<P> The western islands, such as ʻAta (also known as Pylstaart island), Fonuafo'ou, Tofua, Kao, Lata'iki, Late, Fonualei, Toku, Niuatoputapu, and Tafahi, make up the Tongan Volcanic Arch and are all of volcanic origin . They were created from the subduction of the western - moving Pacific plate under the Australia - India plate at the Tonga Trench . The Tongan Islands sit on the Australia - India plate just west of the Tonga Trench . These volcanoes are formed when materials in the descending Pacific plate heat and rise to the surface . There is only limited coral reef development on these islands, except for Niuatoputapu . </P> <P> The eastern islands are nonvolcanic and sit above the mostly submerged Tonga ridge that runs parallel to the Tongan Volcanic Arch and the Tongan Trench . Of these islands, only' Eua has risen high enough to expose its underlying Eocene volcanic bedrock, the rest are either low coral limestone islands (Tongatapu, Vava'u, Lifuka) or sand cay islands (' Uoleva,' Uiha). These islands are surrounded by "a protective and resource - rich labyrinth of fringing, apron and off - shore barrier reefs" that have supported most of the human settlement in Tonga ever since the first Lapita People arrived circa 900 BCE . </P> <P> The Tongan Volcanic Arc has been important in supplying the islands on the Tonga ridge with an andesite tephra soil that has resulted in "an extremely rich soil capable of supporting a high - yield, short - fallow agricultural system ." Also, the andesite / basalt from the volcanoes were initially used as "hammerstones, weaving weights, cooking stones, and decorative pebbles for grave decoration ." Tafahi island in the far north provided volcanic glass to initial human settlers . </P> <P> In December 2014 and January 2015, a volcanic island 1 km wide by 2 km long was created adjacent to the island of Hunga Ha'apai 65 kilometers northwest of Nuku'alofa . The volcanic eruption has built the new island to a height of 100 m composed of ash and large rock fragments . </P>

Pacific islands are formed from coral reefs limestone or