Hydrothermal fluid temperatures can reach 400°C(750°F) or more, but they do not boil under the extreme pressure of the deep ocean. As they pour out of a vent, the fluids encounter cold, oxygenated seawater, causing another, more rapid series of chemical reactions to occur. (Temp.)
But for every 10 meters you dive, the pressure increases by one atmosphere. So if you were to dive to ten meters, the pressure would equal two atmospheres. A hydrothermal vent 2,500 meters deep experiences 250 atmospheres, or 3,672.5 pounds per square inch. (Pressure)
Hot seawater in hydrothermal vents does not boil because of the extreme pressure at the depths where the vents are formed. (Depth)
The bacteria are autotrophs that oxidize hydrogen sulfide in vent water to obtain energy, which is used to produce organic material (i.e. grow themselves).Chemosynthetic bacteria are the primary producers and form the base of vent food webs. All vent animals ultimately depend on the bacteria for food.(Food Chain)
In the early 1960s, marine geologists believed that the amount of heat emanating from the sea floor would be highest in areas where hot magma erupted under the ocean. (History)
There are two different types of hydrothermal vents; Black Smokers, and White Smokers. The black smoker is the hottest of all the hydrothermal vents. It spews out mainly sulfides and iron. (Black & White)
These black smokers are of interest as they are in a more stable area of the Earth's crust, where tectonic forces are less and consequently fields of hydrothermal vents are less common. The world's deepest known black smokers are located in the Cayman Trough, 5,000 m (3.1 miles) below the ocean's surface.