Hunga Ha'apai

Hunga Tonga Hunga Tonga-Hunga Haʻapai
Landsat 8 image of Hunga Tonga-Hunga Haʻapai
Height	149 metres (489 ft)
Location
Coordinates	20°34′S 175°23′W / 20.57°S 175.38°W / -20.57; -175.38 (Hunga Tonga-Hunga Haʻapai)
Country	Tonga
Geology
Type	Submarine volcano
Last eruption	December 2014 to January 2015

Hunga Tonga-Hunga Haʻapai is a volcano located about 30 kilometres (19 miles) south-southeast of Fonuafoʻou (also known as Falcon Island), an island which is part of the nation of Tonga.

The volcano is part of the highly active Tonga-Kermadec Islands volcanic arc, a subduction zone extending from New Zealand north-northeast to Fiji. The volcano lies about 100 kilometres (62 mi) above a very active seismic zone.Magma is formed as two tectonic plates melt together under high heat and pressure, and the superheated rock is forced to the surface. The island arc is formed at the convergent boundary where the Pacific Plate subducts under the Indo-Australian Plate.

The volcano itself is a submarine volcano lying underwater between the two islands, which are the remnants of the western and northern rim of the volcano's caldera. The two islands (part of the Haʻapai group) are about 1.6 kilometres (0.99 mi) apart, and each is about 2 km (1.2 mi) long and composed largely of andesite. Hunga Tonga reaches an elevation of 149 metres (489 ft), while Hunga Haʻapai comes to only 128 metres (420 ft) above sea level. Neither island is large: Hunga Tonga is roughly 390,000 square metres (0.15 sq mi) and Hunga Haʻapai is 650,000 square metres (0.25 sq mi) in size. Neither island is developed due to a lack of an acceptable anchorage, although there are large guano deposits on each island.

Submarine eruptions at a rocky shoal - about 3.2 kilometres (2.0 mi) southeast of Hunga Haʻapai and 3 kilometres (1.9 mi) south of Hunga Tonga - were reported in 1912 and 1937. Another eruption occurred from a fissure 1 kilometre (0.62 mi) south-southeast of Hunga Haʻapai in 1988.