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 diverge ...

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 continen ...

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 Kermadec or de Kermadec may refer to: Geography * Kermadec Islands, a subtropical island arc in the South Pacific Ocean northeast of New Zealand * Kermadec Plate, a long narrow tectonic plate located west of the Kermadec Trench * Kermadec Trench, ...

island arc. 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, the ...

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 ridges ...

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 smaller islands. It is the sixth-largest island count ...

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-largest ...

. 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 Iza ...

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 of ...

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 The Havre Trough (Havre Basin) is a currently actively rifting back-arc basin about to wide, between the Australian Plate and Kermadec microplate. The trough extends northward from New Zealand's offshore Taupō Volcanic Zone commencing at Zea ...

, 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

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 mantle plumes both contribute to the lavas of two of the northern Tonga islands, Tafahi and Niuatoputapu; ocean island basalt (OIB) from the Samoa plume were introduced from 3–4 Ma when subduction in the Vitiaz Trench (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 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 (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