Volcanoes are often formed at plate boundaries. this is a convergent plate boundary. from the choices listed, pick the correct description of what happens before the volcano forms. a) denser continental plate pushes oceanic plate down. oceanic plate melts deep in the earth, magma rises up through weak spot. b) the less dense oceanic plate subducts under the denser continental plate. subducted plate melts due to heat and pressure. melted plate, now magma, rises up to the surface. c) as the more dense oceanic plate subducts under the less dense continental plate, it pulls the front edge of the less dense plate down, creating a deep zone or oceanic trench. d) the more dense oceanic plate subducts under the less dense continental plate. subducted plate melts due to heat and friction. melted plate, now magma, rises up to the surface.