Hydrothermal Vent, a fissure, or crack, on the ocean floor from which heated water flows. The water is rich in hydrogen sulfide, methane, and such elements as iron, copper and calcium.

Hydrothermal vents generally occur at sites along the mid-ocean ridge, an underground mountain chain that extends around the world. Molten rock that lies close to the surface of the ridge heats ocean water that seeps below the ocean floor. Once heated the water rises, carrying dissolved minerals from the molten rock. The minerals typically give the water a dark, cloudy appearance as it streams from the vent. Over time, deposits of minerals around the vent sometimes form, creating towers known as black smokers, or rock chimneys. In some vents the water temperature reaches 750 F. (400 C.), but the water does not boil because of the high pressure of the overlying ocean at the depths where the vents are located.

Hydrothermal vents support biological communities of many types of organisms found nowhere else on earth, including giant tubeworms and unique species of giant clams and mussels. These organisms do not rely on sunlight and photosynthesis as their ultimate source of energy, unlike virtually all other living things.

Hydrothermal vents were discovered in 1977.