Tonga-Kermadec Ridge
The Tonga-Kermadec Ridge is an oceanic ridge in the south-west Pacific Ocean underlying the Tonga-Kermadec island arc.
It is the most linear, fastest converging, and most seismically active subduction boundary on Earth, and consequently has the highest density of submarine volcanoes.

The Tonga-Kermadec Ridge stretches more than north-northeast from New Zealand's North Island. The Pacific Plate subducts westward beneath the Australian Plate along the ridge. It is divided into two segments, the northern Tonga Ridge and southern Kermadec Ridge, by the Louisville Seamount Chain. On its western side, the ridge is flanked by two back-arc basins, the Lau Basin 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, Tonga, and Kermadec microplates.

The Samoa 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 plateaux, north and south of the Tonga-Kermadec Ridge respectively, form part of the Ontong Java-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.
Q104698
oceanic ridge
Concept
Q98
Pacific Ocean
LOC
Q678
Tonga
LOC
Q114935
Kermadec
LOC
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island arc
Concept
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subduction
Concept
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submarine volcano
Concept
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New Zealand
LOC
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North Island
LOC
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Pacific Plate
LOC
Q176318
subducts
Concept
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Australian Plate
LOC
Q2961843
Louisville Seamount Chain
Concept
Q798367
back-arc basin
Concept
Q6497594
Lau Basin
LOC
Q119294
Havre Trough
LOC
Q1200973
Niuafo'ou
LOC
Q1200519
Tonga
LOC
Q1345056
Kermadec
LOC
Q7409927
Samoa
Concept
Q6689569
Louisville
Concept
Q878045
mantle plume
Concept
Q283712
Tafahi
LOC
Q1144842
Niuatoputapu
LOC
Q16964299
ocean island basalt
Concept
None
Vitiaz Trench
UNK
Q5760686
Hikurangi
LOC
Q2869720
Manihiki
LOC
Q4364598
Ontong Java
LOC
Q792425
large igneous province
Concept
Q29467203
Tonga-Kermadec Ridge
LOC
Q29467203
Tonga-Kermadec Ridge
LOC
Q29467203
Tonga-Kermadec Ridge
LOC
Q29467203
Tonga-Kermadec Ridge
LOC
Q29467203
Tonga-Kermadec Ridge
LOC
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lowest point
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