How Do Plates Move?

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. Click on image for full size (11K GIF) Windows Original after Northcott

Earth’s center, or core, is very hot, about 9000 degrees F. This heat causes molten rock deep within the mantle layer to move. Warm material rises, cools, and eventually sinks down. As the cool material sinks towards the Earth’s core it is warmed and rises to the top again. This type of movement is called a convection cell.

We used to assume that Earth’s plates just surfed on top of the mantle’s giant convection cells, but now scientists believe that the plates themselves play an important role in the convection process.

How can plates play an active part in the convention process instead of just surfing along? Just like convection cells, plates have warmer, thinner parts that are more likely to rise, and colder, denser parts that are more likely to sink.

New parts of a plate rise because they are warm and thin. As hot magma rises to the surface at spreading ridges and forms new crust, the new crust may actively push the rest of a plate out of its way. This is called ridge push.

Old parts of a plate are likely to sink down into the mantle at subduction zones because they are colder, thicker and denser than the warm mantle material underneath them. This is called slab pull.

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. Click on image for full size (11K GIF) Windows Original after Northcott

Plates at our planet’s surface move because of the intense heat in the Earth’s core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools, and eventually sink down. As the cooled material sinks down, it is warmed and rises again.

Scientists once thought that Earth’s plates just surfed on top of the mantle’s giant convection cells, but now scientists believe that plates help themselves move instead of just surfing along. Just like convection cells, plates have warmer, thinner parts that are more likely to rise, and colder, denser parts that are more likely to sink.

New parts of a plate rise because they are warm and the plate is thin. As hot magma rises to the surface at spreading ridges and forms new crust, the new crust pushes the rest of a plate out of its way. This is called ridge push.

Old parts of a plate are likely to sink down into the mantle at subduction zones because they are colder and thicker than the warm mantle material underneath them. This is called slab pull.

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. Click on image for full size (11K GIF) Windows Original after Northcott

Plates at our planet’s surface move because heat in the Earth’s core causes molten rock in the mantle layer to flow. We used to think the Earth’s 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.