Unit 4 Tectionic activity- Plates

• Two plates moving towards each other
  • pressure between plates can build and form earthquakes when plates slip 
• Due to decending convection currenta in the mantel 
• Denser oceanic crust gets subducted beneath the less dense continental crust
• Plate melts around 100km in the asthenosphere 
• Melted material is less dense so rises through weaknesses in faults and plate boundaries- creating volcanoes

• Pplates move away from each
• This is due to two convection currents diverginf beneath the surface 
• Pressure from rising magma can lead to doming of the surface and form ridges 
• As the plates move apart faults are produced which magma can rise through
• Rising magma cools and solidifies producing new crust
• Most earthquakes are low magnitude and shallow due to the constant release of pressure

Example: Creation of Caribbean islands

• No magma is released 
• No new crust is formed
• Can produce both shallow earthquakes and high magnitude earthquakes 

• Ridges at diverging plate boundaries have a higher elevation, gravity aids in pulls the plates apart creating a divergent plate boundary.
• New lithosphere moves away from the divergent boundary and cools becoming more dense causing it to sink (subduction zone)
• As it melts it rises due to it being less dense creating mountains on continental crust.
• Sinking oceanic plate explains the slab pull theory, as it sinks it continues to pull the rest of the plate down into the asthenosphere.