| Adams Seamount, Forty Mile Reef | |
| Depth: | 39 m (128 ft)[1] |
| Height: | 3,500 m (11,500 ft) |
| Coordinates: | -25.3667°N -145°W |
| Last Eruption: | 50 BCE ± 1000 years |
Adams Seamount (also known as Forty Mile Reef) is a submarine volcano above the Pitcairn hotspot in the central Pacific Ocean about 100km (100miles) southwest of Pitcairn Island.
Adams is part of a field of about 90 seamounts east-southeast away from Pitcairn Island, and the largest of these. Adams lies southeast of another large seamount, Bounty Seamount. Most of these seamounts except for Adams and Bounty are less than high. They were discovered in 1989 by the RV Sonne research ship.
It is a conical seamount rising 3500m (11,500feet) from the sea floor to about 39m (128feet)[1] or 59- below the surface of the ocean. The total volume of the seamount, whose base has a diameter of about, is about . Adams has two summits, and coral and sand derived from coral has been found on Adams. Given its height, during the last glacial maximum Adams was likely an island.[2]
Its slopes are covered by recent lava flows, volcanic debris and hyaloclastite. Lava flows feature aa lava characteristics and lava tubes, while deeper parts of the edifice are covered with lapilli and scoria. Parasitic vents form cones and mounds on its flanks.
Adams and the other seamounts were created by the Pitcairn hotspot, and these seamounts are its present-day location. 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. The seamounts rise from a 30 million years old crust.
Alkali basalt, trachyte and tholeiite have been dredged from Adams Seamount.
The fresh appearance of samples and the lack of sedimentation indicates that Adams Seamount is a recently active seamount. Potassium-argon dating of rocks dredged from Adams Seamount has yielded Holocene ages, including one age of 3,000 ± 1,000 years before present. Other ages range from 4,000 - 7,000 years before present. Unlike Bounty, Adams Seamount displays no active hydrothermal system.
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. Adams seamount is part of the Pitcairn Islands Marine Reserve.