Explore the Deep Sea

Volcanoes & Vents

Hydrothermal vents: underwater geysers

What happens when tectonic plates move towards each other: subduction, trenches and mountain building.

Diagram showing water movement in seafloor. Image courtesy of H. Edmonds.

Hot fluid jets and wafts from cracks in the seafloor thousands of meters below the ocean surface. The fluid is essentially water that has filtered down into the rock of the Earth's crust through tiny channels and fissures. Surrounding rocks heat the water as it moves downwards, and various minerals dissolve in it. Vents occur where some of the hot fluid finds its way back to the surface. Most areas containing vents are found where the Earth's tectonic plates are moving apart, or in other areas of tectonic activity, such as ocean basins and hotspots.

Plumes of hot fluid

As the hot fluid shoots out of cracks in the rock, it meets the surrounding ocean water, which is cold—just a few degrees above freezing. So the hot fluid begins to cool. The further it moves from the point it came out of the seafloor (the vent), the cooler it gets. But the fluid is so hot when it leaves the seafloor that it can take several hundred meters to cool down to the temperature of the surrounding ocean. Consequently, each vent is marked by a "plume" of warm water that billows into the ocean above. Vents can be tracked down by finding their associated plumes.

Chimneys and smokers

Water billowing from a seafloor vent. Image courtesy of D. Desbruyeres.

Hot vent fluid has many minerals dissolved in it. When it mixes with seawater and cools, minerals precipitate out of solution, forming a dense cloud of what looks like smoke—so some vents are referred to as "smokers." Depending on the fluid's temperature and what minerals are dissolved in it, the smoke can look black or white. Black smokers emit hot fluids containing iron and sulfide. White smoker fluid is cooler and contains whitish compounds of barium, calcium and silicon. The fluid jetting out of these chimneys can be very hot indeed: hundreds of degrees Celsius.

Some minerals drop out of the water right next to the vent; over time, these can build up to form "chimneys." Some chimneys form very fast—growing several inches per day. Large chimneys can grow to over 150 feet (50 m) high and 90 feet (30 m) diameter. As the chimneys grow, they are colonized by animals and microbes which are able to survive in the extreme conditions. …more about investigating minerals deposited by vents

Diffuse flow

In some areas, seawater seeps into cracks in the seafloor and mixes with the rising vent fluid. So by the time the vent fluid exits the seafloor it is cooler, and has a different chemical make-up, than the fluid that gushes out of chimneys (above): tens, rather than hundreds of degrees Celsius. This is still considerably hotter than the background temperature of the ocean, which is just a few degrees above freezing. …more about investigating the chemical make-up of vent fluid

Just add sulfur

Often, the hot vent fluids contain sulfur-rich chemicals. Sulfur is a yellow mineral that was much prized by mediaeval alchemists, and is one of the ingredients of gunpowder. Sulfur compounds are often very poisonous. However, some microbes have evolved the ability to break down the sulfur-containing chemicals in vent fluids to derive energy. This enables the microbes and many other animals to live in great abundance around vents on the ocean floor, despite the fact that there are no plants in the deep ocean. …more about life in the deep

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