Crough Seamount

The region lies between and around the islands of Pitcairn and Easter Island.[4] There, the East Pacific Rise is interrupted by a trapezoid microplate known as the Easter Microplate[5] about 400 kilometres (250 mi) wide. Seafloor spreading occurs at a rate of about 16 centimetres per year (6.3 in/year).[4]

There is a topographic swell that connects the two islands and continues eastward towards Sala y Gomez. The origin of this swell and the various volcanoes and seamounts associated with it has been variously explained as either being due to a mantle plume which forms volcanoes that are then carried away through plate motion or by a "hot line" where a number of simultaneously active volcanic centres develop.[4] This geological lineament may extend all the way to Tonga.[6]

Crough seamount was probably formed by the Easter hotspot that also generated Easter Island[7] albeit with the participation of a nearby fracture zone[8] that modified the trend of the hotspot path.[9] In this case the Easter Island-Sala y Gomez ridge and the Crough Seamount would be conjugate volcanic ridges paired across the East Pacific Rise.[10] although it is possible that two separate hotspots were active on the eastern and western side of the East Pacific Rise.[11][12] Another theory postulates that Crough was formed by its own hotspot, the Crough hotspot.[13]

Together with Ducie and Henderson Crough forms a 1,300 kilometres (810 mi) long westward trending lineament[14] with each volcano becoming older the farther west it lies,[15] and which may be a prolongation of the southern Tuamotus[16] which were generated by the same hotspot.[10] Even farther west the hotspot track may include Oeno, Minerve Reef, Marutea, Acton, Rangiroa and the Line Islands, although a continuation through the Line Islands is problematic if it is assumed that the Easter hotspot generated this track[13] but more plausible if Crough seamount is supposed to be its own hotspot.[17] East of Crough, a series of even younger volcanic ridges continues until the East Pacific Rise[18] where the hotspot may be located.[13] The Crough hotspot may be a conjugate of the Easter hotspot.[19]

Crough is an east-west trending seamount[5] which rises over 2 kilometres (1.2 mi) from the seafloor to a depth of less than 722 metres (2,369 ft)[20] at 650 metres (2,130 ft).[21] It has a flat top and the presence of coral sands indicates that Crough once emerged above sea level before subsiding to its present depth,[20] having formerly hosted corals[22] and pteropods. Wave erosion that took place when Crough emerged above sea level truncated the seamount, turning it into a flat guyot.[23] Pillow lavas crop out between 1,400–950 metres (4,590–3,120 ft).[24] Crough Seamount has a volume of 660 cubic kilometres (160 cu mi), comparable to that of other submarine volcanoes such as Macdonald seamount, Mehetia and Moua Pihaa.[21]

A second seamount lies nearby and partly overlaps with Crough,[1] it is named Thomas Seamount[25] in honour of a geophysicist.[26] This seamount is even shallower than Crough as it reaches a depth of 600 metres (2,000 ft) but has a smaller volume of 600 cubic kilometres (140 cu mi).[21]