When an oceanic plate collides with a continent, it slips under the continental plate. Oceanic sediments scraped off as a result of this contact accumulate in an accretionary wedge. As the oceanic plate sinks, the accretionary wedge increases in volume; sometimes, it rises well above sea level and forms coastal mountains. The continental plate, subjected to considerable force, folds and buckles, giving rise to a chain of subduction mountains. When the oceanic plate reaches the mantle, its rocks melt and become magma. These molten rocks sometimes rise to the surface and are ejected by volcanoes.