Theories of tectonic movement

• CONVECTION CURRENTS

  1. Earth is hottest at the core so lower parts of the asthenosphere heat up and become less dense and rise up
  2. As they move to the top they cool down and become more dense and so sink back down
  3. These circular movements create drag on the plates causing them to move
• SLAB PULL

  1. At destructive plate margins , denser crust is forced under less dense crust
  2. The sinking of the plate edge pulls the rest of the plate towards the boundary
• RIDGE PUSH

  1. At constructive plate margins , magma rises to the surface and forms new crust
  2. the surrounding rocks expand and rise above the surface forming a slope
  3. the new crust cools and becomes denser
  4. gravity causes the denser rock to move downslope away from the plate margin
  5. this results in pressure on the tectonic plate causing them to diverge
• SEA-FLOOR SPREADING

  1. As tectonic plates diverge , magma rises up to fill the gap and cools to create new crust
  2. the new crust is dragged apart leading to more crust being formed
  3. when this happens at plate margins under the sea the sea floor gets wider
  4. this process creates mid-ocean ridges