|Height||149 m (489 feet)|
|Last eruption||March 2009|
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 km (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.
Volcano and caldera
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 km (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 m (489 feet), while Hunga Haʻapai comes to only 128 m (420 feet) above sea level. Neither island is large: Hunga Tonga is roughly 39 hectares (0.15 square miles) and Hunga Haʻapai is 65 hectares (0.25 square miles) 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 km (2.0 mi) southeast of Hunga Haʻapai and 3 km (1.9 mi) south of Hunga Tonga were reported in 1912 and 1937. Another eruption occurred from a fissure 1 km (0.62 mi) south-southeast of Hunga Haʻapai in 1988.
The islands figure in Tongan mythology as one of the few islands which were not overfished, and hence thrown down from heaven to land on earth. Tongans called them the islands which "jump back and forth" (i.e. suffer earthquakes). The first Europeans to see the islands were those with the Dutch explorers Willem Schouten and Jacob Le Maire in 1616, although the British explorer Captain James Cook visited them several times in 1777 and learned their Tongan names.
On March 16, 2009, a submarine eruption near Hunga Tonga-Hunga Haʻapai began spewing steam, smoke, pumice, and ash thousands of feet into the sky above the ocean. By March 21, Tonga's chief geologist, Kelepi Mafi reported, lava and ash from two vents, one on the uninhabited island Hunga Haʻapai and another about 100 metres (330 feet) offshore, had filled the gap between the two vents, creating new land surface that measured hundreds of square metres. The eruption devastated Hunga Haʻapai, covering it in black ash and stripping it of vegetation and fauna.
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- The island arc is formed at the convergent boundary where the Pacific Plate subducts under the Indo-Australian Plate.
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- Dahl, Arthur L. Review of the Protected Areas System in Oceania. IUCN Commission on National Parks and Protected Areas. United Nations Environment Programme, 1986. ISBN 2-88032-509-9
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- Gifford, Edward Winslow. Tongan Myths and Tales. London: The British Museum, 1924.
- Nunn, Patrick D. "Fished Up or Thrown Down: The Geography of Pacific Island Origin Myths." Annals of the Association of American Geographers. 93:2 (November 2004).
- Suren, Peter. Essays on the History of the Discovery and Exploration of Tonga by the Europeans. Nukuʼalofa, Kingdom of Tonga: Friendly Islands Bookshop, 2001; Rutherford, Noel. Friendly Islands: A History of Tonga. Cambridge: Oxford University Press, 1977. ISBN 0-19-550519-0; Cook, James. The Journals of Captain Cook. John Cawte Beaglehole and Philip Edwards. New York: Penguin Classics, 1999. ISBN 0-14-043647-2
- "Tongan Inspectors Head to Undersea Volcano." Associated Press. March 19, 2009.
- The date the eruption began is uncertain. According to the Smithsonian Institution's Global Volcanism program, "Observers flying near the area of Hunga Tonga-Hunga Ha'apai (about 62 km NNW of Nuku'alofa, the capital of Tonga) on 16 or 17 March reported seeing an eruption." See: SI/USGS Weekly Volcanic Activity Report. 11 March-17 March 2009. The report cites Keizo Gates' Web log, dated March 16, 2009, which contains photos allegedly taken from civilian aircraft late on the afternoon of March 16. See: Gates, Keizo. "New Tonga Eruption" Kzo.net. March 16, 2009. The Smithsonian subsequently confirmed that the eruption began on March 16. See: SI/USGS Weekly Volcanic Activity Report. 18 March-24 March 2009.
- Percival, Jenny. "Underwater Volcano Creates New Island Off Tonga." The Guardian. 21 March 2009.
- "'No Living Thing Left' As Tonga Volcano Erupts." Agence France Presse. March 20, 2009.
- "Entertainment," Cape Argus, November 20, 2009.
- "Underwater Volcano Erupts Off Tonga." BBC News. March 19, 2009. - Video showing the March 18, 2009, eruption
- "Expedition To A New Island" - Explorer George Kourounis sets foot on a brand new volcanic island