Gaper – perfect title for this cartoon-like Seamount creature
Image credit – National Geographic Magazine

Seamounts are underwater volcanoes that haven’t broken the surface of the ocean. When they do, they are islands.

In July, an eruption in the Kermadec Seamount range, northeast of New Zealand, threw thousands upon thousands of pumice pieces up to the sea-surface.

In early August a huge mass of ‘brilliant white’ was spotted from the air. An incredible sight, this ‘pumice raft‘ covered near 26,000 square kilometres.

Photo-gallery: Here is a link to an absolutely stunning photo-gallery of the life that exists on our Seamounts. The National Geographic website is a wonderful source of images and information on people and nature. Check out the seamount pages: Seamounts – Life on a Mount – Pictures, More From National Geographic Magazine.

The Kermadec Island chain extends for 240 kilometres, with the east-lying Kermadec Trench reaching 10,000 metres depth. To the west is the Havre Trough, 3,000 metres below sea-level. The Seamount chain is seen extending to the bottom-right of the image.

Marine Conservation: The Kermadec Islands Marine Reserve was declared in 1990 and is administered by New Zealand’s Department of Conservation.

The idea of a no-take Marine Reserve is to allow an area of coastal sea to return to as close to its natural state as possible, by protecting species and habitats (see Enderby, 2006).

Collectively, New Zealand’s 34 Marine Reserves protect 7 per cent of its territorial sea, as far south as the Sub-antarctic Auckland Islands, with the isolated island area of the Kermadecs, the most northern.

Ten reserves are now vested in Fiordland (eight were added in 2005), but almost 99 per cent of marine reserve area is located around the sub-tropical island areas of Auckland and the Kermadecs. New Zealand’s first no-take Marine Reserve was established in 1975 at Auckland’s Cape Rodney – Okakari Point (or Goat Island), one of the world’s first. Check out DOC’s website for more on marine conservation and to view a map of marine conservation areas.

Kermadec ecology: The Kermadec Islands lie 1000 kilometres from New Zealand, inside our Exclusive Economic Zone, and are home to a mix of tropical and temperate marine creatures. The spotted black grouper (a hefty sea bass), while scarce everywhere else, thrives in this nutrient-rich environment. Bottle-nose dolphins are common, and several species of marine turtle come ashore to lay eggs at Raoul, the largest of the islands.

With goats, rats and cats eradicated from the islands, birdlife is now prolific, especially on Macauley Island, which supports the only breeding population of black-capped petrels. In 2008, two years after the islands achieved predator-free status, the Kermadec Red-crowned Parakeet returned to breed in its island home, for the first time in 172 years. Fairy terns, grey ternlets and shearwater populations thrive in their island isolation.

New Zealand lies at the edge of both the Australian and Pacific tectonic plates. To New Zealand’s northeast, and under the North Island, the Pacific Plate is moving towards, and being subducted under the Australian Plate. Credit: Otago University Geology Department, NZ

Geology: Earthquakes are pretty much a daily event in the Kermadecs , as the Pacific and Australian plates slide and buckle against each other. Volcanic eruptions are not quite so common. A smallish eruption was recorded in 2004. Rafts of pumice floated just offshore, and washed up on the beaches for weeks. Note that visits to the islands are restricted by the Department of Conservation.

Seamounts are closely associated with the formation of hydrothermal vents. Studies along the Kermadec Arc have revealed many of these hotwater springs in the ocean floor.

Hydrothermal vent

A hydrothermal plume forms when warm fluids emerge from vents on the seafloor and mix with the surrounding cold seawater. Hydrothermal vents and plumes are of interest to the mining industry, as they are rich in metals like barium, lead, zinc, copper, and the (agriculturally significant) mineral phosphorous.

Chimney structures vary. Black smokers emit dark particles with high levels of sulphur-bearing minerals (sulfides). Dissolved minerals solidify due to the temperature changes between vent fluids and the surrounding seawater, with the resulting tiny metal-rich particles forming ‘smoke’. Vent fluids can reach 350°C, while the surrounding seawater is at 2°C. White smokers emit lighter-coloured minerals like barium, calcium and silicon and tend to have lower temperature plumes.

Coral in the Kermadecs – Image Tom Hitchon: thekermadecs.org/corals-bryozoans

Research: Since 1977, researchers have been studying these deep-sea vents and their unusual chemistry, with the Kermedec region providing outstanding evidence of key stages in the Earth’s geological evolution. New populations of organisms are being discovered all the time, many of them uniquely adapted to the depth, geochemistry and flow of the venting fluids. We are still uncovering the secrets of these mineral-rich ecological powerhouses.

Thanks to GNS Science NZ and The Kermadecs.org for information on hydrothermal vents.

Radio NZ National interview on podcast (19 Nov 2012) with Auckland University’s Mark Costello: Mark is co-leader of a comprehensive marine species stocktake to seek out and catalogue the diverse marine life of the world’s oceans. You can find details at http://www.radionz.co.nz/national/programmes/ninetonoon or go direct to selected images gallery: global marine species diversity. The World Register of Marine Species (WoRMS) has a fascinating website, with an extensive photogallery. 

Smithsonian Seamount Exhibit: From the Smithsonian Institute comes this video, with astonishing footage of the unique organisms found around hydrothermal vents and a clear explanation of the related process of chemosynthesis that is now strongly believed to be associated with the origins of life on earth.

The Havre eruption in July 2012 dispersed clusters of floating pumice across 26,000 square kilometres. The blue area is coloured by volcanic ash. Image credit – NASA satellite picture posted on Wired.com by Erik Klemetti, assistant professor of Geosciences at Denison University.

Related articles

• Wake up call – Kermadec Marine Reserve the focus of Wellington exhibition (stuff.co.nz)
• Submarine Eruption Makes It Three for New Zealand (wired.com)
• Latest NZ eruption caught on satellite (stuff.co.nz)