This image is a cross section through the Earth showing the convection cells of the mantle. Ridge push happens at spreading centers where plates are moving apart. Slab pull happens at subduction zones where one plate is pulled down into the mantle.
Windows Original after Northcott
How Do Plates Move?
Plates at our planetís surface move because heat in the Earthís core causes molten rock in the mantle layer to flow. We used to think the Earthís plates just surfed on top of the moving mantle, but now scientists believe that plates help themselves to move.
How can plates help themselves move instead of just surfing along? Just like convection cells, plates have warmer, thinner parts that rise, and colder, denser parts that sink. New parts of a plate rise because they are warm and thin, pushing the rest of a plate out of its way at spreading ridges . Old parts of a plate sink down into the mantle at subduction zones because they are colder and thicker than the warm mantle underneath them.
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