Together with these seafloor structures the ridge forms the eastward-migrating, 100  million year old Lau–Tonga–Havre–Kermadec arc/back-arc system or complex.

[2] The extension in the Lau–Havre basin results in a higher rate of subduction than convergence along the Australian–Pacific plate boundary.

[3] 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.

[4] 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 initial Hikurangi-Kermadec collision, however, occurred 250 km (160 mi) to the north where a missing piece of the Ontong Java-Hikurangi-Manihiki LIP has already been subducted.