Largest volcano on Earth discovered under Pacific Ocean

Earth's largest volcano - and possibly the second largest in the Solar System - has been discovered at the bottom of the Pacific Ocean.
Covering an area roughly equivalent to the British Isles or the state of New Mexico, the volcano dubbed Tamu Massif, is located about 1,609 km east of Japan.
Tamu Massif is the largest feature of Shatsky Rise, an underwater mountain range formed 130 to 145 million years ago by the eruption of several underwater volcanoes.
Tamu Massif, which became inactive within a few million years after it was formed, covers an area of about 310,798 square kms.

By comparison, Hawaii's Mauna Loa - the largest active volcano on Earth - is approximately 5,179 square kms, or roughly 2 per cent the size of Tamu Massif.
Also, Olympus Mons on Mars, the largest known volcano in our solar system, is only about 25 per cent larger by volume than Tamu Massif.

However, until now, it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points.
Now, researchers have confirmed that the mass of basalt that constitutes Tamu Massif did indeed erupt from a single source near the centre, making it the largest single volcano on Earth.

"Tamu Massif is the biggest single shield volcano ever discovered on Earth. There may be larger volcanoes, because there are bigger igneous features out there such as the Ontong Java Plateau, but we don't know if these features are one volcano or complexes of volcanoes," said William Sager, a professor in the Department of Earth and Atmospheric Sciences at the University of Houston.
Tamu Massif stands out among underwater volcanoes not just for its size, but also its shape. It is low and broad, meaning that the erupted lava flows must have travelled long distances compared to most other volcanoes on Earth.

The study relies on core samples collected on Integrated Ocean Drilling Programme (IODP) Expedition 324 (Shatsky Rise Formation) in 2009, and seismic reflection data gathered on two separate expeditions of the R/V Marcus G Langseth in 2010 and 2012.
The core samples, drilled from several locations on Tamu Massif, showed that thick lava flows (up to 75 feet thick), characterise this volcano.
Seismic data from the R/V Langseth cruises revealed the structure of the volcano, confirming that the lava flows emanated from its summit and flowed hundreds of kilometres downhill into the adjacent basins.
Tamu Massif's top lies about 6,500 feet below the ocean surface, while much of its base is believed to be in waters that are almost 6 km deep.

The study was published in the journal Nature Geoscience.