<P> A volcanic arc is a chain of volcanoes formed above a subducting plate , positioned in an arc shape as seen from above . Offshore volcanoes form islands , resulting in a volcanic island arc . Generally , volcanic arcs result from the subduction of an oceanic tectonic plate under another tectonic plate , and often parallel an oceanic trench . The oceanic plate is saturated with water , and volatiles such as water drastically lower the melting point of the mantle . As the oceanic plate is subducted , it is subjected to greater and greater pressures with increasing depth . This pressure squeezes water out of the plate and introduces it to the mantle . Here the mantle melts and forms magma at depth under the overriding plate . The magma ascends to form an arc of volcanoes parallel to the subduction zone . </P>
<P> A volcanic arc is a chain of volcanoes formed above a subducting plate , positioned in an arc shape as seen from above . Offshore volcanoes form islands , resulting in a volcanic island arc . Generally , volcanic arcs result from the subduction of an oceanic tectonic plate under another tectonic plate , and often parallel an oceanic trench . The oceanic plate is saturated with water , and volatiles such as water drastically lower the melting point of the mantle . As the oceanic plate is subducted , it is subjected to greater and greater pressures with increasing depth . This pressure squeezes water out of the plate and introduces it to the mantle . Here the mantle melts and forms magma at depth under the overriding plate . The magma ascends to form an arc of volcanoes parallel to the subduction zone . </P>
where are volcanoes located in relation to a subduction zone
where are volcanoes located in relation to a subduction zone
parallel to the subduction zone
parallel to the subduction zone