WEATHERING & THE RIVER VALLEY.

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  • WEATHERING & THE RIVER VALLEY.
    • WEATHERING:
      • FREEZE-THAW WEATHERING: mechanical weathering that happens in a drainage basin
        • 1)happens when the temperature alternates above and below 0 degrees Celsius (the freezing point of water)
        • 2)Water gets into rock that has cracks, e.g. granite
        • 3)When the water freezes it expands, which puts pressure on the rock
        • 4)When the water thaws, it contracts, which releases the pressure on the rock.
        • 5)Repeated freezing and thawing widens the cracks and causes the rock to break up.
      • MECHANICAL WEATHERING: breakdown of rock without changing its chemical composition
      • FREEZE-THAW WEATHERING: mechanical weathering that happens in a drainage basin
      • CHEMICAL WEATHERING: breakdown of rock by changing its chemical composition
      • CARBONATION WEATHERING: chemical weathering that happens in warm and wet conditions:
        • rainwater has carbon dioxide dissolved in it, which makes it a weak carbonic acid.
        • carbonic acids react with rock that contains calcium carbonate, e.g. limestone,so the rocks are dissolved by rainwater
      • BIOLOGICAL WEATHERING: breakdown of rocks by living things, e.g. plant roots break down rocks by growing into cracks on their surfaces and pushing them apart
    • THE RIVER VALLEY
      • COURSE: the paths of a river as it flows downhill
      • Rivers flow in channels in valleys.
      • They erode the landscape- wear it down, then transport the material to somewhere else where its deposited
      • The shape of the valley and channel changes along the river depending on whether erosion or deposition is having the most impact.
      • LONG PROFILE: shows how the gradient (steepness) changes over the different courses.
      • CROSS PROFILE: shows what a cross-section of the river looks like
      • UPPER COURSE:
        • GRADIENT: steep.
        • VALLEY AND CHANNEL SHAPE: V-shaped valley, steep sides, narrow, shallow channel
      • MIDDLE COURSE:
        • GRADIENT: medium
        • VALLEY AND CHANNEL SHAPE: gently sloping valley sides, wider, deeper channel
      • LOWER COURSE:
        • GRADIENT: gentle
        • VALLEY AND CHANNEL SHAPE: very wide, almost flat valley. very wide, deep channel.
  • BIOLOGICAL WEATHERING: breakdown of rocks by living things, e.g. plant roots break down rocks by growing into cracks on their surfaces and pushing them apart

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