Plate Boundaries: Apart, Together or Sliding Past

0:00Earth's outer shell is broken into huge, rigid pieces called tectonic plates.

0:06They move a few centimetres a year over the mantle, hot rock that flows very slowly.

0:13Where two plates meet is called a plate boundary.

0:17Do plates only collide there? No. They meet in three main ways: divergent, convergent and transform.

0:26At a divergent boundary, two plates move apart.

0:30Magma, which is melted rock, rises into the gap and cools to make new crust.

0:36Under the ocean, this builds an underwater mountain chain called a mid-ocean ridge.

0:42On land, the crust stretches and sinks to form a rift valley, like the East African Rift.

0:49At a convergent boundary, two plates push together.

0:53When an ocean plate meets a continental plate, the denser ocean plate sinks under it. This is called subduction.

1:02This makes a deep ocean trench, and rising magma builds a line of volcanoes.

1:08When two continental plates collide, neither sinks easily, so the crust crumples and folds into mountains like the Himalayas.

1:17At a transform boundary, plates slide past each other. Here we see them from above.

1:24They grind along a crack called a fault, like the San Andreas Fault.

1:29The plates stick, then slip suddenly, causing an earthquake that can shift a road out of line.

1:36So plates do not only collide: they move apart, push together, or slide past each other.