why do volcanoes occur at destructive plate boundaries
Destructive plate margins Pare where a plate of higher density isP subducted,
or forced underneath,Panother, less dense plate. This occurs due to convection currents in the mantle. These are caused by radioactive decay which produces heat, causing the hotter, less dense material to rise and then sink when it cools down again (like the heating of a room by a radiator). u Volcanoes /u Melting of the mantle occurs above the subducted plate. The magms (melt) is less dense, so it rises up towards the crust.
The magma pushes through the crust, and erupts at the earth #39;s surface as a volcano. This can be very explosive (example, Mount St Helens eruption, May 1980). u Earthquakes /u As the plate is being subducted, it can sometimes become stuck on the overriding plate. The subducting plate is still trying to force its way down into the mantle, so there is a build up of force. This can also drag the overriding plate down with it (a good way to visualise this is to use your hands as the plates and see what happens when one gets #39;stuck #39;).
If enough force builds up, this causes the plates to jolt suddenly past each other, with the overriding plate pinging back up. This releases energy, which is felt as an earthquake. 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.
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