CoachHydrothermal circulation is the flow of sea water down through the cracks of the hot oceanic crust, where it is heated by the magma below and reacts with the rock, and back up to the sea floor, where it comes out at hydrothermal vents. A black smoker is a vent from which very hot water carrying dissolved metals pours out; as it meets the cold sea water, iron sulfides and other minerals precipitate as a black cloud, and build a chimney around the vent.
