Hydrothermal vents are cracks on the ocean floor where hot water flows out. They are often found near areas with volcanic activity, such as mid-ocean ridges, ocean basins, and hotspots where tectonic plates move apart. When hot water from these vents mixes with the ocean, it creates clouds of particles called hydrothermal plumes. Over time, the hot water can form rocks and mineral deposits on the seafloor.
These vents exist because Earth has a lot of water and is geologically active. Under the ocean, vents can create structures called black smokers or white smokers, which release many different elements into the ocean. These elements help shape the chemistry of the ocean. Compared to most deep-sea areas, regions near hydrothermal vents are more biologically active and support complex life. Special bacteria and archaea near vents form the base of the food chain, supporting organisms like giant tube worms, clams, limpets, and shrimp. Scientists believe that similar vents may exist on Jupiter’s moon Europa and Saturn’s moon Enceladus. They also think that ancient vents might have existed on Mars.
Some scientists think hydrothermal vents might have played a role in the beginning of life on Earth. The conditions in these vents can help create molecules needed for life. Certain types of vents, like alkaline vents or those with supercritical CO₂, may be especially good at forming these molecules. However, the origin of life is still a topic of debate, and scientists have many different ideas about how life began.
Physical properties
Hydrothermal vents in the deep ocean usually form along mid-ocean ridges, such as the East Pacific Rise and the Mid-Atlantic Ridge. These areas are where two tectonic plates move apart, and new ocean floor is created.
The water that comes out of hydrothermal vents on the seafloor is mostly seawater that enters the system through cracks and porous rocks near volcanic areas. It also includes some water from magma that rises from deep underground. On land, water in fumaroles and geysers is mostly rainwater and groundwater that seep into the ground. This water may also include some metamorphic water, magma water, and brine from sedimentary rocks, depending on the location.
The water around these vents is usually about 2°C (36°F), but the water that comes out of the vents can be much hotter, ranging from 60°C (140°F) to as high as 464°C (867°F). At these deep ocean depths, the water pressure is so high that the water can exist as a liquid or a supercritical fluid. A supercritical fluid has properties between a liquid and a gas. Pure water becomes supercritical at 375°C (707°F) and 218 atmospheres of pressure. However, when salt is added to the water, the temperature and pressure needed for it to become supercritical increase. Seawater with 3.2% salt becomes supercritical at 407°C (765°F) and 298.5 bars of pressure, which is about 2,960 meters (9,710 feet) below the ocean surface. If hydrothermal water with this salt level vents at higher temperatures and pressures, it is supercritical. The salt content of vent water varies because of processes in the Earth’s crust. For example, water with 2.24% salt becomes supercritical at 400°C (752°F) and 280.5 bars. Therefore, water from the hottest parts of some vents can be a supercritical fluid.
Examples of supercritical venting have been found in several places. At Sister Peak, a vent in the Comfortless Cove Hydrothermal Field, low-salt vapor-type fluids are released. Although supercritical venting was not sustained, a brief burst of water at 464°C (867°F) exceeded supercritical conditions. A nearby site, Turtle Pits, vents low-salt water at 407°C (765°F), which is above the critical point for that salt level. In the Cayman Trough, the Beebe vent site, located about 5,000 meters (16,000 feet) below the ocean surface, has shown continuous supercritical venting at 401°C (754°F) with 2.3% salt.
Although supercritical venting has been observed at multiple locations, its importance for processes like hydrothermal circulation, mineral deposits, chemical exchanges, or life is not yet fully understood.
Hydrothermal vent chimneys begin forming when the mineral anhydrite is deposited. Over time, copper, iron, and zinc sulfides form in the spaces between the minerals, making the chimneys less porous. Some chimneys can grow up to 30 cm (1 foot) per day. In 2007, an exploration near Fiji found that deep-sea vents were a major source of dissolved iron, which plays a role in the iron cycle.
Black smokers and white smokers
Some hydrothermal vents create tall, chimney-like structures. These chimneys form when minerals dissolved in the vent water meet cold seawater. When very hot water from the vent mixes with cold ocean water, the minerals form solid particles that build up the chimneys. Some chimneys can grow as tall as 60 meters (200 feet). For example, a chimney called "Godzilla" near Oregon in the Pacific Ocean reached 40 meters (130 feet) before it collapsed in 1996.
A black smoker is a type of hydrothermal vent found on the ocean floor, usually in the bathyal zone (most common between 2,500 to 3,000 meters (8,200 to 9,800 feet) deep), but also in shallower or deeper areas. Black smokers look like dark, chimney-like towers and release a cloud of black material. These vents release particles rich in sulfur-containing minerals, called sulfides. Black smokers form in groups when extremely hot water (sometimes over 400°C (752°F)) from Earth's crust flows through the ocean floor. This water carries dissolved minerals, especially sulfides. When it meets cold seawater, the minerals form solid particles, creating the dark chimneys. Heat helps these minerals harden into structures. Over time, the sulfides can form large deposits of valuable minerals. Some black smokers near the Azores, part of the Mid-Atlantic Ridge, contain very high levels of dissolved iron, such as up to 24,000 μM in the Rainbow Vent Field.
Black smokers were first discovered in 1979 on the East Pacific Rise by scientists from the Scripps Institution of Oceanography during the RISE Project. They used a deep-sea vehicle called ALVIN. Today, black smokers are found in the Atlantic and Pacific Oceans, usually around 2,100 meters (6,900 feet) deep. The northernmost black smokers are a group called Loki's Castle, found in 2008 near the Mid-Atlantic Ridge between Greenland and Norway. These vents are interesting because they are in a more stable part of Earth's crust, where tectonic activity is less common. The deepest known black smokers are in the Cayman Trough, 5,000 meters (3.1 miles) below the ocean surface.
White smoker vents release lighter-colored minerals, such as those containing barium, calcium, and silicon. These vents often have cooler plumes because they are farther from their heat source.
Black and white smokers may exist together in the same hydrothermal field. Usually, black smokers are closer to the main heat source, while white smokers are farther away. However, white smokers often appear later in a hydrothermal field’s life cycle, as the heat source (magma) moves farther away. At this stage, the water flowing through the vents is mostly seawater, not magma. The minerals from white smokers are rich in calcium and form deposits like sulfate (such as barite and anhydrite) and carbonate minerals.
Hydrothermal plumes
Hydrothermal plumes are mixtures of water and other substances that form when hot fluids from hydrothermal vents are released into the surrounding ocean water. These fluids often have different physical properties, such as temperature and density, and chemical properties, such as pH and the presence of certain ions, compared to regular seawater. These differences create conditions that allow chemical reactions, such as oxidation-reduction and precipitation, to occur.
Hydrothermal vent fluids are much hotter than seawater on the ocean floor, often reaching temperatures between 40°C and over 400°C, while seawater is near 4°C. This makes hydrothermal fluid less dense than seawater, causing it to rise due to buoyancy, forming a hydrothermal plume. This rising stage is called the "buoyant plume" phase. As the plume rises, movement between the plume and seawater creates turbulence, mixing the two fluids. Over time, the plume becomes diluted by seawater and eventually reaches a point where it is neutrally buoyant, meaning it no longer rises and instead spreads sideways across the ocean. This stage is called the "nonbuoyant plume" phase.
Chemical reactions happen alongside the physical changes in hydrothermal plumes. Seawater is generally an oxidizing fluid, while hydrothermal vent fluids are usually reducing. When these fluids mix, reduced chemicals like hydrogen gas, hydrogen sulfide, methane, iron, and manganese react with seawater. In fluids with high hydrogen sulfide levels, dissolved metals like iron and manganese form dark-colored sulfide minerals, such as those seen in "black smokers." Over time, iron and manganese in the plume may oxidize, forming insoluble minerals. For this reason, the area near the vent where metals are actively oxidizing is called the "near field," while the area where metals have fully oxidized is called the "far field."
Scientists use chemical tracers in hydrothermal plumes to locate deep-sea hydrothermal vents. Effective tracers remain chemically unchanged after venting, so their concentration changes are due only to dilution. Noble gases like helium are useful tracers because hydrothermal venting releases higher amounts of helium-3, a rare isotope found only in Earth's interior. This creates unusual helium isotope ratios in seawater that indicate hydrothermal activity. Another tracer is radon, a radioactive gas. Radon-222, which has a half-life of about 3.82 days, can help determine the age of hydrothermal plumes when combined with helium isotope data. Other substances, such as hydrogen, hydrogen sulfide, methane, iron, and manganese, may also indicate hydrothermal plumes but are less reliable as tracers because they react with seawater.
Hydrothermal plumes play a key role in how hydrothermal systems affect ocean chemistry. These vents release many trace metals, including iron, manganese, chromium, copper, zinc, cobalt, nickel, molybdenum, cadmium, vanadium, and tungsten, many of which are important for life. Once these metals enter the water, their movement is influenced by physical and chemical processes. Based on thermodynamic principles, iron and manganese should form insoluble metal (oxy)hydroxide minerals in seawater. However, their interaction with organic compounds and the formation of colloids and nanoparticles can keep them dissolved far from the vent.
Iron and manganese often have the highest concentrations in acidic hydrothermal vent fluids and are biologically significant, especially iron, which is often scarce in marine environments. Their transport over long distances through organic complexation may be an important way that metals cycle through the ocean. Hydrothermal vents also release other biologically important trace metals, such as molybdenum, which may have played a role in the early development of Earth's oceans and the origin of life. However, iron and manganese minerals can also affect ocean chemistry by removing trace metals from seawater. The surfaces of iron (oxy)hydroxide minerals can absorb elements like phosphorus, vanadium, arsenic, and rare earth metals from seawater. Thus, while hydrothermal plumes may add metals like iron and manganese to the ocean, they can also remove other metals and nutrients like phosphorus, acting as a net sink for these elements.
Biology of hydrothermal vents
Life has traditionally been thought to rely on energy from the sun. However, deep-sea organisms near hydrothermal vents do not have access to sunlight. Instead, biological communities around these vents depend on nutrients found in chemical deposits and hydrothermal fluids. Earlier, scientists believed vent organisms relied on marine snow, which comes from organic material falling from the ocean surface. This would link them to plant life and the sun. While some vent organisms do consume marine snow, this alone would not support a large number of life forms. In fact, hydrothermal vent zones have far more organisms than the surrounding sea floor—up to 10,000 to 100,000 times more densely populated.
Hydrothermal vents are part of chemosynthetic-based ecosystems (CBE), where life uses chemical compounds instead of sunlight as an energy source. These ecosystems rely on chemosynthetic bacteria, which convert chemicals like hydrogen sulfide into organic material. The water from hydrothermal vents contains many dissolved minerals and supports large populations of these bacteria. These bacteria use sulfur compounds, which are toxic to most organisms, to produce energy through a process called chemosynthesis.
Hydrothermal vents also contribute to the ocean’s iron supply, which is used by phytoplankton. The oldest known modern biological community linked to a vent is the Figueroa Sulfide from the Early Jurassic period in California. This ecosystem depends on the vent itself for energy, unlike most life on Earth, which relies on sunlight. However, some vent organisms still depend on oxygen produced by photosynthetic life, while others do not require oxygen.
Chemosynthetic bacteria form thick mats that attract small animals like amphipods and copepods, which eat the bacteria directly. Larger animals, such as snails, shrimp, crabs, tube worms, fish, and octopuses, form food chains based on these bacteria. The main groups of organisms found near vents include annelids, gastropods, and crustaceans, with large bivalves, tube worms, and eyeless shrimp making up much of the nonmicrobial life.
Siboglinid tube worms, which can grow over 2 meters tall, are a key part of vent communities. These worms lack mouths and digestive systems and absorb nutrients from bacteria living inside their tissues. Each ounce of their tissue contains about 285 billion bacteria. Their red plumes contain hemoglobin, which carries hydrogen sulfide to the bacteria. In return, the bacteria provide the worms with carbon compounds. Two species found near vents are Tevnia jerichonana and Riftia pachyptila. A community called "Eel City," dominated by the eel Dysommina rugosa, is located near the Nafanua volcanic cone in American Samoa.
Over 100 gastropod species have been identified near hydrothermal vents, and more than 300 new species have been discovered. Some of these species are closely related to others found in distant vent areas. Scientists believe that before the North American Plate moved over the mid-ocean ridge, all vent life in the eastern Pacific was part of a single region. This movement created barriers that led to species evolving separately in different areas. Similar adaptations seen across vents support the theory of evolution.
Black smokers, which are tall, chimney-like structures, are the centers of ecosystems in deep-sea environments. Since sunlight does not reach these depths, organisms like archaea and extremophiles use heat, methane, and sulfur compounds from black smokers to produce energy through chemosynthesis. Larger animals, such as clams and tube worms, feed on these microbes. These microbes also deposit minerals back into the black smoker, completing the life cycle.
A type of phototrophic bacterium, part of the Chlorobiaceae family, was found near a black smoker off Mexico’s coast at a depth of 2,500 meters. These bacteria use the faint light from the smoker for photosynthesis instead of sunlight. This is the first known organism to use non-sunlight for photosynthesis.
New species are frequently discovered near black smokers. For example, the Pompeii worm Alvinella pompejana, which can survive temperatures up to 80°C, was found in the 1980s. The scaly-foot gastropod (Chrysomallon squamiferum), discovered in 2001, uses iron sulfides for its hardened body parts instead of calcium carbonate. Scientists believe the extreme pressure at these depths helps stabilize these materials. This armor may protect the gastropod from predators.
In 2017, researchers found evidence of possible ancient life in hydrothermal vent deposits in Quebec, Canada. These fossils, dated to about 4.28 billion years ago, may be among the oldest life forms on Earth.
Hydrothermal vent ecosystems have high productivity and biomass, but this depends on the symbiotic relationships between organisms. Unlike shallow-water or land-based hydrothermal systems, deep-sea vents rely on partnerships between macroinvertebrates and chemosynthetic bacteria. These bacteria convert inorganic chemicals like hydrogen sulfide into organic compounds that the host organisms use for nutrition. Sulfide is highly toxic to most life, which is why scientists were surprised to find thriving ecosystems at vents in 1977. The bacteria live inside the hosts’ gills, allowing them to survive the harsh conditions. Scientists now study how these bacteria help detoxify sulfide, enabling their hosts to live in such environments.
Discovery and exploration
In 1949, a deep water survey found unusually hot brine in the center of the Red Sea. Later studies in the 1960s confirmed the presence of hot, 60 °C (140 °F) saline brine and related metal-rich muds. These hot solutions were coming from an active underwater rift. The high salt content made the water unsuitable for living organisms. Scientists are currently studying these brines and muds as a possible source of valuable metals.
In June 1976, scientists from the Scripps Institution of Oceanography collected the first evidence of underwater hydrothermal vents along the Galápagos Rift, part of the East Pacific Rise, during the Pleiades II expedition using the Deep-Tow seafloor imaging system. In 1977, the first scientific papers about hydrothermal vents were published by Scripps scientists. Researcher Peter Lonsdale shared images taken by deep-towed cameras, and PhD student Kathleen Crane shared maps and temperature data. Scientists placed devices called transponders at the site, nicknamed "Clam-bake," to allow a return visit the next year with the DSV Alvin submersible.
In 1977, scientists from the National Science Foundation directly observed ecosystems near the Galápagos Rift hydrothermal vents. Jack Corliss of Oregon State University led the submersible study. Corliss and Tjeerd van Andel from Stanford University explored the vents and their ecosystems using the DSV Alvin, a submersible operated by the Woods Hole Oceanographic Institution (WHOI). Other scientists on the expedition included Richard Von Herzen and Robert Ballard of WHOI, Jack Dymond and Louis Gordon of Oregon State University, John Edmond and Tanya Atwater of MIT, Dave Williams of the U.S. Geological Survey, and Kathleen Crane of Scripps. These scientists published their findings in the journal Science. In 1979, biologists led by J. Frederick Grassle of WHOI returned to the same location to study the biological communities discovered two years earlier.
High-temperature hydrothermal vents, called "black smokers," were discovered in spring 1979 by scientists from Scripps using the submersible Alvin. The RISE expedition explored the East Pacific Rise near 21° N to test mapping techniques and find new hydrothermal fields beyond the Galápagos Rift. The expedition was led by Fred Spiess and Ken Macdonald, with participants from the U.S., Mexico, and France. The dive area was chosen based on sulfide mineral mounds discovered by the French CYAMEX expedition in 1978. Before diving, Robert Ballard used a deep-towed instrument to find temperature anomalies. The first dive targeted one of these anomalies. On April 15, 1979, Roger Larson and Bruce Luyendyk found a hydrothermal vent field with a biological community similar to the Galápagos vents. On April 21, William Normark and Thierry Juteau discovered high-temperature vents emitting black mineral particles from chimneys, known as black smokers. Macdonald and Jim Aiken attached a temperature probe to Alvin, measuring the highest recorded temperatures at deep-sea vents (380±30 °C). Analysis of black smoker material showed iron sulfide precipitates are common in the "smoke" and chimney walls.
In 2005, Neptune Resources NL, a mineral exploration company, received permission to explore 35,000 km of the Kermadec Arc in New Zealand’s Exclusive Economic Zone for seafloor massive sulfide deposits, a potential source of lead-zinc-copper sulfides from modern hydrothermal vents. In 2007, scientists announced the discovery of the Medusa hydrothermal vent field near Costa Rica, named after the Greek mythological figure Medusa. The Ashadze hydrothermal field (13°N on the Mid-Atlantic Ridge, -4200 m) was the deepest known high-temperature vent until 2010, when a hydrothermal plume from the Beebe site (-5000 m) was found by scientists from NASA Jet Propulsion Laboratory and WHOI. This site is located on the Mid-Cayman Rise within the Cayman Trough. In early 2013, the deepest known hydrothermal vents were found in the Caribbean Sea at nearly 5,000 meters (16,000 feet).
Oceanographers are studying volcanoes and hydrothermal vents on the Juan de Fuca mid-ocean ridge, where tectonic plates are moving apart. Hydrothermal vents and other geothermal features are being explored in Bahía de Concepción, Baja California Sur, Mexico.
Distribution
Hydrothermal vents are found along the edges where Earth's plates meet, but they can also be located within the Earth's plates, such as at hotspot volcanoes. As of 2009, about 500 active underwater hydrothermal vent areas were known. Of these, about half were seen directly on the seafloor, while the other half were suspected based on signs in the water and/or deposits on the seafloor.
Rogers et al. (2012) identified at least 11 regions with different types of hydrothermal vent systems:
- Mid-Atlantic Ridge region,
- East Scotia Ridge region,
- northern East Pacific Rise region,
- central East Pacific Rise region,
- southern East Pacific Rise region,
- south of the Easter Microplate,
- Indian Ocean region,
- four regions in the western Pacific, and many others.
Exploitation
Hydrothermal vents sometimes create valuable mineral resources by forming deposits of seafloor massive sulfides. One example is the Mount Isa orebody in Queensland, Australia. Many hydrothermal vents contain metals like cobalt, gold, copper, and rare earth elements that are important for electronics. In ancient seafloor environments, hydrothermal activity is thought to have formed Algoma-type banded iron formations, which are sources of iron ore.
In recent years, companies have focused on mining minerals from hydrothermal fields because of rising demand for base metals in the mid-2000s. This could lower mining costs. In Japan, where most minerals are imported, there is strong interest in extracting seafloor resources. In 2017, Japan Oil, Gas and Metals National Corporation (JOGMEC) conducted the world’s first large-scale mining of hydrothermal vent deposits using the Research Vessel Hakurei. This operation took place at the Izena hole/cauldron vent field in the Okinawa Trough, a region with 15 confirmed vent fields.
Two companies are now preparing to mine seafloor massive sulfides (SMS). Nautilus Minerals is working on extracting minerals from its Solwarra deposit in the Bismarck Archipelago, while Neptune Minerals is in an earlier stage with its Rumble II West deposit near the Kermadec Islands. Both companies plan to use modified technology. In 2006, Nautilus Minerals successfully brought over 10 metric tons of SMS to the surface using drum cutters attached to a remotely operated vehicle (ROV). In 2007, Neptune Minerals collected SMS samples using a modified suction pump on an ROV.
Mining hydrothermal vents can harm the environment. Dust from mining equipment may affect filter-feeding organisms. Mining could also collapse vents, release methane clathrates, or cause underwater landslides. Tools used for mining, such as ROVs and surface vessels, create noise and human-made light. Hydrothermal vent organisms live in deep, dark areas and have sensitive hearing. Loud noises from mining could damage their hearing or disrupt communication between them. Light from mining tools and surface vessels may also harm deep-sea organisms, such as shrimp, which can suffer retinal damage from bright lights. Surface lighting can disorient seabirds, leading to injury or death.
Three mining waste processes—side cast sediment release, dewatering, and sediment disturbance—could create sediment plumes. Side cast sediment release happens when material is discarded to the side of the mining area before transporting valuable material to the surface. Dewatering involves releasing water mixed with heavy metals like copper and cobalt from the ship into the ocean. Sediment disturbance occurs when mining activities move the seafloor, redistributing sediment. These processes may release heavy metals, altering ocean chemistry and harming marine life. Increased sediment can smother organisms, disrupt feeding, and reduce gas exchange, threatening populations.
Conservation
The conservation of hydrothermal vents has been a topic of intense debate among ocean scientists for the past 20 years. Some argue that scientists may be the biggest threat to these rare ecosystems. Efforts have been made to create rules for how scientists study vent sites, but there is no official international agreement that all scientists must follow.
A major focus of the conversation about protecting hydrothermal vent ecosystems is deep sea mining. Four types of minerals are being considered for mining: manganese nodules, cobalt-rich crusts, seafloor massive sulfides, and phosphorite nodules. Seafloor massive sulfides found near hydrothermal vents are especially important. Black smokers, which are structures at these vents, produce large amounts of sulfides, mostly iron sulfides like pyrite. This leads to high levels of sulfide deposits near these vents. A key challenge in conservation is balancing the use of sulfides for human needs with the risks of mining them from the deep sea.
The effects of mining deep sea minerals are not fully understood because hydrothermal vent ecosystems are very complex and change quickly. Mining an active vent area would depend on the return of chemosynthetic bacteria, which are essential for the vent’s energy flow. Studies on how vent ecosystems recover after natural events, like volcanic eruptions, show that bacteria can return in 3–5 years, and larger animals may take about 10 years. However, the species that return may differ from those before the event, which can affect critically endangered species, such as certain types of mollusks. More research is needed to understand the long-term effects of mining on these ecosystems.
Shallow hydrothermal vents are also being studied as models for understanding how climate change affects extreme environments. Scientists track changes in specialized organisms living near vents to study effects like ocean acidification, rising temperatures, and heavy metal pollution. The impact of deep sea mining on these climate change models is an area that requires further study.
Geochronological dating
Scientists use certain methods to determine the age of hydrothermal vents. These methods involve dating sulfide minerals, such as pyrite, and sulfate minerals, such as baryte. Common techniques include radiometric dating and electron spin resonance dating. Each method has its own limitations, assumptions, and challenges. Some general challenges include the need for highly pure minerals to be tested, the specific age ranges each method can measure, heating that can erase the ages of older minerals if temperatures exceed certain levels, and the presence of multiple mineral formation events, which can create a mix of different ages. In environments where minerals form in multiple stages, electron spin resonance dating usually provides an average age for the entire mineral sample. Radiometric dating, however, tends to reflect the ages of younger mineral layers because the decay of parent elements occurs over time. This explains why different dating methods may produce different ages for the same sample and why samples taken from the same hydrothermal chimney can show varying ages.
History and formation of hydrothermal vents
Although some scientists who study Earth's chemical processes, such as Rogers et al. (2012), have found locations of hydrothermal vents, the exact places where these vents form in deep ocean areas are not fully known. Most of the ocean floor remains unexplored, with less than 1% of it well understood. Scientists currently know that most hydrothermal vents are found along mid-ocean ridges. Understanding where these systems are located is important because many theories about their formation involve seismic activity, especially near volcanic areas.
During the Paleocene and Eocene periods, when continents split apart, seismic activity caused gases, liquids, and sediments from Earth's interior to erupt. This event created large craters above layers of igneous rock called sills. Sills form when magma pushes between existing rock layers. These craters on the ocean floor contain clusters of hydrothermal vents. Features of these vents include sedimentary layers tilted inward, as well as sandstone structures like dykes, pipes, and breccias. These features are classified as subvolcanic intrusions, which lead to hydrothermal activity. A study used 2D seismic reflection data to describe the structures of these systems, which are located in craters with funnel-shaped sides. These structures are often called chimneys, which form on top of the vents. The interaction between oceanic crust and seawater creates these systems, changing local chemistry and forming deposits rich in different metals. These metal deposits and altered chemistry create conditions that support life, such as thermophiles and other organisms.