Plate tectonics & boundaries

Earth's outer shell is broken into tectonic plates that move a few centimetres per year. Where plates meet, stress builds and releases as earthquakes; magma can reach the surface as volcanoes; and crust can crumple into mountain ranges.

Red dashed lines mark major boundary zones in simplified form — including the Mid-Atlantic Ridge, Pacific Ring of Fire margins, and the Alpine–Himalayan collision belt. Red dots are hotspots where volcanoes can form far from a plate edge (for example Hawaii and Yellowstone).

• Divergent boundaries — plates pull apart; new ocean floor forms (mid-ocean ridges).
• Convergent boundaries — plates collide; subduction zones and mountain building.
• Transform boundaries — plates slide past each other (e.g. San Andreas).

See also: Himalaya & Tibetan Plateau, Caribbean.