An ocean vent sits over a deep fissure in the ocean floor. Ocean vents eject hot, often toxic, fluids and gases into the surrounding seawater. They often mark sites of tectonic activity, and create some of the most hostile habitats on Earth.
 
Ocean vents are a type of hydrothermal vent. Other types of hydrothermal vents include hot springs, geysers, and fumaroles. As their name indicates, all hydrothermal vents are characterized by water (hydro-) and extremely high temperatures (thermal).
 
Tectonic Activity
 
Ocean vents are the product of tectonic activity beneath the ocean floor. Tectonic activity describes the way tectonic plates, giant slabs of Earth’s lithosphere, interact with each other.
 
Ocean vents are found in all ocean basins, although they are most abundant around the Pacific Ocean’s “Ring of Fire,” which also includes active earthquake zones, volcanoes, and ocean trenches.
 
Ocean vents are primarily found around mid-ocean ridges and volcanic arcs. At both mid-ocean ridges and back-arc basins, the molten magma of Earth's asthenosphere wells up close to the surface.
 
Mid-ocean ridges form at divergent plate boundaries, where tectonic plates are moving apart from each other. New oceanic crust is formed at mid-ocean ridges. The Mid-Atlantic Ridge, for instance, runs through the entire Atlantic Ocean, separating the North American and Eurasian plates in the north and the South American and African plates in the south. Ocean vents dot the entire underwater mountain range.
 
Volcanic arcs form at convergent plate boundaries, where a dense tectonic plate is falling beneath a less-dense plate in a process called subduction. Oceanic crust is being destroyed in the subduction zones around volcanic arcs. Volcanic arcs may include volcanoes that rise above sea level, such as Japan’s Ryuku Islands, while some volcanic arcs are seamounts, or underwater mountains.
 
Ocean vents found around volcanic arcs are located on the overriding (less-dense) tectonic plate. This area is called a “back-arc basin.” Back-arc basins are formed as the ocean trench created by subduction migrates “backward” toward the subducting plate in a process called trench rollback. Trench rollback causes the overriding plate to be stretched thin, creating conditions that allow for the formation of ocean vents.
 
Going with the Flow
 
The process that creates ocean vents takes place in three zones: the recharge zone, the reaction zone, and the upflow zone.
 
Vent fluid in the recharge zone is formed by seawater seeping into cracks in the seafloor. As the seawater is warmed by its proximity to magma, it is stripped of its magnesium.
 
At this point, seawater changes to an acidic vent fluid. As an acid, the vent fluid leeches more metals from surrounding rocks of the oceanic crust.
 
The acidic vent fluid continues to heat up as it flows and seeps toward the vent’s source of heat. The closer magma wells to the fluid, the warmer the fluid becomes and the quicker its chemical reaction time will be. 
 
Chemistry and vent outflow are also influenced by the vent fluid’s residence time, or the time it spends in the region close to the heat source.
 
The vent fluid becomes more buoyant in the reaction zone and races back toward the surface. Incoming flows of vent fluid may also push the superheated fluid upward toward the seafloor. Vent fluid has the least amount of time in this upflow zone. 
 
The vent fluid’s temperature drops slightly as it races away from the vent’s heat source. Vent fluid can lose heat in three major ways. First, heat can dissipate into the surrounding rocks. Second, it can mix with cold seawater seeping in from above. Both of these methods involve a transfer of heat (from the vent fluid to either rocks or seawater). This process is called conductive cooling.
 
The third way a vent fluid can lose heat is through decompression. Unlike the interaction of vent fluid with rocks or seawater, decompression does not involve a transfer of heat. The fluid cools through a loss of pressure. (Pressure is higher in the reaction zone, which lies deeper in the Earth.) This process is called adiabatic cooling.
 
Ejection Sites
Hydrothermal vents are where the hot, toxic vent fluids from the upflow zone are spewed from oceanic crust into the surrounding seawater. Hydrothermal vents are narrow and well-sealed, and vent fluids exit at high velocity.
 
Upon contact with the cold, dense ocean, the vent fluid “precipitates” minerals such as sulfates, sulfides, and quartz. These minerals often give ocean vents their characteristic color.
 
Not all vent fluids are violently ejected into seawater from hydrothermal vents, however. Diffuse flows form in areas where vent fluids mix with cold seawater before exiting the seafloor. 
 
Diffuse flows usually cover a larger portion of a vent field than narrow hydrothermal vents. Vent fluids exiting through diffuse flows are usually cooler, less toxic (from mixing with seawater), and exit into the ocean more slowly over a larger area. Diffuse flows also lack the telltale “smoke” of gushing hydrothermal vents.
 
Plumes
As vent fluid is ejected into the ocean, it forms a hydrothermal plume. This plume is more buoyant than seawater, and continues to rise. 
 
As it rises and expands, the plume constantly mixes with seawater and its chemistry is diluted. Eventually, the plume reaches neutral buoyancy (the point where the pressure inside the plume equals the pressure of the surrounding seawater, and the plume no longer rises or sinks). At neutral buoyancy, the plume and its chemistry are entirely dispersed by ocean currents. 
 
Vent Chemistry
 
The chemistry of ocean vents has an enormous impact on the chemistry of the ocean. At mid-ocean ridges, ocean vents help cool new oceanic crust. At volcanic arcs, they contribute to the geology of the seafloor and even underwater mountains.
 
Temperatures at vent fields range from below 50° Celsius (122° Fahrenheit) to more than 400° Celsius (752° Fahrenheit). Some ocean vents are rich in oxygen and oxygen compounds (such as sulfates), while others are anoxic. Some are highly acidic, with a pH as low as 2. Others have a pH as high as 8.
 
The temperature and chemistry of vent fields varies across the ocean, and these factors are influenced by such features as the frequency of volcanic eruptions in the area, the presence and quantity of sediments, the permeability of the seafloor, the composition of rocks in the oceanic crust, the depth of the heat source, the residence time of vent fluids in the reaction zone, and the water-to-rock ratio at the reaction zone.
 
Temperature
Ocean vents help cool the Earth’s interior. In fact, oceanographers and geologists estimate that ocean vents account for a whopping 10% of total heat loss from Earth’s mantle and core.
 
The temperature of vent fluid is always warmer than the surrounding seawater. Seawater at the deepest ocean vents is just above freezing at 2° Celsius (35° Fahrenheit). Energy from the Earth’s superheated mantle and core can heat vent fluid to temperatures of more than to 400° Celsius (752° Fahrenheit). Around diffuse flows, the temperature of vent fluids is usually below 50° Celsius (122° Fahrenheit).
 
The temperature of a vent fluid, and the temperature difference between the vent fluid and surrounding seawater, can determine the chemistry of a vent.
 
For instance, most hydrothermal vents eject vent fluids that would boil at ambient temperatures at sea level. However, at great depths and great temperatures, phase separation (the separation of a liquid into two distinct liquids) prevents vent fluids from boiling. Instead, the chemical reaction between seawater and vent fluid forms a high-salinity brine. This chemical reaction is called brine condensation. 
 
Chemicals
The most characteristic feature of ocean vents is probably the dense particle plumes that inject chemicals into seawater. Vent fluids most often include sulfides and sulfates. Sulfides are negatively charged ions of the mineral sulfur, while sulfates are negatively charged ions of sulfur-oxygen molecules. 
 
Sulfides and sulfates exist in a dazzling array at ocean vents: calcium sulfate, strontium sulfate, zinc sulfide, iron sulfide, copper sulfide, iron sulfide, manganese sulfide. These compounds interact with other elements, including hydrogen, helium, potassium, gold, silver, and cadmium. Perhaps most crucially, vent fluids interact with sodium and chloride, forming salt.
 
As ocean vents eject mineral-rich fluids into the ocean, many of these minerals precipitate, or solidify. Tall, thin vent chimneys are made of these precipitated minerals, including copper, iron, zinc, cadmium, silver, and even gold. 
 
As long as they continue to eject fluid, the chimneys continue to grow. Some chimneys can grow 30 centimeters (almost 12 inches) a day and reach 20 meters (65 feet) tall. Tall chimneys don’t last long, though. The mineral structure is fragile. Powerful undersea currents and pressure often lead to their collapse.
 
Types of Ocean Vents
 
Ocean vents can be classified as black smokers, white smokers, or snowblowers. All these ocean vents form in the same way. Their differences are marked by color, temperature, and chemistry.
 
Black smokers are the largest type of ocean vent, and eject the hottest fluids. Vent fluids spew out of tall chimneys at rates of up to 5 meters per second (16 feet per second). The “smoke” blown from black smokers is a dense cloud of particles, mostly metals such as iron and copper. The metals in the fluid mix with the oxygen in the seawater to form a black cloud. 
 
White smokers generally develop over cooler vents. White smoker fluid is generally more acidic, and chimneys have much higher ratios of minerals such as zinc, cadmium, silver, and gold.
 
Snowblower vents develop around low-temperature diffuse flows, often around lava from underwater volcanoes. Snowblowers earn their nickname by ejecting columns of white, fluffy particles.
 
Unlike the particle plumes of black and white smokers, snowblower particles are not minerals. The ejecta from snowblower vents are made up of billions of tiny, organic microbes. The heat and minerals present in lava interact with seafloor communities of bacteria and archaea, producing flocculent microbial blooms.
 
Ocean Vent Communities
 
Many unique organisms are adapted to life in the harsh environment of an ocean vent. In fact, ocean vents set the current highest temperature possible for life to exist—a fiery 121° Celsius (250° Fahrenheit), found on the Endeavor hydrothermal vents on the Juan de Fuca ridge off the coast of Vancouver, British Columbia, Canada.
 
The producers in ocean vent food webs are extremophiles. Extremophiles thrive in chemically extreme conditions that usually discourage life on Earth. Most food webs on Earth, for instance, rely on the sun. Producers near Earth’s sunlit surface (such as green plants and phytoplankton) use sunlight, water, and carbon dioxide to manufacture simple sugars and oxygen in a process called photosynthesis. 
 
Organisms near an ocean vent do not always have access to sunlight. These organisms depend on a process called chemosynthesis. In chemosynthesis, microbes convert vent fluids such as hydrogen sulfide into energy (simple sugars), water, and sulfur. Sulfur is naturally a yellow, and many bacterial mats have a characteristic golden color as a result.
 
These specialized microbes (mostly bacteria and archaea, single-celled organisms similar to bacteria) live everywhere in the vent community. They live on the vent floor. They live inside chimneys. They even live inside animals like tube worms and mussels. These microbes are the basis of food webs in the ocean vent ecosystem. Tube worms, mussels, and clams use the microbes to produce nutrients. Plankton and shrimp eat the microbes. In turn, predators like crabs, fish, jellies, and octopuses prey on these animals. 
 
The deep ocean is often so dark that many creatures do not have functioning eyes. Their bodies are often gelatinous and lightweight, to offset the crushing pressure of the deep.
 
Ocean vents provide an “oasis” of biological activity on the ocean floor, which is often dominated by abyssal plains. For this reason, ocean vents have one of the highest rates of biomass of any habitat on Earth. Busy, clustered communities of organisms thrive around the vents, while hardy bacterial mats stretch out meters wider. 
 
Exploring Ocean Vents
 
In 1977, oceanographers, led by National Geographic Explorer-in-Residence Robert Ballard, were exploring the Galápagos Rift along the mid-ocean ridge in the eastern Pacific. 
 
The scientists noticed a series of temperature spikes in their data. They wondered how deep-ocean temperatures could change so drastically over such a short distance—from near-freezing to 400°C (750 °F). Ballard and his crew quickly sent cameras to the seafloor to investigate the anomaly.
 
What they discovered, of course, were ocean vents. Fascinated by these undersea features, oceanographers used a submersible to study the vents themselves. They were even more fascinated to discover a diverse, thriving community of living organisms. Until this point, all life on Earth was considered to be dependent on sunlight.
 
Today, oceanographers use an array of instruments to study ocean vents. Bathymetric maps of the seafloor and interactive maps of ocean currents help them identify hydrothermal plumes rising through the ocean. Plumes may be identified through their temperature, chemical structure, and even their color. 
 
One of the innovative ways to identify and study ocean vents is the “tow-yo.” A tow-yo is attached to a research vessel and a collection of sophisticated instruments (called a conductivity-temperature-depth package). The tow-yo raises and lowers the instruments—just like a yo-yo—within a few hundred meters of the water column. This allows oceanographers to determine the shape of the plume and help pinpoint the vent field from which it came.
 
Once a vent field is located, oceanographers use both ROVs and manned vehicles to study ocean vents up-close and personal. In fact Alvin, the sub originally used by Ballard and his team in the 1970s, is still one of the most effective ways scientists investigate the geological, chemical, and biological characteristics of ocean vents. Most vents are far too deep—under far too much pressure, with far too many toxic fluids penetrating the water—to allow study by divers. 
 
These manned and unmanned vehicles collect samples—of the seafloor itself, chimneys, bacteria, and even fish. 
 
Benefits of Ocean Vents
 
Ocean vents are one of the primary determinants of ocean chemistry. (Other major contributors include runoff from rivers and atmospheric changes in the air.)
 
The ocean’s salinity, for example, was not fully understood until ocean vents were discovered in the 1970s. Prior to the discovery, most oceanographers suspected the ocean was salty due to sediments deposited by rivers and streams. Today, we know the ocean is salty because ocean vents eject chemicals directly in the water column.
 
While ocean vents help explain how chemicals such as salt are added to seawater, they can also help explain how chemicals are taken out. For decades, for example, oceanographers could not explain how the concentration of magnesium in the ocean remained constant. Magnesium was being added to seawater from terrestrial sources, but the chemistry of the ocean remained the same. The discovery of ocean vents solved the mystery: Volcanic rocks in the recharge and reaction zones extract magnesium from seawater. The water coming out of the vents has virtually no magnesium in it. 
 
While ocean vents contribute to the ocean’s chemistry, their profound heat only slightly influences ocean temperatures. The reason is that while vent fluids are super-hot, they are super-cooled by the tons of cold water surrounding them. In fact, beyond a meter (3 feet) of a vent, the water is back to a near-freezing 1.7° Celsius (35° Fahrenheit).
 
Industrial Applications
The unusual properties of ocean vents may influence concepts developed by chemical and industrial engineers in a process called biomimicry. Biomimicry is the process of using the natural world as a guide to develop new technologies. 
 
Chemosynthetic bacteria, for instance, may influence the way pharmaceutical companies develop antibiotics and enzymes that combat diseases or injuries.
 
Chemosynthetic bacteria, which convert toxic chemicals to harmless substances, may also provide resources to help clean up hazardous waste or toxic spills in the ocean.
 
Finally, biomimicry may guide engineers to develop ways for machinery to better withstand heat, toxicity, or intense pressure.
 
Mining
Ocean vents are surrounded by seafloor massive sulfide (SMS) deposits. SMS deposits are minerals that harden as vent fluid interacts with seawater.
 
SMS deposits can be material left over from collapsed chimneys or even chimneys themselves. They contain metals such as copper, iron, zinc, lead, silver, and gold. These metals are valuable for human industry and can be sold for high prices.
 
Mining companies have studied ways to extract SMS deposits from the deep ocean. Seafloor mining is a complicated and expensive procedure. The environmental impact is enormous. Microbes and animals are destroyed or displaced as the seafloor is disrupted. 
 
The waters surrounding Papua New Guinea in the South Pacific are rich in SMS deposits. The world’s first major SMS mining operation is expected to begin extraction in this area by 2017.
Ocean Vent
Ocean vents bubble with carbon dioxide, the same gas that carbonates soda—in addition to some nastier stuff, such as hydrogen sulfide.
Anhydrite
Anhydrite, the mineral that makes up the chimneys of black smokers, is actually not black—it’s white before it interacts with other particles in vent fluid and precipitates in a ring around the vent.
Chemosynthetic Communities
Chemosynthetic communities are not limited to ocean vents, or even the ocean. These communities, which can function without sunlight, have been documented at cold seeps, in whale carcasses, and in shipwrecks. On land, chemosynthetic communities thrive in the hot, toxic hydrothermal vents that create hot springs and fumaroles.
Mechanic’s Garage
Most research vessels have enough spare parts to rebuild an entire submersible! When you’re out to sea investigating ocean vents and other seafloor features, you can’t just go to your local hardware store to pick up a new gadget.
Rotten Rocks
How did one scientist describe the snow-white shrimp covering a black smoker? “They look like maggots on a piece of rotting meat!”
Why is the Ocean Salty?
Oceanographers deflected the question until the 1970s. Find out why in this delightful “campfire story” with Robert Ballard.
Homer Simpson is Hot
Just like mountains, vents have individual names. Some vents are named by the scientists who discover them, some are named for geographic features (such as the onion domes of the Kremlin vent field), and some are just fun.
• Godzilla, Sasquatch, Salty Dawg (North Pacific Ocean)
• Champagne (Caribbean Sea)
• Homer Simpson, Scooby, Tweety (South Pacific Ocean)
• Snake Pit, Lucky Strike, the Kremlin (Atlantic Ocean)
• Kairei, Edmond (Indian Ocean)

ET?
The planet Jupiter's moon Europa is probably covered by a huge, ice-capped ocean. Scientists have guessed that Europa's ocean may hide hydrothermal vents . . . and those vents may be the most likely spot for extraterrestrial life in our solar system.

abundant
Adjective

in large amounts.
abyssal plain
Noun

extensive, featureless region of the deep ocean floor.
acid
Noun

chemical compound that reacts with a base to form a salt. Acids can corrode some natural materials. Acids have pH levels lower than 7.
adapt
Verb

to adjust to new surroundings or a new situation.
adiabatic
Adjective

having to do with a process or chemical reaction that occurs without the gain or loss of heat.
air
Noun

layer of gases surrounding Earth.
Alvin
Noun

(1964-present) deep-sea research submersible owned by the U.S. Navy and operated by the Woods Hole Oceanographic Institution.
ambient
Adjective

having to do with the surrounding area or environment.
anhydrite
Noun

(CaSO4) grey-white mineral found in sedimentary rocks. Also known as anhydrous calcium sulfate.
anomaly
Noun

unusual occurrence or abnormality.
anoxic
Adjective

no oxygen in the environment.
antibiotic
Noun

substance that can stop or slow the growth of certain microbes, such as bacteria. Antibiotics do not stop viruses.
archaea
Plural Noun

(singular: archaeon) a group of tiny organisms often living in extreme environments, such as ocean vents and salt lakes.
array
Noun

large group.
asthenosphere
Noun

layer in Earth's mantle between the lithosphere (above) and the upper mantle (below).
atmosphere
Noun

layers of gases surrounding a planet or other celestial body.
back-arc basin
Noun

depression on the ocean floor formed as an ocean trench created by subduction migrates “backward” toward the overriding plate.
bacteria
Plural Noun

(singular: bacterium) single-celled organisms found in every ecosystem on Earth.
bacterial mat
Noun
collection of microorganisms in which cells adhere to each other or to a surface. Also called a microbial mat, biofilm, or slime (although distinct from actual slime molds).
bathymetric map
Noun

representation of spatial information displaying depth underwater.
biological
Adjective

having to do with the study of life and living organisms.
biomass
Noun

living organisms, and the energy contained within them.
biomimicry
Noun

process of using models, systems, and elements of nature as a guide for developing new technology.
black smoker
Noun

type of ocean vent that ejects black mineral fluid (not smoke) into the surrounding water.
boil
Verb

to change from a liquid to a gaseous state.
brine
Noun

water saturated with salt. Brine also refers to oceans and seas, and their water.
brine condensation
Noun

chemical reaction between seawater and vent fluid that forms a high-solidity brine.
buoyant
Adjective

capable of floating.
characteristic
Noun

physical, cultural, or psychological feature of an organism, place, or object.
chemical reaction
Noun

process that involves a change in atoms, ions, or molecules of the substances (reagents) involved.
chemosynthesis
Noun

process by which some microbes turn carbon dioxide and water into carbohydrates using energy obtained from inorganic chemical reactions.
chimney
Noun

tall structure composed of minerals ejected from vents along the ocean floor.
cluster
Verb

to gather together in small groups based on certain characteristics.
collapse
Verb

to fall apart completely.
complicate
Verb

to make more complex, difficult, or detailed.
concentration
Noun

measure of the amount of a substance or grouping in a specific place.
concept
Noun

idea.
conductive
Adjective

able to transmit something, such as electricity or heat.
convergent plate boundary
Noun

area where two or more tectonic plates bump into each other. Also called a collision zone.
convert
Verb

to change or to be changed.
convert
Verb

to change or to be changed.
core
Noun

the extremely hot center of Earth, another planet, or a star.
crew
Noun

workers or employees on a boat or ship.
crucial
Adjective

very important.
data
Plural Noun

(singular: datum) information collected during a scientific study.
dazzling
Adjective

amazing or extremely impressive.
decompression
Noun

gradual reduction in atmospheric pressure.
dense
Adjective

having parts or molecules that are packed closely together.
destroy
Verb

to ruin or make useless.
determinant
Noun

influencing agent or factor.
determine
Verb

to decide.
diffuse flow
Noun

an area of the sea floor that forms due to a low-temperature, slow-moving ocean vent.
dilute
Verb

to weaken or reduce.
discourage
Verb

to disapprove or encourage someone not to do something.
disperse
Verb

to scatter or spread out widely.
displace
Verb

to remove or force to evacuate.
disrupt
Verb

to interrupt.
dissipate
Verb

to scatter and disappear.
divergent boundary
Noun

area where two or more tectonic plates are moving away from each other. Also called an extensional boundary.
diverse
Adjective

varied or having many different types.
dominate
Verb

to overpower or control.
drastic
Adjective

severe or extreme.
earthquake
Noun

the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.
ecosystem
Noun

community and interactions of living and nonliving things in an area.
effective
Adjective

useful or able to perform a task.
eject
Verb

to get rid of or throw out.
ejecta
Noun

material ejected from a crater, usually by an erupting volcano or meteorite impact.
engineer
Noun

person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).
enormous
Adjective

very large.
environment
Noun

conditions that surround and influence an organism or community.
environmental impact
Noun

incident or activity's total effect on the surrounding environment.
enzyme
Noun

proteins that accelerate the vital processes in an organism.
estimate
Verb

to guess based on knowledge of the situation or object.
expensive
Adjective

very costly.
Explorer-in-Residence
Noun

pre-eminent explorers and scientists collaborating with the National Geographic Society to make groundbreaking discoveries that generate critical scientific information, conservation-related initiatives and compelling stories.
extract
Verb

to pull out.
extremophile
Noun

microbe that is adapted to survive in very harsh environments, such as freezing or boiling water.
fascinate
Verb

to cause an interest in.
fissure
Noun

narrow opening or crack.
flocculent
Adjective

having fluffy, cloud-like, soft particles.
fluid
Noun

material that is able to flow and change shape.
food web
Noun

all related food chains in an ecosystem. Also called a food cycle.
fragile
Noun

delicate or easily broken.
frequency
Noun

rate of occurrence, or the number of things happening in a specific area over specific time period.
fumarole
Noun

vent from which steam is emitted.
function
Verb

to work or work correctly.
gas
Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.
gelatinous
Adjective

resembling or behaving like a jelly, gel, or gelatin.
geology
Noun

study of the physical history of the Earth, its composition, its structure, and the processes that form and change it.
geyser
Noun

natural hot spring that sometimes erupts with water or steam.
gush
Verb

to flow suddenly and forcefully.
habitat
Noun

environment where an organism lives throughout the year or for shorter periods of time.
hardy
Adjective

strong or able to withstand severe weather.
hazardous waste
Noun

manufacturing byproduct that is toxic or harmful to people and the environment.
hostile
Adjective

confrontational or unfriendly.
hot spring
Noun

small flow of water flowing naturally from an underground water source heated by hot or molten rock.
hydrothermal plume
Noun

vent fluid ejected into the ocean.
hydrothermal vent
Noun

opening on the seafloor that emits hot, mineral-rich solutions.
identify
Verb

to recognize or establish the identity of something.
impact
Noun

meaning or effect.
indicate
Verb

to display or show.
industry
Noun

activity that produces goods and services.
influence
Noun

force that effects the actions, behavior, or policies of others.
inject
Verb

to force something (usually a liquid) into a cavity or tissue.
innovate
Verb

to invent or introduce something new.
innovative
Adjective

new, advanced, or original.
instrument
Noun

tool.
investigate
Verb

to study or examine in order to learn a series of facts.
ion
Noun

electrically charged atom or group of atoms, formed by the atom having gained or lost an electron.
lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.
leech
Noun

carnivorous or bloodsucking worm.
lithosphere
Noun

outer, solid portion of the Earth. Also called the geosphere.
machinery
Noun

mechanical appliances or tools used in manufacturing.
magma
Noun

molten, or partially melted, rock beneath the Earth's surface.
magnesium
Noun

chemical element with the symbol Mg.
manned
Adjective

carrying one or more people.
mantle
Noun

middle layer of the Earth, made of mostly solid rock.
metal
Noun

category of elements that are usually solid and shiny at room temperature.
microbe
Noun

tiny organism, usually a bacterium.
mid-ocean ridge
Noun

underwater mountain range.
migrate
Verb

to move from one place or activity to another.
mineral
Noun

nutrient needed to help cells, organs, and tissues to function.
mining
Noun

process of extracting ore from the Earth.
molecule
Noun

smallest physical unit of a substance, consisting of two or more atoms linked together.
molten
Adjective

solid material turned to liquid by heat.
neutral buoyancy
Noun

condition in which an object's density is equal to that of the fluid in which it is emerged.
nutrient
Noun

substance an organism needs for energy, growth, and life.
oasis
Noun

area made fertile by a source of fresh water in an otherwise arid region.
ocean basin
Noun

depression in the Earth's surface located entirely beneath the ocean.
ocean current
Noun

continuous, predictable, directional movement of seawater.
oceanic crust
Noun

thin layer of the Earth that sits beneath ocean basins.
oceanographer
Noun

person who studies the ocean.
ocean trench
Noun

a long, deep depression in the ocean floor.
ocean vent
Noun

underwater fissure from which geothermally heated fluid is ejected.
ocean vent
Noun

underwater fissure from which geothermally heated fluid is ejected.
organic
Adjective

composed of living or once-living material.
organism
Noun

living or once-living thing.
particle
Noun

small piece of material.
permeability
Noun

measure of a substance's ability to have a another substance penetrate or diffuse it.
pH
Noun

measure of a substance's acid or basic composition. Distilled water is neutral, a 7 on the pH scale. Acids are below 7, and bases are above.
pharmaceutical
Noun

drug or having to do with drugs and medications.
phase separation
Noun

separation of a single solution into two distinct liquids.
photosynthesis
Noun

process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.
phytoplankton
Noun

microscopic organism that lives in the ocean and can convert light energy to chemical energy through photosynthesis.
precipitate
Verb

to separate a solid from a solution.
predator
Noun

animal that hunts other animals for food.
pressure
Noun

force pressed on an object by another object or condition, such as gravity.
prey
Verb

to target, victimize, or devour.
prior
Adjective

before or ahead of.
producer
Noun

organism on the food chain that can produce its own energy and nutrients. Also called an autotroph.
proximity
Noun

nearness.
quartz
Noun

common type of mineral.
ratio
Noun

relationship between numbers or numerical values.
Reaction Zone
Noun

phase in the ocean vent process where the vent fluid is closest to its source of heat.
Recharge Zone
Noun

phase in the ocean vent process in which seawater seeps into fissures in the ocean floor.
research vessel
Noun

ship or boat equipped to carry out scientific experiments or collect data.
residence time
Noun

amount of time a water molecule spends in one place in the water cycle.
Ring of Fire
Noun

horseshoe-shaped string of volcanoes and earthquake sites around edges of the Pacific Ocean.
river
Noun

large stream of flowing fresh water.
ROV
Noun

remotely operated vehicle.
runoff
Noun

overflow of fluid from a farm or industrial factory.
salinity
Noun

saltiness.
salt
Noun

(sodium chloride, NaCl) crystalline mineral often used as a seasoning or preservative for food.
seafloor massive sulfide (SMS) deposit
Noun

minerals that form from underwater hydrothermal vents.
sea level
Noun

base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.
seamount
Noun

underwater mountain.
sediment
Noun

solid material transported and deposited by water, ice, and wind.
seep
Verb

to slowly flow through a border.
snowblower
Noun

low-temperature ocean vent in which flocculent microbes are ejected.
snowblower
Noun

low-temperature ocean vent in which flocculent microbes are ejected.
sophisticated
Adjective

knowledgeable or complex.
specialize
Verb

to study, work, or take an interest in one area of a larger field of ideas.
spew
Verb

to eject or discharge violently.
spike
Verb

to increase quickly.
subduction
Noun

process of one tectonic plate melting, sliding, or falling beneath another.
submersible
Noun

small submarine used for research and exploration.
sulfate
Noun

(SO42-) negatively charged ion (salt) of a sulfur-oxygen molecule.
sulfide
Noun

(S2-) negatively charged ion of sulfur, or a chemical compound containing such an ion.
sulfur
Noun

chemical element with the symbol S.
suspect
Verb

to assume or believe something.
tectonic activity
Noun

movement of tectonic plates resulting in geologic activity such as volcanic eruptions and earthquakes.
tectonic plate
Noun

massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Also called lithospheric plate.
temperature
Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.
terrestrial
Adjective

having to do with the Earth or dry land.
thrive
Verb

to develop and be successful.
tow-yo
Noun

machinery that tows a complex set of instruments (the Conductivity-Temperature-Depth package) behind a research vessel, constantly raising and lowering the CTD to allow oceanographers to determine the shape of a hydrothermal plume.
toxic
Adjective

poisonous.
trench rollback
Noun

subduction process in which the leading edge of a subducting plate is "rolled back" toward the subducting plate. Also called hinge migration, hinge retreat, or hinge rollback.
unique
Adjective

one of a kind.
Upflow Zone
Noun

phase in the ocean vent process in which super-heated vent fluid gushes upward toward the seafloor.
valuable
Adjective

worth a considerable amount of money or esteem.
velocity
Noun

measurement of the rate and direction of change in the position of an object.
vent field
Noun

collection of related hydrothermal vents.
vent fluid
Noun

chemicals ejected by hydrothermal vents.
volcanic arc
Noun

chain of volcanoes formed at a subduction zone.
volcano
Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.
water column
Noun

area reaching from the sediment of a body of water to its surface.
well up
Verb

to swell or build up.
white smoker
Noun

type of ocean vent that ejects white mineral fluid into the surrounding water.

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    Editor

    Jeannie Evers, Emdash Editing

    Producer

    Caryl-Sue, National Geographic Society

    Last Updated

    July 23, 2015

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