Magma rises up from the mantle and adds new sea floor to the separating plates. Fractures develop as the plates are pulled apart. The superheated water is forced back up to the sea floor carrying dissolved minerals leached from the basalt ocean plate. A vent forms when the jet of water shoots through the sea floor and its dissolved minerals begin to precipitate out. The color depends on the minerals present in the water.
Growth continues as long as there is a supply of hydrothermal fluid.
Vents have been located at depths varying from 1500 to 4000 meters. Green plants use sunlight to make food by the process of photosynthesis. In the darkness of the ocean depths there is no sunlight for photosynthesis. The answer is found in bacteria that can use another source of energy to make food. Water coming out of a vent is rich not only in dissolved minerals but also in chemosynthetic bacteria .