Subduction is the process in which one plate is pushed downward beneath another plate into the underlying mantle when plates move towards each other. The plate that is denser will slide under the thicker, less dense plate. Faulting occurs in the process. It is the process in which rocks break and move or are displaced along the fractures. The subducted plate usually moves in jerks, resulting in earthquakes. The area where the subduction occurs is the subduction zone. A long, narrow, deep depression forms in this area. It is called an oceanic trench.
The jerky movement, as well as the friction between the plates causes much heat, and together with the heat from the mantle and from radioactive decay, causes the subducted plate to melt. Magma is produced by the melting plate. It rises through fractures in the crust and reaches the surface to form volcanoes. In the end, the heat may be so intense that large areas of the crust are melted, forming granites just below the surface. The boundary of such plate movements is 'destructive' as part of the plate melts during subduction and is destroyed. As plates move towards each other, the opposing force between them is so great that the massive folding or the bending of rocks also occurs at the edges of the less dense plate. A range of fold mountains, such as the Himalayas, is formed.
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