Earth’s Changing Surface

							Movement of the Earth’s
       Crust
            Essential Questions
 Describe how the Earth’s crust is deformed.
    –How does the formation of mountains, valleys,
    plateaus, and domes relate to stress?
    –How do faulting and folding change the
    appearance of the Earth’s surface?


 Define isostasy and explain its effect on the
 movement of the Earth’s crust.
         How Does Earth’s Surface
                Change?
• Stress pushes and pulls on the Earth’s
  crust.
• The rocks slowly change shape and
  volume
• They move up or down or sideways
• The breaking, folding or tilting of rocks is
  called deformation.
• 3 types of stress – compression, tension
  and shearing.
         What is Compression?
• Squeezes the rocks of the crust. Moves
  particles closer making rocks more dense.
• Rocks are pushed both higher up and
  deeper down.
            What is Tension?
• Pulls on rocks of crust
  causing them to
  stretch out over a
  larger area.
• Becomes thinner in
  the middle
• Volume increases
  while density
  decreases
            What is Shearing
• Pushes rocks of crust in 2 opposite directions.
• Causes rocks to twist or tear.
• Not compressed or stretched, just bent or
  broken apart
       What are the results of
      compression, tension and
            shearing?
• Change a rock’s volume, shape or both
• Can cause rocks to fracture, or crack
• Fractures along numerous flat surfaces
  which show no displacement are called
  joints. They are generally parallel to each
  other.
• If rocks have joints that form in more than
  one direction they may break into blocks.
           What is Faulting
• A break or crack along which rocks move
  is called a fault.
• Rocks on one side of a fault slide past the
  rocks on the other side.
• Movement can be up, down or sideways.
• Earthquakes often occur along faults
  What are the two blocks of rocks
       that make up a fault?
• Hanging wall – block of rock above the fault
• Foot wall – block of rock below the fault
     What are the types of faults?
• Normal fault – tension
  acts on a fault and the
  hanging wall moves
  down relative to the
  foot wall
               Reverse Faults
• Reverse fault –
  compression acts on
  a fault and the
  hanging wall moves
  up relative to the foot
  wall.
                  Thrust Faults
• Thrust fault – special type
  of reverse fault where the
  hanging wall slides over
  the foot wall. The
  movements are almost
  horizontal where normal
  and regular reverse faults
  are mostly vertical. Thrust
  faults often cause older
  rocks to be above younger
  rocks.
• Lateral fault –
  shearing causes
  blocks of rock to slide
  horizontally past each
  other
     What are faulted Mountains and
                Valleys?
• Fault-block mountains –
  caused by blocks of rock
  uplifted by normal faults
  – Ex. Cordilleran mountain
    region of North America.
    Extends from central
    Mexico to Oregon, and
    Idaho. Includes western
    Utah, Nevada and eastern
    California
• Rift valleys – formed when the block of land
  between 2 normal faults slides downward.
  – Ex. Death Valley in California
               What is folding?
• Fold – a bend in a rock.
• Anticline – upward fold in
  a rock
• Syncline – downward fold
  in a rock
• Folds vary in sizes
• Ex. Of folded mountains –
  Appalachian mountains
  extend from Alabama to
  Canada
Why do some rocks fold and some
            fault?
• Temperature is one factor – hotter more likely to
  fold
• Pressure – greater pressure, more likely to fold
• Rock type
  – brittle – break when stress is applied
  – ductile – bend under stress
• Application of stress
  – if applied gradually the rocks will usually fold
  – if applied suddenly the rock will usually fault
                 What are plateaus?
• Large area of flat land raised high above sea level, wider
  than it is tall, surrounded by steep cliffs
• Rock layers in a plateau remain flat
• Formed by:
   – a slow flat-topped fold, Ex. The Appalachian plateau which lies
     west of the Appalachian mountain.
   – Vertical faulting, Ex. Colorado Plateau which lies west of the
     Rocky Mountains
   – Series of molten rock flows, Ex. Columbia Plateau, in Oregon,
     Washington and Idaho
• Rivers often carve a plateau into many smaller plateaus.
  Ex. Colorado river carving the Colorado Plateau forms
  the Grand Canyon
          What are Domes?
• Uplifted area created by rising magma. Magma
  pushed upward but does not reach the Earth’s
  surface. Stress causes the rock layers to fold
  upward. Eventually magma cools and forms
  hardened rock.

• When domes wear away they form many
  separate peaks called dome mountains. Ex.
  Black Hills of South Dakota and Wyoming
                What is Isostasy?
• The balance of the downward force of the crust
  and the upward force of the mantle

• The more material that is added to an area of
  crust, the lower the crust floats on the mantle.
  The less material on the crust, the higher the
  crust will float on the mantle
• Examples of changes
   – melting glaciers removing weight from the crust – end
     up floating higher
   – added mud and sand from river discharge causes
     crust to float lower.
Isostasy
                                     Credits

 http://www.eos.ubc.ca/~ehearn/research2.html

   http://www2.nature.nps.gov/geology/usgsnps/deform/ghangft.html
    http://wapi.isu.edu/envgeo/EG5_earthqks/eg_mod5.htm
   http://www.geo.cornell.edu/geology/classes/RWA/GS_326/326_Gallery.html

p://www.geol.lsu.edu/henry/Geology3041/lectures/21MetamorphicIntro/MetamorphicIntro.ht
 http://www.consrv.ca.gov/CGS/information/publications/teacher_features/faults.htm
 http://library.thinkquest.org/17457/volcanoes/features.plateaus.php

 http://www.lpi.usra.edu/science/treiman/greatdesert/workshop/volcanos2/index.html

 http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tectonics_landforms/folding.html
dw.ethz.ch/index_en.cfm?content=english/ausstellung/geologie_palaeontologie/gesteinsdef