Chapter 2: Section 3

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Chapter 2 Section 3

• Internal Forces shaping the Earth

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A Human Perspective

• Sally Ride, Americas first female astronaut,
  wrote the following after one of her trips into
  space
• I also became an instant believer in plate
  tectonics India really is crashing into Asia,
  and Saudi Arabia and Egypt really are pulling
  apart, making the Red Sea even wider. Even though
  their respective motion is really no more than
  mere inches a year, the view from overhead makes
  the theory come alive.
• From space, ride was seeing evidence of the
  internal forces that have shaped the earths
  surface.

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Plate Movement

• Most Scientists assume that the force is a
  process called convection. Convection is a
  circular movement caused when a material is
  heated, expands rises, then cools falls.
  This process is thought to be occurring in the
  hot, pliable mantle rock beneath the plates

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The Earths Major Plates
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Plate Tectonics

• Divergent boundary Plates move apart or spread.
• Convergent boundary (subduction)Plates collide
  with each other, causing one plate to either dive
  under or ride up over the other plate.
• Convergent (Collision) Crashing into one another
  resulting in the formation of mts.
• Transform Boundary Plates slide past one another.

• The Earths surface is elastic. Physical
  geographers now know that Earths crust is broken
  into a series of huge, rigid slabs or Plates,
  some of them as large as continents.
• The movement of these plates is called Plate
  tectonics.
• They shape our land.
• Tectonics plates move in one of four ways

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Seafloor Spreading

• After WWII, scientists began to use sonar to map
  the floor of the Atlantic Ocean. They also began
  to investigate the age of the rocks on the
  seafloor as well as other features of the ocean
  landscape.
• Ex Mid-Atlantic Ridge, Pacific Rim, some of
  these ridges emerge as islands.
• The theory of seafloor spreading is that molten
  rock from the mantle rises under the mid-oceanic
  ridge and breaks through the rift. As the
  seafloor moves away from the ridge, it carries
  older rocks away.

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Seafloor Spreading

• Seafloor spreading (Divergent) is the movement of
  two oceanic plates away from each other, which
  results in the formation of new oceanic crust
  (from magma that comes from within the Earth's
  mantle) along a a mid-ocean ridge.

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Convergent Subduction

• Oceanic Plate and Continental Plate can cause
  volcanoes
• Two Oceanic Plates same, one may be push under
  cause magma activity
• Two Continental Plates Create mts

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Earthquakes

• When plates grind or slip past each other at a
  fault the earth shakes or trembles.
• Seismograph will measures the size of the waves
  created by an earthquake.
• Richter Scale uses information collected by a
  seismographs to determine the relative strength
  of an earthquake.
• San Andrea fault line in California.

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Tsunami

• A tsunami is undetectable far out in the ocean,
  but once it reaches shallow water, this
  fast-traveling wave grows very large.

• A tsunami is a very large sea wave that is
  generated by a disturbance along the ocean floor.
  This disturbance can be an earthquake, a
  landslide, or a volcanic eruption.

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Volcanism

• Heat from the upper levels of the mantle forces
  its way to the surface at weak places in the
  Earths crust leading to volcanism.
• When magma erupted through the surface it is
  called lava.

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Hot Spots Mantle thermal plumes

• In 1963, J. Tuzo Wilson, the Canadian
  geophysicist who discovered transform faults,
  came up with an ingenious idea that became known
  as the "hotspot" theory. Wilson noted that in
  certain locations around the world, such as
  Hawaii, volcanism has been active for very long
  periods of time. This could only happen, he
  reasoned, if relatively small, long-lasting, and
  exceptionally hot regions -- called hotspots --
  existed below the plates that would provide
  localized sources of high heat energy (thermal
  plumes) to sustain volcanism.

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Ring of Fire a zone around the rim of the
Pacific Ocean, is the location of vast majority
of active volcanoes.