The Stokes Magnetic Anomaly (also known as the Stokes Magnetic Anomaly System, SMAS, New Zealand Junction Magnetic Anomaly, JMA, great Nelson magnetic disturbance, Junction Anomaly, Campbell Magnetic Anomaly System, CMAS) is a

magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

on the Earth's surface that extends from

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

to the Chatham Rise with complexity consistent with the theory of

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

History

It is named after Captain (later Admiral) John Lort Stokes by G. C. Farr in 1916 as he described it first although such naming has proved controversial, hence many of the alternative names. The magnetic declinations were observed by Captain Stokes when captaining

HMS Acheron Eight vessels of the Royal Navy have been named HMS ''Acheron'' after Acheron, a river of Hades in Greek mythology. * was an 8-gun bomb vessel purchased in 1803 and captured and burnt by the French frigates and near Gibraltar on 4 February 18 ...

and Commander (later Admiral)

Byron Drury Admiral Byron Drury (1815–1888) was a British naval officer. Biography Drury was born in Harrow on the Hill, the son of Rev. Henry Drury, of Harrow School; at which place he, and his father, Dr. Drury, were masters for about 70 years. Byron ...

HMS Pandora Ten ships of the Royal Navy have been named HMS ''Pandora'' after the mythological Pandora. Another was planned, but the name was reassigned to another ship: * , a 24-gun sixth rate launched in 1779. She was sent to capture the ''Bounty'' mut ...

between 1851 and 1853.

Geology

The Stokes Magnetic Anomaly has been characterised for over and was essential for understanding the geology of Zealandia as a mainly underwater continent. It extends from south of

to almost the eastern edge of the Campbell Plateau. Over much of its length it has peaks about to apart, although this is not the case for much of its New Zealand west coast course. Where the anomaly crosses

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

it is displaced by approximately right angle changes in direction for a total of running down the western side of New Zealand from the

Northland Peninsula The Northland Peninsula, called the North Auckland Peninsula in earlier times, is in the far north of the North Island of New Zealand. It is joined to the rest of the island by the Auckland isthmus, a narrow piece of land between the Waitematā H ...

in the

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-largest ...

to Fiordland but then exiting New Zealand's

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

on its

Otago Otago (, ; mi, Ōtākou ) is a region of New Zealand located in the southern half of the South Island administered by the Otago Regional Council. It has an area of approximately , making it the country's second largest local government reg ...

east coast. The Stokes Magnetic Anomaly has been related to magnetic anomaly extending in

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

as the east Lachlan Fold Belt or New England Fold Belt as an extension of where it commences near the western

Challenger Plateau The Challenger Plateau is a large submarine plateau west of New Zealand and south of the Lord Howe Rise. It has an approximate diameter of and an area of about . The water depth over the plateau varies between to and is covered by up to of se ...

and

Lord Howe Rise The Lord Howe Rise is a deep sea plateau which extends from south west of New Caledonia to the Challenger Plateau, west of New Zealand in the south west of the Pacific Ocean. To its west is the Tasman Basin and to the east is the New Caledonia ...

. This gives an age of up to 83 million years before present in its formation but alternatively, it may be extended to represent the earliest ocean crust formed between New Zealand and

Marie Byrd Land Marie Byrd Land (MBL) is an unclaimed region of Antarctica. With an area of , it is the largest unclaimed territory on Earth. It was named after the wife of American naval officer Richard E. Byrd, who explored the region in the early 20th centur ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

so could be even older.

References

External links

* * * {{cite web, url=http://wdmam.org/download.php#downloadmap , title=World Digital Magnetic Anomaly Map version 2.0, access-date=2022-09-05 Magnetic anomalies Geomagnetism Zealandia Continental fragments Continents Geology of New Zealand Geography of New Caledonia Geography of Oceania Geography of the New Zealand seabed