Deformation of the Earths Crust

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Deformation of the Earths Crust
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What is deformation?

• Bending, tilting, and breaking of the Earths
  crust
• Deformation is most commonly a result of plate
  tectonics
• But, another means of deforming the Earths crust
  results from Isostacy

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What is Isostacy?

• It is the balance between two forces the crust
  pressing down on the mantle and the mantle
  pushing up on the crust
• The balance between these two forces is when the
  two forces are at equilibrium, the crust moves
  neither up or down

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Mechanics of Isostacy

• If an object is floating, and mass is added to
  it, or it becomes thicker, the object will sink.
• If an object is floating, and mass is removed, or
  it becomes thinner, then more of the object will
  float.

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Isostatic Adjustment

• Ways that the crust can gain more mass
• deposition of sediment, addition of mountains
  or volcanism, glaciation
• Ways that the crust can loose mass weathering,
  glacial rebound

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Deposition of Sediment
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Venetian Subsidence
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Subsidence
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Rebound of the crust from Weathering
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Formation of the Appalachians
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1811 New Madrid, Missouri earthquake

• In the top three of largest earthquakes to strike
  North America
• At least 8.0 magnitude
• Changed the course of the Mississippi river,
  toppled trees, swallowed farms..

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Why an earthquake in Missouri?

• North America is bending back to normal, crustal
  rebound.
• As the Appalachians undergo weathering, they are
  getting lighter, so the crust in that location is
  moving back up.
• Another cause besides weathering.

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Glacial Rebound

• During ice ages, the continents become covered
  with thick extensive ice sheets that weight down
  the crust, eventually warping it.
• When the glaciers retreat and melt, the crust
  rebounds and tries to bend back to normal.