Plates Key Terms

Crust: The outer layer of the earth 

Plate: A section of the earth's crust 

Plate margin: The boundary where two plates meet 

Mantle: The dense mostly solid layer of the earth between the outer core and the crust. 

Convection currents: The circular currents of heat in the mantle 

Destructive: A plate margin where two plates are moving towards each other, resulting in one plate sinking beneath the other. 

Constructive: Two plates that are moving apart

Conservative: Two plates sliding alongside each other

Earthquake: A sudden, often violent shift in the rocks forming the earth's crust, which is felt at the surface

Volcano: An opening in the earth's crust through which molten lava, ash and gases are ejected. 

Oceanic crust: A tectonic plate made of dense iron rich rock that forms the ocean floor. 

Continental crust: A tectonic plate made of low density continental rock that will not sink under another plate. 

Subduction: When oceanic crust sinks under continental crust at a destructive margin

Collision: When two plates of continental crust meet 'head on' and 'buckle'.

Past exam questions: 

Explain how volcanoes from at destructive plate margins

• Convection currents in the lower mantle cause the plates to move towards each other
• If plates are continental v oceanic crust, the oceanic (denser) crust will sink below the continental (lighter) crust in a process called subduction. 
• Great pressure is exerted and heat is produced from friction between the plates which destroys (melts) the oceanic plate to form magma. 
• The magma is lighter than its surroundings so rises to the surface causing violent volcanic eruptions. 

Explain how earthquakes occur at conservative plate margins

• Plates moving in similar directions (but not the same)
• The pressure builds up as the plates stick 
• Sudden release causing the jerking movement which is the earthquake 
• For example the San Andreas Fault