How hydrothermal systems work

Part of Hall of Planet Earth.

How Do Hydrothermal Systems Work? AMNH/R.Mickens

At mid-ocean ridges, cold seawater is drawn down, heated, and forced to circulate through an extensive system of cracks above bodies of molten rock. The hot water dissolves some of the minerals in the rock, and carries them up to the ocean floor. When the mineral-laden water, whose temperature may exceed 400 degrees Centigrade, vents into the cold ocean, some of the dissolved minerals immediately separate out to form particles of metal sulfides, which accumulate around the vents.