The Rarotonga hotspot is a
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates ...
hotspot
Hotspot, Hot Spot or Hot spot may refer to:
Places
* Hot Spot, Kentucky, a community in the United States
Arts, entertainment, and media Fictional entities
* Hot Spot (comics), a name for the DC Comics character Isaiah Crockett
* Hot Spot (Tra ...
in the southern
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
. The hotspot was responsible for the formation of
Rarotonga
Rarotonga is the largest and most populous of the Cook Islands. The island is volcanic, with an area of , and is home to almost 75% of the country's population, with 13,007 of a total population of 17,434. The Cook Islands' Parliament buildings a ...
and some volcanics of
Aitutaki
Aitutaki, also traditionally known as Araura and Utataki, is the second most-populated island in the Cook Islands, after Rarotonga. It is an "almost atoll", with fifteen islets in a lagoon adjacent to the main island. Total land area is , and the ...
.
In addition to these volcanoes in the
Cook Islands
)
, image_map = Cook Islands on the globe (small islands magnified) (Polynesia centered).svg
, capital = Avarua
, coordinates =
, largest_city = Avarua
, official_languages =
, langu ...
, the composition of volcanic rocks in
Samoa
Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands (Savai'i and Upolu); two smaller, inhabited islands (Manono Island, Manono an ...
and in the
Lau Basin
The Lau Basin is a back-arc basin (also addressed as "interarc basin") at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau-Colville ...
may have been influenced by the Rarotonga hotspot, and some
atoll
An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can ...
s and
seamount
A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise a ...
s in the
Marshall Islands
The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Internati ...
may have formed on the hotspot as well.
Geology
Oceanic plateau
An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides.
There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the ...
s and linear volcanic chains dot the floor of the
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...
. Their formation has been explained with
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...
s which rise from the
core-mantle boundary and spread out when they rise, forming a large "head" that causes intense volcanic activity once it hits the
crust. This volcanism is responsible for the formation of the oceanic plateaus. Later, the remnant "tail" of the plume is still rising and induces the formation of volcano chains as the crust moves over the plume tail, thus forming the linear chains.
A number of
hotspot
Hotspot, Hot Spot or Hot spot may refer to:
Places
* Hot Spot, Kentucky, a community in the United States
Arts, entertainment, and media Fictional entities
* Hot Spot (comics), a name for the DC Comics character Isaiah Crockett
* Hot Spot (Tra ...
s are or were active in the Pacific Ocean and some of these may be the product of
mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...
s. Other hotspots such as Rarotonga appear to have been active only for short time periods; many of these are located in
French Polynesia
)Territorial motto: ( en, "Great Tahiti of the Golden Haze")
, anthem =
, song_type = Regional anthem
, song = "Ia Ora 'O Tahiti Nui"
, image_map = French Polynesia on the globe (French Polynesia centered).svg
, map_alt = Location of French ...
where there is a
superswell. Such hotspot volcanism may be the product of shallow processes. Later research has suggested however that the
Macdonald hotspot, the Rarotonga hotspot and the
Rurutu hotspot are long lived hotspots that were active as far back as the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
; they may be over 100 million years old and in such case the oldest still active hotspots in the Pacific. These hotspots together may have built the
Cook-
Austral Islands
The Austral Islands (french: Îles Australes, officially ''Archipel des Australes;'' ty, Tuha'a Pae) are the southernmost group of islands in French Polynesia, an overseas country of the French Republic in the South Pacific. Geographically, t ...
together, resulting in overlapping ages of the volcanoes.
Seismic tomography
Seismic tomography or seismotomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on ...
has found slow velocity anomalies underneath the Rarotonga hotspot, down to depths of about
with more recent research indicating that they root at about depth.
The anomaly lies at over depth with no evidence of shallower anomalies, however.
The Rarotonga hotspot and other regional hotspots appear to be anchored to a deep mantle structure called a
large low shear-wave velocity province.
Products
The Rarotonga hotspot is reliably linked only to the formation of
Rarotonga
Rarotonga is the largest and most populous of the Cook Islands. The island is volcanic, with an area of , and is home to almost 75% of the country's population, with 13,007 of a total population of 17,434. The Cook Islands' Parliament buildings a ...
and to volcanism on
Aitutaki
Aitutaki, also traditionally known as Araura and Utataki, is the second most-populated island in the Cook Islands, after Rarotonga. It is an "almost atoll", with fifteen islets in a lagoon adjacent to the main island. Total land area is , and the ...
, potential volcanic structures between the
Tonga Trench and Rarotonga that may have been formed by the same hotspot are poorly studied. Rarotonga itself is young but there is little indication of volcanism either southeast or northwest from it
and no evidence of its current position.
Other candidate volcanoes/structures formed by the Rarotonga hotspot or influenced by it are:
*
Rarotonga
Rarotonga is the largest and most populous of the Cook Islands. The island is volcanic, with an area of , and is home to almost 75% of the country's population, with 13,007 of a total population of 17,434. The Cook Islands' Parliament buildings a ...
.
* The young volcanics of
Aitutaki
Aitutaki, also traditionally known as Araura and Utataki, is the second most-populated island in the Cook Islands, after Rarotonga. It is an "almost atoll", with fifteen islets in a lagoon adjacent to the main island. Total land area is , and the ...
. An origin of the young volcanics as
rejuvenated volcanism cannot be ruled out, however.
*
Rose Atoll
Rose Atoll, sometimes called Rose Island or Motu O Manu ("Bird Island") by people of the nearby Manu'a Islands, is an oceanic atoll within the U.S. territory of American Samoa. An uninhabited wildlife refuge, it is the southernmost point bel ...
and Malulu Seamount may have been formed by the Rarotonga hotspot, but other hotspots are also candidates. The connection to Rarotonga is supported by geochemical traits.
* Uo Mamae seamount in Samoa share geochemical traits with the Rarotonga hotspot and plate motion reconstructions indicate that the hotspot track passed through it. Potentially, the hotspot formed Uo Mamae and local tectonic processes later (940,000 years ago) triggered
rejuvenated volcanism.
* The composition of rejuvenated volcanism in
Samoa
Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands (Savai'i and Upolu); two smaller, inhabited islands (Manono Island, Manono an ...
may bear traces of the influence of the Rarotonga hotspot, which passed across Samoa in the past.
* Reconstructions of the path of the Rarotonga hotspot imply that part of its output was
subducted
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
into the
Tonga Trench;
back-arc magma
Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
s may thus ended up entraining material formerly produced by the Rarotonga hotspot. Backarc volcanic rocks in the
Lau Basin
The Lau Basin is a back-arc basin (also addressed as "interarc basin") at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau-Colville ...
bear traces of such influence.
* The
Marshall Islands
The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Internati ...
underwent vigorous volcanic and geological activity while they passed over the Rarotonga hotspot and neighbouring hotspots.
** Geochemical traits and plate reconstruction links the
Ralik Chain
The Ralik Chain ( Marshallese: , ) is a chain of islands within the island nation of the Marshall Islands. Ralik means "sunset". It is west of the Ratak Chain. In 1999 the total population of the Ralik islands was 19,915. Christopher Loeak, who ...
to the Rarotonga hotspot less than 80 million years ago.
**
Limalok guyot was close to the Rarotonga and Rurutu hotspots 62 million years ago. The plate reconstructions point towards Rurutu being the origin of Limalok, while geochemical traits match Rarotonga best.
**
Lo-En guyot
In marine geology, a guyot (pronounced ), also known as a tablemount, is an isolated underwater volcanic mountain (seamount) with a flat top more than below the surface of the sea. The diameters of these flat summits can exceed .[Campanian
The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...]
volcanic activity
**
Eniwetok
Enewetak Atoll (; also spelled Eniwetok Atoll or sometimes Eniewetok; mh, Ānewetak, , or , ; known to the Japanese as Brown Atoll or Brown Island; ja, ブラウン環礁) is a large coral atoll of 40 islands in the Pacific Ocean and with ...
was located close to the Rarotonga hotspot about 76.9 million years ago; this date corresponds to the a
radiometric age obtained on the upper volcano.
** A cluster of volcanoes close to Eniwetok and Ujlan may be the product of the Rarotonga hotspot.
** Volcanic activity at
Wōdejebato coincides with a period where the Rarotonga hotspot, the
Rurutu hotspot and the
Tahiti hotspot
The Society hotspot is a volcanic hotspot in the south Pacific Ocean which is responsible for the formation of the Society Islands, an archipelago of fourteen volcanic islands and atolls spanning around 720 km of the ocean which formed between ...
were all three located close to the seamount.
* Geochemical traits and plate reconstruction links the
Magellan Seamounts to the Rarotonga hotspot less than 80 million years ago.
* The
Western Pacific Seamount Province
Western may refer to:
Places
*Western, Nebraska, a village in the US
*Western, New York, a town in the US
*Western Creek, Tasmania, a locality in Australia
*Western Junction, Tasmania, a locality in Australia
*Western world, countries that id ...
has been argued to be the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
path of the Rarotonga hotspot, but its older members appear to be offset slightly north of the reconstructed path.
Some seamounts on the reconstructed path of the Rarotonga hotspot share geochemical traits with the hotspot, but with different
lead
Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...
isotope ratio
The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundanc ...
s.
* Hemler Guyot has similar isotope ratios as Rarotonga and its reconstructed position match those of the Rarotonga hotspot.
References
Sources
*
*
*
*
*
{{Hotspots
Geology of the Pacific Ocean
Hotspots of the Pacific Ocean
Rarotonga