Marine Atlas: Maximizing Benefits for Tonga

SMOKE UNDER WATER, FIRE IN THE SEA: TECTONIC ACTIVITY

Tonga is located on the Pacific Ring of Fire, a highly active tectonic zone. Above water, this tectonic activity means that the people of Tonga are under threat from possible earthquakes and tsunamis. Underwater, the tectonic activity produces magnificent underwater volcanoes and hydrothermal vents that, in turn, spawn unique, complex but fragile ecosystems that contribute to Tonga’s rich marine biodiversity. These features also deposit minerals, making them an attractive, if conflicting, target for deep-sea mining exploration and extraction.

The Tongan islands sit on the Tonga-Kermadec Arc, an arc of volcanic islands that stretches from New Zealand to Tonga. This island arc was formed by the subduction of the Pacific plate, which began around 45 million years ago (Ma) (Neall and Trewick, 2008). The western islands, including ‘Ata, Fonuafo’ou, Tofua, Kao, Lateiki, Late, Fonu- alei, Toku, Niuatoputapu and Tafahi, are volcanic in origin. The eastern islands are non-volcanic and instead low coral limestone islands. In 2015, the eruption of the Hunga Tonga volcano created a new island 45 kilometres north-west of Tonga’s capital, Nuku’alofa. Evidently, the island-building process is an active and ongoing one and plate tectonics are the driving force behind this process. Aside from the shallow-water areas surrounding these islands, the majority of Tonga’s national waters are deeper than 2,000 metres (with a mean depth of around 3,500 metres) and reach depths exceeding 10,800 metres at the deep ocean floor. There are still many mysteries around sea-floor hydrothermal vent systems, with their complicated biological, chemical and geological relationships. Only by exploring, recording and monitoring deep- sea hydrothermal systems is there a chance of protecting them and the benefits they provide. But what are hydrothermal vents exactly? They are fissures in the Earth’s surface from which geother- mally heated water (up to 450°C) escapes. Vents are commonly found in volcanically active areas, such as areas between tectonic plates. Under the sea, hydrothermal vents may develop black or white smokers. These roughly cylindrical chimney structures can reach heights of 60 metres, form- ing from either black or white minerals that are dissolved in the vent fluid.

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In an effort to study a variety of marine or- ganisms that have evolved to live in extreme environments, the Japanese QUELLE2013 project (Quest for the Limit of Life) was the first exploration to be undertaken with a manned research submersible in Tonga’s waters, in January 2013. QUELLE2013 was a global-scale voyage of scientific surveys and research on ecosystems in hydro- thermal vent areas and other unique and extreme environments in the Indian, Atlantic and Pacific Oceans. The main survey area was Horizon Deep in the Tonga Trench—the world’s second deep- est point in the ocean, at 10,850 metres. The objectives of the survey were to: “(i) describe the environmental characteristics of the “hadal zone”, including depths of greater than 10,000 meters, and sample the organisms living in this environment, and (ii) find out exactly what is going on there, unravel the correlation be- tween organisms and their habitats, and learn how the trench environment was created.” have unique biodiversity. Chemosynthetic bacteria and archaea, both single-celled organisms, form the base of a food chain supporting diverse organ- isms, including giant tube worms, clams, limpets and shrimp. Some scientists even suggest that life on Earth may have originated around hydrothermal vents. Along with their unique biodiversity, these vents are also a hotspot of minerals. Massive sulfides (including gold and copper), cobalt and rare earth metals occur in high concentrations in vent systems, which are increasingly being ex-

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plored for their mineral resources (see also chapter “Underwater Wild West”).

As the map shows, Tonga’s waters harbour not only numerous deep-sea hydrothermal vents, but also 18 volcanoes. The majority of these volcanoes are active, including Hunga Tonga-Hunga Ha’apai. In 2015, Hunga Tonga-Hunga Ha’apai erupted, creating a new island measuring 500 metres across and 250 metres high. This was a demon- stration of the dynamic process by which many of Tonga’s islands have been created. The volcanoes run in a chain to the west of the main Tongan is- lands, forming large seamounts rising from the sea floor (see also chapter “Underwater mountains”). The numerous known hydrothermal vents can also be found to the west of the main Tongan islands, where a line of vents runs north to south. Tectonic activity is key to the creation of the Pacif- ic Islands and atolls, many of which sit upon active or inactive volcanoes (see also chapter “Underwa- ter mountains”). But where does all the heat fuelling vents and volcanoes come from? The Pacific region is one of the most tectonically active regions in the world. The Pacific Ring of Fire, which stretches clockwise from New Zealand all the way around to South America, experiences around 90 per cent of the world’s earthquakes. Pacific Island countries such as Tonga are part of the Pacific tectonic plate and are therefore subject to volcanic and seismic activity. Tectonic activity is common around Tonga, with many earthquakes registered in the region, including several of magnitude 7 and above. The earthquakes are concentrated to the west of the Tonga Trench, with a particularly high concen- tration around the islands in the northern Tongan waters. Earthquakes can, under certain circum- stances, generate tsunamis. In 2009, an earth- quake measuring 8.1 occurred along the Kerma- dec-Tonga subduction zone, generating a tsunami that affected Tonga, Samoa and American Samoa. Waves up to 6 metres high struck the northern islands, resulting in extensive damage, injuries and deaths (see also chapters “Still waters run deep” and “Voyage to the bottom of the sea”).

The black and white smokers and their miner- al-rich warm water attract many organisms and

MAXIMIZING BENEFITS FOR TONGA

SUPPORTING VALUES

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