GCSE Geography | Destructive Plate Margins (Tectonic Hazards 5)

When two plates collide they form a destructive margin - this is also known as a convergent margin as two plates are converging. The resulting effect is dependent on what sort of plates are colliding. There are three types of convergence.

Continental vs continental

Our first type of convergence is continental vs continental. When two continental plates collide they cannot sink into the mantle, so there is no subduction. Instead the plates are forced to crumple upwards, creating fold mountains, such as the Himalayas. This process can cause shallow focus earthquakes, but not volcanoes as there is no magma here. Over time fold mountains will continue to compress and grow higher.

Continental vs oceanic

Our second type of convergence is when continental and oceanic plates collide, as seen in the diagram below. When this happens the oceanic plate, which is denser, gets pushed under the continental plate into the mantle – this is called subduction. The exact point of collision is marked by a bending of the oceanic plate to create a deep ocean trench. As the two plates collide the continental plate is pushed upwards and buckled into a chain of fold mountains. As the oceanic plate subducts, it melts due to heat and friction, creating magma. Friction between these plates may also cause earthquakes to occur. The magma then rises in great plumes to form steep sided composite volcanoes, which can have very explosive eruptions.

Oceanic vs oceanic

Our last type of convergence is oceanic vs oceanic. If two oceanic plates collide the younger of the two plates will force the oldest plate downwards - this is because oceanic plates get denser over time. This will lead to subduction, causing the plate to melt due to heat and friction, which will create magma. When this molten rock meets the ocean, water it will cool rapidly to form island arcs which contain volcanoes – like the ones in the Caribbean Sea.