Earth�s Internal Processes by T4zZpUK


									Earth’s Internal Processes

       Plate Tectonics
• Recall that the Earth is composed of several
• Inner Core- Solid iron/nickel
• Outer Core- Molten iron/nickel
• Mantel- “Plastic” Molten Rock
• Crust- Solid Rock
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• Throughout most of history people believed
  that the continents were permanent and
• Alfred Wegener was one of the first to
  suggest the continents used to be joined
  together in one Super-continent he called
  Pangea, meaning “all land”
           Continental Drift
• Wegener proposed the hypothesis of
  continental drift which suggested that the
  continents were like icebergs of granite
  floating in a sea of more dense basalt.
• While now accepted as the truth this idea
  was laughed at until sufficient evidence was
• One of the first pieces of evidence to support
  continental drift was the discovery of fossils.
• An ancient freshwater reptile, Mesosaurus, was
  found in both Africa and South America.
• Tropical plant fossils were found in places that
  they would not normally be able to grow.
• Conclusion… the continents are moving.
             Evidence (cont)
• Evidence of glaciers were found in places were
  they could not have developed.
• People also noticed that similar rocks could be
  found on opposite sides of the Atlantic.
• The rocks near the mid-ocean ridge are much
  newer than the rocks that are farther away.
• It was concluded that the seafloor was spreading
  along the mid-oceanic ridge.
         High Tech Evidence
• Later studies showed that the rocks in the
  seafloor had alternating bands of magnetism
  that correlated with reversals in Earth’s
  Magnetic Field.
• Today very accurate lasers have determined
  that most continents are drifting at a rate of
  about 1inch per year.
             Plate Tectonics
• The Theory of Plate Tectonics states that
  the Earth’s crust is divided into sections
  called plates.
• These plates are moved around by
  convection currents in the mantle.
            Boundary Issues
• If all the plates are moving in different
  directions how do their boundaries interact.
• There are three types of plate boundaries
  – Divergent
  – Convergent
  – Transform
       Divergent Boundaries
• Divergent boundaries exist where two plates
  are moving apart from one another.
• Divergent boundaries in the ocean form mid
  ocean rifts and ridges.
• On continents they form rift valleys like
  Africa’s Great Rift Valley.
        Convergent Boundary
• When two plates are moving toward each
  other one of three convergent boundaries
  will form.
• This depends on the density of each of the
  plates involved
           Subduction Zone
• Where a seafloor plate impacts a less dense
  continental plate and sinks below it.
• The sinking plate brings water with it
  helping to create volcanoes.
• A similar type of convergent boundary
  occurs when two oceanic plates collide.
• Both tend to create volcanoes, earthquakes,
  and trenches.
               Going up?
• When two continental plates impact, they
  tend to move upward.
• This process created some of the biggest
  mountains in the world.
• The Himalayas were created as the Indian
  Plate smashed into the Asian Plate.
• They are still pushing up at about
     Transform Fault Boundary
• Transform fault boundaries occur where plates are
  sliding past or along side one another.
• These boundaries are known for many powerful
  earthquakes that release energy that builds up as
  the plates snag on one another.
• The San Andreas Fault is a famous transform fault
  boundary located under California.
• Earthquakes are caused by the motion of Earth’s
• We can measure the seismic waves caused by an
• We can also see where the waves originated and
  find the focus or point of origin for an earthquake.
• Most foci occur along plate boundaries, also called
             Seismic Waves
• Two types of seismic waves radiate out from the
  focus of an earthquake
• Primary waves move particles back and forth like
  sound waves.
• Secondary waves move particles up and down like
  ocean waves
• On the surface these two waves join to give the
  ground an elliptical motion.
• Earthquakes cause massive damage to man made
        Seismic Waves (cont)
• Seismic waves don’t just locate the focus or
• They can also be used to map Earth’s
  interior because only primary waves are
  able to travel through molten rock.
• They can show us the location of magma
  chambers beneath volcanoes.
       Measuring Earthquakes
• Earthquakes can be measured using a
  seismometer, which traces the affect of the
  seismic waves on a rotating drum.
• These tracings can be used to measure the
  energy or strength of the earthquake which
  is described with the Richter Scale.
               Richter Scale
• Is a log base scale.
• A 2.00 earthquake is 10 times stronger than a 1.00
• Under 4.00 is considered to be minor and over
  6.00 is considered to be strong.
• Weaker earthquakes are very common while
  strong earthquakes are very rare.
• The strongest recorded earthquake was a 9.5 in
  Chile in 1960.
• When an earthquake strikes under or near water
  the waves it releases can travel through the water
  generating an enormous wave.
• These waves can cause lots of damage when they
  hit shore.
• Dec 26, 2004 an earthquake of the coast of
  Sumatra generated a tsunami that had a death toll
  of 230,000 people and traveled across the entire
  Indian Ocean
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• Volcanoes are mountains that form as lava
  and ash from repeated eruptions from a vent
  build up layer by layer.
• The lava comes from magma chambers
  below the Earth’s surface.
• The opening at the top of the volcanoes vent
  is called the crater or cauldera.
• Divergent Boundaries - lava erupts through the
  rifts and cools. Mid-oceanic Ridge, Iceland.
• Convergent Boundaries. Occur as water mixes
  with lava increasing pressure. Mt. St. Helens, Mt
• Hot Spots - Some volcanoes occur as hotspots in
  the mantle heat portions of the crust enough to
  melt them and build up pressure. Hawaii,
   – Hot spots stay in place as plates move above them
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          Types of Eruptions
• Eruptions can either be explosive and
  violent or lava can quietly seep out of a
• Magma that has lots of gasses trapped
  inside tend to erupt more violently than
  magma with little gas.
• Basaltic magma tends to trap less gas than
  granitic magma because it is more liquid.
             Pyroclastic Flows
• Translated roughly to fire rock these are the result
  of explosive granitic eruptions.
• Mixture of hot gas and rock (tephra) that moves
  away from the volcano at speeds of up to 450mph
  and temperatures of near 2000ºF
• Often the most deadly aspect of a volcano, a
  pyroclastic flow was responsible for the creation
  of the ruins of Pompeii
         Types of Volcanoes
• Shield Volcanoes form when quiet
  eruptions build up shallow layers of igneous
• Cinder Cone Volcanoes form as tephra
  builds up to form a steep sided mountain.
• Composite or Strato-volcanoes form when a
  volcano regularly switches between quiet
  and violent eruptions.

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