Editing Geography of Tonga (section)

==Geology==
Though administratively divided into the three main island groups of Tongatapu, Ha'apai, and Vava'u (excluding the outlying islands), the Tonga archipelago is actually made of two geologically different parallel chains of islands.

The western islands, such as [[ʻAta]] (also known as Pylstaart island), Fonuafo'ou, [[Tofua]], [[Kao (island)|Kao]], [[Lata'iki]], [[Late (Tonga)|Late]], [[Fonualei]], [[Tokū, Tonga|Toku]], [[Niuatoputapu]], and [[Tafahi]], make up the Tongan Volcanic Arc and are all of volcanic origin.<ref name="burley">David V. Burley, ''Tongan Archaeology and the Tongan Past, 2850-150 B.P'', Journal of World Prehistory, Vol. 12, No. 3 (September 1998)</ref>  They were created from the [[subduction]] of the westwards-moving [[Pacific Plate|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.<ref name="burley"/>

The eastern islands are not volcanic and sit above the mostly submerged Tonga ridge that runs parallel to the Tongan Volcanic Arc 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]], [[ʻUiha|'Uiha]]).<ref name="burley"/>  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.<ref name="burley"/>

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."<ref name="burley"/>  Tafahi island in the far north provided volcanic glass to initial human settlers.<ref name="burley"/>

In December 2014 and January 2015, a volcanic island 1&nbsp;km wide by 2&nbsp;km long was created adjacent to the island of [[Hunga Tonga–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.<ref>{{cite web | url=http://news.discovery.com/earth/weather-extreme-events/tongan-volcano-creates-new-island-150117.htm | title=D news | access-date=January 21, 2015 | archive-date=May 13, 2016 | archive-url=https://web.archive.org/web/20160513201753/http://news.discovery.com/earth/weather-extreme-events/tongan-volcano-creates-new-island-150117.htm | url-status=dead }}</ref> In regards to volcanism, Tonga has moderate volcanic activity. [[Fonualei]] (elev. 180 m) has shown frequent activity in recent years, while [[Niuafo'ou]] (elev. 260 m), which last erupted in 1985, has forced evacuations; other historically active volcanoes include Late and Tofua. Natural hazards include earthquakes and volcanic activity at Fonuafo'ou (Falcon Shoal/Island) and Late'iki ([[Metis Shoal]]/Island).