Hydrothermal vents are openings on the ocean floor where water heated by the Earth’s heat flows out. These vents 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 vents mixes with ocean water, it creates visible clouds called hydrothermal plumes. Over time, this hot water can form rocks and mineral deposits on the seafloor.
Hydrothermal vents form because Earth is geologically active and has large amounts of water both on its surface and inside its crust. Under the ocean, these vents can create structures called black smokers or white smokers, which release many different elements into the ocean. This process helps shape the chemical balance of the ocean. Compared to most deep-sea areas, regions around hydrothermal vents are more biologically active. These areas support unique life forms, such as giant tube worms, clams, limpets, and shrimp, which rely on bacteria and archaea that use chemicals from vent water instead of sunlight. These microbes form the base of the food chain in these environments.
Scientists believe that active hydrothermal vents may exist on Jupiter’s moon Europa and Saturn’s moon Enceladus. It is also thought that ancient hydrothermal vents might have once existed on Mars. Some researchers suggest that hydrothermal vents could have played a role in the early development of life on Earth. Studies show that the conditions in certain vents, like alkaline vents or those with supercritical carbon dioxide, may help form molecules essential for life. However, how life began is still a topic of scientific debate, and many different ideas exist about this process.
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 are places where two tectonic plates move apart, and new ocean floor is created.
The water that comes out of seafloor hydrothermal vents is mostly seawater that moves into the vent system near a volcano through cracks and porous rocks or volcanic layers. It also includes some water from magma that rises from deep underground. On land, most water in fumarole and geyser systems comes from rainwater and groundwater that seep into the ground from the surface. This water may also include some metamorphic water, magma water, and brine from rocks, depending on the location. The amounts of each type of water vary depending on where the vents are.
At these deep ocean depths, the surrounding water is about 2°C (36°F). However, water that comes out of hydrothermal vents can be much hotter, from 60°C (140°F) up to 464°C (867°F). Because of the high pressure at these depths, water can exist as a liquid or as a supercritical fluid at these high temperatures. The critical point for pure water is 375°C (707°F) at a pressure of 218 atmospheres.
Adding salt to the water increases the temperature and pressure needed to reach the critical point. For seawater with 3.2% salt by weight, the critical point is 407°C (765°F) and 298.5 bars, which corresponds to a depth of about 2,960 meters (9,710 feet) below sea level. If a hydrothermal fluid with this salt level vents at temperatures and pressures above these values, it is supercritical. The salt content of vent fluids varies widely due to changes in the rock layers. The critical point for fluids with less salt is at lower temperatures and pressures than seawater but higher than pure water. For example, a fluid with 2.24% salt has a critical point at 400°C (752°F) and 280.5 bars. Therefore, water from the hottest parts of some vents can be a supercritical fluid, which has properties between a gas and a liquid.
Examples of supercritical venting have been found at several locations. At Sister Peak (Comfortless Cove Hydrothermal Field, 4°48′S 12°22′W, depth 2,996 meters or 9,829 feet), low-salt vapor-type fluids are released. Although sustained venting was not supercritical, a brief burst of 464°C (867°F) exceeded supercritical conditions. A nearby site, Turtle Pits, vents low-salt fluid at 407°C (765°F), which is above the critical point for that salt level. In the Cayman Trough, a vent site called Beebe, the deepest known hydrothermal site at about 5,000 meters (16,000 feet) below sea level, has shown continuous supercritical venting at 401°C (754°F) with 2.3% salt.
Although supercritical conditions have been observed at multiple sites, scientists do not yet know the importance of supercritical venting for processes like hydrothermal circulation, mineral formation, chemical exchanges, or life.
The early stages of a vent chimney begin with the formation of the mineral anhydrite. Over time, copper, iron, and zinc sulfides deposit in the chimney, making it less porous. Vent chimneys can grow up to 30 centimeters (1 foot) per day. In April 2007, an exploration of deep-sea vents near Fiji found these vents to be a major source of dissolved iron (see iron cycle).
Black smokers and white smokers
Some hydrothermal vents create tall, tube-shaped structures called chimneys. These chimneys form when minerals in the hot vent water mix with cold seawater. The minerals come out of the water as tiny particles, building up the chimneys. Some chimneys can grow as tall as 60 meters (200 feet). One example is "Godzilla," a chimney on the deep seafloor near Oregon in the Pacific Ocean. It reached 40 meters (130 feet) before it collapsed in 1996.
A black smoker is a type of hydrothermal vent found on the seafloor, usually in areas between 2,500 to 3,000 meters (8,200 to 9,800 feet) deep, but also in shallower or deeper regions. They look like dark, chimney-like structures that release a cloud of black material. Black smokers often release particles rich in sulfur-containing minerals called sulfides. These vents form in groups when very hot water from deep inside Earth flows through the ocean floor. This water can be hotter than 400 degrees Celsius (752 degrees Fahrenheit) and carries dissolved minerals from Earth's crust, especially sulfides. When this hot water meets cold ocean water, the minerals form solid particles, creating dark, chimney-like structures around each vent. Heat helps these structures grow thicker over time. Over time, the metal sulfides can form large deposits of valuable minerals. Some black smokers near the Azores in the Mid-Atlantic Ridge contain very high amounts of dissolved iron, such as up to 24,000 microM 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 were observed using the deep-sea vehicle ALVIN from the Woods Hole Oceanographic Institution. Today, black smokers are found in the Atlantic and Pacific Oceans, usually at about 2,100 meters (6,900 feet) deep. The northernmost black smokers are a group of five called Loki's Castle, discovered in 2008 by scientists from the University of Bergen near 73°N on the Mid-Atlantic Ridge between Greenland and Norway. These vents are of interest because they are in a more stable part of Earth's crust, where tectonic forces are weaker and hydrothermal vents are less common. The deepest known black smokers are in the Cayman Trough, 5,000 meters (3.1 miles) below the ocean's 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 appear together in the same hydrothermal field. Usually, black smokers are closer to the main heat source, while white smokers are farther away. White smokers often form later in a hydrothermal field's life cycle as the heat source moves farther away. At this stage, the water is mostly seawater instead of magma, and the minerals deposited are rich in calcium, forming sulfate (such as barite and anhydrite) and carbonate deposits.
Hydrothermal plumes
Hydrothermal plumes are fluid structures that form when hot hydrothermal fluids are released into the water above active hydrothermal vent sites. These fluids often have different physical properties (such as temperature and density) and chemical properties (such as pH, Eh, and major ions) compared to seawater. These differences create physical and chemical changes that support various chemical reactions, including oxidation-reduction reactions and precipitation reactions.
Hydrothermal vent fluids are much hotter than seawater near the ocean floor (40 to over 400 °C compared to about 4 °C). Because these fluids are less dense than seawater, they rise through the water column due to buoyancy, forming a hydrothermal plume. This rising stage is called the "buoyant plume" phase. During this phase, movement between the plume and surrounding seawater creates turbulence that mixes the two fluids, gradually diluting the plume with seawater. Eventually, the plume becomes neutrally buoyant at a certain height above the seafloor, marking the "nonbuoyant plume" phase. At this point, the plume stops rising and begins to spread horizontally across the ocean, sometimes for thousands of kilometers.
Chemical reactions happen alongside the physical changes in hydrothermal plumes. Seawater is generally an oxidizing fluid, while hydrothermal vent fluids are often reducing. This means that chemicals like hydrogen gas, hydrogen sulfide, methane, iron, and manganese found in vent fluids react when mixed with seawater. In fluids with high hydrogen sulfide levels, dissolved metals like iron and manganese form dark-colored sulfide minerals (seen in "black smokers"). Over time, these metals oxidize to form insoluble iron and manganese (oxy)hydroxide minerals. For this reason, the region near the vent where metals are actively oxidized is called the "near field," while the region where metals are fully oxidized is called the "far field."
Scientists use chemical tracers in hydrothermal plumes to locate deep-sea hydrothermal vents. Effective tracers should not react chemically after venting, so changes in their concentration are due only to dilution. Noble gas helium is a useful tracer because hydrothermal venting releases higher amounts of helium-3, a rare isotope found only in Earth's interior. This creates unusual helium isotope patterns in seawater that indicate hydrothermal activity. Another tracer is radon, a radioactive gas. Radon-222, which has the longest half-life among radon isotopes (about 3.82 days), can help determine the age of hydrothermal plumes when combined with helium isotope data. Other reactive components like hydrogen gas, hydrogen sulfide, methane, and metals such as 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 marine biogeochemistry. These vents release many trace metals into the ocean, including iron, manganese, chromium, copper, zinc, cobalt, nickel, molybdenum, cadmium, vanadium, and tungsten, many of which are important for life. Physical and chemical processes determine what happens to these metals after they enter the water column. According to thermodynamic principles, iron and manganese should oxidize in seawater to form insoluble metal (oxy)hydroxide minerals. However, interactions with organic compounds and the formation of colloids and nanoparticles can keep these elements suspended in the water 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 limited in marine environments. The long-distance transport of iron and manganese through organic complexation may be an important way these metals cycle through the ocean. Hydrothermal vents also release other biologically important trace metals like molybdenum, which may have played a role in the early chemical development of Earth's oceans and the origin of life. However, iron and manganese precipitates can also affect ocean biogeochemistry 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 depend on energy from the sun. However, deep-sea organisms near hydrothermal vents do not have access to sunlight. Instead, biological communities around these vents rely on nutrients from chemical deposits and hot fluids found in the vent areas. Scientists once believed that vent organisms depended on marine snow, which is organic material that falls from the ocean above. This would mean they relied on plants and the sun for energy. Some vent organisms do eat this material, but this alone would not support a large number of life forms. In fact, hydrothermal vent zones have far more organisms than the surrounding seafloor—up to 10,000 to 100,000 times more.
Hydrothermal vents are ecosystems where life uses chemicals instead of sunlight for energy. This process is called chemosynthesis. These ecosystems support many life forms because vent organisms depend on bacteria that use chemicals to create food. The water from hydrothermal vents contains dissolved minerals that help these bacteria grow. These bacteria use sulfur compounds, such as hydrogen sulfide, to produce organic material. Hydrogen sulfide is toxic to most organisms, but the bacteria convert it into energy.
Hydrothermal vents also provide iron to the ocean, which is used by phytoplankton, tiny plants that float on the ocean surface. The oldest known biological community linked to a hydrothermal vent is called the Figueroa Sulfide, found in California from the Early Jurassic period. This ecosystem depends on the vent for energy, unlike most life on Earth, which relies on sunlight. Some vent organisms use oxygen from photosynthetic organisms, while others do not need oxygen.
Chemosynthetic bacteria form thick mats that attract small animals like amphipods and copepods, which eat the bacteria. Larger animals, such as snails, shrimp, crabs, tube worms, fish, and octopuses, form a food chain based on these bacteria. Common groups of organisms near vents include worms, snails, and crustaceans. Some of the most common nonmicrobial animals are large clams, tube worms, and eyeless shrimp.
Siboglinid tube worms, which can grow over 2 meters (6.6 feet) long, are a key part of vent communities. These worms lack mouths and digestive systems. Instead, they absorb nutrients from bacteria living inside their bodies. Each ounce of their tissue contains about 285 billion bacteria. The worms have red plumes that carry hemoglobin, a protein that helps transfer hydrogen sulfide to the bacteria. In return, the bacteria provide the worms with carbon-based nutrients. Two known species of tube worms are Tevnia jerichonana and Riftia pachyptila. A community called "Eel City" is mostly made up of a type of eel, Dysommina rugosa, and is located near a volcanic cone in American Samoa.
Over 100 species of snails have been found near hydrothermal vents. More than 300 new species have been discovered, many of which are closely related to species found in other parts of the world. Scientists believe that before the North American Plate moved over a mid-ocean ridge, all vent species in the eastern Pacific were part of a single region. Later, this movement caused species in different areas to evolve separately. Similar species found at different vents support the idea of natural selection and evolution.
Even though life is sparse at great ocean depths, hydrothermal vents support entire ecosystems. Sunlight does not reach these areas, so organisms like archaea and extremophiles use heat, methane, and sulfur compounds from vents to create energy through chemosynthesis. Larger animals, such as clams and tube worms, eat these microbes. These microbes also help form the mineral deposits around vents, completing the life cycle.
A type of bacteria that uses light other than sunlight for photosynthesis was found near a black smoker in the ocean off Mexico. This bacteria belongs to the Chlorobiaceae family and uses the faint glow from the vent instead of sunlight. This discovery shows that some organisms can use light from other sources for energy.
New species are often found near hydrothermal vents. For example, the Pompeii worm (Alvinella pompejana), which can survive temperatures up to 80°C (176°F), was discovered in the 1980s. Another species, the scaly-foot gastropod (Chrysomallon squamiferum), was found in 2001 near hydrothermal vents in the Indian Ocean. This worm uses iron sulfides to build its hard outer layer instead of calcium carbonate. Scientists believe the extreme pressure at these depths helps stabilize the iron sulfides for use in the worm’s body. This hard shell may protect the worm from predators.
In 2017, scientists found evidence of possible ancient life in hydrothermal vent deposits in Quebec, Canada. These fossils may be over 4.28 billion years old, dating back to when the Earth was very young.
Hydrothermal vent ecosystems have large amounts of life, but this depends on the relationships between organisms. Unlike shallow-water and land hydrothermal systems, deep-sea vents rely on symbiotic relationships between animals and bacteria. These bacteria use chemicals like hydrogen sulfide to create food, which the animals then use for energy. Hydrogen sulfide is highly toxic, so scientists were surprised when they found thriving life near vents in 1977. They discovered that these animals host bacteria in their bodies, which help them survive the toxic environment. Scientists are now studying how these bacteria help their hosts process the poison.
Discovery and exploration
In 1949, a deep water survey found unusually hot salty water in the center of the Red Sea. Later studies in the 1960s confirmed the presence of hot, 60 °C (140 °F) salty water and muds rich in metals. These hot solutions came from an active underwater rift. The very salty water made it hard for living things to survive. Scientists are now studying these brines and muds to see if they contain metals that can be mined.
In June 1976, scientists from the Scripps Institution of Oceanography found the first evidence of underwater hydrothermal vents along the Galápagos Rift, part of the East Pacific Rise, during the Pleiades II expedition. They used a seafloor imaging system called Deep-Tow. In 1977, scientists from Scripps published the first scientific papers about these vents. Researcher Peter Lonsdale shared photos taken by deep-towed cameras, and student Kathleen Crane shared maps and temperature data. Scientists placed devices at the site, called "Clam-bake," to help return for more studies the next year using the DSV Alvin.
In 1977, scientists first directly observed ecosystems near the Galápagos Rift hydrothermal vents. These ecosystems rely on chemical processes instead of sunlight. A group of marine geologists, funded by the National Science Foundation, returned to the Clam-bake sites. Jack Corliss of Oregon State University led the submersible study. Corliss and Tjeerd van Andel from Stanford University collected samples and observed the vents and their ecosystems in the DSV Alvin, a research submersible operated by Woods Hole Oceanographic Institution (WHOI). Other scientists on the cruise 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. They published their findings in the journal Science. In 1979, biologists led by J. Frederick Grassle, then at WHOI, returned to the same location to study the biological communities discovered two years earlier.
High-temperature hydrothermal vents, called "black smokers," were found 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 of the seafloor 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 because the French CYAMEX expedition in 1978 found mounds of sulfide minerals on the seafloor. Before diving, Robert Ballard used a deep-towed instrument to find temperature changes in the water. The first dive targeted one of these areas. On April 15, 1979, during a dive to 2,600 meters, Roger Larson and Bruce Luyendyk found a vent field with life similar to the Galápagos vents. On April 21, William Normark and Thierry Juteau discovered high-temperature vents that released black mineral particles from chimneys, called "black smokers." Macdonald and Jim Aiken attached a temperature probe to Alvin, which recorded the highest temperatures ever measured at deep-sea vents (380±30 °C). Studies of black smoker material showed that iron sulfide minerals are common in the "smoke" and chimney walls.
In 2005, Neptune Resources NL, a mining company, received permission to explore 35,000 km of the Kermadec Arc in New Zealand’s Exclusive Economic Zone for seafloor sulfide deposits, which may contain lead, zinc, and copper from modern hydrothermal vents. In 2007, scientists announced the discovery of a vent field near Costa Rica, named the Medusa hydrothermal vent field. The Ashadze hydrothermal field (13°N on the Mid-Atlantic Ridge, -4200 m deep) was the deepest known high-temperature vent until 2010, when a hydrothermal plume from the Beebe site (18°33′N 81°43′W, -5000 m deep) was found by scientists from NASA and WHOI. This site is on the Mid-Cayman Rise within the Cayman Trough. In early 2013, scientists discovered the deepest known hydrothermal vents in the Caribbean Sea at nearly 5,000 meters (16,000 feet) deep.
Oceanographers are studying volcanoes and hydrothermal vents on the Juan de Fuca mid-ocean ridge, where tectonic plates are moving apart. Scientists are also exploring hydrothermal vents and other geothermal features in Bahía de Concepción, Baja California Sur, Mexico.
Distribution
Hydrothermal vents are found along the edges where Earth's plates meet, although they can also be located within the middle of plates, such as at hotspot volcanoes. As of 2009, there were about 500 known active underwater hydrothermal vent fields. Approximately half of these were seen directly on the ocean floor, while the other half were identified using signs in the water or deposits on the ocean floor.
Rogers et al. (2012) found at least 11 different regions with unique life forms associated with hydrothermal vent systems.
Exploitation
Hydrothermal vents sometimes create usable mineral resources through the formation of seafloor massive sulfide deposits. The Mount Isa orebody in Queensland, Australia, is a good example. Many hydrothermal vents contain valuable metals like cobalt, gold, copper, and rare earth metals used in electronics. In the Archean era, hydrothermal venting on the seafloor helped form Algoma-type banded iron formations, which are important sources of iron ore.
In the mid-2000s, rising prices for base metals led mineral exploration companies to focus on extracting resources from hydrothermal fields on the seafloor. This process could potentially reduce costs.
In countries like Japan, where most minerals are imported, there is strong interest in mining seafloor resources. Japan’s first large-scale seafloor mining of hydrothermal vent deposits occurred in August–September 2017. The Japan Oil, Gas and Metals National Corporation (JOGMEC) used the Research Vessel Hakurei to mine the 'Izena hole/cauldron' vent field in the Okinawa Trough, a region with 15 known vent fields.
Two companies are currently 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 existing 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 used a modified suction pump on an ROV to collect SMS samples.
Seafloor mining can harm the environment. For example, dust from mining machines may affect filter-feeding organisms, and mining could cause vents to collapse or release methane clathrates. It might also trigger underwater landslides.
Mining tools can also create noise and light pollution. Seafloor mining would use ROVs and surface vessels, which produce noise. Hydrothermal vent organisms live deep in the ocean and have sensitive hearing. Sudden noise from machines could harm their hearing or disrupt communication between organisms, as many benthic species rely on low-frequency sounds. Mining tools also create human-made light on the seafloor and on the ocean surface. Deep-sea organisms are adapted to dark conditions, and studies suggest that bright lights could damage their eyes. Surface vessels may also use lights that disorient seabirds, causing them to collide with objects or become exhausted.
Three mining waste processes—side cast sediment release, dewatering, and sediment disturbance—could create sediment plumes. Side cast sediment release happens when material is moved aside during mining by ROVs, potentially forming plumes. Dewatering involves removing water from mined material, which may release heavy metals like copper and cobalt into the water. Sediment disturbance occurs when mining activity disrupts the seafloor, redistributing sediment.
Environmental concerns include the release of heavy metals and increased sediment. Heavy metals from dewatering could alter ocean chemistry and harm marine life. Excess sediment from mining could smother organisms, disrupt feeding, and interfere with gas exchange. These processes may also increase sedimentation rates on the seafloor.
Conservation
The conservation of hydrothermal vents has been a topic of debate among ocean scientists for the past 20 years. Some argue that scientists may be the ones causing the most harm to these rare underwater habitats. Efforts have been made to create rules for how scientists study vent sites, but there is no official international agreement that legally requires scientists to follow these rules.
A major issue in protecting hydrothermal vent ecosystems is deep sea mining. Scientists are considering extracting four types of minerals from the ocean floor: manganese nodules, cobalt-rich crusts, seafloor massive sulfides, and phosphorite nodules. Seafloor massive sulfide deposits near hydrothermal vents are a central focus of these discussions. As explained earlier, black smokers create large amounts of sulfides, mostly in the form of iron sulfides like pyrite. This leads to high concentrations of sulfides near these vents. A key challenge in conservation is balancing the use of sulfides in a way that supports the environment with the need to mine them for commercial purposes.
The effects of mining deep sea minerals are not well understood because hydrothermal vent ecosystems are highly dynamic and change quickly. Mining an active vent area would depend on the regrowth of bacteria that use chemicals for energy, as these bacteria are the main source of energy for the ecosystem. It is difficult to study the effects of mining because no large-scale research has been conducted. However, scientists have studied how vent ecosystems recover after volcanic events. These studies show that bacteria can return to an area in 3–5 years, while larger sea creatures take about 10 years to return. Researchers also noticed changes in the types of species living in the ecosystem after destruction, with some new species moving in. These changes may threaten certain species that are already at risk, such as mollusks. More research is needed to understand how long-term mining might affect species recovery.
Shallow hydrothermal vents have also been suggested as models for studying climate change in extreme environments. Scientists track how specialized organisms in these areas respond to changes like ocean acidification, rising temperatures, and heavy metal pollution. The impact of deep sea mining on these studies is an area that needs further exploration.
Geochronological dating
Scientists use methods like radiometric dating and electron spin resonance dating to determine the ages of hydrothermal vents. These methods often involve studying sulfide minerals, such as pyrite, and sulfate minerals, such as baryte. Each dating method has its own limits, assumptions, and difficulties. Common challenges include the need for very pure minerals, the specific age ranges each method can measure, and the risk of heating minerals above certain temperatures, which can erase the ages of older minerals. Additionally, when minerals form in multiple stages, the results can be complicated. In such cases, electron spin resonance dating typically shows the average age of all the minerals, while radiometric dating tends to reflect the ages of the youngest mineral layers due to the decay of parent nuclei. This explains why different dating methods may give different ages for the same sample and why samples from the same hydrothermal chimney can have varying ages.
History and formation of hydrothermal vents
Some scientists who study Earth's chemical processes, like Rogers et al. (2012), have found some locations of hydrothermal vents. However, the exact places where these vents form in deep ocean areas are not fully understood. Most of the ocean floor remains unexplored, with less than 1% of it well studied. Scientists currently know that most hydrothermal vents are found along mid-ocean ridges, which are underwater mountain ranges. Understanding the location of these systems 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 formed large craters above layers of igneous rock called sills. Sills are rock layers created when magma cools between existing rock layers. These craters on the seafloor contain clusters of hydrothermal vents. Features of these vents include sedimentary layers that slope inward, as well as sandstone structures like dykes, pipes, and broken rock. These features are classified as subvolcanic intrusions, which cause hydrothermal activity. A study used 2D seismic reflection data to describe the structure 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.