Folding and Faulting

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Folding and Faulting

• By Justin Noftall

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Folds

• A fold is when the earths crust is pushed up
  from its sides. There are six types of folds
  that may occur
• Anticline
• Syncline
• Tight Fold
• Overfold
• Recumbent Fold
• Nappe Fold

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Anticline

• An anticline occurs when a tectonic plate is
  compressed by movement of other plates. This
  causes the center of the compressed plate to bend
  in an upwards motion.
• Fold mountains are formed when the crust is
  pushed up as tectonic plates collide. When
  formed, these mountains are usually enormous like
  the newly formed Rocky Mountains in Western
  Canada and the United States
• To the top right is a picture of an anticline.
  Beneath is a picture of the Rocky Mountains.

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Syncline

• A syncline is similar to an anticline, in that it
  is formed by the compression of a tectonic plate.
  However, a syncline occurs when the plate bends
  in a downward motion.
• The lowest part of the syncline is known as the
  trough.
• To the top right is a diagram of a syncline fold
  (The bottom of the fold center is the trough).
  Beneath, is an example of a syncline in
  California. Can you distinguish the trough in
  this picture?

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Tight Fold

• A tight fold is a sharp peaked anticline or
  syncline.
• It is just a regular anticline or syncline, but
  was compressed with a greater force causing the
  angle to be much smaller.
• Folds such as these occur to form steep mountain
  slopes like those in Whistler, British Columbia.
• To the left is a photo of a tight fold formed by
  extreme pressure on these rocks.

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Overfold

• An overfold takes place when folding rock becomes
  bent or warped.
• Sometimes the folds can become so disfigured that
  they may even overlap each other.
• An example of overfolding is shown in the diagram
  below.

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Recumbent Fold

• This type of fold is compressed so much that it
  is no longer vertical.
• There is a large extent of overlapping and it can
  take the form of an s.
• To the right is a diagram that shows the process
  of recumbent folding.

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Nappe Folding

• This fold is similar to a recumbent fold because
  of the extent of folding and overlapping.
  However, nappe folding becomes so overturned that
  rock layers become fractured.
• To the right is a picture of someone standing
  under a fractured fold.

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Faults

• A fault is when tension and compression
  associated with plate movement is so great that
  blocks of rock fracture or break apart. This
  process can occur very rapidly, in the form of
  earthquakes. The damage caused by this event can
  be very destructive and cause severe changes to
  the earths surface. There are five types of
  faults that can occur
• Normal Fault
• Reverse Fault
• Tear Fault
• Rift Valley
• Horst Fault

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Normal Fault

• This occurs when rocks move away from each other
  due to the land moving apart.
• When the rocks move apart, the side with the less
  stable tectonic plate drops below the side with
  the more stable plate.
• On the top right is the movement of a normal
  fault. A picture is also shown below. Notice
  the displacement of the different types of rock
  on each side of the fault.

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Reverse Fault

• Reverse faults are the opposite of normal faults.
  Rocks are compressed such that one plate moves
  up while the other descends below it.
• When plates compress and crack, usually the more
  dense one is forced under the less dense one.
  This is similar to the action of the continental
  crust colliding with the oceanic crust. Here the
  more dense crust, being the oceanic crust is
  forced under the continental crust.
• To the right is an animation of a reverse fault.
  Below that is a real picture of what a reverse
  fault looks like.

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Tear Fault

• A tear fault, also known as a transform fault,
  occurs when two tectonic plates slide in a
  lateral motion past each other.
• This type of fault causes the most severe
  earthquakes because they grind against each
  other. These earthquakes can either be shallow
  or deep and cause tremors over a short or long
  period of time.
• Tear faults can occur frequently, especially
  along the coast of California.

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Rift Valley

• A rift valley is when two normal faults occur
  parallel to each other and the land sinks between
  the faults.
• There are two major examples of this. One being
  the Great Rift Valley in North Africa and the
  other, the San Andreas Fault in California.
• The top right picture is San Andreas Fault and on
  the bottom right is a diagram of what a rift
  valley looks like.

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Horst Fault

• A Horst is the opposite of a rift valley. The
  land between the parallel faults is forced upward
  because the two faults are being pushed together.
• This process can take a long time to occur
  because the average plate movement is one inch
  per year.
• There are examples of horst faults on the left.

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Summary

• Folding and faulting has a major influence on the
  way the earth looks. Mountains form and disappear
  over time, as well as large rift valleys and
  other features. This has an impact on where and
  how we live.

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The End