Capricorn Seamount is a
seamount in
Tonga. It rises 4 kilometres (2.5 mi) to a depth of about 360 m (1,180 ft) and is capped off by a 15 km (9.3 mi) wide summit platform. It appears to be a submerged volcano of
Miocene age that may be part of a volcanic chain with
Niue. Capricorn Seamount is located on the eastern flank of the
Tonga Trench and is in the process of breaking up; in turn the trench has been altered by the interaction with the downgoing seamount.
The large[6]guyot rises over 4 kilometres (2.5 mi)[7] from the eastern flank of the
Tonga Trench[2] to a depth of 360 metres (1,180 ft).[1] It features a 15 kilometres (9.3 mi) wide[7] flat top at 800–1,000 metres (2,600–3,300 ft) depth, which tilts gently westwards. A north-northeast trending
scarp separates the flat top from another, shallower flat-topped knoll on the eastern side of the flat top which also tilts westwards;[4] the shallowest point of the seamount lies on this knoll.[8] Additional volcanic cones dot the slopes of Capricorn Seamount.[9] At its foot the seamount is 100 kilometres (62 mi) wide.[10] The
crust underneath the seamount is 75-95 million years old[11] and is thickened, perhaps by the seamount's
lava flows.[12]
Albacore,
bigeye and
yellowfin aggregate at the seamount, and
fishing catch rates are much higher than in the open ocean.[17] The seamount has been used for fishing for a long time.[3]
Origin, geologic history and present-day interaction with the Tonga Trench
Capricorn Seamount likely formed in the
Miocene (23-5 million years ago[11]) as a volcano, perhaps part of a
hotspot track which also includes
Niue.[7] The volcano was later eroded until it received a flat summit surface, and eventually submerged.[18] It is unclear whether it ever featured
coral reefs as no evidence of such growth has been found[19] although foraminifera data point to their past existence.[20]
The seamount is about to enter the Tonga Trench[21] and is breaking up in the process.[22] It appears that the collision of the seamount with the trench has caused the formation of a
fault linked to the "Fonualei discontinuity".[23] The tilting of the summit platform was the first evidence of the existence of
subduction processes.[24] In about 500,000 years the top of the seamount will end up at the bottom of the trench.[25] Capricorn Seamount is not the first seamount there to be subducted into the Tonga Trench, and previous subduction events may have deformed the trench.[26] An
earthquake (Mw 8.0) occurred in 1919 at the trench next to Capricorn Seamount[27] and caused a
tsunami; it might also have induced a submarine
landslide on the seamount.[28]Earthquakes occur underneath Capricorn Seamount where
normal faults are apparent in the seafloor.[29]
^
abArredondo, Katrina M.; Billen, Magali I. (1 April 2012). "Rapid weakening of subducting plates from trench-parallel estimates of flexural rigidity". Physics of the Earth and Planetary Interiors. 196–197: 3.
Bibcode:
2012PEPI..196....1A.
doi:
10.1016/j.pepi.2012.02.007.
ISSN0031-9201.
^Wright, Dawn J. (2000). "Bathymetry of the Tonga Trench and Forearc: a map series". Marine Geophysical Researches. 21 (5): 502.
doi:
10.1023/A:1026514914220.
S2CID6072675.
^Fisher, Robert L. (1974), "Pacific-Type Continental Margins", in Burk, Creighton A.; Drake, Charles L. (eds.), The Geology of Continental Margins, Springer, p. 26,
doi:
10.1007/978-3-662-01141-6_3,
ISBN978-3-662-01141-6
^Morton, AE (2003). Evidence for large tsunami in the Tongan Islands. Geological Society of America Abstracts with Programs.
^White, R. B.; Wiens, D. A. (December 2002). "Outer Rise Seismicity and Dynamics: Implications for Plate Rheology and Seamount Loading at the Tonga Subduction Zone". AGUFM. 2002: T52B–1201.
Bibcode:
2002AGUFM.T52B1201W.
Lonsdale, Peter (December 1986). "A multibeam reconnaissance of the Tonga Trench axis and its intersection with the Louisville guyot chain". Marine Geophysical Researches. 8 (4): 295–327.
Bibcode:
1986MarGR...8..295L.
doi:
10.1007/BF02084016.
S2CID129800530.