Field notes: three kinds of plate margin

Earth’s lithosphere is divided into tectonic plates that move slowly over the mantle. A plate margin is where neighbouring plates meet. At a margin where plates move apart, magma rises into the gap and cools to form new crust; underwater, this can build a mid-ocean ridge. At a margin where plates move towards each other, a denser oceanic plate meeting a continental plate may sink beneath it, producing earthquakes, melting and volcanoes. When two continental plates collide, neither sinks easily, so folded mountains can form. At a margin where plates slide past one another, friction may lock them temporarily; when they suddenly slip, an earthquake can occur. No crust is created or destroyed at a sliding margin. Hazards and landforms depend on the type of movement and the rocks involved.