Formation of Earthquakes & Volcanoes (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Convection currents

• The heat within the Earth's core (geothermal energy), which is estimated to reach up to between 5000 and 6000°C, is generated by radioactive decay

• Heat rises from the Earth's core and creates convection currents in the mantle

• The tectonic plates which make up the crust move on top of the semi-molten mantle below

• The current theory of tectonic plate movement is called slab pull theory 

  • This means that plate movement is caused by more than just convection currents

  • The heavier oceanic plates subduct and pull the lighter plates along with them

  

Plate boundaries

• Volcanic eruptions and earthquakes most commonly occur at or near plate boundaries

Divergent (constructive) boundaries

• Plates move apart

• Magma rises to fill the gap, creating new crust

• Produces:

  • Mid-ocean ridges

  • Volcanoes (often gentle lava eruptions)

  • Shallow earthquakes

• Example: Mid-Atlantic Ridge (Iceland)

Convergent (destructive) boundaries

• Plates move towards each other

• One plate subducts beneath another

• The subducting plate melts, forming magma that rises to create a volcanic arc

• Produces:

  • Powerful earthquakes

  • Explosive volcanoes

  • Ocean trenches

• Example: Andes (Nazca Plate beneath South American Plate)

Conservative (transform) boundaries

• Plates slide past one another horizontally

• No crust is created or destroyed

• Friction locks plates together until stress is released as sudden, violent earthquakes

• No volcanoes because there is no magma generation

• Example: San Andreas Fault, California