Tectonic plates

Three ways plates meet

Plates pull apart at spreading ridges, where hot rock rises and new crust forms, such as the Mid-Atlantic Ridge. They push together at convergent boundaries: one plate may dive under the other into the mantle (a subduction zone, with a deep ocean trench, strong earthquakes and volcanoes), or two continents may crumple into mountains, like the Himalaya. And they slide past each other at transform faults, such as California's San Andreas Fault.

Why the boundaries light up

The middles of plates are fairly rigid and quiet. At the edges the rocks lock together, slowly bend, then suddenly slip, so earthquakes cluster along boundaries. Subduction zones produce the largest and deepest earthquakes because a whole plate is grinding down into the mantle.

What moves the plates

Plates are pulled and pushed by the slow movement of hot rock in the mantle beneath them, and above all by the weight of old, cold plates sinking at subduction zones, which drags the rest of the plate behind them.

What the toggles show

Oceanic spreading ridge

Plates move apart under the sea; magma fills the gap and makes new ocean floor.

Continental rift

A continent is being stretched and may split apart one day, like the East African Rift.

Subduction zone

One plate sinks beneath another into the mantle, forming a trench and, further in, a line of volcanoes. Japan, the Andes and the islands east and south of Taiwan sit on subduction zones.

Oceanic convergent boundary

Two plates converge under the ocean.

Continental collision

Two plates carrying continents push together, thickening the crust into high mountains.

Oceanic transform fault

Plates slide past each other sideways, offsetting the spreading ridges.

Continental transform fault

Plates slide past each other on land, like the San Andreas Fault in California.