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Oceanic trench
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Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches

Oceanic trenches are prominent, long, narrow topographic depressions of the ocean floor. They are typically 50 to 100 kilometers (30 to 60 mi) wide and 3 to 4 km (1.9 to 2.5 mi) below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about 50,000 km (31,000 mi) of oceanic trenches worldwide, mostly around the Pacific Ocean, but also in the eastern Indian Ocean and a few other locations. The greatest ocean depth measured is in the Challenger Deep of the Mariana Trench, at a depth of 10,994 m (36,070 ft) below sea level.

Oceanic trenches are a feature of the Earth's distinctive plate tectonics. They mark the locations of convergent plate boundaries, along which lithospheric plates move towards each other at rates that vary from a few millimeters to over ten centimeters per year. Oceanic lithosphere moves into trenches at a global rate of about 3 km2 (1.2 sq mi) per year.[1] A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab. Trenches are generally parallel to and about 200 km (120 mi) from a volcanic arc.

Much of the fluid trapped in sediments of the subducting slab returns to the surface at the oceanic trench, producing mud volcanoes and cold seeps. These support unique biomes based on chemotrophic microorganisms. There is concern that plastic debris is accumulating in trenches and threatening these communities.

Geographic distribution

[edit]
Major Pacific trenches (1–10) and fracture zones (11–20): 1. Kermadec 2. Tonga 3. Bougainville 4. Mariana 5. Izu–Ogasawara 6. Japan 7. Kuril–Kamchatka 8. Aleutian 9. Middle America 10. Peru–Chile 11. Mendocino 12. Murray 13. Molokai 14. Clarion 15. Clipperton 16. Challenger 17. Eltanin 18. Udintsev 19. East Pacific Rise (S-shaped) 20. Nazca Ridge

There are approximately 50,000 km (31,000 mi) of convergent plate margins worldwide. These are mostly located around the Pacific Ocean, but are also found in the eastern Indian Ocean, with a few shorter convergent margin segments in other parts of the Indian Ocean, in the Atlantic Ocean, and in the Mediterranean.[2] They are found on the oceanward side of island arcs and Andean-type orogens.[3] Globally, there are over 50 major ocean trenches covering an area of 1.9 million km2 or about 0.5% of the oceans.[4]

Trenches are geomorphologically distinct from troughs. Troughs are elongated depressions of the sea floor with steep sides and flat bottoms, while trenches are characterized by a V-shaped profile.[4] Trenches that are partially infilled are sometimes described as troughs, for example the Makran Trough.[5] Some trenches are completely buried and lack bathymetric expression as in the Cascadia subduction zone,[6] which is completely filled with sediments.[7] Despite their appearance, in these instances the fundamental plate-tectonic structure is still an oceanic trench. Some troughs look similar to oceanic trenches but possess other tectonic structures. One example is the Lesser Antilles Trough, which is the forearc basin of the Lesser Antilles subduction zone.[8] Also not a trench is the New Caledonia trough, which is an extensional sedimentary basin related to the Tonga-Kermadec subduction zone.[9] Additionally, the Cayman Trough, which is a pull-apart basin within a transform fault zone,[10] is not an oceanic trench.

Trenches, along with volcanic arcs and Wadati–Benioff zones (zones of earthquakes under a volcanic arc) are diagnostic of convergent plate boundaries and their deeper manifestations, subduction zones.[2][3][11] Here, two tectonic plates are drifting into each other at a rate of a few millimeters to over 10 centimeters (4 in) per year. At least one of the plates is oceanic lithosphere, which plunges under the other plate to be recycled in the Earth's mantle.

Trenches are related to, but distinct from, continental collision zones, such as the Himalayas. Unlike in trenches, in continental collision zones continental crust enters a subduction zone. When buoyant continental crust enters a trench, subduction comes to a halt and the area becomes a zone of continental collision. Features analogous to trenches are associated with collision zones. One such feature is the peripheral foreland basin, a sediment-filled foredeep. Examples of peripheral foreland basins include the floodplains of the Ganges River and the Tigris-Euphrates river system.[2]

History of the term "trench"

[edit]

Trenches were not clearly defined until the late 1940s and 1950s. The bathymetry of the ocean was poorly known prior to the Challenger expedition of 1872–1876,[12] which took 492 soundings of the deep ocean.[13] At station #225, the expedition discovered Challenger Deep,[14] now known to be the southern end of the Mariana Trench. The laying of transatlantic telegraph cables on the seafloor between the continents during the late 19th and early 20th centuries provided further motivation for improved bathymetry.[15] The term trench, in its modern sense of a prominent elongated depression of the sea bottom, was first used by Johnstone in his 1923 textbook An Introduction to Oceanography.[16][2]

During the 1920s and 1930s, Felix Andries Vening Meinesz measured gravity over trenches using a newly developed gravimeter that could measure gravity from aboard a submarine.[11] He proposed the tectogene hypothesis to explain the belts of negative gravity anomalies that were found near island arcs. According to this hypothesis, the belts were zones of downwelling of light crustal rock arising from subcrustal convection currents. The tectogene hypothesis was further developed by Griggs in 1939, using an analogue model based on a pair of rotating drums. Harry Hammond Hess substantially revised the theory based on his geological analysis.[17]

World War II in the Pacific led to great improvements of bathymetry, particularly in the western Pacific. In light of these new measurements, the linear nature of the deeps became clear. There was a rapid growth of deep sea research efforts, especially the widespread use of echosounders in the 1950s and 1960s. These efforts confirmed the morphological utility of the term "trench." Important trenches were identified, sampled, and mapped via sonar.

The early phase of trench exploration reached its peak with the 1960 descent of the Bathyscaphe Trieste to the bottom of the Challenger Deep. Following Robert S. Dietz' and Harry Hess' promulgation of the seafloor spreading hypothesis in the early 1960s and the plate tectonic revolution in the late 1960s, the oceanic trench became an important concept in plate tectonic theory.[11]

Morphology

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Cross section of an oceanic trench formed along an oceanic-oceanic convergent boundary
The Peru–Chile Trench is located just left of the sharp line between the blue deep ocean (on the left) and the light blue continental shelf, along the west coast of South America. It runs along an oceanic-continental boundary, where the oceanic Nazca plate subducts beneath the continental South American plate

Oceanic trenches are 50 to 100 kilometers (30 to 60 mi) wide and have an asymmetric V-shape, with the steeper slope (8 to 20 degrees) on the inner (overriding) side of the trench and the gentler slope (around 5 degrees) on the outer (subducting) side of the trench.[18][19] The bottom of the trench marks the boundary between the subducting and overriding plates, known as the basal plate boundary shear[20] or the subduction décollement.[2] The depth of the trench depends on the starting depth of the oceanic lithosphere as it begins its plunge into the trench, the angle at which the slab plunges, and the amount of sedimentation in the trench. Both starting depth and subduction angle are greater for older oceanic lithosphere, which is reflected in the deep trenches of the western Pacific. Here the bottoms of the Marianas and the Tonga–Kermadec trenches are up to 10–11 kilometers (6.2–6.8 mi) below sea level. In the eastern Pacific, where the subducting oceanic lithosphere is much younger, the depth of the Peru-Chile trench is around 7 to 8 kilometers (4.3 to 5.0 mi).[18]

Though narrow, oceanic trenches are remarkably long and continuous, forming the largest linear depressions on earth. An individual trench can be thousands of kilometers long.[3] Most trenches are convex towards the subducting slab, which is attributed to the spherical geometry of the Earth.[21]

The trench asymmetry reflects the different physical mechanisms that determine the inner and outer slope angle. The outer slope angle of the trench is determined by the bending radius of the subducting slab, as determined by its elastic thickness. Since oceanic lithosphere thickens with age, the outer slope angle is ultimately determined by the age of the subducting slab.[22][20] The inner slope angle is determined by the angle of repose of the overriding plate edge.[20] This reflects frequent earthquakes along the trench that prevent oversteepening of the inner slope.[2]

As the subducting plate approaches the trench, it bends slightly upwards before beginning its plunge into the depths. As a result, the outer trench slope is bounded by an outer trench high. This is subtle, often only tens of meters high, and is typically located a few tens of kilometers from the trench axis. On the outer slope itself, where the plate begins to bend downwards into the trench, the upper part of the subducting slab is broken by bending faults that give the outer trench slope a horst and graben topography. The formation of these bending faults is suppressed where oceanic ridges or large seamounts are subducting into the trench, but the bending faults cut right across smaller seamounts. Where the subducting slab is only thinly veneered with sediments, the outer slope will often show seafloor spreading ridges oblique to the horst and graben ridges.[20]

Sedimentation

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Trench morphology is strongly modified by the amount of sedimentation in the trench. This varies from practically no sedimentation, as in the Tonga-Kermadec trench, to completely filled with sediments, as with the Cascadia subduction zone. Sedimentation is largely controlled by whether the trench is near a continental sediment source.[21] The range of sedimentation is well illustrated by the Chilean trench. The north Chile portion of the trench, which lies along the Atacama Desert with its very slow rate of weathering, is sediment-starved, with from 20 to a few hundred meters of sediments on the trench floor. The tectonic morphology of this trench segment is fully exposed on the ocean bottom. The central Chile segment of the trench is moderately sedimented, with sediments onlapping onto pelagic sediments or ocean basement of the subducting slab, but the trench morphology is still clearly discernible. The southern Chile segment of the trench is fully sedimented, to the point where the outer rise and slope are no longer discernible. Other fully sedimented trenches include the Makran Trough, where sediments are up to 7.5 kilometers (4.7 mi) thick; the Cascadia subduction zone, which is completed buried by 3 to 4 kilometers (1.9 to 2.5 mi) of sediments; and the northernmost Sumatra subduction zone, which is buried under 6 kilometers (3.7 mi) of sediments.[23]

Sediments are sometimes transported along the axis of an oceanic trench. The central Chile trench experiences transport of sediments from source fans along an axial channel.[24] Similar transport of sediments has been documented in the Aleutian trench.[2]

In addition to sedimentation from rivers draining into a trench, sedimentation also takes place from landslides on the tectonically steepened inner slope, often driven by megathrust earthquakes. The Reloca Slide of the central Chile trench is an example of this process.[25]

Erosive versus accretionary margins

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Convergent margins are classified as erosive or accretionary, and this has a strong influence on the morphology of the inner slope of the trench. Erosive margins, such as the northern Peru-Chile, Tonga-Kermadec, and Mariana trenches, correspond to sediment-starved trenches.[3] The subducting slab erodes material from the lower part of the overriding slab, reducing its volume. The edge of the slab experiences subsidence and steepening, with normal faulting. The slope is underlain by relative strong igneous and metamorphic rock, which maintains a high angle of repose.[26] Over half of all convergent margins are erosive margins.[2]

Accretionary margins, such as the southern Peru-Chile, Cascadia, and Aleutians, are associated with moderately to heavily sedimented trenches. As the slab subducts, sediments are "bulldozed" onto the edge of the overriding plate, producing an accretionary wedge or accretionary prism. This builds the overriding plate outwards. Because the sediments lack strength, their angle of repose is gentler than the rock making up the inner slope of erosive margin trenches. The inner slope is underlain by imbricated thrust sheets of sediments. The inner slope topography is roughened by localized mass wasting.[26] Cascadia has practically no bathymetric expression of the outer rise and trench, due to complete sediment filling, but the inner trench slope is complex, with many thrust ridges. These compete with canyon formation by rivers draining into the trench. Inner trench slopes of erosive margins rarely show thrust ridges.[19]

Accretionary prisms grow in two ways. The first is by frontal accretion, in which sediments are scraped off the downgoing plate and emplaced at the front of the accretionary prism.[2] As the accretionary wedge grows, older sediments further from the trench become increasingly lithified, and faults and other structural features are steepened by rotation towards the trench.[27] The other mechanism for accretionary prism growth is underplating[2] (also known as basal accretion[28]) of subducted sediments, together with some oceanic crust, along the shallow parts of the subduction decollement. The Franciscan Group of California is interpreted as an ancient accretionary prism in which underplating is recorded as tectonic mélanges and duplex structures.[2]

Oceanic trench formed along an oceanic-oceanic convergent boundary
The Mariana Trench contains the deepest part of the world's oceans, and runs along an oceanic-oceanic convergent boundary. It is the result of the oceanic Pacific plate subducting beneath the oceanic Mariana plate.

Earthquakes

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Frequent megathrust earthquakes modify the inner slope of the trench by triggering massive landslides. These leave semicircular landslide scarps with slopes of up to 20 degrees on the headwalls and sidewalls.[29]

Subduction of seamounts and aseismic ridges into the trench may increase aseismic creep and reduce the severity of earthquakes. Contrariwise, subduction of large amounts of sediments may allow ruptures along the subduction décollement to propagate for great distances to produce megathrust earthquakes.[30]

Trench rollback

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Trenches seem positionally stable over time, but scientists believe that some trenches—particularly those associated with subduction zones where two oceanic plates converge—move backward into the subducting plate.[31][32] This is called trench rollback or retreat, hinge rollback or retreat, slab rollback or retreat and is one explanation for the existence of back-arc basins.

Forces perpendicular to the slab (the portion of the subducting plate within the mantle) are responsible for steepening of the slab and, ultimately, the movement of the hinge and trench at the surface.[33] These forces arise from the negative buoyancy of the slab with respect to the mantle[34] modified by the geometry of the slab itself.[35] The extension in the overriding plate, in response to the subsequent subhorizontal mantle flow from the displacement of the slab, can result in formation of a back-arc basin.[36]

Processes involved

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Several forces are involved in the process of slab rollback. Two forces acting against each other at the interface of the two subducting plates exert forces against one another. The subducting plate exerts a bending force (FPB) that supplies pressure during subduction, while the overriding plate exerts a force against the subducting plate (FTS). The slab pull force (FSP) is caused by the negative buoyancy of the plate driving the plate to greater depths. The resisting force from the surrounding mantle opposes the slab pull forces. Interactions with the 660-km discontinuity cause a deflection due to the buoyancy at the phase transition (F660).[35] The unique interplay of these forces is what generates slab rollback. When the deep slab section obstructs the down-going motion of the shallow slab section, slab rollback occurs. The subducting slab undergoes backward sinking due to the negative buoyancy forces causing a retrogradation of the trench hinge along the surface. Upwelling of the mantle around the slab can create favorable conditions for the formation of a back-arc basin.[36]

Seismic tomography provides evidence for slab rollback. Results demonstrate high temperature anomalies within the mantle suggesting subducted material is present in the mantle.[37] Ophiolites are viewed as evidence for such mechanisms as high pressure and temperature rocks are rapidly brought to the surface through the processes of slab rollback, which provides space for the exhumation of ophiolites.

Slab rollback is not always a continuous process suggesting an episodic nature.[34] The episodic nature of the rollback is explained by a change in the density of the subducting plate, such as the arrival of buoyant lithosphere (a continent, arc, ridge, or plateau), a change in the subduction dynamics, or a change in the plate kinematics. The age of the subducting plates does not have any effect on slab rollback.[35] Nearby continental collisions have an effect on slab rollback. Continental collisions induce mantle flow and extrusion of mantle material, which causes stretching and arc-trench rollback.[36] In the area of the Southeast Pacific, there have been several rollback events resulting in the formation of numerous back-arc basins.[34]

Mantle interactions

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Interactions with the mantle discontinuities play a significant role in slab rollback. Stagnation at the 660-km discontinuity causes retrograde slab motion due to the suction forces acting at the surface.[35] Slab rollback induces mantle return flow, which causes extension from the shear stresses at the base of the overriding plate. As slab rollback velocities increase, circular mantle flow velocities also increase, accelerating extension rates.[33] Extension rates are altered when the slab interacts with the discontinuities within the mantle at 410 km and 660 km depth. Slabs can either penetrate directly into the lower mantle, or can be retarded due to the phase transition at 660 km depth creating a difference in buoyancy. An increase in retrograde trench migration (slab rollback) (2–4 cm/yr) is a result of flattened slabs at the 660-km discontinuity where the slab does not penetrate into the lower mantle.[38] This is the case for the Japan, Java and Izu–Bonin trenches. These flattened slabs are only temporarily arrested in the transition zone. The subsequent displacement into the lower mantle is caused by slab pull forces, or the destabilization of the slab from warming and broadening due to thermal diffusion. Slabs that penetrate directly into the lower mantle result in slower slab rollback rates (~1–3 cm/yr) such as the Mariana arc, Tonga arcs.[38]

The Puerto Rico Trench

Hydrothermal activity and associated biomes

[edit]

As sediments are subducted at the bottom of trenches, much of their fluid content is expelled and moves back along the subduction décollement to emerge on the inner slope as mud volcanoes and cold seeps. Methane clathrates and gas hydrates also accumulate in the inner slope, and there is concern that their breakdown could contribute to global warming.[2]

The fluids released at mud volcanoes and cold seeps are rich in methane and hydrogen sulfide, providing chemical energy for chemotrophic microorganisms that form the base of a unique trench biome. Cold seep communities have been identified in the inner trench slopes of the western Pacific (especially Japan[39]), South America, Barbados, the Mediterranean, Makran, and the Sunda trench. These are found at depths as great as 6,000 meters (20,000 ft).[2] The genome of the extremophile Deinococcus from Challenger Deep has sequenced for its ecological insights and potential industrial uses.[40]

Because trenches are the lowest points in the ocean floor, there is concern that plastic debris may accumulate in trenches and endanger the fragile trench biomes.[41]

Deepest oceanic trenches

[edit]

Recent measurements, where the salinity and temperature of the water was measured throughout the dive, have uncertainties of about 15 m (49 ft).[42] Older measurements may be off by hundreds of meters.

Trench Ocean Lowest Point Maximum Depth Source
Mariana Trench Pacific Ocean Challenger Deep 10,925 m (35,843 ft) [42][43]
Tonga Trench Pacific Ocean Horizon Deep 10,820 m (35,500 ft) [42]
Philippine Trench Pacific Ocean Emden Deep 10,540 m (34,580 ft) [44]
Kuril–Kamchatka Trench Pacific Ocean 10,542 m (34,587 ft) [44]
Kermadec Trench Pacific Ocean 10,047 m (32,963 ft) [44]
Izu–Bonin Trench (Izu–Ogasawara Trench) Pacific Ocean 9,810 m (32,190 ft) [44]
New Britain Trench Pacific Ocean (Solomon Sea) Planet Deep 9,140 m (29,990 ft) [45]
Puerto Rico Trench Atlantic Ocean Milwaukee Deep 8,376 m (27,480 ft) [42][46]
South Sandwich Trench Atlantic Ocean Meteor Deep 8,266 m (27,119 ft) [42][47]
Peru–Chile Trench or Atacama Trench Pacific Ocean Richards Deep 8,055 m (26,427 ft) [44]
Japan Trench Pacific Ocean 8,412 m (27,498 ft) [44]
Cayman Trench Atlantic Ocean Caribbean Deep 7,686 m (25,217 ft) [44]
South Sandwich Trench Southern Ocean Factorian Deep 7,334 m (24,062 ft) [42][47]
Sunda Trench Indian Ocean Java Deep 7,192 m (23,596 ft) [44][43]
Mauritius Trench Indian Ocean Mauritius Point 6,875 m (22,556 ft) [44]
India Trench Indian Ocean Between India & Maldives 7,225 m (23,704 ft) [44]
Ceylon Trench Indian Ocean Sri Lanka Deep 6,400 m (21,000 ft) [44]
Somalia Trench Indian Ocean Somali Deep 6,084 m (19,961 ft) [44]
Madagascar Trench Indian Ocean Madagascar Deep 6,048 m (19,843 ft) [44]
Puerto Rico Trench Atlantic Ocean Rio Bermuda Deep 5,625 m (18,455 ft) [44]
Mid-Atlantic Ridge Arctic Ocean Molloy Deep 5,550 m (18,210 ft) [42][43]

Notable oceanic trenches

[edit]
Trench Location
Aleutian Trench South of the Aleutian Islands, west of Alaska
Bougainville Trench South of New Guinea
Cayman Trench Western Caribbean
Cedros Trench (inactive) Pacific coast of Baja California
Hikurangi Trough East of New Zealand
Hjort Trench Southwest of New Zealand
Izu–Ogasawara Trench Near Izu and Bonin islands
Japan Trench East of Japan
Kermadec Trench * Northeast of New Zealand
Kuril–Kamchatka Trench * Near Kuril Islands
Manila Trench West of Luzon, Philippines
Mariana Trench * Western Pacific Ocean; east of Mariana Islands
Middle America Trench Eastern Pacific Ocean; off coast of Mexico, Guatemala, El Salvador, Nicaragua, Costa Rica
New Hebrides Trench West of Vanuatu (New Hebrides Islands).
Peru–Chile Trench Eastern Pacific Ocean; off coast of Peru & Chile
Philippine Trench * East of the Philippines
Puerto Rico Trench Boundary of Caribbean and Atlantic Ocean
Puysegur trench Southwest of New Zealand
Ryukyu Trench Eastern edge of Japan's Ryukyu Islands
South Sandwich Trench East of the South Sandwich Islands
Sunda Trench Curves from south of Java to west of Sumatra and the Andaman and Nicobar Islands
Tonga Trench * Near Tonga
Yap Trench Western Pacific Ocean; between Palau Islands and Mariana Trench

(*) The five deepest trenches in the world

Ancient oceanic trenches

[edit]
Trench Location
Intermontane Trench Western North America; between the Intermontane Islands and North America
Insular Trench Western North America; between the Insular Islands and the Intermontane Islands
Farallon Trench Western North America
Tethys Trench South of Turkey, Iran, Tibet and Southeast Asia

See also

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References

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Bibliography

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Further reading

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Oceanic trench

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from Grokipedia
An oceanic trench is a long, narrow, and deep topographic depression in the seafloor, representing the deepest regions of the and forming at convergent plate boundaries where one tectonic plate subducts beneath another through the process of . These features typically measure 50 to 100 kilometers wide and can extend for thousands of kilometers in length, with slopes averaging 4 to 5 degrees and depths ranging from 8 to 11 kilometers. The process occurs because is denser than or adjacent , allowing the descending plate to sink into the mantle, often accompanied by intense seismic activity and the recycling of . Oceanic trenches encircle the in a pattern known as the , but they also occur in the Atlantic, Indian, and Southern Oceans wherever zones are present. Notable examples include the in the western Pacific, which hosts the at approximately 10,935 meters—the deepest known point on —with pressures exceeding 1,000 atmospheres; the Peru-Chile Trench along the western South American coast, formed by the Nazca Plate subducting under the South American Plate; and the in the Atlantic, resulting from the North American Plate subducting beneath the Caribbean Plate. These trenches are fundamental to Earth's , marking active zones that drive , generate volcanic island arcs and mountain ranges, and facilitate the chemical exchange between the surface and the mantle through the subduction and melting of oceanic plates. They also support unique deep-sea ecosystems in the , adapted to extreme pressures and darkness, though exploration remains limited due to technological challenges.

Definition and Characteristics

Geological Definition

An oceanic trench is defined as a long, narrow topographic depression in the ocean floor, typically extending 2-4 km deeper than the surrounding abyssal seafloor, and formed primarily at convergent plate boundaries where denser oceanic lithosphere is subducted beneath another tectonic plate. These features mark the sites of intense compressional forces, where the downgoing plate bends and creates a pronounced flexural depression in the overriding plate. Oceanic trenches are distinct from other seafloor features such as mid-ocean ridges, which arise at divergent boundaries through crustal and spreading, or fracture zones, which represent transform offsets with irregular, fault-dominated topography lacking the deep, continuous depressions of trenches. Trenches often display an arcuate, curved geometry and are paralleled by volcanic arcs on the overriding plate, resulting from of the subducted slab. Typical dimensions of oceanic trenches include lengths ranging from 1,000 to 4,000 km, widths of 50-100 km, and maximum depths approaching 11 km below . For instance, the in the has been measured at 10,935 ± 6 m as the deepest known point.

Key Physical Properties

Oceanic trenches exhibit characteristic V-shaped cross-sections in their depth profiles, formed by the steep descent of the seafloor into the trench axis. These profiles are typically asymmetric, with steeper inner slopes (landward side) ranging from 8 to 20 degrees and gentler outer slopes (seaward side) around 5 degrees. The V-shape results in a narrow axial , often less than 10 kilometers wide at the base, where depths can exceed 6,000 meters. Sediment accumulation in oceanic trenches varies significantly by margin type, with thicknesses reaching 1-2 kilometers in accretionary margins due to the offscraping and piling of incoming . In contrast, erosive margins feature thinner sediment layers, typically under 500 meters, as subducted material is more readily removed without substantial buildup. The primary composition consists of turbidites—coarse-grained deposits from landslides—and finer pelagic oozes derived from biological remains and wind-blown dust settling over vast areas. Key bathymetric features include the outer rise, a broad bulge in the approximately 100-200 kilometers seaward of the trench, caused by flexural bending of the subducting plate. This rise is often accompanied by normal faulting that creates a series of subparallel scarps staircasing down toward the trench. On the inner wall, thrusting and normal faulting further disrupt the slope, contributing to a rugged that traps sediments in isolated basins. Modern mapping of these properties relies on multibeam sonar systems, which emit multiple acoustic beams to generate high-resolution seafloor images with resolutions down to 1-10 meters. Submersibles and autonomous underwater vehicles complement this by providing close-up visual and sampling data in extreme depths. In the 2020s, global datasets like the GEBCO_2025 Grid (released August 2025) have incorporated extensive multibeam surveys to update trench , enhancing accuracy for previously under-mapped regions.

Formation and Tectonic Context

Subduction Zone Mechanics

Subduction zones form where one oceanic lithospheric plate converges with and descends beneath another plate, creating oceanic trenches as the leading edge of the denser oceanic lithosphere sinks into . This descent typically occurs at dip angles ranging from 30° to 60°, primarily driven by the negative of the cold, subducting slab (slab pull) and the gravitational sliding of elevated material (ridge push). Slab pull exerts the dominant force, estimated to be several times stronger than ridge push, pulling the plate toward the subduction zone while ridge push provides additional traction from behind. The descending slab is traced by a seismically active, known as the Benioff zone (or Wadati-Benioff zone), where earthquakes occur along the interface and within the slab itself. This zone forms a dipping seismic band that extends from shallow depths near the to as deep as 700 km, reflecting the progressive and deformation of the into . Trench formation results from the flexural bending of the overriding plate under the load of the subducting slab, which causes and creates the characteristic topographic depression. The mechanical response is governed by the plate's elastic properties, with the flexural parameter α given by \alpha = \sqrt{{grok:render&&&type=render_inline_citation&&&citation_id=4&&&citation_type=wikipedia}}{\frac{4D}{\Delta \rho g}} where DD is the flexural rigidity related to the effective elastic thickness, Δρ\Delta \rho is the density contrast between the infill material and the mantle, and gg is gravitational acceleration. This bending accommodates the vertical load and horizontal stresses at the margin, influencing the trench's profile. Subduction rates vary globally from 2 to 10 cm/year, affecting trench depth and overall morphology; slower rates allow for greater sediment accumulation and shallower profiles, while faster rates enhance slab steepness and deeper incisions. These variations contribute to the diverse patterns observed in trench distributions worldwide.

Role in Plate Tectonics

Oceanic trenches serve as primary sites for the of oceanic lithosphere into through processes. At these convergent boundaries, the denser oceanic plate descends beneath another plate, returning aged and material to depths exceeding 100 km. This is essential for maintaining the balance of Earth's crustal materials, with an estimated global volume flux of approximately 20 km³/year for basaltic oceanic crust entering via zones. The concept of such crustal profoundly influenced the development of theory, highlighting trenches as key locations where surface materials are continuously renewed and cycled back into the deep interior. Trenches are closely associated with the formation of island arcs and continental margins, where subducting slabs trigger and extension that shape surrounding tectonic features. Island arcs develop as volcanic chains above the descending slab, typically 100-300 km from the trench axis, and serve as major contributors to continental growth through the accretion of arc-derived materials to overriding plates. Additionally, trenches initiate back-arc basins via extension in the overriding plate, driven by slab or toroidal flow around the slab edge, which allows and further influences margin evolution. These processes enable the incorporation of oceanic and arc terranes into continents, promoting long-term crustal expansion. Subduction at oceanic trenches plays a pivotal role in Earth's thermal budget by facilitating and the majority of planetary heat loss. The descent of cold lithospheric slabs drives vigorous convective currents in , accounting for about 90% of Earth's internal heat dissipation, with the remainder primarily through mantle plumes. This convective activity, powered by slab pull, regulates global from the core- boundary to the surface, influencing plate motions and surface . Recent whole-mantle models, incorporating post-2020 seismic and geodynamic data, emphasize the role of trenches in slab dynamics, particularly stagnation in transition zone at 410-660 km depth. These simulations reveal that subducted slabs from trenches often accumulate and stagnate in the transition zone due to phase transitions and viscosity increases, before partial penetration into the or remobilization, affecting long-term patterns and intraplate . Such models integrate global to show how trench-initiated modulates whole-mantle flow, with implications for seismic activity along Benioff zones.

Global Distribution and Morphology

Geographic Patterns

Oceanic trenches exhibit a highly uneven global distribution, with the vast majority concentrated along the margins of the as part of the , a seismically active belt encircling the basin. This region accounts for approximately 80% of all oceanic trenches worldwide, driven by the intense activity surrounding the Pacific Plate. In contrast, the Atlantic and Indian Oceans host far fewer and generally shorter trenches, reflecting less extensive convergent boundaries in these basins, while the features notable examples like the South Sandwich Trench. Globally, there are over 50 major oceanic trenches, nearly all associated with convergent plate margins where an oceanic plate is subducted beneath a continental or another oceanic plate. In the Pacific Ocean, trenches form an interconnected network totaling around 40,000 km in length, curving from the in the north through the Mariana and trenches in the west, to the Peru-Chile Trench along the eastern margin. This extensive clustering underscores the Pacific's role as the primary locus of plate convergence, where multiple oceanic plates interact with surrounding continental margins. The Atlantic Ocean features only a handful of short trenches, such as the , which extends about 810 km and marks the boundary between the North American and plates. Similarly, the contains limited trench systems, exemplified by the Java Trench, a 3,200 km-long feature south of resulting from the subduction of the Indo-Australian Plate beneath the Sunda Plate. Recent mapping efforts have enhanced resolution of seafloor topography, with the Seabed 2030 project releasing the International Bathymetric Chart of the (IBCAO) Version 5.0 in 2025, adding over 1.4 million square kilometers of detailed and improving grid resolution to 100 meters. These advancements highlight progress in under-explored regions and global seafloor understanding.

Structural Profiles and Dimensions

Oceanic trenches exhibit a wide range of dimensions, with typical lengths spanning 500 to 5,000 kilometers and depths ranging from 6 to 11 kilometers below . These elongated depressions form narrow, linear features along convergent plate boundaries, where the scale of length accommodates the curvature of zones, while depths reflect the balance between tectonic loading and isostatic adjustment of the overriding plate. For instance, major trenches in the collectively displace approximately 1% of the total ocean volume, underscoring their significant contribution to global bathymetric . Cross-sectional profiles of oceanic trenches vary based on subduction dynamics and the characteristics of the incoming . In fast-subducting zones, such as those in the western Pacific, profiles are often asymmetric, featuring steeper inner slopes (up to 20 degrees) due to compressional forces and sediment underplating, while outer slopes are gentler. Conversely, slower subduction settings, like parts of the Atlantic margins, display more symmetric profiles with balanced slopes on both sides. The age of the subducting plays a key role in these variations; older, cooler crust (greater than 80 million years) promotes steeper profiles by enhancing slab rigidity and resistance to bending. Seismic reflection data reveal detailed structural features within trench profiles, including normal faulting along the inner slope that accommodates extension as the overriding plate bends, and extensive fracturing on the outer high, where the incoming plate undergoes initial deformation. These insights, derived from multi-channel seismic surveys, highlight how fault systems control sediment distribution and fluid migration, influencing trench morphology over time. Advancements in the 2020s have refined our understanding through high-resolution global databases, such as the General of the Oceans (GEBCO) compilation, which integrates satellite altimetry and shipborne data to model typical trench depths of 6 to 10 kilometers. This database provides a comprehensive framework for analyzing profile variations across clustered geographic regions, enabling more precise modeling of tectonic influences.

Sedimentary and Margin Dynamics

Sedimentation Patterns

Sediments accumulating in oceanic trenches derive primarily from two sources: flows transporting terrigenous material from continental margins via channels, and pelagic rain consisting of fine biogenic oozes and authigenic particles settling from overlying surface waters. Turbidites dominate in trenches proximal to landmasses, delivering sand- and silt-sized fractions in episodic layers, while pelagic contributions form a continuous but thinner blanket of and siliceous oozes in more isolated settings. These inputs create a heterogeneous fill, with turbidites often comprising mass-transport deposits interbedded with hemipelagic layers. Sedimentation rates in active trenches vary from 10 to 100 mm/kyr, driven by the frequency and volume of turbidite events near continental sources, contrasting with slower pelagic rates of less than 1 mm/kyr in distal areas. These rates reflect the balance between rapid depositional pulses from slope failures and steady background settling, with higher values observed in tectonically active margins like the Japan and Peru-Chile trenches. Sedimentation patterns exhibit clear zonation, featuring the thickest axial fill along the trench bottom—reaching up to 5 km in well-supplied systems such as the Makran subduction zone—and flanking slope aprons of thinner, more variable deposits. The axial zone accumulates stacked turbidite sequences channeled along the trench axis, while slope aprons build outward through hemipelagic draping and minor slumps, creating a wedge-shaped profile that tapers toward the overriding plate. Under the extreme pressures of the hadal environment (exceeding 100 MPa), these sediments undergo diagenesis, including progressive dewatering and compaction that expels interstitial fluids and compacts clay-rich layers, altering their physical properties prior to subduction. The weight of accumulated sediments induces flexural of the subducting oceanic plate, enhancing trench depth and promoting further deposition in a feedback loop that shapes long-term morphology. Numerical models simulating trench infilling over 100 Ma timescales demonstrate how sustained rates of tens of mm/kyr can fill depressions by 1–2 km, with removing material at the inner wall and maintaining dynamic equilibrium, as seen in reconstructions of the ancient Tethys subduction system.

Erosive vs. Accretionary Margins

Oceanic trenches form at convergent plate boundaries where one tectonic plate subducts beneath another, and the nature of the overriding plate margin—whether accretionary or erosive—fundamentally influences behavior, trench morphology, and long-term tectonic evolution. In accretionary margins, incoming oceanic sediments are primarily scraped off the subducting plate at the trench axis through frontal accretion, building wedge-shaped prisms that protrude seaward and can extend 100-200 km wide, as observed in the Sunda margin off . These prisms consist of deformed and imbricated sediments, often incorporating slivers of , and represent about 43% of global subduction zones, facilitating net growth of the overriding plate. In contrast, erosive margins dominate the remaining ~57%, where sediments are largely subducted or underplated beneath the forearc, leading to basal erosion of the overriding plate and progressive trench deepening without significant prism development. Erosive margins, prevalent along Pacific Ring of Fire trenches such as the Peru-Chile and Mariana systems, exhibit steeper slab dips often reaching 45° or more, which enhances mechanical abrasion and subduction of trench-fill materials. Here, underplating occurs when subducted sediments are accreted deeper within the , but overall favors recycling into the mantle, resulting in forearc subsidence and exposure of basement rocks. Seismic reflection profiles provide evidence of this underthrusting, revealing continuous sediment layers extending beneath the margin without widespread offscraping, as documented in the north Chilean margin. This process contrasts with accretionary margins, where shallower slab angles (typically 10-30°) and thicker sediment piles promote wedge formation and limit deep subduction. The transition between accretionary and erosive margins often occurs in zones influenced by varying supply and convergence rates, with erosive conditions favored when incoming thickness is less than 1 km and plate convergence exceeds 6 cm/yr, as seen in the transition along the southern margin. High convergence rates increase shear stresses at the plate interface, promoting over accretion, while abundant from nearby continental sources, such as in the Sumatra-Andaman system, supports prism building. from these transitional areas, including the Hikurangi margin, highlight underthrusting of packages that can switch between modes over geological time, driven by fluctuations in these controls. Overall, these dynamics underscore how margin type modulates crustal recycling, with erosive systems contributing disproportionately to destruction.

Geological Processes and Hazards

Trench Rollback Mechanisms

Trench rollback refers to the oceanward migration of the subduction away from the overriding plate, typically at rates of 1–10 cm/year, primarily driven by the negative of the subducting oceanic slab relative to the surrounding mantle. This process occurs as the dense slab sinks into the mantle, pulling the hinge backward and inducing extension in the overriding plate. The negative arises from the slab's composition, which is cooler and denser than the ambient mantle, creating a gravitational force that promotes slab pull and hinge retreat. Key mechanisms include retreat, where the subduction hinge bends and migrates seaward due to the slab's descent, and the initiation of back-arc spreading, which forms extensional basins behind the to accommodate the induced tension. retreat is facilitated by the slab's ability to bend at the , allowing the upper plate to respond with deformation or rifting, while back-arc spreading often develops when rates exceed the overriding plate's resistance, leading to seafloor creation similar to mid-ocean ridges. These processes are interconnected, with velocities influencing the style and intensity of extension in the back-arc region. The Mediterranean region exemplifies extreme , where the subduction of the African plate beneath has driven rapid retreat over millions of years, particularly in the Hellenic and Calabrian arcs, resulting in widespread formation and orogenic extension. In the , exceptionally fast rates of up to 16 cm/year highlight how slab dynamics can accelerate migration in young, fast-converging systems.

Associated Seismicity and Earthquakes

Oceanic trenches, as key features of subduction zones, are primary loci for intense seismic activity, where the convergence of tectonic plates generates a range of earthquakes from shallow megathrust events to deep-focus ruptures. These earthquakes occur along the subduction interface and within descending slabs, reflecting the dynamic stresses of plate subduction. The seismicity patterns in trenches highlight their role in accommodating plate motion through brittle failure at various depths. Megathrust earthquakes, which dominate trench-associated , result from sudden slip along the shallow to intermediate portions of the interface, often reaching moment magnitudes (Mw) exceeding 9.0. The largest recorded such event was the in the Chile-Peru trench, with Mw 9.5, which ruptured over 1,000 km of the plate boundary. These events typically recur on intervals of 100 to 500 years, influenced by frictional properties and stress accumulation along the megathrust, with deeper segments failing more frequently to trigger shallower great ruptures. Deeper within subduction slabs, earthquakes extend to depths of up to 670 km, forming inclined seismic bands known as Wadati-Benioff zones that trace the descending . These deep-focus events, occurring below 300 km, are enabled by mechanisms such as transformational faulting, where phase changes in metastable minerals like generate shear instabilities under high pressure and low temperatures. Such quakes provide critical insights into slab integrity and dehydration processes at mantle depths. Trench-related earthquakes frequently generate due to the large-scale vertical seafloor displacement along the interface, with trench geometry—particularly shallow slip near the trench axis—amplifying wave heights by enhancing initial water column disturbance. The 2011 Tohoku earthquake (Mw 9.0) in the exemplifies this, where rupture propagating to within 7 km of the seafloor produced waves up to 40 meters high, devastating coastal regions. Advancements in seismic monitoring, including submarine networks and early warning systems deployed along Pacific trenches, have enhanced detection and forecasting capabilities as of 2024-2025. These improvements, such as expanded fiber-optic sensing and integration, have refined hazard models through better characterization of interplate coupling.

Hydrothermal Systems and Biology

Vent Formation and Activity

Hydrothermal vents in oceanic trenches primarily occur in forearc settings, arising from the circulation of seawater through fractures in the oceanic crust and mantle wedge, where fluids are heated by low-temperature (<200°C) dehydration reactions and serpentinization within or above the subducting slab. This process is facilitated by the bending and faulting of the incoming plate at the trench, which enhances permeability and allows cold seawater to infiltrate the crust, where it interacts with the thermally perturbed slab interface. The heated fluids ascend, often forming diffuse venting or low-temperature chimneys with mineral precipitates, rather than high-temperature black smokers typical of mid-ocean ridges. The chemical composition of these vent fluids is characterized by elevated levels of (H₂) and (CH₄), with alkaline typically ranging from 9 to 12. These signatures result primarily from serpentinization of ultramafic rocks in the mantle wedge, where water reacts with and to produce H₂ and CH₄ under reducing conditions. In trench settings, such fluids may also incorporate volatiles released from devolatilization of the slab, contributing to the unique geochemical profile compared to systems. Venting activity in trenches is generally episodic, with periods of intense discharge alternating with quiescence, influenced by tectonic stress, slab dynamics, and recharge cycles. Hydrothermal systems in subduction zones play a key role in chemical cycling and at convergent margins, with fluxes estimated on the order of 10¹¹ to 10¹² moles per year globally. Notable examples include low-temperature serpentinization-driven vents at sites like the South Chamorro Seamount in the Mariana .

Deep-Sea Ecosystems

The , encompassing depths greater than 6,000 meters within oceanic trenches, hosts unique biological communities adapted to extreme hydrostatic pressures reaching up to 1,100 atmospheres and near-freezing temperatures. Over 1,000 have been recorded in this zone globally, excluding , with notable examples including scavenging amphipods such as Hirondellea gigas and snailfishes like Pseudoliparis , which dominate the vertebrate fauna. These organisms form dense assemblages around organic falls and chemosynthetic habitats, contributing to a despite the isolation and harsh conditions. A key feature of hadal ecosystems is their reliance on rather than sunlight-dependent , enabling food webs independent of surface productivity. microbes, primarily , oxidize (H₂S) from fluids, (H₂), or (CH₄) from organic or vent fluids to fix carbon, forming the base of these ecosystems. This process supports symbiotic relationships in macrofauna, such as hadal worms (e.g., Paralvinella spp.) and bivalves adapted to , which harbor these microbes in their tissues for energy production, allowing dense colonies to thrive in otherwise nutrient-poor sediments. In 2025, chemosynthetic tubeworms and molluscs were discovered thriving at depths up to 9,533 meters in Pacific trenches like the Izu-Ogasawara, expanding known hadal symbioses. In trench settings, these chemosynthetic communities, often associated with , sustain higher than surrounding heterotrophic areas. Organisms in hadal trenches exhibit remarkable adaptations to high pressure and limited resources. Piezophilic , obligately adapted to hydrostatic pressures exceeding 600 atmospheres, dominate microbial assemblages and possess genomic modifications like enhanced membrane fluidity and pressure-resistant enzymes to maintain cellular functions. Among , gigantism is observed in some , such as the supergiant amphipod Alicella gigantea, which can reach lengths of 340 mm—potentially linked to increased oxygen availability or reduced predation at depth—contrasting with smaller relatives in shallower waters. Hadal also display vertical distribution patterns, with some mobile like snailfishes undertaking limited migrations along trench slopes to exploit varying food resources or oxygen levels. Recent expeditions in 2024 have advanced understanding through metagenomic analyses of the , revealing high microbial novelty with up to 30% of sequences representing previously unknown lineages across , highlighting the untapped diversity in hadal sediments. These studies underscore the role of trench isolation in fostering endemic microbial evolution, with implications for global biogeochemical cycles.

Notable Examples and Records

Deepest Trenches

The holds the record for the deepest known point in the world's oceans at , measured at 10,935 ± 6 meters using pressure-derived methods from submersible transects conducted in 2020. Within the same trench, serves as a secondary extreme, reaching a depth of 10,780 meters as determined by direct submersible measurement during the 2019 Five Deeps Expedition. These measurements highlight the trench's role as the primary benchmark for oceanic depth extremes, with exceeding all others by over 100 meters. Other notable extremes include the Tonga Trench's Horizon Deep at 10,823 meters, confirmed through direct descent and bathymetric surveys in 2019, placing it as the second-deepest location globally. The features at 10,540 meters, verified by manned dives in 2021 that also documented environmental conditions at full depth. These sites represent the hadal zone's most profound points, where pressures exceed 1,000 atmospheres and temperatures hover near freezing. The evolution of depth measurements began with the 1875 , which used a weighted rope to sound 4,475 fathoms (approximately 8,184 meters) in the , marking the first detection of such profound depths despite the method's limitations in accuracy and resolution. Subsequent advancements shifted to acoustic in the mid-20th century, followed by multibeam in the 1980s and 1990s, which refined estimates to within tens of meters. Modern unmanned dives, employing remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) with pressure sensors and laser altimeters, have achieved sub-meter precision, as seen in the 2020 submersible transects that corrected earlier biases due to sound velocity variations. Exploration of these deepest trenches tests the limits of hadal ecosystems, revealing unique adaptations in microbial and faunal life under extreme hydrostatic pressure, as documented in NOAA-led surveys of the zone from 6,000 to 11,000 meters. Additionally, these sites hold potential for resource exploration, including polymetallic nodules and rare-earth elements, though access challenges and environmental protections limit current activities.

Significant Trenches Worldwide

The Peru-Chile Trench stands out as the longest continuous oceanic trench on Earth, stretching approximately 5,900 km along the western margin of where the Nazca Plate subducts beneath the South American Plate. This extensive feature has played a pivotal role in regional , notably as the epicenter of the , a moment magnitude 9.5 event that ruptured over 1,000 km of the plate boundary and triggered widespread tsunamis across the Pacific. The trench's length facilitates prolonged strain accumulation, contributing to its history of generating some of the planet's most powerful seismic events. Further north in the northwest Pacific, the Kuril-Kamchatka Trench exemplifies high linked to rapid of the Pacific Plate beneath the Okhotsk Plate, extending about 2,100 km from the to the . This trench is closely associated with the Kuril-Kamchatka , where ongoing plate convergence at rates exceeding 80 mm per year drives frequent moderate-to-large earthquakes and sustains active along a parallel chain of stratovolcanoes. The region's intense activity underscores the trench's influence on arc magmatism and seismic hazard assessment in one of the world's most dynamic zones. In the , the Java Trench serves as a key example of along the Sunda margin, where the Australian Plate descends beneath the Sunda Plate at depths reaching 7,290 m in its deepest sections. It has a notable history of generating tsunamigenic earthquakes, including the 1994 Java (Mw 7.8) and the 2006 Pangandaran event (Mw 7.7), both of which produced unexpectedly large waves due to slow rupture propagation along the shallow megathrust. These events highlight the trench's potential for localized but devastating hazards in densely populated Indonesian coastal areas. The Tonga-Kermadec Trench system is one of the most active volcanic arcs globally, part of which features ~75% of its 33 major volcanoes being hydrothermally active due to of the Pacific Plate beneath the Australian Plate. This includes significant eruptive activity at Home Reef from 2022 to 2024, which expanded a temporary formation during phases in 2023 and 2024.

Historical and Ancient Perspectives

Discovery and Terminology History

The earliest systematic explorations of the ocean floor, which revealed the existence of profound depressions later recognized as oceanic trenches, occurred during the HMS Challenger expedition from 1872 to 1876. This British Royal Navy voyage, converted into a scientific , conducted over 360 deep-sea soundings using weighted lines, identifying exceptionally deep areas in the western Pacific, including a sounding of approximately 8,184 meters in the region of what would become known as the , near the . These measurements marked the first global effort to map oceanic depths and laid the groundwork for understanding submarine topography, though the full extent of trench networks remained unclear due to the limitations of wireline sounding techniques. Advancements in the transformed trench discovery through the widespread adoption of echo-sounding technology following , enabling precise acoustic profiling of the seafloor. By the 1950s, surveys from vessels like the HMS Challenger II revealed a global system of interconnected deeps exceeding 6,000 meters, confirming trenches as prominent features associated with tectonic boundaries. The term "trench" itself gained prominence in geological literature through Harry Hess's 1962 paper "History of Ocean Basins," where he described these features as sites of in the context of emerging theory, shifting from earlier vague designations like "oceanic deeps" to a tectonically informed . Key exploratory milestones underscored the challenges and significance of trench investigation, beginning with the 1960 dive of the Trieste to the Mariana Trench's . Piloted by and , the submersible reached a depth of about 10,916 meters, the first manned descent to such extremes, providing initial biological and geological observations from the . This was followed in the by James Cameron's solo dive in the submersible on March 26, 2012, to the same site at approximately 10,908 meters, collecting samples and high-resolution imagery that advanced understanding of trench environments. Terminology for these features evolved from 19th-century references to "deeps" or "abyssal depressions" to more standardized terms post-World War I, when the military connotation of "" from warfare influenced oceanographic descriptions of their narrow, linear morphology. The of "hadal trenches" emerged in , coined by Danish oceanographer Anton Frederik Bruun to denote depths beyond 6,000 meters primarily within subduction-related trenches, distinguishing them from shallower abyssal plains. As of 2025, nomenclature updates by bodies like the have refined classifications for minor trench features, such as intra-trench basins and scarps, to support high-resolution mapping from recent expeditions in the Pacific.

Fossil Trenches in the Geological Record

Ancient oceanic trenches, no longer active at the surface, are preserved in the geological record through various proxy indicators that reveal past zones. complexes, which consist of uplifted and obducted sequences of and mantle rocks, serve as key evidence of former mid-ocean ridges and subduction initiation points. These complexes often mark suture zones where continental blocks collided, preserving fragments of ancient oceanic lithosphere. metamorphism, characterized by high-pressure, low-temperature conditions, indicates subduction of crustal material to depths of 20-30 km, typically forming in accretionary prisms adjacent to trenches. deposits, chaotic mixtures of deformed sedimentary, volcanic, and metamorphic rocks, further proxy trench environments by representing scraped-off sediments and disrupted oceanic plate during -accretion processes. Prominent examples include the Tethyan trenches preserved within the , which formed during the to closure of the Neo-Tethys Ocean. These trenches are documented through suites in regions like the and , where subduction-related deformation and metamorphism record the convergence of and fragments. In , remnants of trenches associated with the ( period) are evident in the northern Appalachians, linked to the closure of the . These features include blueschist-facies rocks and mélanges that highlight the of beneath and terranes. The identification of fossil trenches provides critical evidence for supercontinent cycles, illustrating episodic assembly and breakup of continents over hundreds of millions of years, as conceptualized in the . These ancient structures help reconstruct plate motions and orogenic evolution, showing how zones facilitated continental collisions like those forming Pangea. Additionally, slab remnants from these trenches are detectable via mantle tomography, which images high-velocity anomalies in the deep mantle as subducted that sank over geological time. Such remnants influence present-day mantle dynamics and confirm long-term histories.

References

  1. https://education.nationalgeographic.org/resource/ocean-trench/
  2. https://pubs.usgs.gov/gip/dynamic/understanding.html
  3. https://oceanexplorer.noaa.gov/ocean-fact/tectonic-features/
  4. https://www.britannica.com/place/Challenger-Deep
  5. https://www.whoi.edu/ocean-learning-hub/ocean-topics/how-the-ocean-works/seafloor-below/ocean-trenches/
  6. https://personal.utdallas.edu/~rjstern/pdfs/OceanicTrenchesEoG221.pdf
  7. https://oceanexplorer.noaa.gov/ocean-fact/mid-ocean-ridge/
  8. https://www.usgs.gov/special-topics/subduction-zone-science/science/introduction-subduction-zones-amazing-events
  9. https://pubs.usgs.gov/of/1996/0076a/report.pdf
  10. https://www.sciencedirect.com/science/article/pii/S0967063721001813
  11. https://www.sciencedirect.com/science/article/pii/S0079661117302768
  12. https://hal.science/hal-03022505v1/document
  13. https://samples.jblearning.com/0763759937/59933_CH04_092_133.pdf
  14. https://serc.carleton.edu/margins/collection/71216.html
  15. https://link.springer.com/content/pdf/10.1007/978-3-662-01141-6_15
  16. https://www.utdallas.edu/~rjstern/pdfs/TrenchProof.pdf
  17. https://marineemlab.ucsd.edu/steve/bio/SerpentCSEM2.pdf
  18. https://oceanexplorer.noaa.gov/technology/sonar-multibeam/
  19. https://nora.nerc.ac.uk/id/eprint/530930/
  20. https://www.gebco.net/data-products/gridded-bathymetry-data/gebco2025-grid
  21. https://academic.oup.com/gji/article/43/1/163/586101
  22. https://geosci.uchicago.edu/~kite/doc/Geodynamics_Turcotte_Schubert_ch_3.pdf
  23. https://www.nature.com/articles/s41467-020-15580-7
  24. https://basin.earth.ncu.edu.tw/download/courses/seminar_MSc/2012/1129_1_1.pdf
  25. https://par.nsf.gov/servlets/purl/10321658
  26. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019RG000689
  27. https://tos.org/oceanography/assets/docs/20-1_martinez.pdf
  28. https://escweb.wr.usgs.gov/share/mooney/133.pdf
  29. https://www.pnas.org/doi/10.1073/pnas.2414632122
  30. https://www.science.org/doi/10.1126/sciadv.adt9106
  31. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/trench
  32. https://www.worldatlas.com/oceans/how-do-ocean-trenches-form.html
  33. https://manoa.hawaii.edu/exploringourfluidearth/physical/ocean-floor/continental-movement-plate-tectonics
  34. https://www.britannica.com/place/Puerto-Rico-Trench
  35. https://www.bgs.ac.uk/news/scientists-reveal-extraordinary-ecosystems-in-the-deepest-part-of-the-indian-ocean/
  36. https://seabed2030.org/2025/02/03/new-arctic-ocean-map-marks-key-milestone-in-global-seafloor-mapping/
  37. https://www.gebco.net/
  38. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012JB009312
  39. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2006TC001983
  40. https://se.copernicus.org/articles/13/1455/2022/
  41. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2003JB002593
  42. https://pubs.geoscienceworld.org/gsa/geosphere/article/16/4/953/587435/Subduction-of-trench-fill-sediments-beneath-an
  43. https://digital.csic.es/bitstream/10261/25365/3/Ranero_et_al_2008.pdf
  44. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2003rg000127
  45. https://oceanrep.geomar.de/10649/1/Tectonics.pdf
  46. https://academic.oup.com/gji/article/180/1/34/599617
  47. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/91rg00969
  48. https://academic.oup.com/gji/article/201/1/172/730123
  49. https://www.sciencedirect.com/science/article/abs/pii/S0012825208000184
  50. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GC001090
  51. https://www.sciencedirect.com/science/article/pii/S0012825222003269
  52. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009TC002562
  53. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL110127
  54. https://www.annualreviews.org/doi/10.1146/annurev-earth-053018-060314
  55. https://www.sciencedirect.com/science/article/pii/S027737911300139X
  56. https://www.researchgate.net/publication/324170738_Chilean_megathrust_earthquake_recurrence_linked_to_frictional_contrast_at_depth
  57. https://academic.oup.com/gji/article-pdf/192/2/837/17051773/ggs054.pdf
  58. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JB031779
  59. https://www.annualreviews.org/doi/10.1146/annurev-earth-071719-055216
  60. https://pmc.ncbi.nlm.nih.gov/articles/PMC5057117/
  61. https://rallen.berkeley.edu/pub/2025Gou/GouEtAl-SeafloorDASforEEW-BSSA-2024.pdf
  62. https://www.unesco.org/en/articles/pacific-ocean-tsunami-unescos-early-warning-system-proves-once-again-its-effectiveness
  63. https://agupubs.onlinelibrary.wiley.com/doi/10.1002/ggge.20205
  64. https://www.geochemicalperspectivesletters.org/article1916/
  65. https://www.whoi.edu/oceanus/feature/how-to-build-a-black-smoker-chimney/
  66. https://tos.org/oceanography/assets/docs/20-1_tivey.pdf
  67. https://pmc.ncbi.nlm.nih.gov/articles/PMC10581274/
  68. https://www.nature.com/articles/s41598-021-90199-2
  69. https://www.sciencedirect.com/science/article/pii/S0012821X2300064X
  70. http://macbio-pacific.info/wp-content/uploads/2016/02/SUMA-Tonga-digital-lo-res.pdf
  71. https://pmc.ncbi.nlm.nih.gov/articles/PMC7671157/
  72. https://www.whoi.edu/oceanus/feature/the-discovery-of-hydrothermal-vents/
  73. https://www.nature.com/articles/s41586-024-076xx-x
  74. https://pubs.usgs.gov/gip/dynamic/exploring.html
  75. https://pmc.ncbi.nlm.nih.gov/articles/PMC8477399/
  76. https://pmc.ncbi.nlm.nih.gov/articles/PMC12092127/
  77. https://www.pnas.org/doi/10.1073/pnas.1322003111
  78. https://www.nature.com/articles/s41597-024-03762-7
  79. https://spj.science.org/doi/10.34133/olar.0067
  80. https://pmc.ncbi.nlm.nih.gov/articles/PMC11291871/
  81. https://fivedeeps.com/home/expedition/pacific/live/
  82. https://tritonsubs.com/confirmed-horizon-deep-second-deepest-point-on-the-planet/
  83. https://caladanoceanic.com/expeditions/philippinetrench/
  84. https://www.history.com/articles/mariana-trench-hms-challenger
  85. https://oceanexplorer.noaa.gov/expedition-feature/okeanos-ex2102-features-hadalzone/
  86. https://www.nature.com/articles/s43017-024-00595-1
  87. https://www.sciencedirect.com/science/article/abs/pii/S096706370100084X
  88. https://www.nature.com/articles/s41586-025-09317-z
  89. https://pubs.usgs.gov/of/2016/1192/ofr20161192.kmz
  90. https://www.sciencedirect.com/science/article/pii/S001282521830429X
  91. https://pubs.usgs.gov/of/2010/1083/n/pdf/of2010-1083-N.pdf
  92. https://www.nature.com/articles/ncomms5923
  93. https://www.nature.com/articles/s41598-025-95197-2
  94. https://divediscover.whoi.edu/history-of-oceanography/the-challenger-expedition/
  95. https://pubs.geoscienceworld.org/gsa/books/book/847/chapter/3918672/History-of-Ocean-Basins
  96. https://www.usni.org/magazines/naval-history-magazine/2020/february/triestes-deepest-dive
  97. https://deepseachallenge.com/the-expedition/the-mariana-trench/
  98. https://www.sciencedirect.com/science/article/abs/pii/S0967063722001005
  99. https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2025.1543885/full
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