Over the past few years, devastating tsunamis off the coast of the Indian Ocean have killed hundreds of thousands of people. Even more alarmingly, scientists predict that these tsunamis, as well as a series of earthquakes and volcanic eruptions, may eventually threaten Hawaii, California, and Oregon. The cause of this trinity of natural disasters is plate tectonics. Perhaps the greatest advance made in the field of earth science, the plate-tectonics theory argues that the surface of the Earth is broken into large plates, which change in size and position over time.