CHAPTER 5 GLOBAL LANDFORMS

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CHAPTER 5 GLOBAL LANDFORMS

• All land on the earth is constantly being changed
• Forces shaping the land are either primary forces
  or secondary forces
• Primary landforms are formed by internal forces
  within the earth
• Secondary landforms are formed by external forces
  such as water, ice and wind

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Primary Landforms

• Forces inside of the earth create primary
  landforms
• These forces continue to push up the surface and
  break it apart
• The earth is composed of four layers
• Solid inner core
• Liquid outer core
• Mantle
• Crust

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Forces Beneath the Crust

• The earths surface is bent and broken by heat
  and by rock movements in the crust and upper
  mantle
• The melted, liquid rock from within the earth
  that spills out onto the surface is called lava
• The opening in the earths crust through which
  lava flows is called a volcano

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More Forces

• When rock layers are bent, the result is a fold
• When rock layers break and move apart, the
  result is a fault
• The vibrations caused by movement along a fault
  is called an earthquake
• The weight and hardness of rocks also play a role
  in shaping the earths crust

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THEORY OF PLATE TECTONICS

• This theory helps to explain how the worlds
  large landforms were formed
• The earths crust and upper mantle are divided
  into more than a dozen huge slabs called plates
  which are constantly moving around, carrying the
  continents and ocean floors with them

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Plate Boundaries

• Sometimes plates move away from each other,
  resulting in a mid-ocean ridge on the abyssal
  plain of the ocean floor
• Islands created by this process are volcanic
• Sometime a heavier plate dives under another
  plate and sinks into the upper mantle, creating
  trenches on the ocean floor
• The process of one plate diving under another is
  called subduction

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Colliding Plates

• When one of the colliding plates has a continent
  on it, the lighter rocks of the continent crumple
  and form a mountain range such as the Andes
• Sometimes two continental plates collide and the
  lighter rocks of the continent move together
  building huge mountains such as the Himalayas

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When Plates Slide Past Each Other

• When plates pass one another, low mountains may
  result such as those under the San Andreas Fault
  system in California
• Earthquakes frequently occur in this situation

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Drifting Continents

• German scientist, Alfred Wegener proposed in 1912
  that all continents were once part of a
  supercontinent that broke into pieces and fell
  apart in a process called continental drift.
• Proof of this process includes mid-oceanic
  mountain ranges, younger ocean floors than
  continents and trenches, earthquakes and
  volcanoes.

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Plate Tectonics and the Earths History

• 200 million years ago there was one
  supercontinent called Pangaea
• Pangaea then broke into two small
  superconctinents called Laurasia and Gondwanaland
• These then split and drifted to form the modern
  continents
• Continental drift continues today.