What is a hydrothermal vent?

Hydrothermal vents form near mid-ocean ridges and other volcanic areas, where seawater seeps into the crust, is heated by magma and bursts back out. The water can reach around 400 °C but does not boil because of the immense pressure of the deep ocean. As dissolved minerals hit cold seawater they precipitate, building chimneys; the darkest are known as black smokers. Vents were first discovered in 1977 near the Galápagos Islands by scientists aboard the submersible Alvin. Their communities of tube worms, clams and bacteria live on chemosynthesis, using chemicals rather than sunlight for energy.