Plate boundaries

• Oceanic-oceanic divergent

  • 2 oceanic plate move apart
  • Decrease in overlying pressure cause the underlying mantle to melt in magma
  • Magma rises through the weak area in the crust to the earth’s surface & fills gaps
  • Lava cools & solidifies to form basaltic rocks
  • The rocks form a new oceanic crust
  • An extensive underwater mountain chain (mid-ocean ridge) forms
• Oceanic-oceanic divergent (2)

  • Centre of the ridge is a deep rift valley with steeps sides
  • Magma rises through the weak area in the crust to the earth’s surface, forming submarine volcanoes
  • After many eruptions, volcanoes may break the surface of the ocean to form volcanic islands
  • Earthquake may occur due to stress & tension released when plates move
• Continental-continental divergent

  • 2 continental plates move apart
  • Rocks eventually fracture to form parallel faults
  • Rocks between these faults collapses to form a deep rift valley with steep sides
  • The decrease in overlying pressure causes underlying mantle to melt into magma
  • Magma rises through weak areas in the crust to the earth’s surface, forming volcanoes
  • Earthquakes may occur as stress and tension are released when plates move
• Oceanic-oceanic convergent

  • 2 oceanic plate collide
  • Denser plate subducts beneath the other plate
  • A deep depression (oceanic trench) is form
  • The subduction plate sinks into the mantle, high pressure forces water out of its oceanic crust
  • Water lowers the melting point of the overlying mantle, causing it to melt into magma
  • Magma rises through the weak areas in the crust to the earth’s surface
  • Forms a chain of volcanoes (volcanic islands)
  • Earthquake may occur due to friction along the subducting plate
• Continental-continental convergent

  • 2 continental plates collide
  • Subduction does not take plate as the continental plates are too buoyant
  • Enormous pressure causes the rocks to be uplifted & buckled to form fold mountains
  • Earthquake may occur due to the enormous build-up of pressure
  • Magma does not rise to the surface -> no volcanoes
• Oceanic-continental convergent

  • Oceanic and continental plates collide
  • Denser oceanic plate subducts beneath the continental plate
  • Forms an oceanic trench in the subduction zone
  • The subduction plate sinks into the mantle, high pressure forces water out of its crust
  • Water lowers the melting point of the mantle, causing it to melt into magma
  • Magma rises through the weak areas in the crust to the earth’s surface, forming volcanoes on the continental plate
• Oceanic-continental convergent (2)

  • Earthquakes may occur due to friction along the subducting oceanic plate
  • Enormous pressure cause the rocks on the continental plate to be uplifted & buckled, forming fold mountains
• Transform plate boundaries

  • 2 plates slide past each other, no crust is created/destroyed
  • Stress caused by the plate movement produces a fault (a zone of fractures between 2 blocks of rocks)
  • Earthquakes may occur as 1 plate suddenly slips past another
  • Magma does not rise to the earth’s surface -> no volcanoes