Capricorn Seamount is a

seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

Tonga Tonga, officially the Kingdom of Tonga, is an island country in Polynesia, part of Oceania. The country has 171 islands, of which 45 are inhabited. Its total surface area is about , scattered over in the southern Pacific Ocean. accordin ...

. It rises to a depth of about and is capped off by a wide summit platform. It appears to be a submerged volcano of

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

age that may be part of a volcanic chain with

Niue Niue is a self-governing island country in free association with New Zealand. It is situated in the South Pacific Ocean and is part of Polynesia, and predominantly inhabited by Polynesians. One of the world's largest coral islands, Niue is c ...

. Capricorn Seamount is located on the eastern flank of the

Tonga Trench The Tonga Trench is an oceanic trench located in the southwestern Pacific Ocean. It is the deepest trench in the Southern hemisphere and the second deepest on Earth after the Mariana Trench. The fastest plate-tectonic velocity on Earth is occurri ...

and is in the process of breaking up; in turn the trench has been altered by the interaction with the downgoing seamount.

Geography, research history and name

The Capricorn Seamount lies east of Vava'u Island in

and inside of Tonga's

exclusive economic zone An exclusive economic zone (EEZ), as prescribed by the 1982 United Nations Convention on the Law of the Sea, is an area of the sea in which a sovereign state has exclusive rights regarding the exploration and use of marine natural resource, reso ...

. First examined by the during the Capricorn Expedition of the

Scripps Institution of Oceanography Scripps Institution of Oceanography (SIO) is the center for oceanography and Earth science at the University of California, San Diego. Its main campus is located in La Jolla, with additional facilities in Point Loma. Founded in 1903 and incorpo ...

, it was successfully

dredged Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing dams ...

in 1958 by the during the Pacific Cruise of the New Zealand Oceanographic Institute. It is also known as Capricorn guyot, Gora Kaprikorn and Capricorn tablemount.

Geomorphology and geology

The large

guyot In marine geology, a guyot (), also called a tablemount, is an isolated underwater volcanic mountain (seamount) with a flat top more than below the surface of the sea. The diameters of these flat summits can exceed . Guyots are most commonly fo ...

rises over from the eastern flank of the

to a depth of . It features a wide flat top at depth, which tilts gently westwards. A north-northeast trending scarp separates the flat top from another, shallower flat-topped knoll on the eastern side of the flat top which also tilts westwards; the shallowest point of the seamount lies on this knoll. Additional volcanic cones dot the slopes of Capricorn Seamount. At its foot the seamount is wide. The crust underneath the seamount is 75-95 million years old and is thickened, perhaps by the seamount's

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s. A cap of

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

s lies on Capricorn Seamount; its thickness is unknown.

Dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing d ...

has yielded pelagic ooze containing abyssal

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% ...

breccia Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

, dark

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

, dead

coral Corals are colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

fecal pellet Feces (also known as faeces or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relatively small amount of ...

s, fossils of

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

s and pteropods,

s with brown

manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cel ...

encrustations,

otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...

s and sand. The foraminifera are of recent to

Plio-Pleistocene The Plio-Pleistocene is an informally described geological pseudo-period, which begins about 5 million years ago (Mya) and, drawing forward, combines the time ranges of the formally defined Pliocene and Pleistocene epochs—marking from about 5&n ...

age and the limestones formed in shallow water.

Fisheries

Albacore The albacore (''Thunnus alalunga''), known also as the longfin tuna, is a species of tuna of the order Scombriformes. It is found in temperate and tropical waters across the globe in the epipelagic and mesopelagic zones. There are six distinct ...

bigeye The Priacanthidae, the bigeyes, are a family of 18 species of marine ray-finned fishes. " Catalufa" is an alternate common name for some members of the Priacanthidae. The etymology of the scientific name (, to bite + , thorn) refers to the fam ...

and yellowfin aggregate at the seamount, and

fishing Fishing is the activity of trying to catch fish. Fish are often caught as wildlife from the natural environment (Freshwater ecosystem, freshwater or Marine ecosystem, marine), but may also be caught from Fish stocking, stocked Body of water, ...

catch rates are much higher than in the open ocean. The seamount has been used for fishing for a long time.

Origin, geologic history and present-day interaction with the Tonga Trench

Capricorn Seamount likely formed in the

(23-5 million years ago) as a volcano, perhaps part of a hotspot track which also includes

. The volcano was later eroded until it received a flat summit surface, and eventually submerged. It is unclear whether it ever featured

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in group ...

s as no evidence of such growth has been found although foraminifera data point to their past existence. The seamount is about to enter the Tonga Trench and is breaking up in the process. It appears that the collision of the seamount with the trench has caused the formation of a fault linked to the "Fonualei discontinuity". The tilting of the summit platform was the first evidence of the existence of

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

processes. In about 500,000 years the top of the seamount will end up at the bottom of the trench. Capricorn Seamount is not the first seamount there to be subducted into the Tonga Trench, and previous subduction events may have deformed the trench. An

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

() occurred in 1919 at the trench next to Capricorn Seamount and caused a

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

; it might also have induced a submarine

landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

on the seamount.

Earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

s occur underneath Capricorn Seamount where

normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

s are apparent in the seafloor.

References

Sources

* * * * * * {{refend Miocene volcanoes Seamounts of the Pacific Ocean Geography of Tonga