why do volcanoes occur at destructive plate boundaries

At a compressional or destructive boundary the plates are moving towards each other. This usually involves a
continental plate and an oceanic plate. The oceanic plate is denser than the continental plate so, as they move together, the oceanic plate is forced underneath the continental plate. The point at which this happens is called the subduction zone. As the oceanic plate is forced below the continental plate it melts to form magma and earthquakes are triggered.

The magma collects to form a magma chamber A region under the surface of the Earth where hot molten magma collects. This magma then rises up through cracks in the continental crust. As pressure builds up, a volcanic eruption may occur. The diagram below shows how the oceanic plate is pushed underneath the continental plate, causing mountains and possibly volcanoes to form along the destructive plate boundary.

As the plates push together, the continental crust is squashed together and forced upwards. This is called folding. The process of folding creates fold mountains. Fold mountains can also be formed where two continental plates push towards each other. This is how mountain ranges such as the Himalayas and the Alps were formed. Now try a. There are a number of different types of plate boundary. A destructive plate boundary is sometimes called a convergent or tensional plate margin.

This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate A section of the crust that makes up the Earth's landmasses. Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface. An example of a destructive plate boundary is where the Nazca plate is forced under the South American Plate.

Collision zones form when two continental plates collide. Neither plate is forced under the other, and so both are forced up and form fold mountains. A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed. An example of a constructive plate boundary is the mid-Atlantic Ridge.

A conservative plate boundary, sometimes called a transform plate margin, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds. Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake A sudden shaking of the ground which releases energy. This occurs at the San Andreas Fault in California.