1 ) 

Opposing convection currents lead to the divergence of plates. As plates pull apart magma intrudes leading to the formation of ridges.

2 ) 

As plates slide past each other, fault lines emerge which, following the build-up of substantial pressure, lead to the development of major earthquakes.

3 ) 

Subduction occurs where two plates converge. Subduction can lead to the formation of features such as deep sea trenches and island arcs.

4 ) 

Radioactive decay is the main process. As the plate slides over the place experiencing the decay, the magma is forced through the plate leading to the formation of island chains.