Samoa hotspot

The Samoa hotspot is a volcanic hotspot located in the south Pacific Ocean. The hotspot model describes a hot upwelling plume of magma through the Earth's crust as an explanation of how volcanic islands are formed. The hotspot idea came from J. Tuzo Wilson in 1963 based on the Hawaii volcanic island chain.

In theory, the Samoa hotspot is based on the Pacific Tectonic Plate traveling over a fixed hotspot located deep underneath the Samoan Islands.[1] The Samoa hotspot includes the Samoan Islands (American Samoa and Samoa), and extends to the islands of Uvea or Wallis Island (Wallis and Futuna) and Niulakita (Tuvalu), as well as the submerged Pasco banks and Alexa Bank.[2]

As the Pacific Plate moves slowly over the hotspot, thermal activity builds up and is released in magma plume spewing through the Earth's crust, forming each island in a chain. The Samoa islands generally lie in a straight line, east to west, in the same direction of the tectonic plate 'drifting' over the hotspot.[3]

Volcano eruption Mt Matavanu - Savai'i - 1905 - photo by Thomas Andrew
Mt Matavanu eruption on Savai'i island, 1905.

A characteristic of a “classic” hotspot, like the Hawaii hotspot, results in islands located further from the hotspot being progressively older with newer and younger islands closest to the fixed hotspot, like the Loihi Seamount, the only submarine volcano which has been studied in detail by scientists. The scientific research from Loihi has resulted in a 'Hawaii' model for hotspots primarily limited to the information gathered from the Hawaii islands.[4]

However, the Samoa hotspot is currently an enigma for scientists.[5] In the Samoa Islands, the easternmost island of Ta'u and the westernmost island of Savai'i have both erupted in the past 150 years. The most recent eruption on Sava'i occurred with Mount Matavanu (1905–1911) and on Ta'u in 1866.[6]

Hotspots
The Samoa hotspot is marked 35 on map.
Hotspot(geology)-1
Diagram showing how islands are formed by hotspots

Vailulu'u

In 1975, geophysicist Rockne Johnson discovered the Vailulu'u Seamount, 45 km east of Ta'u island in American Samoa which has since been studied by an international team of scientists. Within the summit crater of Vailulu'u is an active underwater volcanic cone called Nafanua,[5] named after a war goddess in Samoan mythology. The study of Vailulu'u provides scientists with another possible model for hotspots[4] as an alternative to the Hawaii hotspot model.

An important difference between Vailulu'u and Loihi in Hawaii, is a total lack of tholeiitic basalt compositions at Vailulu'u[4] although both are located at the easternmost point of their respective island chains.

The northern Tonga Islands (Vava'u and Niuatoputapu) are moving away from Fiji on the Australian plate at rates of about 130 mm/yr and 160 mm/yr, respectively, while Niue and Rarotonga on the Pacific plate are approaching the Australian plate at about 80 mm/yr. This implies that Pacific plate is tearing at the corner of the trench-transform boundary at a rate that is the sum of these two (160 + 80) 240 mm/yr.[7]

See also

References

  1. ^ Russell, Jamie A. "Hotspot Lesson: Samoan Hotspot". Enduring Resources Earth Science Education. Retrieved 2 December 2009.
  2. ^ "Samoan Hotspot Trail". Archived from the original on December 23, 2010. Retrieved 2009-12-01.CS1 maint: BOT: original-url status unknown (link)
  3. ^ "This volcano we live on". Natural History Guide to American Samoa. Retrieved 2 December 2009.
  4. ^ a b c Hart, S. R.; Staudigel, H.; Koppers, A. A.; Blusztajn, J.; Baker, E. T.; Workman, R.; Jackson, M.; Hauri, E.; Kurz, M.; Sims, K.; Fornari, D.; Saal, A.; Lyons, S. (2000). "Vailulu'u undersea volcano: The new Samoa" (PDF). Geochemistry, Geophysics, Geosystems. 1 (12). doi:10.1029/2000GC000108. Retrieved 14 January 2017.
  5. ^ a b Lippsett, Laurence (3 September 2009). "Voyage to Vailulu'u". Woods Hole Oceanographic Institution. Retrieved 2 December 2009.
  6. ^ Steadman, David W. (200). Extinction & biogeography of tropical Pacific birds. University of Chicago Press. p. 22. ISBN 0-226-77142-3. Retrieved 2 December 2009.
  7. ^ W. Jason Morgan and Jason Phipps Morgan. Plate velocities in hotspot reference frame: electronic supplement (PDF). p. 111. Retrieved 2010-04-23.CS1 maint: uses authors parameter (link)
Adams Seamount

Adams Seamount (also known as Forty Mile Reef) is a submarine volcano above the Pitcairn hotspot in the central Pacific Ocean about 100 kilometres (62 mi) southwest of Pitcairn Island.

Alexa Bank

Alexa Bank is a seamount in Samoa, northwest of Rotuma. The seamount reaches a depth of 18–21 metres (59–69 ft) below sea level and has the appearance of an atoll with a flat top and steep slopes. Some active coral growth takes place at its top, but if it ever was an active atoll it has now drowned. It was probably formed by the Samoa hotspot 24 million years ago, although older volcanism about 40 million years ago has also been identified.

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.

Ioah Guyot

Ioah Guyot is a seamount in the Pacific Ocean, close to the Marshall Islands. Part of the Magellan Seamounts, it is a shield volcano that has erupted alkali basalt and hawaiite 87 million years ago, but may have continued erupting into the Miocene. During the Cretaceous, reefs developed on the guyot.

Macdonald hotspot

The Macdonald hotspot is a volcanic hotspot in the southern Pacific Ocean. The hotspot was responsible for the formation of the Macdonald Seamount, and possibly the Austral-Cook Islands chain. It probably did not generate all of the volcanism in the Austral and Cook Islands as age data imply that several additional hotspots were needed to generate some volcanoes.

In addition to the volcanoes in the Austral Islands and Cook Islands, Tokelau, the Gilbert Islands, the Phoenix Islands and several of the Marshall Islands as well as several seamounts in the Marshall Islands may have been formed by the Macdonald hotspot.

Malumalu

Malumalu seamount lies in American Samoa and forms a topographic structure together with Savaii, Upolu and Tutuila close to the Tonga Trench which lies about 100 kilometres (62 mi) south. Malumalu lies about 66 kilometres (41 mi) south of Ofu island and is also known as "Southeast Bank".The seamount is a young volcano at the eastern end of a lineament that begins on Tutuila. This lineament has been named the "Malu trend" and contrasted to the "Vai Trend" farther northeast which runs between Ofu, Ta'u and Vailulu'u, comparable to the "Kea" and "Loa" trends in Hawaii. Malumalu is not much older than Vailulu'u, which has erupted in historical time. Actinide isotope ratios indicate the occurrence of at least three volcanic events in the last 300,000 years, including at least two in the last 150,000 years and at least one in the last 8,000 years. According to one model of the behaviour of the Samoa hotspot volcanic activity at Malumalu will decline in the next 10,000 - 100,000 years as the mantle plume is pushed farther northeast to Vailulu'u by mantle flow generated by the Tonga slab.

National Park of American Samoa

The National Park of American Samoa is a national park in the United States territory of American Samoa, distributed across three islands: Tutuila, Ofu, and Ta‘ū. The park preserves and protects coral reefs, tropical rainforests, fruit bats, and the Samoan culture. Popular activities include hiking and snorkeling. Of the park's 13,500 acres (5,500 ha), 9,000 acres (3,600 ha) is land and 4,500 acres (1,800 ha) is coral reefs and ocean. The park is the only American National Park Service system unit south of the equator.

Niulakita

Niulakita is the southernmost island of Tuvalu, and also the name of the only village on this island. Niulakita has a population of 27 (2012 census). The residents of Niulakita have moved to the island from Niutao. Niulakita is represented in the Parliament of Tuvalu by the members of the constituency of Niutao.

Pasco banks

The Pasco Banks refers to a naturally occurring geological and marine formation in the south Pacific Ocean. The Pasco Banks is a long ridge-like seamount that rises from about 200 m to within 30 m of the ocean's surface. Covered in patchy coral reef, it attracts large schools of baitfish, mainly rainbow runner, which in turn are preyed upon by larger predatory fishes. This abundance of fish has made the Pasco Banks a popular and reliable fishing location for hundreds of years.

Samoa

Samoa (), officially the Independent State of Samoa (Samoan: Malo Saʻoloto Tutoʻatasi o Sāmoa; Samoan: Sāmoa, IPA: [ˈsaːmoa]) and, until 4 July 1997, known as Western Samoa, is a country consisting of two main islands, Savai'i and Upolu, and four smaller islands (Manono, Apolima, Fanuatapu, and Namua). The capital city is Apia. The Lapita people discovered and settled the Samoan Islands around 3,500 years ago. They developed a unique Samoan language and Samoan cultural identity.

Samoa is a unitary parliamentary democracy with eleven administrative divisions. The country is a member of the Commonwealth of Nations. Western Samoa was admitted to the United Nations on 15 December 1976. The entire island group, which includes American Samoa, was called "Navigator Islands" by European explorers before the 20th century because of the Samoans' seafaring skills. The country was governed by New Zealand until its independence in 1962.

In July 2017, Va'aletoa Sualauvi II became the head of state, succeeding Tuiatua Tupua Tamasese Efi. The Prime Minister Tuila'epa came back to power after a landslide victory in March 2016, beginning a fifth term for the premier.

Samoan Islands

The Samoan Islands are an archipelago covering 3,030 km2 (1,170 sq mi) in the central South Pacific, forming part of Polynesia and the wider region of Oceania. Administratively, the archipelago comprises all of Samoa and most of American Samoa (apart from Swains Island, which is part of the Tokelau Islands). The two Samoan jurisdictions are separated by 64 km (40 mi) of ocean.

The population of the Samoan Islands is approximately 250,000, sharing a common language, Samoan, a culture, known as fa'a Samoa and an indigenous form of governance called fa'amatai.

Most Samoans are full-blooded and are one of the largest Polynesian populations in the world.The oldest evidence of human activity in the Samoan Islands dates to around 1050 BCE. This comes from a Lapita site at Mulifanua wharf on Upolu island.

In 1768, the eastern islands were visited by French explorer Bougainville, who named them the Navigator Islands, a name used by missionaries until about 1845 and in official European dispatches until about 1870.

Savai'i

Savaiʻi is the largest (area 1,694 km2) and highest (Mt Silisili at 1,858 m) island in Samoa and the Samoan Islands chain. The island is the sixth largest in Polynesia, behind the three main islands of New Zealand and the Hawaiian Islands of Hawaii and Maui.

The island of Savai'i is also referred to by Samoans as Salafai, a classical Samoan term used in oratory and prose. The island is home to 43,142 people (2006 Census) who make up 24% of the country's population.

The only township and ferry terminal is Salelologa, the main entry point to the island, situated at the east end of Savai'i. A tar sealed road serves as the one main highway, connecting most of the villages with local buses reaching most settlements.

Savai'i is made up of six itūmālō (political districts). Each district is made up of villages with strong traditional ties of kinship, history, land and matai chief titles. There is also some limited ecotourism development which operates mostly within the villages. The Mau, Samoa's non-violent movement for political independence during colonialism in the early 1900s, had its beginnings on Savai'i with the Mau a Pule movement.The island is the largest shield volcano in the South Pacific with recent eruptions in the early 1900s. The central region comprises the Central Savai'i Rainforest with 72,699 hectares (727 km2) that forms the largest continuous patch of rainforest in Polynesia. It is dotted with more than 100 volcanic craters and contains most of Samoa's native species of flora and fauna, making it globally significant in world conservation areas.

Tonga Trench

The Tonga Trench is an oceanic trench located in the south-west Pacific Ocean. It is the deepest trench of the Southern Hemisphere and the second deepest on Earth. The fastest plate tectonic velocity on Earth occurs as the Pacific Plate is being subducted westward in the trench.

When the Apollo 13 mission was aborted in 1970 following an explosion in an oxygen tank, the radioisotope thermoelectric generator broke up in the atmosphere and the heat source plunged in or near the Tonga Trench. Atmospheric and oceanic monitoring indicate no release of nuclear fuel has occurred.

Ujlān volcanic complex

Ujlān volcanic complex is a group of seamounts in the Marshall Islands. The complex consists of the seamounts Ļajutōkwa, Ļalibjet, Likelep, Ļotāb and Ujlān which with a minimum depth of 1,250 metres (4,100 ft) is the shallowest part of the complex; sometimes Ujelang Atoll is also considered to be a part of the complex; Eniwetok atoll and Lo-En seamount form a cluster together with this volcanic complex.These are simple single-peaked seamounts with the exception of the three-peaked Ujlān and there appear to be two rift zones associated with the complex. Between the seamounts the seafloor is covered with debris while the seamounts themselves are covered with varying thicknesses of pelagic sediments; however in general volcanic rocks and mostly breccia are the dominant components. Minerals found in samples from the volcanic complex include biotite, hornblende and plagioclase. Video observation has noted sediment deposits with ferromanganese knolls on some of the seamounts. There is little evidence of reefs but most seamounts were affected by slumps; in addition there are frequently terraces and volcanic cones on the seamounts.The volcanic complex and neighbouring structures may be of Cretaceous age but with some scatter. Likelep features probably Campanian-age rocks and radiometric dating has yielded an age of 81.4–82.8 million years ago for Ļalibjet, 81.2 ± 0.5 for Ļajutōkwa, 82.5 ± 0.2 for Likelep, 79.7 ± 0.4 for Ļotāb and 80.1 ± 0.5 for Ujlān. The complex is also known as the Ujlān seamount trail and its formation of this complex may be related to the Rarotonga hotspot while the geochemistry shows affinities to the Samoa hotspot.The seamount complex is located within the exclusive economic zone of the Marshall Islands, and Ļalibjet has been considered a site for cobalt mining. The names of the seamounts come from Marshallese; Ļajutōkwa was the first navigator chief in the northern Marshall Islands, Ļalibjet is a sea god, Likelep is a place on Ujlān and Ļotāb like his ancestor Litōrmalū is a legendary navigator. One source has given Ļalibjet as the old name for Likelep.

Ultra low velocity zone

Ultra low velocity zones (ULVZs) are patches on the core-mantle boundary that have extremely low seismic velocities. The zones are mapped to be hundreds of kilometers in diameter and tens of kilometers thick. Their shear wave velocities can be up to 30% lower than surrounding material. The composition and origin of the zones remain uncertain. The zones appear to correlate with edges of the African and Pacific Large low-shear-velocity provinces (LLSVPs) as well as the location of hotspots.

Vailulu'u

Vailulu'u is a volcanic seamount discovered in 1975. It rises from the sea floor to a depth of 593 m and is located between Ta'u and Rose islands at the eastern end of the Samoa hotspot chain. The basaltic seamount is considered to mark the current location of the Samoa hotspot. The summit of Vailulu'u contains a 2 km wide, 400 m deep oval-shaped caldera. Two principal rift zones extend east and west from the summit, parallel to the trend of the Samoan hotspot. A third less prominent rift extends southeast of the summit.

Eruptions at Vailulu'u were recorded in 1973. An earthquake swarm in 1995 may have been related to an eruption from the seamount. Turbid water above the summit shows evidence of ongoing hydrothermal plume activity. Vailulu'u may breach the surface of the ocean and officially become an island if a high rate of eruptions continue.

Vlinder Guyot

Vlinder Guyot (also known as Alba Seamount after Francisco Alba, companion of Ferdinand Magellan) is a guyot in the Western Pacific Ocean. It rises to a depth of 1,500 metres (4,900 ft) and has a flat top covering an area of 40 by 50 kilometres (25 mi × 31 mi). On top of this flat top lie some volcanic cones, one of which rises to a depth of 551 metres (1,808 ft) below sea level. Vlinder Guyot has noticeable rift zones, including an older and lower volcano to the northwest and Oma Vlinder seamount south.

Vlinder Guyot formed about 95 million years ago, presumably as a consequence of hotspot volcanism. The volcanic island became an atoll with active reefs that eventually drowned in the Albian-Cenomanian, although renewed volcanic activity until the Miocene sometimes sustained shallow water environments. The guyot is currently settled by numerous types of animals and is part of an area leased for mining purposes.

Wallis (island)

Wallis (Wallisian: ʻUvea) is a Polynesian island in the Pacific Ocean belonging to the French overseas collectivity (collectivité d'outre-mer, or COM) of Wallis and Futuna. It lies north of Tonga, northeast of Fiji, east-northeast of the Hoorn Islands, east of Fiji's Rotuma, southeast of Tuvalu, southwest of Tokelau and west of Samoa. Its area is almost 100 km2 (39 sq mi) with almost 11,000 people. Its capital is Matāʻutu. Roman Catholicism is the predominant religion. Its highest point is Mount Lulu Fakahega (131 metres, 430 ft). Wallis is of volcanic origin with fertile soil and some remaining lakes. Rainfall is plentiful.

It was part of the Tongan maritime empire from around the 13th to 16th century. By that time the influence of the Tuʻi Tonga had declined so much that ʻUvea became important in itself. The big fortress of Talietumu close to Lotoalahi in Mua was the last holdout of the Tongans until they were defeated. The island was renamed "Wallis" after a Cornish navigator, Captain Samuel Wallis, who saw it while sailing aboard HMS Dolphin on 16 August 1767. On 5 April 1842, the authorities of Wallis Island requested protection by France with a protectorate treaty signed in April 1887. After a referendum in 1959, Wallis became a French Overseas Territory in 1961.

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