The Osbourn Seamount is a

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 ...

in the south-west

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 ...

. It is the westernmost and oldest unsubducted seamount of the

Louisville Ridge The Louisville Ridge, often now referred to as the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. One of the longest seamount chains on Earth, it stretches some Vander ...

, with an estimated age of 78.8 ± 1.3 . Like other seamounts comprising the Louisville Ridge, it was formed by the

Louisville hotspot The Louisville hotspot is a volcanic hotspot responsible for the volcanic activity that has formed the Louisville Ridge in the southern Pacific Ocean. Location The Louisville hotspot is believed to lie close to the Pacific-Antarctic Ridge, altho ...

which is currently located away near the Pacific-Antarctic Ridge. Osbourn Seamount will eventually be destroyed by

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

in the

Tonga Tonga, officially the Kingdom of Tonga, is an island country in Polynesia, part of Oceania. The country has 171 islands, of which 45 are inhabited. Its total surface area is about , scattered over in the southern Pacific Ocean. accordin ...

and

Kermadec Kermadec or de Kermadec may refer to: Geography * Kermadec Islands, a subtropical island arc in the South Pacific Ocean northeast of New Zealand * Kermadec Plate, a long narrow tectonic plate located west of the Kermadec Trench * Kermadec Trench, ...

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 / 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 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. Whatever the area of subduction of the Louisville chain is associated with a relative seismic gap beneath the Tonga forearc. This implies that the subduction of the volcanoes compared to normal sediment has a significant impact in terms of normal relief of stress but it is unclear if the subducted volcanoes relieve it as suggested by some or increase it. Further the change in trend if the subducted Louisville chain compared to present is backed up by compositional analysis of recent arc volcanism as the volcanics from the Louisville chain are recycled. The Osbourn Seamount is the same age as the

Detroit Seamount Detroit Seamount, which was formed around 76 million years ago, is one of the oldest seamounts of the Hawaiian-Emperor seamount chain (Meiji Seamount is the oldest, at 82 million years). It lies near the northernmost end of the chain and is sout ...

(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.

References

; Notes ; Sources * * * Guyots Seamounts of the Pacific Ocean Hotspot volcanoes Cretaceous volcanoes Polygenetic volcanoes {{marine-geo-stub