Volcanic giant found in the Pacific Ocean

An international team of scientists may have uncovered the biggest volcano on Earth, a colossal extinct structure lying under the north-western Pacific Ocean, at the boundary of three tectonic plates some 1600 km east of Japan.

Tamu Massif

Covering an area roughly equivalent to the British Isles or 450 x 650 km, the rounded-dome basalt volcano named Tamu Massif is comparable in size to the Olympus Mons Volcano on Mars. This places it among the largest known volcanoes in the Solar System.

Professor William Sager from the Department of Earth and Atmospheric Sciences at the University of Houston and colleagues used seismic data and rock samples drilled from the seabed of the Shatsky Rise oceanic plateau to image and analyse the structure of Tamu Massif, which formed about 145 million years ago.

Biggest single shield volcano

“Tamu Massif is the biggest single shield volcano ever discovered on Earth,” says Professor Sager in a press release from the University of Houston. “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.”

Tamu Massif stands out among underwater volcanoes for both its size and shape. It is low and broad, with the erupted lava flows having travelled long distances.

“It’s not high but very wide, so the flank slopes are very gradual,” says Professor Sager. “In fact, if you were standing on its flank, you would have trouble telling which way is downhill. We know that it is a single immense volcano constructed from massive lava flows that emanated from the centre of the volcano to form a broad, shield-like shape. Before now, we didn’t know this because oceanic plateaus are huge features hidden beneath the sea. They have found a good place to hide.”

Shatsky Rise – underwater mountain range

Professor Sager first began studying the Shatsky Rise oceanic plateau about 20 years ago when he was at Texas A&M University’s (TAMU) College of Geosciences. The Shatsky Rise is an underwater mountain range formed 130–145 million years ago by the eruption of several underwater volcanoes. Tamu Massif, named after the professor’s former university, is the largest feature of the Shatsky Rise. However, until now, it was widely believed that Tamu Massif was a composite of many eruption points.

The research team integrated core samples and data collected on board the research vessel JOIDES Resolution in 2009 (on Integrated Ocean Drilling Program (IODP) Expedition 324) with seismic reflection data gathered on two separate expeditions of the research vessel Marcus G Langseth (on cruises MGL1004 and MGL1206) in 2010 and 2012. This confirmed that the mass of basalt that constitutes Tamu Massif erupted from a single source near the centre – making it one giant volcano. The lava flow, up to 23 m thick, emanated from the summit and flowed hundreds of kilometres downhill to create the massive low-gradient (around 1° and less) shield. The top of the volcano lies almost 2 km below the ocean surface, while much of its base lies in waters that are almost 6.5 km deep.

Clues about how volcanoes form

“Its shape is different from any other sub-marine volcano found on Earth and it’s very possible it can give us some clues about how massive volcanoes can form,” says Professor Sager. “An immense amount of magma came from the centre, and this magma had to have come from the Earth’s mantle. So this is important information for geologists trying to understand how the Earth’s interior works.”

Since this article was written, scientists have continue to study Tamu Massif and in 2016 a joint China-US study found that it could be the biggest volcano in our solar system, find out more in this article.