Why are volcanoes found in destructive plate margins?
Volcanoes are actually found at both convergent (destructive) and divergent (constructive) plate margins. They are also sometimes found in the middle of plates (not along active margins). They form at convergent plate margins, where an oceanic plate subducts beneath another plate, because the subducting slab plunges down into the hotter upper mantle (thus increasing temperatures) and brings down with it some water (which decreases the melting point of silicate rocks) and these processes cause melting above the subducted slab in the upper mantle. This melted material is less buoyant and works its way up to the Earth’s surface and may erupt, forming a volcano.
