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78-684: The Lau–Colville Ridge is an extinct oceanic ridge located on the oceanic Australian Plate in the south-west Pacific Ocean extending about 2,700 km (1,700 mi) from the south east of Fiji to the continental shelf margin of the North Island of New Zealand . It was an historic subduction boundary between the Australian Plate and the Pacific Plate and has important tectonic relationships to its east where very active spreading and subduction processes exist today. It

156-468: A common feature at oceanic spreading centers. A feature of the elevated ridges is their relatively high heat flow values, of about 1–10 μcal/cm s, or roughly 0.04–0.4 W/m . Most crust in the ocean basins is less than 200 million years old, which is much younger than the 4.54 billion year age of Earth . This fact reflects the process of lithosphere recycling into the Earth's mantle during subduction . As

234-424: A crustal thickness of 7 km (4.3 mi), this amounts to about 19 km (4.6 cu mi) of new ocean crust formed every year. Seafloor The seabed (also known as the seafloor , sea floor , ocean floor , and ocean bottom ) is the bottom of the ocean . All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics . Most of

312-439: A globe-spanning mid-ocean ridge system, as well as undersea volcanoes , oceanic trenches , submarine canyons , oceanic plateaus and abyssal plains . The mass of the oceans is approximately 1.35 × 10   metric tons , or about 1/4400 of the total mass of the Earth. The oceans cover an area of 3.618 × 10  km with a mean depth of 3,682 m, resulting in an estimated volume of 1.332 × 10  km . Each region of

390-501: A rate anywhere from 1 mm to 1 cm every 1000 years. Hydrogenous sediments are uncommon. They only occur with changes in oceanic conditions such as temperature and pressure. Rarer still are cosmogenous sediments. Hydrogenous sediments are formed from dissolved chemicals that precipitate from the ocean water, or along the mid-ocean ridges, they can form by metallic elements binding onto rocks that have water of more than 300 °C circulating around them. When these elements mix with

468-553: A ship of the Lamont–Doherty Earth Observatory of Columbia University , traversed the Atlantic Ocean, recording echo sounder data on the depth of the ocean floor. A team led by Marie Tharp and Bruce Heezen concluded that there was an enormous mountain chain with a rift valley at its crest, running up the middle of the Atlantic Ocean. Scientists named it the 'Mid-Atlantic Ridge'. Other research showed that

546-408: A subduction zone drags the rest of the plate along behind it. The slab pull mechanism is considered to be contributing more than the ridge push. A process previously proposed to contribute to plate motion and the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor" due to deep convection (see image). However, some studies have shown that the upper mantle ( asthenosphere )

624-402: Is absorbed before it can reach deep ocean water, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains the benthic food chain ; most organisms in the benthic zone are scavengers or detritivores . Seabed topography ( ocean topography or marine topography ) refers to

702-434: Is a vertical coordinate used in geology, paleontology , oceanography , and petrology (see ocean drilling ). The acronym "mbsf" (meaning "meters below the seafloor") is a common convention used for depths below the seafloor. Sediments in the seabed vary in origin, from eroded land materials carried into the ocean by rivers or wind flow, waste and decompositions of sea creatures, and precipitation of chemicals within

780-420: Is a global scale ion-exchange system. Hydrothermal vents at spreading centers introduce various amounts of iron , sulfur , manganese , silicon , and other elements into the ocean, some of which are recycled into the ocean crust. Helium-3 , an isotope that accompanies volcanism from the mantle, is emitted by hydrothermal vents and can be detected in plumes within the ocean. Fast spreading rates will expand

858-477: Is abundant in the deep sea around hydrothermal vents . Large deep sea communities of marine life have been discovered around black and white smokers – vents emitting chemicals toxic to humans and most vertebrates . This marine life receives its energy both from the extreme temperature difference (typically a drop of 150 degrees) and from chemosynthesis by bacteria . Brine pools are another seabed feature, usually connected to cold seeps . In shallow areas,

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936-590: Is controversial. Environmental advocacy groups such as Greenpeace and the Deep Sea Mining Campaign claimed that seabed mining has the potential to damage deep sea ecosystems and spread pollution from heavy metal-laden plumes. Critics have called for moratoria or permanent bans. Opposition campaigns enlisted the support of some industry figures, including firms reliant on the target metals. Individual countries with significant deposits within their exclusive economic zones (EEZ's) are exploring

1014-447: Is divided into layers or zones, each with typical features of salinity, pressure, temperature and marine life , according to their depth. Lying along the top of the abyssal plain is the abyssal zone , whose lower boundary lies at about 6,000 m (20,000 ft). The hadal zone – which includes the oceanic trenches, lies between 6,000 and 11,000 metres (20,000–36,000 ft) and is the deepest oceanic zone. Depth below seafloor

1092-461: Is estimated that the global ocean floor holds more than 120 million tons of cobalt, five times the amount found in terrestrial reserves. As of July 2024 , only exploratory licenses have been issued, with no commercial-scale deep sea mining operations yet. The International Seabed Authority (ISA) regulates all mineral-related activities in international waters and has granted 31 exploration licenses so far: 19 for polymetallic nodules, mostly in

1170-474: Is from mafic picro- basalt to dacite with arc-type element patterns intermediate between Pacific mid ocean ridge basalt and subducted lithosphere. The South Fiji Basin to the west of the Lau–Colville Ridge contains back‐arc basin basalts up to 33 million years old that were erupted during spreading and some ocean island like basalts erupted several million years after spreading ceased in the basin which

1248-443: Is in a constant state of 'renewal' at the mid-ocean ridges by the processes of seafloor spreading and plate tectonics. New magma steadily emerges onto the ocean floor and intrudes into the existing ocean crust at and near rifts along the ridge axes. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis. New magma of basalt composition emerges at and near

1326-414: Is not moving so quickly. This means that larger grains of sediment may come together in higher energy conditions and smaller grains in lower energy conditions. Benthos (from Ancient Greek βένθος ( bénthos )  'the depths [of the sea]'), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river , lake , or stream , also known as

1404-498: Is now the inactive part of an eastward-migrating, 100 million year old Lau-Tonga-Havre-Kermadec arc/back-arc system or complex and is important in understanding submarine arc volcanism because of these relationships. To its west is the South Fiji Basin whose northern bedrock is Oligocene in origin. It is divided into two segments as the ridge is flanked on its eastern side by two southward propagating back-arc basins ,

1482-480: Is the next most abundant material on the seafloor. Biogenous sediments are biologically produced by living creatures. Sediments made up of at least 30% biogenous material are called "oozes." There are two types of oozes: Calcareous oozes and Siliceous oozes. Plankton grow in ocean waters and create the materials that become oozes on the seabed. Calcareous oozes are predominantly composed of calcium shells found in phytoplankton such as coccolithophores and zooplankton like

1560-478: Is the result of changes in the volume of the ocean basins which are, in turn, affected by rates of seafloor spreading along the mid-ocean ridges. The 100 to 170 meters higher sea level of the Cretaceous Period (144–65 Ma) is partly attributed to plate tectonics because thermal expansion and the absence of ice sheets only account for some of the extra sea level. Seafloor spreading on mid-ocean ridges

1638-561: Is through their descriptive classification. These sediments vary in size, anywhere from 1/4096 of a mm to greater than 256 mm. The different types are: boulder, cobble, pebble, granule, sand, silt, and clay, each type becoming finer in grain. The grain size indicates the type of sediment and the environment in which it was created. Larger grains sink faster and can only be pushed by rapid flowing water (high energy environment) whereas small grains sink very slowly and can be suspended by slight water movement, accumulating in conditions where water

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1716-440: Is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and observations of the seismic discontinuity in the upper mantle at about 400 km (250 mi). On the other hand, some of the world's largest tectonic plates such as

1794-451: Is underlain by denser material and is deeper. Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. Rates can be computed by mapping marine magnetic anomalies that span mid-ocean ridges. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of

1872-585: The North American plate and South American plate are in motion, yet only are being subducted in restricted locations such as the Lesser Antilles Arc and Scotia Arc , pointing to action by the ridge push body force on these plates. Computer modeling of the plates and mantle motions suggest that plate motion and mantle convection are not connected, and the main plate driving force is slab pull. Increased rates of seafloor spreading (i.e.

1950-473: The Southwest Indian Ridge ). The spreading center or axis commonly connects to a transform fault oriented at right angles to the axis. The flanks of mid-ocean ridges are in many places marked by the inactive scars of transform faults called fracture zones . At faster spreading rates the axes often display overlapping spreading centers that lack connecting transform faults. The depth of

2028-437: The abyssal plain regions of the ocean are relatively flat and covered in many layers of sediments. Sediments in these flat areas come from various sources, including but not limited to: land erosion sediments from rivers, chemically precipitated sediments from hydrothermal vents, Microorganism activity, sea currents eroding the seabed and transporting sediments to the deeper ocean, and phytoplankton shell materials. Where

2106-453: The benthic zone . This community lives in or near marine or freshwater sedimentary environments , from tidal pools along the foreshore , out to the continental shelf , and then down to the abyssal depths . Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column . The pressure difference can be very significant (approximately one atmosphere for every 10 metres of water depth). Because light

2184-465: The longest mountain range in the world. The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes , the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long. At the spreading center on a mid-ocean ridge, the depth of the seafloor is approximately 2,600 meters (8,500 ft). On

2262-809: The CCZ; 7 for polymetallic sulphides in mid-ocean ridges ; and 5 for cobalt-rich crusts in the Western Pacific Ocean . There is a push for deep sea mining to commence by 2025, when regulations by the ISA are expected to be completed. Deep sea mining is also possible in the exclusive economic zone (EEZ) of countries, such as Norway , where it has been approved. In 2022, the Cook Islands Seabed Minerals Authority (SBMA) granted three exploration licenses for cobalt-rich polymetallic nodules within their EEZ. Papua New Guinea

2340-769: The East Pacific Rise lack rift valleys. The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–145 mm/yr. The highest known rate is over 200 mm/yr in the Miocene on the East Pacific Rise. Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges (e.g., the Gakkel Ridge in the Arctic Ocean and

2418-680: The Mid-Atlantic Ridge have spread much less far (showing a steeper profile) than faster ridges such as the East Pacific Rise (gentle profile) for the same amount of time and cooling and consequent bathymetric deepening. Slow-spreading ridges (less than 40 mm/yr) generally have large rift valleys , sometimes as wide as 10–20 km (6.2–12.4 mi), and very rugged terrain at the ridge crest that can have relief of up to 1,000 m (3,300 ft). By contrast, fast-spreading ridges (greater than 90 mm/yr) such as

Lau–Colville Ridge - Misplaced Pages Continue

2496-536: The amount of plastic thought – per Jambeck et al., 2015 – to currently enter the oceans annually. Deep sea mining is the extraction of minerals from the seabed of the deep sea . The main ores of commercial interest are polymetallic nodules , which are found at depths of 4–6 km (2.5–3.7 mi) primarily on the abyssal plain . The Clarion–Clipperton zone (CCZ) alone contains over 21 billion metric tons of these nodules, with minerals such as copper , nickel , and cobalt making up 2.5% of their weight. It

2574-427: The asthenosphere at ocean trenches . Two processes, ridge-push and slab pull , are thought to be responsible for spreading at mid-ocean ridges. Ridge push refers to the gravitational sliding of the ocean plate that is raised above the hotter asthenosphere, thus creating a body force causing sliding of the plate downslope. In slab pull the weight of a tectonic plate being subducted (pulled) below an overlying plate at

2652-478: The axis because of decompression melting in the underlying Earth's mantle . The isentropic upwelling solid mantle material exceeds the solidus temperature and melts. The crystallized magma forms a new crust of basalt known as MORB for mid-ocean ridge basalt, and gabbro below it in the lower oceanic crust . Mid-ocean ridge basalt is a tholeiitic basalt and is low in incompatible elements . Hydrothermal vents fueled by magmatic and volcanic heat are

2730-490: The axis changes in a systematic way with shallower depths between offsets such as transform faults and overlapping spreading centers dividing the axis into segments. One hypothesis for different along-axis depths is variations in magma supply to the spreading center. Ultra-slow spreading ridges form both magmatic and amagmatic (currently lack volcanic activity) ridge segments without transform faults. Mid-ocean ridges exhibit active volcanism and seismicity . The oceanic crust

2808-485: The balance between sedimentary processes and hydrodynamics however, anthropogenic influences can impact the natural system more than any physical driver. Marine topographies include coastal and oceanic landforms ranging from coastal estuaries and shorelines to continental shelves and coral reefs . Further out in the open ocean, they include underwater and deep sea features such as ocean rises and seamounts . The submerged surface has mountainous features, including

2886-450: The cold sea water they precipitate from the cooling water. Known as manganese nodules , they are composed of layers of different metals like manganese, iron, nickel, cobalt, and copper, and they are always found on the surface of the ocean floor. Cosmogenous sediments are the remains of space debris such as comets and asteroids, made up of silicates and various metals that have impacted the Earth. Another way that sediments are described

2964-465: The continental slope and the abyssal plain usually has a more gradual descent, and is called the continental rise , which is caused by sediment cascading down the continental slope. The mid-ocean ridge , as its name implies, is a mountainous rise through the middle of all the oceans, between the continents. Typically a rift runs along the edge of this ridge. Along tectonic plate edges there are typically oceanic trenches – deep valleys, created by

3042-407: The discovery of the worldwide extent of the mid-ocean ridge in the 1950s, geologists faced a new task: explaining how such an enormous geological structure could have formed. In the 1960s, geologists discovered and began to propose mechanisms for seafloor spreading . The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegener's theory to be expanded so that it included

3120-534: The field preserved in the oceanic crust comprise a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at known intervals throughout its history, the pattern of geomagnetic reversals in the ocean crust can be used as an indicator of age; given the crustal age and distance from the ridge axis, spreading rates can be calculated. Spreading rates range from approximately 10–200 mm/yr. Slow-spreading ridges such as

3198-474: The floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot sima [rising] from depth". However, Wegener did not pursue this observation in his later works and his theory was dismissed by geologists because there was no mechanism to explain how continents could plow through ocean crust , and the theory became largely forgotten. Following

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3276-416: The foraminiferans. These calcareous oozes are never found deeper than about 4,000 to 5,000 meters because at further depths the calcium dissolves. Similarly, Siliceous oozes are dominated by the siliceous shells of phytoplankton like diatoms and zooplankton such as radiolarians. Depending on the productivity of these planktonic organisms, the shell material that collects when these organisms die may build up at

3354-484: The globe are linked by plate tectonic boundaries and the trace of the ridges across the ocean floor appears similar to the seam of a baseball . The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi). The mid-ocean ridges of the world are connected and form the Ocean Ridge, a single global mid-oceanic ridge system that is part of every ocean , making it

3432-444: The mantle circulation movement from the mid-ocean mountain ridge to the oceanic trench. Hotspot volcanic island ridges are created by volcanic activity, erupting periodically, as the tectonic plates pass over a hotspot. In areas with volcanic activity and in the oceanic trenches there are hydrothermal vents – releasing high pressure and extremely hot water and chemicals into the typically freezing water around it. Deep ocean water

3510-532: The mid-ocean ridge causing basalt reactions with seawater to happen more rapidly. The magnesium/calcium ratio will be lower because more magnesium ions are being removed from seawater and consumed by the rock, and more calcium ions are being removed from the rock and released into seawater. Hydrothermal activity at the ridge crest is efficient in removing magnesium. A lower Mg/Ca ratio favors the precipitation of low-Mg calcite polymorphs of calcium carbonate ( calcite seas ). Slow spreading at mid-ocean ridges has

3588-548: The mid-ocean ridge from the South Atlantic into the Indian Ocean early in the twentieth century. Although the first-discovered section of the ridge system runs down the middle of the Atlantic Ocean, it was found that most mid-ocean ridges are located away from the center of other ocean basins. Alfred Wegener proposed the theory of continental drift in 1912. He stated: "the Mid-Atlantic Ridge ... zone in which

3666-402: The movement of oceanic crust as well as the continents. Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a major paradigm shift in geological thinking. It is estimated that along Earth's mid-ocean ridges every year 2.7 km (1.0 sq mi) of new seafloor is formed by this process. With

3744-749: The northern Lau Ridge (called historically the South Fiji Ridge and also known as the Fiji Ridge , Neckes Ridge and Southern Fiji Ridge ) that forms the western boundary of the Lau Basin and has contributed to many islands south east of Fiji. The Lau Basin to its east currently contains 6 million year old active spreading centers between the Australian and Niuafo'ou or Tonga microplates. The southern Colville Ridge (also known as Khrebet Kolvil-Lau from Russian Хребет Колвил-Лау )forms

3822-665: The northern Lau Ridge. Currently back-arc spreading to the east of the Lau Ridge in the adjacent Lau Basin occurs along a number of spreading centers and the Valu Fa Ridge (VFR). As we come south down the Lau Basin spreading rates decrease being for the Central Lau Spreading Centre (CLSC) 120 mm (4.7 in)/year, just above Eastern Lau Spreading Center (ELSC) 102 mm (4.0 in)/year, at

3900-415: The ocean is very deep, where the seabed is known as the abyssal plain . Seafloor spreading creates mid-ocean ridges along the center line of major ocean basins, where the seabed is slightly shallower than the surrounding abyssal plain. From the abyssal plain, the seabed slopes upward toward the continents and becomes, in order from deep to shallow, the continental rise , slope , and shelf . The depth within

3978-403: The oceanic crust and lithosphere moves away from the ridge axis, the peridotite in the underlying mantle lithosphere cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere , which sits above the less rigid and viscous asthenosphere . The oceanic lithosphere is formed at an oceanic ridge, while the lithosphere is subducted back into

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4056-448: The oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources. The structure of the oceans, starting with the continents, begins usually with a continental shelf , continues to the continental slope – which is a steep descent into the ocean, until reaching the abyssal plain – a topographic plain , the beginning of the seabed, and its main area. The border between

4134-455: The opposite effect and will result in a higher Mg/Ca ratio favoring the precipitation of aragonite and high-Mg calcite polymorphs of calcium carbonate ( aragonite seas ). Experiments show that most modern high-Mg calcite organisms would have been low-Mg calcite in past calcite seas, meaning that the Mg/Ca ratio in an organism's skeleton varies with the Mg/Ca ratio of the seawater in which it

4212-574: The rate of expansion of the mid-ocean ridge) have caused the global ( eustatic ) sea level to rise over very long timescales (millions of years). Increased seafloor spreading means that the mid-ocean ridge will then expand and form a broader ridge with decreased average depth, taking up more space in the ocean basin. This displaces the overlying ocean and causes sea levels to rise. Sealevel change can be attributed to other factors ( thermal expansion , ice melting, and mantle convection creating dynamic topography ). Over very long timescales, however, it

4290-440: The ridge crest was seismically active and fresh lavas were found in the rift valley. Also, crustal heat flow was higher here than elsewhere in the Atlantic Ocean basin. At first, the ridge was thought to be a feature specific to the Atlantic Ocean. However, as surveys of the ocean floor continued around the world, it was discovered that every ocean contains parts of the mid-ocean ridge system. The German Meteor expedition traced

4368-416: The ridge flanks, the depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is correlated with its age (age of the lithosphere where depth is measured). The depth-age relation can be modeled by the cooling of a lithosphere plate or mantle half-space. A good approximation is that the depth of the seafloor at a location on a spreading mid-ocean ridge is proportional to

4446-537: The sea water itself, including some from outer space. There are four basic types of sediment of the sea floor: Terrigenous sediment is the most abundant sediment found on the seafloor. Terrigenous sediments come from the continents. These materials are eroded from continents and transported by wind and water to the ocean. Fluvial sediments are transported from land by rivers and glaciers, such as clay, silt, mud, and glacial flour. Aeolian sediments are transported by wind, such as dust and volcanic ash. Biogenous sediment

4524-429: The seabed , and these satellite-derived maps are used extensively in the study and exploration of the ocean floor. In 2020 scientists created what may be the first scientific estimate of how much microplastic currently resides in Earth's seafloor , after investigating six areas of ~3 km depth ~300 km off the Australian coast. They found the highly variable microplastic counts to be proportionate to plastic on

4602-468: The seabed are governed by the physics of sediment transport and by the biology of the creatures living in the seabed and in the ocean waters above. Physically, seabed sediments often come from the erosion of material on land and from other rarer sources, such as volcanic ash . Sea currents transport sediments, especially in shallow waters where tidal energy and wave energy cause resuspension of seabed sediments. Biologically, microorganisms living within

4680-440: The seabed can host sediments created by marine life such as corals, fish, algae, crabs, marine plants and other organisms. The seabed has been explored by submersibles such as Alvin and, to some extent, scuba divers with special equipment. Hydrothermal vents were discovered in 1977 by researchers using an underwater camera platform. In recent years satellite measurements of ocean surface topography show very clear maps of

4758-404: The seabed has typical features such as common sediment composition, typical topography, salinity of water layers above it, marine life, magnetic direction of rocks, and sedimentation . Some features of the seabed include flat abyssal plains , mid-ocean ridges , deep trenches , and hydrothermal vents . Seabed topography is flat where layers of sediments cover the tectonic features. For example,

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4836-751: The seabed itself, such as the depth down through a sediment core , is known as the "depth below seafloor". The ecological environment of the seabed and the deepest waters are collectively known, as a habitat for creatures, as the " benthos ". Most of the seabed throughout the world's oceans is covered in layers of marine sediments . Categorized by where the materials come from or composition, these sediments are classified as either: from land ( terrigenous ), from biological organisms (biogenous), from chemical reactions (hydrogenous), and from space (cosmogenous). Categorized by size, these sediments range from very small particles called clays and silts , known as mud, to larger particles from sand to boulders . Features of

4914-501: The seabed sediments change seabed chemistry. Marine organisms create sediments, both within the seabed and in the water above. For example, phytoplankton with silicate or calcium carbonate shells grow in abundance in the upper ocean, and when they die, their shells sink to the seafloor to become seabed sediments. Human impacts on the seabed are diverse. Examples of human effects on the seabed include exploration, plastic pollution, and exploitation by mining and dredging operations. To map

4992-592: The seabed, ships use acoustic technology to map water depths throughout the world. Submersible vehicles help researchers study unique seabed ecosystems such as hydrothermal vents . Plastic pollution is a global phenomenon, and because the ocean is the ultimate destination for global waterways, much of the world's plastic ends up in the ocean and some sinks to the seabed. Exploitation of the seabed involves extracting valuable minerals from sulfide deposits via deep sea mining, as well as dredging sand from shallow environments for construction and beach nourishment . Most of

5070-411: The seafloor is actively spreading and sedimentation is relatively light, such as in the northern and eastern Atlantic Ocean , the original tectonic activity can be clearly seen as straight line "cracks" or "vents" thousands of kilometers long. These underwater mountain ranges are known as mid-ocean ridges . Other seabed environments include hydrothermal vents, cold seeps, and shallow areas. Marine life

5148-431: The seafloor were analyzed by oceanographers Matthew Fontaine Maury and Charles Wyville Thomson and revealed a prominent rise in the seafloor that ran down the Atlantic basin from north to south. Sonar echo sounders confirmed this in the early twentieth century. It was not until after World War II , when the ocean floor was surveyed in more detail, that the full extent of mid-ocean ridges became known. The Vema ,

5226-584: The separating plates, and emerges as lava , creating new oceanic crust and lithosphere upon cooling. The first discovered mid-ocean ridge was the Mid-Atlantic Ridge , which is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are traditionally called mid-ocean ridges. Mid-ocean ridges around

5304-410: The shape of the land ( topography ) when it interfaces with the ocean. These shapes are obvious along coastlines, but they occur also in significant ways underwater. The effectiveness of marine habitats is partially defined by these shapes, including the way they interact with and shape ocean currents , and the way sunlight diminishes when these landforms occupy increasing depths. Tidal networks depend on

5382-439: The square root of the age of the seafloor. The overall shape of ridges results from Pratt isostasy : close to the ridge axis, there is a hot, low-density mantle supporting the oceanic crust. As the oceanic plate cools, away from the ridge axis, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens, and the density increases. Thus older seafloor

5460-472: The start of the Valu Fa Ridge (VFR) to the south 69 mm (2.7 in)/year, and at its southern end 48 mm (1.9 in)/year, consistent with the southward propagation previously mentioned. These spreading centers have now partially dismembered the Lau Ridge. To the south it is now thought seafloor spreading at the Havre Trough started about 5.5–5.0 million years ago in response to the rollback of

5538-399: The subducting Pacific Plate and terminated abruptly about 3.0–2.5 million years ago, perhaps explaining the long noted lack of a mid oceanic ridge structure but rather rift like subsidance. Oceanic ridge The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness between

5616-533: The subject. Some children's play songs include elements such as "There's a hole at the bottom of the sea", or "A sailor went to sea... but all that he could see was the bottom of the deep blue sea". On and under the seabed are archaeological sites of historic interest, such as shipwrecks and sunken towns. This underwater cultural heritage is protected by the UNESCO Convention on the Protection of

5694-412: The surface and the angle of the seafloor slope. By averaging the microplastic mass per cm , they estimated that Earth's seafloor contains ~14 million tons of microplastic – about double the amount they estimated based on data from earlier studies – despite calling both estimates "conservative" as coastal areas are known to contain much more microplastic pollution . These estimates are about one to two times

5772-403: The water column. Related technologies include robotic mining machines, as surface ships, and offshore and onshore metal refineries. Wind farms, solar energy, electric vehicles , and battery technologies use many of the deep-sea metals. Electric vehicle batteries are the main driver of the critical metals demand that incentivizes deep sea mining. The environmental impact of deep sea mining

5850-671: The western boundary of the Havre Trough . The Havre Trough has had rift extension for the last 2 million years between the Australian plate and the Kermadec microplate and this extends into Zealandia 's continental Taupō Rift and New Zealand's Taupō Volcanic Zone . The remnant andesitic volcanic arc Lau Ridge was mainly active between 14 and 6 million years ago although late volcanism persisted until 2.5 million years ago. The Colville Ridge has been found to have volcanics aged between 7.5 to 2.6 million years ago. The composition range

5928-692: Was before 22 million years ago Directly to the east of the ridge in its central portion the Lau basin contains an area of sediment that has been called the Western Sedimentary Basin. The sediments in the Havre Trough can be up to 1.5 km (0.93 mi) thick. The late Miocene rifting of about 6 million years ago initiated in what was an old forearc (called the Vitiaz Arc) and was in Cretaceous - Eocene arc crust that became part of

6006-549: Was grown. The mineralogy of reef-building and sediment-producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by the rate of sea-floor spreading. The first indications that a ridge bisects the Atlantic Ocean basin came from the results of the British Challenger expedition in the nineteenth century. Soundings from lines dropped to

6084-516: Was the first country to approve a deep sea mining permit for the Solwara 1 project, despite three independent reviews highlighting significant gaps and flaws in the environmental impact statement. The most common commercial model of deep sea mining proposed involves a caterpillar-track hydraulic collector and a riser lift system bringing the harvested ore to a production support vessel with dynamic positioning , and then depositing extra discharge down

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