Briefly discuss the relationship between plate tectonics, volcanic activity, earthquakes and ...

The earth's crust and mantle are not completely solid and stationary. Heat from the core melts the overlying mantle rocks to produce magma or lava. Like all fluids the mantle moves is slow convective currents as hot rock rises, cools and sinks back toward the core to be heated again. The semi-fluid upper mantle moves against the outer crust producing movements called plate tectonics. Where plates collide and one dives under another (subduction), diverge and spread apart (rift valleys) or slide past one another, the movements can cause shock waves that we feel as earthquakes. Or, crust movements in faults may expose the underlying liquid mantle which erupts upwards causing a volcano. When earthquakes and volcanic activity occur under the ocean, there may a sudden displacement of enormous amounts of sea water. The force of the displacement may travel hundreds or thousands of kilometers until it reaches a shoreline and produces a tsunami. It was an underwater earthquake that caused the devastating tsunami that struck northern Japan in April, 2011.