CONVECTION CURRENTS

• As a substance like water is heated, the less dense particles rise while denser particles sink.
• Once the hot less dense particles cool down, they sink and the other less dense particles rise
• Heat is produced in the core that produces convection in the mantle.
• The hot, less dense rising material spreads out as it reaches the upper mantle causing upward and sideward forces.
• The upward and sideward forces lift and split the lithosphere, at divergent plate boundaries. The hot magma flows out the mantle and cools down to form new ocean crust.
• Ridge push - as the older seafloor sinks, the weight of the uplifted ridge pushes the oceanic crust towards the trench at the subduction zone.
• Slab pull - the weight of the subducting plate pulls the trailing slab into the subduction zone; just like the tablecloth slipping off the table.