According to the theory plate tectonics the earth crust is broken into about 12 plates that float on horror softer rocks in the underlying mantle these plates move about the earth just inches each year these slight movements are responsible in great part for earthquakes and volcanoes that happen on earth what is the source of energy that drives this plate movement

The source of energy that drives this plate movement is the earth´s core, where the internal heat produces forces and convection movements that move the plates.

Explanation:  

Plates can move due to the intense heat produced in the earth´s core. This heat makes melt material move in the mantle. This movement is known as convection. This is the process by which energy is transmitted in a fluid through currents. Convection currents make tectonic plates move.

The convection currents are the result of heating by temperature gradients. While the hot mantle emerges from the deepest areas near the core, the cold mantle sinks, creating a circular convection current. These play an important role in fluids circulation and might be responsible for the movements of the lithospheric plates that are over the mantle. The temperature in the oceanic lithospheric plates is much inferior to the mantle´s temperature, so the lithospheric pieces sink, creating a descendent current.

Near the terrestrial core, the temperature might reach up to 3,500ºC, and solid materials in these areas melt and fuse. When fusing, materials lose density, becoming lighter and ascending again to the surface, creating the ascending currents. The currents of ascending materials are known as thermal feathers or plumes.