Plate Tectonics The earth’s crust is made up of tectonic plates Tectonic plates move or float on top of the upper mantle. However they do not float freely. The plates are forced in specific directions by the flow of magma beneath.

Plate Tectonics – cont’d Plates move with the flow of magma. The magma closer to the core heats and then rises towards the surface as its density decreases. Once the rising magma reaches the lithosphere it moves in opposite directions. It cools, falls back towards the core and the cycle repeats. The magma forms convectional currents.

Plate Tectonics – Convection Currents

Forces on Plates Tensional Forces occur where two tectonic plates are pulled apart. The tension is created as the plates move away from each other. Also called diverging plates or boundaries Compressional Forces occur where two tectonic plates push together. They compress against each other. Also called converging plates or boundaries Each of these are caused by convection currents of magma beneath the earth’s crust

Where’s the TENSION? A B C

Where’s the Subduction / Compression?