What moves a tectonic plate?
Follow the forces at a spreading ridge and a subduction zone.
New plate forms
Magma rises at a spreading ridge and cools to form new oceanic lithosphere. The ridge stands higher than the older ocean floor.
Ridge push
Gravity makes the raised lithosphere move away from the ridge. This contributes to plate movement.
Old plate cools
Oceanic lithosphere cools and becomes denser as it moves away from the ridge.
Slab pull
At a subduction zone, dense oceanic lithosphere sinks into the mantle. The sinking slab pulls the rest of the plate behind it.
Earthquake
Friction can lock parts of a plate boundary. Stress builds as plates keep moving. Sudden slip releases energy as seismic waves.
Try it yourself
Explain how slab pull contributes to plate movement.
One possible answer
Old oceanic lithosphere becomes dense enough to sink at a subduction zone. Gravity pulls the slab down, and it draws the rest of the plate towards the boundary.
Check your answer: did you address the question, use accurate evidence and explain the link?
Check your understanding
Are slab pull and an earthquake the same process?
Check the explanation
No. Slab pull contributes to plate motion. An earthquake occurs when stored stress is released by sudden slip.
Put it to use
Sources and teaching notes
Original teaching sequence. Artwork is an imagined editorial scene, separate from geographical evidence.