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Scientists study NZ's undersea volcanoes - 03/03/1999

New Zealand and American scientists are to spend the next two weeks exploring 10 submarine volcanoes northeast of White Island.

It will be the first systematic study of all the undersea volcanoes and their hot vents in this region – the most intensive area of submarine volcanism off New Zealand’s coast.

The scientists will use sophisticated equipment deployed from the research ship Tangaroa to "sniff out" hydrothermal plumes or "black smokers". Once located, the plumes will be subjected to intensive scientific analysis.

Hydrothermal plumes are the result of metal-rich, high-temperature fluids that discharge from vents in the seafloor. As they enter the frigid ocean, the metals in solution precipitate out as fine-grained particles, creating an effect like smoke.

Expedition leader, Cornel de Ronde of the Institute of Geological & Nuclear Sciences Limited (GNS), said a potent array of equipment had been assembled, some of which had not been used in this part of the Pacific.

" We expect to gather a huge amount of new information. It should tell us more about the plumbing of submarine volcanoes, the geochemical makeup of New Zealand’s offshore mineral resources, and the flow of elements such as iron and manganese into the southern oceans,’’ Dr de Ronde said.

It is not known how many of the 10 undersea volcanoes are host to black smokers. A joint New Zealand-German research expedition last year on the research ship Sonne took underwater video of some of the volcanoes, and found active black smokers associated with the Brothers Volcano. However, the Sonne did not do any water sampling and stopped only briefly at other volcanoes in the region.

The first area to be studied on this expedition will be off White Island where the Sonne found thermal venting last year. The furthest is Brothers Volcano, about 400km northeast of White Island. In between are nine more volcanoes, which have been mapped but not investigated for signs of seafloor venting.

" This expedition takes us to the next level. We’ll not only map the plumes over a 400km-long area, but we’ll compile detailed records of their chemical and physical characteristics.

" One of the instruments we’ll be using is so sensitive, it can detect parts per million of managanese and iron which are common elements in hydrothermal plumes.’’

The GNS-led expedition has the name New Zealand-American Plume Mapping Expedition (NZAPLUME). Collaborating with GNS are scientists from the Seattle-based National Ocean and Atmospheric Administration (NOAA), and the National Institute of Water and Atmospheric Research (NIWA).

Gary Massoth and Ed Baker of NOAA, who are part of the expedition, are world leaders in mapping and analysing submarine hydrothermal plumes, Dr de Ronde said. Mr Massoth will start working fulltime for GNS after this expedition.

To find the mineral-rich hydrothermal plumes, a metal frame packed with instruments will be lowered from the ship on a long steel cable. The instruments will tell the scientists when a plume is encountered. With the ship stationary, scientists will then analyse the plume by lowering the instruments to within meters of the vent. This will include collecting 20-litre samples of seawater for later analysis.

The plumes do not usually rise more than 400m above their vent source. This means some of the sampling will be done in deep water – about 1800m deep at Brothers Volcano.

Black smokers, which form chimney-like structures on the seafloor, were first discovered in the late 1970s. They are the undersea equivalent of the geothermal and volcanic activity in Rotorua or Taupo.

Their existence in New Zealand waters was suggested in 1996 when a piece of one was dredged to the surface by the Tangaroa.

Before the fluid enters the ocean, it is commonly between 300 and 370 degrees Celsius and under high pressure. Under these conditions it dissolves minerals in the surrounding rocks much like hot tea dissolves sugar.

As it enters the seawater it cools rapidly and the rich mineral cocktail precipitates out forming black clouds containing iron, manganese, zinc, copper and sometimes gold. The fine particles form chimneys that grow like stalagmites on the ocean floor.

There are about 25 places worldwide where black smokers are known to occur. The ones off New Zealand are unusual because of the presence of gold and the shallow depth of the vents. Most other black smokers are on mid-ocean ridges at depths of 2.5km to 3km.

Studying black smokers gives scientists a better understanding of New Zealand’s on-land geothermal fields and volcanoes. It also gives them an insight into New Zealand’s offshore mineral potential.

Black smokers are also an increasing focus because of their possible links to the origins of life on Earth.

" There’s a growing body of scientific opinion that an environment like that associated with seafloor hydrothermal vents would have been an essential ingredient to get living organisms started on Earth,’’ Dr de Ronde said.

" The energy source was hot water rather than sunlight, and there would have been a wealth of minerals for micro-organisms to feed on.’’

 

  • The expedition sets off from Wellington on March 4 and arrives back at Auckland on March 19.

 

Contact: Cornel de Ronde
Minerals Geologist
Institute of Geological & Nuclear Sciences Limited
Ph: 04-570-4637 (reception), 04-570-4633 (direct)

or John Callan
Communications Co-ordinator
Institute of Geological & Nuclear Sciences Limited
Ph: 04-570-1444 (reception), 04-570-4732 (direct)