The Tonga-Kermadec Ridge is an

oceanic ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a di ...

in the south-west

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

underlying the

Tonga Tonga (, ; ), officially the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about , scattered over in ...

- Kermadec

island arc Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alo ...

. It is the most linear, fastest converging, and most seismically active

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

boundary on Earth, and consequently has the highest density of

submarine volcano Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. Many submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridge ...

es. The Tonga-Kermadec Ridge stretches more than north-northeast from

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-larges ...

. The

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and I ...

subducts Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

westward beneath the

Australian Plate The Australian Plate is a major tectonic plate in the eastern and, largely, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to India and Antarctica until approximately when India broke ...

along the ridge. It is divided into two segments, the northern Tonga Ridge and southern Kermadec Ridge, by the

Louisville Seamount Chain The Louisville Ridge, also known as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. As one of the longest seamount chains on Earth it stretches some Vanderkluysen, ...

. On its western side, the ridge is flanked by two

back-arc basin A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most ...

s, the

Lau Basin The Lau Basin is a back-arc basin (also addressed as "interarc basin") at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau-Colville ...

and Havre Trough, that began opening at 6 and 2 Ma respectively. Together with these younger basins the ridge forms the eastward-migrating, 100 Ma-old Lau-Tonga-Havre-Kermadec arc/back-arc system or complex. The extension in the Lau-Havre basin results in a higher rate of subduction than convergence along the Australian-Pacific plate boundary. The rates of extension, subduction, and convergence all increase northwards in this complex, subduction at a rate of and extension at a rate of . As a result, the Tonga-Kermadec Ridge moves independently of both tectonic plates and forms the Tonga-Kermadec Plate, in its turn fragmented into the Niuafo'ou,

, and Kermadec microplates. The

Samoa Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands (Savai'i and Upolu); two smaller, inhabited islands (Manono Island, Manono an ...

and

Louisville Louisville ( , , ) is the largest city in the Commonwealth of Kentucky and the 28th most-populous city in the United States. Louisville is the historical seat and, since 2003, the nominal seat of Jefferson County, on the Indiana border. ...

mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...

s both contribute to the lavas of two of the northern Tonga islands,

Tafahi Tafahi is a small () island in the north of the Tonga archipelago, in fact closer to Savaii (Samoa) than to the main islands of Tonga. It is only north-northeast away from Niuatoputapu, and fishermen commute in small outboard motorboats almost d ...

and

Niuatoputapu Niuatoputapu is a high island in the island nation of Tonga, Pacific Ocean. Its highest point is , and its area is . Its name means ''sacred island''. Older European names for the island are Traitors Island or Keppel Island. Niuatoputapu is ...

;

ocean island basalt Ocean island basalt (OIB) is a volcanic rock, usually basaltic in composition, erupted in oceans away from tectonic plate boundaries. Although ocean island basaltic magma is mainly erupted as basalt lava, the basaltic magma is sometimes modified b ...

(OIB) from the Samoa plume were introduced from 3–4 Ma when subduction in the

Vitiaz Trench Vityaz may refer to: * Bogatyr, a folk or epic hero in Slavic culture Aircraft and spacecraft *Vityaz, the call sign of spacecraft Soyuz TM-14 *Russky Vityaz, an aircraft built by Igor Sikorsky in 1913 Military * , a ''Bogatyr'' class screw corv ...

(north-west of Tonga) ceased. The lavas of the Louisville Seamount Chain were generated 80–90 Ma but began to subduct under the Tonga-Kermadec Ridge at 8 Ma. The

Hikurangi Hikurangi is a settlement in Northland, New Zealand. The city of Whangārei is 17 km (11 miles) to the south, and Kawakawa is 39 km (24 miles) northwest. The Glenbervie Forest is southeast of the settlement. State Highway 1 ...

and

Manihiki 250px, Map of Manihiki Atoll Manihiki is an atoll in the northern group of the Cook Islands known informally as the "Island of Pearls". It is located in the Northern Cook Island chain, approximately north of the capital island of Rarotonga, ma ...

plateaux, north and south of the Tonga-Kermadec Ridge respectively, form part of the

Ontong Java Ontong Java Atoll or Luangiua, (formerly ''Lord Howe Atoll'', not to be confused with Lord Howe Island) is one of the largest atolls on earth. Geographically it belongs to a scattered group of three atolls which includes nearby Nukumanu Atol ...

-Hikurangi-Manihiki

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...

(LIP), the largest volcanic event on Earth during the past 200 million years. The Osbourn Trough, located just north of the Tonga-Kermadec and Louisville intersection, is the palaeo-spreading centre between the Hikurangi and Manihiki plateaux away from which the age of the Pacific Plate increases from 85 Ma to 144 Ma. The subduction of the Hikurangi Plateau beneath New Zealand and the southern part of the Kermadec Arc has resulted in large volumes of lava and a high density of volcanoes in the arc. The initial Hikurangi-Kermadec collision, however, occurred to the north where a missing piece of the Ontong Java-Hikurangi-Manihiki LIP has already been subducted.

References

; Notes ; Sources * * * * * * {{Oceanic features of Zealandia, state=collapsed Underwater ridges of the Pacific Ocean Geography of the New Zealand seabed Subduction zones

See also

References