plate tectonics

• Inner core


  Solid ball of iron/nickel, very hot due to pressure and radioactive decay (contains elements such as uranium that give off heat when they decompose)
• Outer core


  Semi-molten, iron/nickel
• Mantle


  Mainly solid rock, high in silicon. Top layer is semi-molten magma (asthenosphere)
• Asthenosphere


  Semi-molten layer constantly moves due to convection currents, powered by heat from core
• Lithosphere


  Broken up into plates, majority within mantle. Top is the crust (land and sea)
• Crust


  Thin top of lithosphere, oceanic crust is dense and destroyed by plate movement, continental crust is less dense and not destroyed
• Plate tectonic theory


  Lithosphere is broken into tectonic plates that move due to convection currents in asthenosphere
• Plate boundaries

  • Destructive (plates move towards each other)
  • Constructive (plates move away from each other)
  • Conservative (plates move parallel to each other)
• Destructive plate boundary (continental and oceanic)

  1. Denser oceanic plate subducts below continental plate

  2. Subduction leaves deep ocean trench

  3. Fold mountains occur from upward push of sediment

  4. Oceanic crust melts in asthenosphere

  5. Pressurised magma forces through weak areas in continental plate, causing explosive composite volcanoes
• Destructive plate boundary (oceanic and oceanic)

  1. Heavier plate subducts leaving ocean trench

  2. Fold mountains occur

  3. Pressure causes underwater volcanoes and island arcs
• Destructive plate boundary (continental and continental)

  1. Pressure builds up, ancient oceanic crust slightly subducted but no continental subduction

  2. Pile up of continental crust forms fold mountains
• Constructive plate boundary (oceanic and oceanic)

  1. Magma rises in gap, forming new land as it cools

  2. Less explosive underwater volcanoes

  3. Sea floor spreading as new land forms
• Constructive plate boundary (continental to continental)

  1. Land in middle forced apart, forming rift valley

  2. Volcanoes form where magma rises

  3. Gap likely fills with water, separating completely

  4. Lifted rock areas are horsts, valley is graben
• Ridge push: Gravity pushes plates further apart at higher elevation
• Slab pull: Subducting plate pulls rest of plate down, causing further subduction
• Conservative plate boundary

  1. Plates move parallel, in different directions or speeds

  2. No plates destroyed, so no landforms created

  3. Pressure builds up, can displace water on oceanic crust or cause fault lines on continental crust
• Hotspots


  Areas of volcanic activity not related to plate boundaries, caused by hot magma plumes from mantle burning through crust
• Hotspot volcanoes and islands form as plates move over stationary plume