Seafloor Geology: Hydrothermal Vents

Many of us are familiar with “Old Faithful,” a geyser in Yellowstone National Park in the United States. This geyser erupts several times a day, spouting boiling water heated by volcanic rock deep within the Earth’s crust.

A hydrothermal vent is a geyser on the seafloor. It continuously gushes super-heated, mineral-rich water that supports a diverse community of organisms.

Although most of the deep ocean is sparsely populated, vent sites teem with a fascinating array of life, from towering tubeworms to little-known species of octopus.

Hydrothermal vents were discovered in 1977 in the Pacific Ocean. Since then, they have been found in the Atlantic, Indian, and Arctic oceans. Most vents occur at an average depth of about 2,100 meters (7,000 ft.) in areas of seafloor spreading along the Mid-Ocean Ridge system — the underwater mountain chain that snakes around the globe.

How do hydrothermal vents form? In some areas along the Mid-Ocean Ridge, the huge plates that form the Earth’s crust are moving apart, causing deep cracks in the ocean floor. Seawater seeps into these openings and is heated by the molten rock, or magma, beneath the crust. As the water heats up, it rises.

When this “hot spring” gushes out into the ocean, its temperature may be as high as 400°C (752°F) or more. Yet this water typically does not boil because of the pressure from the tremendous weight of the ocean above.

Chimneys top some vents. These smokestacks are formed from dissolved metals that precipitate out (form into particles) when the super-heated vent water meets the surrounding seawater, which is only a few degrees above freezing.

Geologists are intrigued by how rapidly vent chimneys grow — as much as a whopping 30 centimeters (12 in) a day! “Godzilla,” a vent chimney in the Pacific Ocean off Oregon, reached the height of a 15-story building before it toppled. In 2000, University of Washington scientists discovered the “Lost City” vent field in the Atlantic Ocean. It has the tallest vent chimneys known, up to 60 meters high (196 ft.).

There are many reasons why scientists want to learn more about hydrothermal vents. Besides providing habitat for an intriguing community of life, these underwater geysers are believed to play an important role in the ocean’s temperature, chemistry, and circulation patterns.

Scientists also are fascinated by the unusual life that inhabits vent sites. These creatures that live in darkness, from tiny bacteria to giant tubeworms, may light the way to the development of new drugs, industrial processes, and other products useful to us all.


To understand Earth’s structure, think of a hard-boiled egg. The crust is like the egg’s thin shell. The mantle is the egg white, and the core is the yolk. However, the Earth’s core is divided into two parts: a liquid outer core and a solid inner core.