Scientists at the University of Houston have uncovered the largest single volcano on Earth, located under water about 1,600 kilometres east off the coast of Japan.

Covering about 311,000 square kilometres, an area equivalent to the state of New Mexico, the Tamu Massif volcano is considerably bigger than the Mauna Loa in Hawaii, the largest active volcano on Earth, which only comes in at 5,200 square kilometres.

The newly discovered volcano is as big as some of the volcanoes on Mars, placing it among the largest in the solar system.

"Tamu Massif is the largest single shield volcano ever discovered on earth," reports William Sager, a professor at the department of Earth and Atmospheric Sciences at the University of Houston. A shield volcano is one that is built almost entirely of fluid lava flows.

Sager and his team have published their findings in the upcoming issue of Nature Geoscience, due out on Sept. 8.

The Tamu Massif is the largest feature of the underwater mountain range known as the Shatsky Rise, which formed 130 to 145 million years ago by the eruption of several underwater volcanoes.

Until now, scientists couldn’t determine whether the Tamu Massif was a single volcano or a composite of many eruption points.

Sager’s team used core samples and seismic data collected from a research ship to verify that it was a single entity.

Researchers were able to confirm that a mass of basalt that makes up the Tamu Massif erupted from a single source near its centre. The seismic information unveiled the structure of the volcano, confirming that lava flowed from its summit and hundreds of kilometres downhill into basins

2,000 metres below ocean surface

The massif is unique not only because of its size but its shape. It’s low and wide, which means that the lava flows must have travelled long distances compared to other volcanoes on earth.

"It’s not high… so the flank slopes are very gradual," notes Sager. "If you were standing on its flank, you would have trouble telling which way is downhill."

The team believes the Tamu Massif is about 145 million years old and became inactive within a few million years after its formation. The top of it lies 2,000 metres below the ocean’s surface.

"Its shape is different from any other sub-marine volcano found on Earth," says Sager. "An immense amount of magma came from the centre, and this magma had to come from the Earth’s mantle. So this is important information for geologists trying to understand how the Earth’s interior works."

Sager has put his own imprint on the discovery. The volcano’s name is an abbreviation of Texas A&M University, where Sager worked for 29 years before heading over to the University of Houston. Massif is the French word for "massive," and a scientific term for a large mountain mass.