Deforming the Earth’s Crust

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Deforming the Earths Crust
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Deformation

• Stress is the amount of force per unit area on a
  given material
• The process by which the shape of a rock changes
  because of stress is called deformation

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Deformation

• Two types of deformation can occur to rocks under
  stress
• Layers can bend when stress is applied to them
• When too much stress is applied, they can reach
  their elastic limit and break

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Compression Tension

• Compression is the type of stress that occurs
  when an object is squeezed
• Tension is stress that occurs when forces act to
  stretch an object such

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Folding

• Folding is the bending of rock layers because of
  stress in the Earths crust
• Scientists assume that all rock layers start off
  horizontal
• So when scientists see a fold, they know
  deformation has occurred

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Types of Folds

• There are two main types of folds
• Anticlines, upward, arching fold
• Synclines, downward, trough-like folds

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Faulting

• Some rock layers break when too much stress is
  applied to them.
• The surface along which a rocks break and slide
  past each other is called a fault

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Faulting

• The two sides of a fault are known as the hanging
  wall and the footwall
• The type of fault that forms is dependent on
  where the hanging and footwall are located

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Types of Faulting

• There are three types of faults that occur
• Normal Faults
• Reverse Faults
• Strike-Slip Faults

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Normal Faults

• When rocks are pulled apart because of tension,
  normal faults often form
• When a normal fault moves, it causes the hanging
  wall to move down relative to the footwall

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Reverse Fault

• When rocks are pushed together by compression,
  reverse faults often form
• When a reverse fault moves, it causes the hanging
  wall to move up relative to the footwall
• Special type of reverse fault occurs when the
  hanging walls continues to be pushed over top of
  footwall called a thrust fault

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Strike-Slip Fault

• Forms when opposing forces cause rock to break
  and move horizontally
• If you were standing on one side of the fault
  when it moved, the ground on the other side would
  appear to move to your left or right

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Thrust Fault
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Plate Tectonics Mountain Building

• When tectonic plates collide, land features that
  start as folds and faults, can eventually become
  large mountain ranges
• When tectonic plates undergo compression and
  tension, they can form mountains in several ways

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Folded Mountains

• Form when rock layers are squeezed together and
  pushed upward
• These mountains form at convergent plate
  boundaries
• Appalachian Mountains 390 million years ago

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Fault-Block Mountains

• When tectonic forces put enough tension on the
  Earths crust, a large number of normal faults
  can occur
• Fault-Block mountains form when tension causes
  large blocks of the Earths crust to drop down
  relative to other blocks
• Often leaves sharp, jagged peaks

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Volcanic Mountains

• Located at convergent plate boundaries where
  oceanic crust sinks into the asthenosphere at
  subduction zones
• The rock that is melted at subduction zones forms
  magma which rises to the surface and erupts

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Volcanic Mountains

• Sometimes these mountains can rise above the sea
  and become islands
• A majority of the tectonically active volcanic
  mountains have formed around the Pacific Plate
  which is known as the Ring of Fire

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Uplift and Subsidence

• Uplift is the rising of regions of Earths crust
  to higher elevations
• Subsidence is known as the sinking of Earths
  crust to lower regions

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Uplifting of Depressed Rock

• One way areas rise without deforming is a process
  known as rebound
• Rebound occurs when the crust slowly springs back
  to its previous elevation
• Rebound happens when a weight is removed from a
  region ( glacial melting)

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Tectonic Letdown

• Subsidence can occur when the lithosphere becomes
  stretched
• A rift zone is a set of deep cracks that forms at
  a divergent plate boundary
• As the plates move apart, the rift zone begins to
  subside between the plates

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Question 1

• What are two types of deformation?

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Answer

• Layers of rock can bend when stress is applied to
  them and if too much pressure is applied then the
  layers can break

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Question 2

• What type of fold has an upward, arching fold
  that looks like the letter A?
• Syncline
• Monocline
• Anticline

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Answer

• The answer is C. An anticline has an upward,
  arching fold

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Question 3

• What type of fault forms when opposing forces
  cause rock to break and move horizontally?
• Normal Fault
• Reverse Fault
• Strike-Slip Fault

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Answer

• The answer is C. A strike-slip fault is formed
  when opposing forces cause the rock to break and
  move horizontally.