chemical Weathering

ii erosion
II. erosion
  • Erosion – movement of weathered materials such as gravel, soil, and sand
  • 3 most common causes of erosion:
    • 1. water
    • 2. wind
    • 3. glaciers
  • Important part of the cycle that has made and kept the earth a place where living things can survive
a water
A. Water
  • Water is the greatest cause of erosion, because over time, water can cut into the hardest rock and wear it away
  • Water moving down a streambed carries sediment (small particles of soil, sand, and gravel)…that sediment helps grind away the surface of rocks
  • The rock and soil that is carried away with erosion eventually creates other landforms
  • The Mississippi River carries approximately 159 million tons of sediment a year
  • Crashing ocean surf causes steep bluffs, cliffs, or sand dunes
b wind
B. Wind
  • Cause of erosion in areas where there is little water and few plants to hold the soil in place
  • In the Great Plains, the rich fertile soil that they once had was blown away by the wind during a drought…this area is now known as the “Dust Bowl” because they cannot grow anything there anymore
  • The wind can also deposit mineral-rich dust and silt called loess, which can help areas that once were barren
  • Sandstorms can cause erosion by carving or smoothing the surfaces of rock formations and man-made objects
c glaciers
C. glaciers
  • Glaciers – huge, slow-moving sheets of ice
  • Form over many years as layers of unmelted snow are pressed together, thaw slightly, and then turn to ice
  • As glaciers move, they carry dirt, rocks, and boulders
  • The time periods where much of the earth is covered in glaciers are known as Ice Ages – geologists believe that we’ve had at least 4
  • Much of the U.S. was formed by glaciers (Great Lakes, Long Island, etc.)
  • Glaciers slide forward because of how heavy they are and only pieces of it move at a time (oozes)