Plate Boundaries


    1.    Explain the differences between divergent, convergent, and transform plate boundaries.

    2.    Describe the land features associated with each type of plate boundary.

    3.    Give examples of land structures found at each plate boundary.

    4.    Discuss the formation and breakup of Pangaea including the mechanism and the approximate time of its breakup.




All around the Earth the topography of the continents is undergoing constant change.  We are reminded daily by the occurrence of earthquakes and the occasional eruption of volcanoes.  The change is due to the movements of tectonic plates and the boundaries between them.  There are three major types of boundaries.  Each is classified according to the type of movement.

Plate Boundaries
Associated with plate boundaries
bulletSeismic activities (earthquakes)
bulletMountain building
bulletRift valley formation
Types of plate boundaries
  •   Divergent
          Boundary between two lithospheric plates that are moving apart
          Most exist along oceanic ridges
          Seafloor spreading occurs at this type of boundary
    bulletForms fractures
    bulletFractures fill with molten material
    When the border occurs on a continent, rift or rift valleys form


    ( mid-atlantic%20ridge%203.jpg)                                            ( painted%20mid-ocean%20ridge.jpg)

    bulletThe Great Rift Valley







    ( images/Somali_3.jpg)


    bulletConvergent boundaries
    bulletFormed when two plates are moving towards each other
    bulletSets up subduction boundaries
    bulletOceanic Oceanic boundaries
    bulletOften forms volcanoes
    bulletIsland arcs form as volcanoes emerge
    bulletAleutian Islands
    bulletAlaskan Peninsula




    ( intro/oceanocean.gif)



    bulletContinental Oceanic boundaries
    bulletForms a subduction zones with a deep ocean trench
    bulletMore dense oceanic plate dives under the less dense continental plate
    bulletVolcanic arcs (mountain ranges) form
    bulletSierra Nevada

    ( exam1images/Fg16_09b.jpg)


    bulletContinental Continental (collision) boundaries
    bulletDoes not always form a subduction zone
    bulletCan produce mountains

    ( ewilson/Himalayas.jpg)

    bulletTransform boundaries
    bulletPlates slide past one another
    bulletNo new crust is created
    bulletNo crust is destroyed
    Transform faults - San Andreas
    bulletMost are in oceanic crust

      ( PlateTec/SanAndreas.JPG)



    Formation and Breakup of Pangaea

    Although no one can be certain how long Pangaea was together most data supports that 250 million years the Earth consisted as one super continent called Pangaea.  Since the oldest rocks on the Earth's floor are around 200 million years old, most scientists believe that the continent began to break up at that time.

    bulletBreakup began about 200 million years ago
    bulletN.America and Africa separated between 200 and 165 million years ago
    bulletAfrica and S.America separated about 135 million years ago

    ( 5globesbutton.gif)