Cape Johnson Guyot is also known as Cape Johnson Seamount or Cape Johnson Tablemount. The guyot was named by Harry Hammond Hess, after his ship the USS Cape Johnson; Hess had also named the kind of flat-topped seamount "guyot" and another seamount was named after Hess himself. The seamount was first described in a 1946 publication. Both Hess and Cape Johnson were discovered during the same cruise and Cape Johnson Guyot is the type locality of guyots.
Geography and geology
The seamount lies in the Mid-Pacific Mountains on their southern side and is a submarine mountain with a flat top that rises over 3,000 metres (10,000 ft) to a depth of 1,692 metres (5,551 ft)-1,778 metres (5,833 ft). The flat top has an oval shape and a surface area of 6 by 12 nautical miles (11 km × 22 km; 6.9 mi × 13.8 mi); it is characterized by a limestone dome on the summit, buried beneath sediments; in turn a volcanic hill is buried within the limestone dome. The top of the seamount has a hummocky appearance which has been interpreted as a sediment cover and its southeastern sector has a bank-like shape that resembles that of an atoll. Cape Johnson Guyot is considered to be of Middle Cretaceous age with an age of 120 million years reported and shallow-water fossils were emplaced on it at that time.
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The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.The tectonic plates continue to move today. The slowest spreading ridge is the Gakkel Ridge on the Arctic Ocean floor, which spreads at less than 2.5 cm/year (1 in/year), while the fastest, the East Pacific Rise near Easter Island, has a spreading rate of over 15 cm/year (6 in/year).
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