Global patterns of plate margins

• What evidence shows that the lithosphere and crust are broken into tectonic plates?

  Seismic data shows earthquakes in narrow bands
• What are the three types of plate boundaries?

  Divergent, Convergent, Conservative
• What occurs at divergent plate boundaries?

  Magma rises through the asthenosphere
• What are mid-ocean ridges known for?

  Long mountain chains at average depth of 2.5 km
• How are mid-ocean ridges characterized?

  They have frequent intervals split by transform faults
• What happens along transform faults?

  Volcanic activity is absent, but earthquakes occur
• What is the characteristic of fast spreading boundaries?

  Up to 16.5 cm per year
• What landforms are associated with fast spreading boundaries?

  Broad and smooth mountain chains
• What is the characteristic of medium spreading boundaries?

  1. 10 cm per year
• What is the characteristic of slow spreading boundaries?

  1. 3 cm per year with steep slopes
• Where is most magma erupted along divergent boundaries?

  Underwater, forming pillow lavas
• How are underwater rift valleys formed?

  Magma rises, reducing pressure and liquefying
• What did the extrusion of magma in the North Atlantic create?

  Iceland
• How are black smokers formed?

  Sea water seeps into rifts and is superheated
• Where are rift zones found?

  On the ocean floor and land
• What must the crust be like for continental crust to be pulled away?

  Very thin
• What is an example of a rift zone?

  The Red Sea northwards to Turkey
• What happens when oceanic and continental plates converge?

  The denser oceanic plate is forced under
• What are oceanic trenches?

  Long, narrow depressions with depths of 6000-11000 m
• What do oceanic trenches mark?

  The zone of subduction of oceanic crust
• What angle do oceanic plates subduct under continental plates?

  30-70 degrees
• What occurs while the oceanic plate subducts under the continental plate?

  Intense pressure and friction cause earthquakes
• What happens to oceanic plates during subduction?

  Dehydration triggers partial melting of the plate
• What forms when rising magma reaches the surface?

  Volcanoes
• What happens at oceanic-oceanic plate margins?

  The older, denser plate subducts under the other
• What forms at an oceanic-oceanic plate?

  Island arcs, like the Antilles
• What is common at convergent boundaries?

  Large earthquakes
• What percentage of earthquakes occur along conservative or convergent boundaries?

  80%
• Where is a famous area with island arcs?

  The Pacific 'Ring of Fire'
• What happens at continental-continental plates?

  Little to no subduction occurs
• What is an example of a continental-continental plate?

  The collision of African and Eurasian plates
• What happens at conservative plate margins?

  Plates slide past each other without volcanic activity
• What causes earthquakes at conservative margins?

  Frictional resistance to movement builds pressure
• What causes the largest earthquakes in conservative margins?

  Fracturing rocks release enormous energy
• What isn’t usually formed at conservative margins?

  Landforms, only tears or exposed rocks
• Give an example of a conservative plate boundary.

  California, North America and Pacific Plate