Adams Seamount (also known as Forty Mile Reef ^[2]) is a submarine volcano above the Pitcairn hotspot in the central Pacific Ocean about 100 kilometres (62 mi) southwest of Pitcairn Island.

Geography and geomorphology

Adams is part of a field of about 90 seamounts 90 kilometres (56 mi) east-southeast away from Pitcairn Island, and the largest of these. ^[3] Adams lies southeast of another large seamount, Bounty Seamount. ^[4] Most of these seamounts except for Adams and Bounty are less than 0.5 kilometres (0.31 mi) high. ^[5] They were discovered in 1989 by the RV Sonne research ship. ^[6]

It is a conical ^[7] seamount rising 3,500 metres (11,483 ft) from the sea floor to about 39 metres (128 ft) ^[1] or 59–75 metres (194–246 ft) below the surface of the ocean. ^[2] The total volume of the seamount, whose base has a diameter of about 30 kilometres (19 mi), is about 858 cubic kilometres (206 cu mi). ^[8] Adams has two summits, ^[9] and coral and sand derived from coral has been found on Adams. ^[5] Given its height, during the last glacial maximum Adams was likely an island. ^[10]

Its slopes are covered by recent lava flows, volcanic debris and hyaloclastite. ^[9] Lava flows feature aa lava characteristics and lava tubes, while deeper parts of the edifice are covered with lapilli and scoria. ^[11] Parasitic vents form cones and mounds on its flanks. ^[12]

Geology

Adams and the other seamounts were created by the Pitcairn hotspot, and these seamounts are its present-day location. ^[3] This hotspot is one among several hotspots in the Pacific Ocean, along with the Austral hotspot, Hawaii hotspot, Louisville hotspot, Samoa hotspot and Society hotspot. ^[6] The seamounts rise from a 30 million years old crust. ^[13]

Alkali basalt, trachyte ^[9] and tholeiite have been dredged from Adams Seamount. ^[14]

Eruption history

The fresh appearance of samples and the lack of sedimentation indicates that Adams Seamount is a recently active seamount. ^[3] Potassium-argon dating of rocks dredged from Adams Seamount has yielded Holocene ages, including one age of 3,000 ± 1,000 years before present. ^[13] Other ages range from 4,000 - 7,000 years before present. ^[15] Unlike Bounty, Adams Seamount displays no active hydrothermal system. ^[5]

Biology

Adams seamount features a coral reef, one of the deepest tropical reefs in the world. It is mainly formed by Pocillopora sp. and Porites deformis corals, but also many reef fish and sharks; it is used as a fishing ground by Pitcairn. ^[2] Adams seamount is part of the Pitcairn Islands Marine Reserve. ^[16]

References

Sources