The Marquesas hotspot is a volcanic hotspot in the central Pacific Ocean. It is responsible for the Marquesas Islands, a group of 12 volcanic islands and one of the five archipelagos of French Polynesia.
Allison Guyot (formerly known as Navoceano Guyot) is a tablemount (guyot) in the underwater Mid-Pacific Mountains of the Pacific Ocean. It is a trapezoidal flat mountain rising 1,500 metres above the seafloor to a depth of less than 1,500 m, with a summit platform 35 by 70 kilometres wide. The Mid-Pacific Mountains lie west of Hawaii and northeast of the Marshall Islands, but at the time of their formation were located in the Southern Hemisphere.
The tablemount was probably formed by a hotspot in the present-day Southern Pacific before plate tectonics moved it to its current location. Several hotspots, including the Easter, Marquesas and Society hotspots, may have been involved in the formation of the Mid-Pacific Mountains. Volcanic activity is dated to have occurred circa 111–85 million years ago and formed a volcanic island. Subsequently, carbonate deposition commenced as Allison Guyot subsided and eventually buried the island, forming an atoll-like structure and a carbonate platform. Among other animals, crocodilians lived on Allison Guyot.
The platform emerged above sea level during the Albian and Turonian ages. It drowned about 99 ± 2 million years ago for unknown reasons; possibly a phase of renewed emergence damaged the reefs, or it was located in unfavourable waters. Later, pelagic sedimentation commenced on the seamount and led to the deposition of sediments including limestone, ooze and sand, which bear traces of climatic events and ocean currents.Arago hotspot
Arago hotspot is a hotspot in the Pacific Ocean, presently located below the Arago seamount close to the island of Rurutu, French Polynesia.
Arago is part of a family of hotspots in the southern Pacific, which include the Society hotspot and the Macdonald hotspot among others. These are structures beneath Earth's crust which generate volcanoes and which are in part formed by mantle plumes, although Arago itself might have a shallower origin. As the Pacific plate moves over the hotspots, new volcanoes form and old volcanoes are carried away; sometimes an older volcano is carried over the hotspot and is then uplifted as happened with Rurutu.
The Arago hotspot is responsible for the formation of Arago seamount and uplift on Rurutu; however reconstructions of the past positions of tectonic plates and geochemistry suggest that other islands and seamounts were constructed by the Arago hotspot during the past 120 million years. These potentially include Tuvalu, Gilbert Islands, the Ratak Chain of the Marshall Islands as well as part of the Austral Islands and Cook Islands.Geography of the Marquesas Islands
The Marquesas Islands are the island group farthest from any continent in the world, lying between 400 and 600 miles (600 and 1,000 km) south of the equator and approximately 1,000 miles (1,600 km) northeast of Tahiti. They fall naturally into two geographical divisions: the northern group, consisting of Eïao, Hatutu (Hatutaa), Motu One, and the islands centered on the large island of Nuku Hiva: Motu Iti (Hatu Iti), Ua Pou, Motu Oa and Ua Huka, and the southern group of Fatu Uku, Tahuata, Moho Tani (Motane), Terihi, Fatu Hiva and Motu Nao (Thomasset Rock), clustered around the main island of Hiva `Oa.
With a combined land area of 1,274 km² (492 sq. miles), the Marquesas are among the largest island groups of French Polynesia, Nuku Hiva being the second largest island in the entire territory, after Tahiti. With the exception of Motu One, all the islands of the Marquesas are of volcanic origin.
In contrast to the common perception of lush tropical vegetation that goes culturally hand-in-hand with the appellation Polynesia, the Marquesas are remarkably dry islands. Although the islands lie within the tropics, they are the first major break in the prevailing easterly winds spawned from the extraordinarily dry (from an atmospheric perspective) Humboldt Current. The annual rainfall is generally around 1,270 millimetres (50 in), but this average is misleading because of very high variability. In La Niña years, rainfall can decline to less than 500 millimetres (20 in), whilst in El Niño years when the ocean warms it can reach 2,800 millimetres (110 in). Unlike the rest of French Polynesia, most rain falls during the cooler months, with May to July usually the wettest and November the driest.
Because of their exceptionally variable climate, the islands are subject to extreme drought and flood conditions. Only those that reach higher elevations (generally, above about 2,500 feet above sea level) have reliable precipitation. This has led to historical fluctuations in water supply, which has been a crucial factor in the sustainability of human populations in certain sections of the various islands throughout the archipelago. This is especially evident in the low historical population of Ua Huka (maximum elevation 2,812 ft.) and the intermittent inhabitability of Eiao (maximum elevation 1,890 ft.).
The Marquesas Islands are thought to have formed from a center of upwelling magma called the Marquesas hotspot.Geology of the Pacific Ocean
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).Hotspot (geology)
In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.Index of French Polynesia-related articles
This page list topics related to French Polynesia.MIT Guyot
MIT Guyot is a guyot in the Pacific Ocean that rises to a depth of 1,323 metres (4,341 ft). It has a 20-kilometre-long (12 mi) summit platform and formed during the Cretaceous in the region of present-day French Polynesia through volcanic eruptions.
The volcano was eventually covered by a carbonate platform resembling that of a present-day atoll which was colonized by a number of animals. A major volcanic episode disrupted this platform, which subsequently redeveloped until it drowned in the late Albian.Marquesas Islands
The Marquesas Islands (; French: Îles Marquises or Archipel des Marquises or Marquises; Marquesan: Te Henua (K)enana (North Marquesan) and Te Fenua ʻEnata (South Marquesan), both meaning "the land of men") are a group of volcanic islands in French Polynesia, an overseas collectivity of France in the southern Pacific Ocean. The Marquesas are located at 9.7812° S, 139.0817° W. The highest point is the peak of Mount Oave (French: Mont Oave) on Ua Pou island at 1,230 m (4,035 ft) above sea level.Research based on 2010 studies suggests the islands were colonized rapidly in two successive waves by indigenous colonists from West Polynesia, beginning c. 1025–1120 AD, leading to the development of a "remarkably uniform culture, human biology and language."The Marquesas Islands form one of the five administrative divisions (subdivisions administratives) of French Polynesia. The capital of the Marquesas Islands administrative subdivision is the settlement of Taiohae on the island of Nuku Hiva. The population of the Marquesas Islands was 9,346 inhabitants at the August 2017 census.Musicians Seamounts
Musicians Seamounts are a chain of seamounts in the Pacific Ocean, north of the Hawaiian Ridge. There are about 65 seamounts, some of which are named after musicians. These seamounts exist in two chains, one of which has been attributed to a probably now-extinct hotspot called the Euterpe hotspot. Others may have formed in response to plate tectonics associated with the boundary between the Pacific Plate and the former Farallon Plate.
The seamounts were constructed on young oceanic crust during the Cretaceous, but a second phase of volcanic activity took place during the Eocene. Deep sea coral reefs occur on the seamounts.Ua Huka
Ua Huka is one of the Marquesas Islands, in French Polynesia, an overseas territory of France in the Pacific Ocean. It is situated in the northern group of the archipelago, approximately 25 mi (40 km) to the east of Nuku Hiva, at 8°54′S 139°33′W.Wōdejebato
Wōdejebato (formerly known as Sylvania) is a Cretaceous guyot or tablemount in the northern Marshall Islands, Pacific Ocean. Wōdejebato is probably a shield volcano and is connected through a submarine ridge to the smaller Pikinni Atoll 74 kilometres (46 mi) southeast of the guyot; unlike Wōdejebato, Pikinni rises above sea level. The seamount rises for 4,420 metres (14,500 ft) to 1,335 metres (4,380 ft) depth and is formed by basaltic rocks. The name Wōdejebato refers to a sea god of Pikinni.
It was probably formed by a hotspot in what is present-day French Polynesia before plate tectonics moved it to its present-day location. The Macdonald, Rarotonga, Rurutu and Society hotspots may have been involved in its formation. The first volcanic phase took place in the Cenomanian and was followed by the formation of a carbonate platform that quickly disappeared below the sea. A second volcanic episode between 85 and 78.4 million years ago (in the Campanian) led to the formation of an island. This island was eventually eroded and rudist reefs generated an atoll or atoll-like structure, covering the former island with carbonates and thus a second carbonate platform.
The second carbonate platform drowned about 68 million years ago (in the Maastrichtian), perhaps because at that time it was moving through the equatorial area which may have been too hot or too nutrient-rich to support the growth of a coral reef. Thermal subsidence lowered the drowned seamount to its present depth. After a hiatus, sedimentation commenced on the seamount and led to the deposition of manganese crusts and pelagic sediments, some of which were later modified by phosphate.