CoachAn oceanic island is a volcanic island that rises from the ocean floor, built on oceanic lithosphere. An island of a hotspot chain passes through four eruptive stages: a preshield stage of small eruptions of alkalic lava on the sea floor; the shield stage, in which tholeiitic lava builds the bulk of the volcano while it lies over the hotspot; a postshield stage of fewer, more alkalic eruptions, which cap the shield; and, after a pause, a rejuvenated stage of rare, small alkalic eruptions. Erosion and sinking then take over.
