An unusually shaped scientific research ship, Joides Resolution, is docked at Auckland's Freyberg Wharf this weekend between expeditions – the first time it has visited the city for seven years.

The 140m-long ship has just returned from placing two seafloor observatories into the Hikurangi Fault east of Gisborne to collect new information on this huge undersea structure - our largest geological threat.

A distinctive feature of the ship is a drilling derrick rising 60m above the water line.

It is used to take core samples of sediment and rock from under the seabed for scientists to analyse.

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The ship will leave port on Wednesday on a world-first mission to sink probes into the heart of the active undersea Brothers Volcano northeast of White Island.

The aim is to study the specially adapted life forms that live in these extreme environments and learn more about the inner plumbing of the volcano.

The ship is operated by the 23-nation International Ocean Discovery Program of which New Zealand is a member.

It has been in New Zealand waters since July 2017 undertaking six back-to-back voyages of discovery.

IODP is an international research collaboration that runs seagoing expeditions to study Earth's history and dynamics as recorded in sediments and rocks beneath the ocean floor.

New Zealand participates in IODP through a consortium of research organisations and universities in Australia and New Zealand, including GNS Science, Niwa, the University of Auckland, Victoria University of Wellington, and University of Otago.