The Louisville hotspot has produced the Louisville Ridge, which is one of the longest seamount chains on Earth, stretching some 4,300 km (2,672 mi) from the Pacific-Antarctic Ridge where it subducts under the Indo-Australian Plate as part of the Pacific Plate.
The Louisville hotspot is believed to have been active since at least 78.8 ± 1.3 Ma based on age of the age of the oldest seamount (Osbourn ). This duration is comparable to that of the Hawaiian-Emperor seamount chain, although the rate of volcanism at the two chains are relatively different and the Louisville Ridge has a relatively small bend compared to that in the Hawaiian-Emperior chain. During the Early Oligocene period, the Louisville hotspot's magma source rate was much steadier than the Hawaii hotspot rate, and had a lower total volume in eruption. During the Late Oligocene, the magma source decreased to a small fraction of that in the Hawaiian-Emperor seamount chain, such that none of the volcanoes has emerged above sea level in the past 11 million years. The Louisville Ridge is only half as wide as the Hawaiian-Emperior seamount chain. Therefore, unlike the Hawaii hotspot, the Louisville hotspot is believed to have decreased in activity with time.
The Louisville hotspot may have created the Ontong Java Plateau, the world's largest oceanic plateau, around 120 million years ago. The modelled locations of the plateau and hotspot at the time do not coincide under one recent plate reconstruction, arguing against this, although other factors mean their linkage may still be possible.
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.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.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).Hollister Ridge
Hollister Ridge is a group of seamounts in the Pacific Ocean. They lie west from the Pacific-Antarctic Ridge and form three ridges that form a line; one of the ridges rises to a depth of 100 metres (330 ft) and in the past formed an island. The seamounts are composed out of basaltic and other rocks and their ages range from about 2.5 million years ago to latest Pleistocene; an acoustic swarm recorded in the southern Pacific Ocean in 1991-1992 is considered to be the manifestation of a historical eruption of the Hollister Ridge.
The origin of the Hollister Ridge is unclear, with various proposed mechanisms involving the neighbouring Pacific-Antarctic Ridge, crustal weaknesses and the Louisville hotspot.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.Large igneous province
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics. The formation of some of the LIPs the past 500 million years coincide in time with mass extinctions and rapid climatic changes, which has led to numerous hypotheses about the causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems.List of largest volcanic eruptions
In a volcanic eruption, lava, volcanic bombs and ash, and various gases are expelled from a volcanic vent and fissure. While many eruptions only pose dangers to the immediately surrounding area, Earth's largest eruptions can have a major regional or even global impact, with some affecting the climate and contributing to mass extinctions. Volcanic eruptions can generally be characterized as either explosive eruptions, sudden ejections of rock and ash, or effusive eruptions, relatively gentle outpourings of lava. A separate list is given below for each type.
There have probably been many such eruptions during Earth's history beyond those shown in these lists. However erosion and plate tectonics have taken their toll, and many eruptions have not left enough evidence for geologists to establish their size. Even for the eruptions listed here, estimates of the volume erupted can be subject to considerable uncertainty.Louisville Ridge
The Louisville Ridge, also known as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts in the Southwest Pacific Ocean. As one of the longest seamount chains on Earth it stretches some 4,300 km (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate. The movement of the Pacific Plate over the Louisville hotspot formed the chain.
Depth-sounding data first revealed the existence of the seamount chain in 1972.Macquarie Triple Junction
The Macquarie Triple Junction is a geologically active tectonic boundary located at 61°30′S 161°0′E at which the Indo-Australian Plate, Pacific Plate, and Antarctic Plate collide and interact. The term Triple Junction is given to particular tectonic boundaries at which three separate tectonic plates meet at a specific, singular location. The Macquarie Triple Junction is located on the seafloor of the southern region of the Pacific Ocean, just south of New Zealand. This tectonic boundary was named in respect to the nearby Macquarie Island, which is located southeast of New Zealand.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.Ontong Java Plateau
The Ontong Java Plateau (OJP) is a huge oceanic plateau located in the southwestern Pacific Ocean, north of the Solomon Islands.
The OJP was emplaced around 120 million years ago (Ma) with a much smaller volcanic event around 90 Ma. Two other southwestern Pacific plateaus, Manihiki and Hikurangi, now separated from the OJP by Cretaceous ocean basins, are of similar age and composition and probably formed as a single plateau and a contiguous large igneous province together with the OJP.
When emplaced this Ontong Java–Manihiki–Hikurangi plateau covered 1% of Earth's surface and represented a volume of 80 million km3 (19 million cu mi) of basaltic magma.
This "Ontong Java event", first proposed in 1991, represents the largest volcanic event of the past 200 million years, with a magma emplacement rate estimated at up to 22 km3 (5.3 cu mi) per year over 3 million years, several times larger than the Deccan Traps.
The smooth surface of the OJP is punctuated by seamounts such as the Ontong Java Atoll, the largest atoll in the world.Osbourn Seamount
The Osbourn Seamount is a seamount in the south-west Pacific Ocean. It is the western-most and oldest unsubducted seamount of the Louisville Ridge, with an estimated age of 78.8 ± 1.3 Ma. Like other seamounts comprising the Louisville Ridge, it was formed by the Louisville hotspot which is currently located 4,300 km (2,700 mi) away near the Pacific-Antarctic Ridge.Osbourn Seamount will eventually be destroyed by subduction in the Tonga and Kermadec trenches once it is carried into the trenches by the ongoing plate motion. The trench-chain collision zone is moving southward at a rate of 200 km (120 mi)/Ma because of the oblique angle between the trench and the Louisville chain. This further shortens the seamount's lifespan.
The flat top of the seamount is currently tilting down toward the trench because the seamount is sitting on the edge of the trench where the Australian Plate is being bent by subduction.A bathymetric high c. 2 km (1.2 mi) north-west of the Osbourn Seamount has been interpreted as the currently subducting portion of the Louisville chain, but this continuation is not aligned with the existent chain. The Osbourn Seamount is the same age as the Detroit Seamount (75.8±0.6 Ma), one of the oldest of the Hawaii–Emperor seamount chain, and a clockwise bend in the Louisville chain near Osbourn is similar to the Detroit-Meiji bend in the Hawaii–Emperor chain.Outline of oceanography
The following outline is provided as an overview of and introduction to Oceanography.Pacific-Antarctic Ridge
The Pacific-Antarctic Ridge (PAR) is a divergent tectonic plate boundary located on the seafloor of the South Pacific Ocean, separating the Pacific Plate from the Antarctic Plate. It is regarded as the southern section of the East Pacific Rise in some usages, generally south of the Challenger Fracture Zone and stretching to the Macquarie Triple Junction south of New Zealand.Timeline of volcanism on Earth
This timeline of volcanism on Earth is a list of major volcanic eruptions of approximately at least magnitude 6 on the Volcanic Explosivity Index (VEI) or equivalent sulfur dioxide emission around the Quaternary period (from 2.58 Mya to the present).
Some eruptions cooled the global climate—inducing a volcanic winter—depending on the amount of sulfur dioxide emitted and the magnitude of the eruption. Before the present Holocene epoch, the criteria are less strict because of scarce data availability, partly since later eruptions have destroyed the evidence. Only some eruptions before the Neogene period (from 23 Mya to 2.58 Mya) are listed. Known large eruptions after the Paleogene period (from 66 Mya to 23 Mya) are listed, especially those relating to the Yellowstone hotspot, the Santorini caldera, and the Taupo Volcanic Zone.
Active volcanoes such as Stromboli, Mount Etna and Kilauea do not appear on this list, but some back-arc basin volcanoes that generated calderas do appear. Some dangerous volcanoes in "populated areas" appear many times: so Santorini, six times and Yellowstone hotspot, twenty-one times. The Bismarck volcanic arc, New Britain, and the Taupo Volcanic Zone, New Zealand, appear often too.
In addition to the events listed below, are many examples of eruptions in the Holocene on the Kamchatka Peninsula, which are described in a supplemental table by Peter Ward.