These seamounts have the shape of ridges and display calderas. The Aureka ( ) and Make ( ) seamounts are part of the Ngatemato track. Dredged rocks are weakly tholeiitic basalts of Oligocene age. They are about 1,500 metres (4,900 ft) high and 20 kilometres (12 mi) wide at their base. Despite being smaller in size than the Macdonald seamounts however the Ngatemato seamounts have larger volumes which is masked by stronger plate deformation; the magma output that created the Ngatemato and Taukina chains when summed up is about 0.04 cubic kilometres per year (0.0096 cu mi/a).
The seamounts were discovered in 1996 by the RV Maurice Ewing in the Austral Islands. Potassium-argon dating yields ages of about 30 million years; the seamounts developed close to the East Pacific Rise. Away from the Austral Islands the Ngatemato seamounts merge with the Foundation seamounts, with which they may share an origin.
Macdonald seamount and associated seamounts as well as the Taukina seamounts developed close to the Ngatemato seamounts, the deformation of the Pacific Plate imposed by the Ngatemato seamounts may have triggered the formation of these other two seamounts. Alternatively the Ngatemato seamounts and Macdonald may have been formed by individual hotspots, such as the Foundation hotspot in Ngatemato's case, although the Ngatemato seamounts may to fit a lithospheric fracture-induced volcanism model better than the mantle plume model. Finally, it is possible that the formation of the seamounts was directed by the interaction between the Foundation hotspot and lithospheric fractures.
Foundation Seamounts are a series of seamounts in the southern Pacific Ocean. Discovered in 1992, these seamounts form a 1,350 kilometres (840 mi) long chain which starts from the Pacific-Antarctic Ridge. Some of these seamounts may have once emerged from the ocean.
The Foundation Seamounts were probably formed by a now-weakening mantle plume called the Foundation hotspot that is located close to the Pacific-Antarctic Ridge. It is possible that this hotspot generated additional volcanoes, such as the Ngatemato and Taukina seamounts farther west. The oldest volcanism on the Foundation Seamounts occurred 21 million years ago, while the youngest volcanism appears to be hydrothermal venting and the eruption of a lava flow between 1997-2001 where the Foundation Seamounts intersect the Pacific-Antarctic Ridge.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.Macdonald seamount
Macdonald seamount (named after Gordon A. MacDonald) is a seamount in Polynesia, southeast of the Austral Islands and in the neighbourhood of a system of seamounts that include the Ngatemato seamounts and the Taukina seamount. It rises 4,200 metres (13,800 ft) from the seafloor to a depth of about 40 metres (130 ft) and has a flat top, but the height of its top appears to vary with volcanic activity. There are some subsidiary cones such as Macdocald seamount. The seamount was discovered in 1967 and has been periodically active with gas release and seismic activity since then. There is hydrothermal activity on Macdonald, and the vents are populated by hyperthermophilic bacteria.
Macdonald seamount is the currently active volcano of the Macdonald hotspot, a volcanic hotspot that has formed this seamount and some other volcanoes. Eruptions occurred in 1967, 1977, 1979–1983 and 1987–1989, and earthquakes were recorded in 2007. The activity, which has produced basaltic rocks, has modified the shape of the volcano and may lead to the formation of an island in the future.Outline of oceanography
The following outline is provided as an overview of and introduction to Oceanography.Taukina seamounts
Taukina seamounts are a series of seamounts on the Pacific Plate. The Macdonald hotspot and the Ngatemato seamounts are located nearby. The Taukina and Ngatemato seamounts were discovered in 1996 by the RV Maurice Ewing and both are named after families in Rapa Iti.The Taukina seamounts are formed by small volcanoes, with heights of 1,500–1,000 metres (4,900–3,300 ft) and widths of 6–10 kilometres (3.7–6.2 mi). They often feature a caldera on their summit. Tholeiitic rocks make up the seamounts.The shape of the Taukina seamounts resembles that of the seamounts that form on the East Pacific Rise. An alternate theory of origin is that the Ngatemato seamounts deformed the Pacific plate enough with their weight to trigger the eruption of magma.