The Pitcairn hotspot is a

volcanic A volcano is commonly defined as a vent or fissure 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 fo ...

hotspot located in the south-central

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. Over the past 11 million years, it has formed the Pitcairn-Gambier hotspot chain. It is responsible for creating the

Pitcairn Islands The Pitcairn Islands ( ; Pitkern: '), officially Pitcairn, Henderson, Ducie and Oeno Islands, are a group of four volcanic islands in the southern Pacific Ocean that form the sole British Overseas Territories, British Overseas Territory in the ...

and two large

seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

s named Adams and Bounty, as well as atolls at

Moruroa Moruroa (Mururoa, Mururura), also historically known as Aopuni, is an atoll which forms part of the Tuamotu Archipelago in French Polynesia in the southern Pacific Ocean. It is located about southeast of Tahiti. Administratively Moruroa Atoll i ...

, Fangataufa and the

Gambier Islands The Gambier Islands ( or ) are an archipelago in French Polynesia, located at the southeast terminus of the Tuamotu archipelago. They cover an area of , and are made up of the Mangareva Islands, a group of high islands remnants of a caldera alo ...

. The hotspot is currently located at Adams and Bounty, which are ~60 kilometers East-Southeast of Pitcairn Island.Global Volcanism Program: Adams Seamount
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Current hotspot location

The current hotspot location is west of the spreading center known as the

East Pacific Rise The East Pacific Rise (EPR) is a mid-ocean rise (usually termed an oceanic rise and not a mid-ocean ridge due to its higher rate of spreading that results in less elevation increase and more regular terrain), at a divergent tectonic plate bound ...

; an area near where the

Nazca plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

and the Pacific plate are diverging around 20°S, 115°W. This is where material is thought to be sourced from the core-mantle boundary, rising to surface as a localized plume. Opponents of the hotspot theory instead attribute Pitcairn hotspot to upwelling at the western end of the Easter fracture zone.

Morphology

Multibeam bathymetry shows that the two largest seamounts, Adams and Bounty, rise 2000m above the seafloor. Several other smaller, volcanically active seamounts exist that are shorter than 2000m in height. Bathymetry records have estimated the volume of erupted lava due to volcanic activity to be about 5900 km³ within a radius of about 110 kilometers.

Petrology

The larger edifices show much more extensive volcanic activity and a wider range of compositions than the smaller. The four different types of rocks that are erupted are classified as either

picrite basalt Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich ...

alkali basalt Alkali basalt or alkali olivine basalt is a dark-colored, porphyritic volcanic rock usually found in oceanic and continental areas associated with volcanic activity, such as oceanic islands, continental rifts and volcanic fields. Alkali basalt i ...

, trachyandesite and

trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanite, aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava (or shallow intrus ...

. Areas have been observed on Bounty showing pillow basalts and giant tubular

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

to tabular/blocky trachy-andesite and trachyte flows scattered across the slope of the

Pyroclast Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...

s and

hyaloclastite Hyaloclastite is a volcanoclastic accumulation or breccia consisting of glass (from the Greek ''hyalus'') fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin marg ...

s have also been observed on the main seamounts displaying a geologic history of the seamounts and past environment around them.

Pitcairn-Gambier hotspot chain

The hotspot has formed a chain of

seamounts A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

over the past 11 million years with several other large seamounts along the chain as well, organized from older to younger the further east you go. Some of these islands make up the

. They are named the Pitcairn proper, Henderson, Ducie and Oeno. The islands were first discovered by Europeans in 1767 and it is considered one of the most remote islands inhabited on earth. Multibeam bathymetry and bottom imaging has shown there to be hundreds or volcanic structures in a 9500 square kilometer area around the

Pitcairn Island Pitcairn Island is the only inhabited island of the Pitcairn Islands, in the southern Pacific Ocean, of which many inhabitants are descendants of mutineers of HMS ''Bounty''. Geography The island is of volcanic origin, with a rugged cliff ...

area. East of the main island, there are several active volcanoes that are only just below the surface, less than 500 meters deep.

Morphology

Several seamounts makes up the Pitcairn-Gambier hotspot chain. These include

, now an

atoll An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most ...

that formed about 11 Ma, Fangataufa, now an atoll that formed about 10 Ma,

, islands and atolls that formed about 6.5 Ma, Pitcairn Islands about 0.7 Ma and Pitcairn seamounts about 0.5 Ma. This chain spreads from 21.5 degrees S, 139 degrees W to 25 degrees S, 129.5 degrees W.

Geochemistry

The seamount chain has varying ratios of ²⁰⁶Pb/²⁰⁴Pb isotopic composition, ranging from 18.99 to 19.62, depending on how far away from where the hotspot currently lies and how long ago it was formed by the hotspot. Ratios of 87Sr/ 86Sr were calculated to range between 0.70292 and 0.70367 and ratios of ¹⁴³Nd/¹⁴⁴Nd were calculated to be between 0.51303 and 0.51288.

Trace element __NOTOC__ A trace element is a chemical element of a minute quantity, a trace amount, especially used in referring to a micronutrient, but is also used to refer to minor elements in the composition of a rock, or other chemical substance. In nutr ...

ratios seemed relatively constant during tests.

Formation

Using methods of modeling of lead isotopes, the date set for different rocks around Pitcairn hotspot were estimated to be from 0.6 and 0.7 Ma. The hotspot has four islands that have formed since the hotspot's origin.

References

External links

* {{Hotspots Hotspots of the Pacific Ocean Geology of Oceania Geography of the Pitcairn Islands

Current hotspot location

Morphology

Petrology

Pitcairn-Gambier hotspot chain

Morphology

Geochemistry

Formation

See also

References

External links