The point at which two plates meet is called a plate boundary or margin.
A convergent plate boundary also known as a destructive plate boundary, usually involves an oceanic plate and a continental plate. The plates move towards one another and this movement can cause earthquakes and volcanoes.
As the plates collide, the oceanic plate is forced beneath the continental plate. This is known as subduction and results in the formation of an ocean trench. This happens because the oceanic plate is denser (heavier) than the continental plate.
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 a composite volcano, also known as a stratovolcano. The volcanic eruptions are often violent, with lots of steam, gas and ash.
If two continental plates collide, neither can sink and so the land buckles upwards to form fold mountains. This is called a collision boundary. Earthquakes can occur at collision boundaries.
At a divergent plate boundary - also known as a constructive plate boundary, the plates move apart from one another. When this happens the magma from the mantle rises up to make (or construct) new crust. The movement of the plates over the mantle can cause earthquakes. Rising magma can also create shield volcanoes.
Landforms at a divergent plate boundary include ocean ridges, eg the Mid-Atlantic ridge (where the Eurasian plate and the North Atlantic plate are moving apart from each other under the Atlantic Ocean), rift valleys eg the East African Rift Valley and shield volcanoes.
At a conservative plate boundary, the plates slide past each other in opposite directions, or in the same direction but at different speeds. As the plates try to move, friction occurs and plates become stuck. Pressure builds up because the plates are still trying to move. When the pressure is released, it sends out huge amounts of energy causing an earthquake. The earthquakes at a conservative plate boundary can be very destructive as they occur close to the Earth's surface. There are no volcanoes at a conservative plate boundary.