Plate boundaries

Plates meet in three ways. At a divergent boundary they move apart: molten rock rises to fill the gap and makes new crust, as at the mid-ocean ridges and the Red Sea, with many volcanoes and small earthquakes. At a convergent boundary they push together: an oceanic plate sinks under the other one, making a deep trench, strong earthquakes and, as the sinking rock heats up and melts, a line of volcanoes; where two continents meet, neither sinks and the crust crumples into high mountains. At a transform boundary the plates slide past each other sideways, neither making nor destroying crust, with many earthquakes; most are on the ocean floor. Earthquakes and volcanoes therefore lie mostly in belts along plate edges, the largest being the ring round the Pacific Ocean, where the Pacific plate sinks under the plates around it.