What is plate tectonics?
Plate tectonics is the theory that Earth’s rigid outer shell is divided into large moving pieces. The boundaries of these plates help explain earthquakes, volcanoes and mountain building.
How do plates move?
The lithosphere includes the crust and the rigid uppermost mantle; hotter rock beneath it can deform slowly over geological time. Plates usually move by centimeters per year. No single mechanism explains all motion: the pull of sinking slabs, movement away from mid-ocean ridges and heat transfer in the mantle all matter. Magnetic stripes and the age pattern of the ocean floor provide independent evidence of seafloor spreading.
Boundaries and consequences
New oceanic crust can form at divergent boundaries; at convergent boundaries one plate may sink beneath another or colliding continents may raise mountains. Plates sliding sideways can also produce major earthquakes. Not every earthquake involves a volcano, and not every volcano sits on a plate boundary: hotspot volcanoes are an exception. Plate motion helps locate long-term hazards, but cannot predict the exact day and magnitude of a particular earthquake. Local faults, soil and building strength also matter to risk.