Tectonic theories

Question 1

Convection current theory

Answer 1

1)Material in the mantle (magma) is heated by the core.
2) The heated material expands, becomes less dense, and rises towards the surface.
3) The rising magma spreads out under the rigid crust and exerts a driving force on the the overlying plates, causing them to move
4) The material then cools slightly, becomes more dense, and begins to sink towards the core.
5) The magma is then heated again by the core, and the convection process is then repeated.

Question 2

Slab-pull force

Answer 2

1) When 2 plates converge, the denser oceanic crust is pulled down by gravity as it subducts beneath the less dense crust.
2) The denser oceanic crust sinks deeper into the mantle under its own weight, pulling the rest of the plate with it. Hence, contributing to further convergence.