There are two different types of crust that lie on each plate and each has its own characteristics. The oceanic crust is young, thin and dense. It is always being destroyed and recreated. The continental crust, however, is old, light and thick. It is permanent and does not sink, unlike the oceanic.
Destructive plate margins, those that move together, are usually where oceanic crust meets continental. As oceanic material is slightly denser, it is forced downwards under the continental material. Where this process takes place is called the subduction zone. Constructive plate margins, where the plates are moving apart, act very differently. As the continental regions more apart, new oceanic crust is created to fill the gap. This new crust is made when lava from beneath the earth’s surface rises up through a gap in the rock.
Tectonic plates create a number of landforms and often natural disasters. Destructive plate margins cause violent volcanoes and earthquakes, as well as deep-ocean trenches and fold mountains. Constructive plate margins also cause volcanoes and earthquakes, although these would not be as violent. They also result in the formation of mid-ocean ridges.
Earthquakes occur because of a slow build up of pressure in the earth’s rocks. When this pressure is quickly released it travels to the surface of the earth and causes it to shake. This happens at both destructive and constructive plate boundaries because pressure is built up when plates move either together or apart. Similarly, volcanoes occur at both boundaries. They form when molten rock from under the earth’s crust is surfaced. This is usually because the plates moving have created a gap or crack for material to be pushed through.
At a destructive plate margin, when the plates are pushed together yet one doesn’t subduct, material is pushed upwards, this is how the Fold Mountains are formed. The Andes are an example of Fold Mountains formed at a destructive plate margin.
