Erimo Seamount

Erimo Seamount lies southeast of Cape Erimo of Hokkaido, Japan. The seamount lies close to the intersection between the Kuril–Kamchatka Trench to the northeast and the Japan Trench to the south.[2][1] Erimo Seamount lies 15 kilometres (9.3 mi) oceanward[4] and south and east from the trenches[5] and it forms the northern tip of the Japan Trench; there the Pacific Plate subducts at a rate of 8 centimetres per year (3.1 in/year), together with the seamounts on it[6] such as Erimo which is currently entering the trench.[7] Other seamounts in the area are Takuyo-Daiichi to the east-northeast and Ryofu-Daini to the east-southeast,[1] and there is evidence of another seamount northwest of Erimo and in the process of being subducted.[8] Possibly, as such a seamount or a seamount chain subducted it indented the trenches, forming a 20 kilometres (12 mi) re-entrant.[9]

The seamount is a guyot[10] which rises about 4.2 kilometres (2.6 mi) to a depth of 3,700 metres (12,100 ft)[6]-3,800 metres (12,500 ft), where a flat top is covered by early Cretaceous limestone[11] that contains gastropods,[12] green algae and red algae from that time.[13] Erimo Seamount is cut by normal faults that run parallel to the Kuril-Kamchatka Trench,[7] and the seamount is tilting[14] and beginning to break apart as its subduction starts.[15] It has a volume of about 1,100 cubic kilometres (260 cu mi), making it a mid-sized seamount by Pacific Ocean seamount standards, with an northeast-southwest elongated shape and a maximum width of 35 kilometres (22 mi)[11] and recognizable rift zones.[10] The crust underneath Erimo contains the magnetic anomaly M8[5] and has an age of about 120 million years.[11]

Volcanic rocks dredged from Erimo Seamount include alkali basalt,[16] brecciated basalts, silty sandstone,[17] trachyandesites or trachytes.[18] During the Cretaceous, carbonate rocks were emplaced at shallow depth on the seamount, which subsided by about 3 kilometres (1.9 mi). As the seamount has entered the trench, further subsidence of about 800 metres (2,600 ft) has taken place.[19]