Why do many oceanic volcanoes occur as long lines of volcanoes that are active at only one end? O The lithosphere moves over a stable hotspot in the mantle. The mantle convection cell under the crust carries the magma source from one end of the line of volcanoes t O The mantle plume that feeds the volcano rotates around the Earth's core, tracing new volcanoes as it does O The spreading lithosphere pushes the underlying magma source across the ocean floor. O The active volcanoes are gradually moving away from the oceanic ndge.