This illustration of a small segment of midocean ridge crest shows the development of hydrothermal plumes. Plumes issue from small sites on the ridge crest, often as a result of an intrusion of a magma dike during an episode of seafloor spreading. The hot fluids rise and grow increasingly diluted by the surrounding seawater. They eventually reach a level of equal buoyancy, where local bottom currents carry them away from their source. Image courtesy of Submarine Ring of Fire 2002, NOAA/OER.