Out of the Deep
Photograph by Stephen Low, SLP
A polymetallic sulfide chimney thrusts upward like the barnacled bow of some ancient ship at a sprawling hydrothermal vent field prosaically named TAG (for Trans-Atlantic Geotraverse). How do these mineral sculptures grow? When seawater seeps into deep cracks in the ocean's crust, it is heated by the magma below. The water expands and rises, becoming saturated with hydrogen sulfide and metals leached from rockiron, zinc, copper, and even some gold. When this waterheated to 650°-700°F (340°-400°C)shoots out of a hydrothermal vent into the frigid sea, metal sulfides crystallize and accrete to form chimneys that can rise several stories high. Metal sulfides also precipitate out of the rising plume of water, creating at some vents the illusion of black smoke.