When the plate sinks into the mantle it melts to form magma. The pressure of the magma builds up beneath the Earth's surface. The magma escapes through weaknesses in the rock and rises up through ...

These convergent boundaries also occur where a plate of ocean dives ... A mid-ocean ridge would then mark the boundary between the plates. Mountains and a rift can be seen along the San Andreas ...

New crust is continually being pushed away from divergent boundaries (where sea-floor spreading occurs), increasing Earth's surface. But the Earth isn't getting any bigger. What happens, then, to ...