Oceanographers led by Dr William Sager from the University of Houston have discovered what they say is the biggest single volcano yet documented on our planet.

The volcano, named Tamu Massif after Texas A&M University, is believed to be about 145 million years old. It became inactive within a few million years after it was formed.

The top of Tamu Massif lies about 6,500 feet (1,981 m) below the ocean surface, while much of its base is believed to be in waters that are almost 4 miles (6.4 km) deep.

Dr Sager and his colleagues from Japan, UK and the United States examined a large underwater area in the northwest Pacific known as the Shatsky Rise, located about 1,000 miles east of Japan. They had found that the plateau contained three enormous mounds.

“We got tired of referring to them as the one on the left, the one on the right and the big one,” said Dr Sager, who with colleagues reported the discovery in the journal Nature Geoscience.

“We knew it was big, but we had no idea it was one large volcano. Our final calculations have determined it is about 120,000 square miles in area, or about the size of the state of New Mexico, making it by far the largest ever discovered on Earth. It rivals in size some of the largest volcanoes in the solar system, such as Olympus Mons on Mars.”

Olympus Mons, the largest volcano on Mars, is so big that it can be seen with many common backyard telescopes. The largest active volcano on Earth is Mauna Loa in Hawaii, which has erupted off and on for the past 700,000 years. But it is about 2,000 square miles in size, a tiny fraction of Tamu Massif.

“What is unusual about the volcano is its slope – it’s not high, but very wide, so the flank slopes are very gradual. 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 center of the volcano to form a broad, shield-like shape,” Dr Sager said.

“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. An immense amount of magma came from the center, 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,” he concluded.

______

Bibliographic information: William W. Sager et al. An immense shield volcano within the Shatsky Rise oceanic plateau, northwest Pacific Ocean. Nature Geoscience, published online September 05, 2013; doi: 10.1038/ngeo1934