The world's largest volcano deprived of its title after magnetic anomalies reveals its true nature

The world's largest volcano lost its title after scientists discovered that it had formed by the spread of the seabed rather than by a single eruption.

Tamu Massif is an extinct volcano in the Pacific Ocean, about 1,000 km east of Japan. It covers an area of ​​120,000 square miles, which is about the size of New Mexico. It is part of the Shatsky Rise submarine mountain range, which formed about 145 million years ago during a series of volcanic eruptions. Previously, it was unclear whether Tamu Massif was the result of multiple eruptions of different volcanoes, or a single huge volcano.

In 2013, researchers led by William Sager, of the University of Houston, announced that the volcano was the result of a massive eruption in the center of the mountain, making it the world's largest shield volcano and the largest in the world. 39, one of the most important in the solar system. However, new research also conducted by Sager has now shown that the volcano was not what it initially seemed.

"After our 2013 article saying that Tamu Massif is the biggest shield volcano in the world, there were still things that harassed me," he said. Newsweek. The Tamu Massif is located at a triple junction of thick ridges – the junction point of the boundaries of three tectonic plates. The interaction of the volcano with this geological feature – also a type of volcano – was not clear.

Sager said they wanted to know more about the formation of the volcano by examining its magnetic signature. The Earth is surrounded by a magnetic field in constant motion. Sometimes the whole field rocks – if you were looking at a compass during a period of inversion, the north would be headed south and vice versa.

The magma contains magnetic minerals. Thus, when it cools and solidifies, it aligns to the magnetic field, thus providing a record of its position at that precise moment. Because of the way the Earth's crust divides, scientists can use this information to determine the global magnetic field. "Subtract the expected value from the magnetic field and you will get" anomalies, "positive and negative magnetic," said Sager.

"I thought that the magnetic signature would be revealing because magnetic anomalies formed by spreading ridges surround the Tamu Massif.I wanted to know if they would die on the edges or how deep in the volcano they go."

The magnetic field reversals spread over thousands, even millions of years, so if Tamu Massif had erupted into a single event, there would be no anomalies. However, an eruptive period that would last much longer could have a turning back.

To find out, the team went to Tamu Massif aboard the research vessel of the Schmidt Ocean Institute Falkor make a magnetic anomaly card. Their findings showed that there were magnetic anomalies in the volcano that corresponded to anomalies observed on its edges. "A huge shield volcano should not form magnetic tapes," said Sager. "If it has formed in a short time (a period of polarity), it will have a coherent global anomaly.If it has formed during several periods of polarity, the anomaly should be irregular. Lava flows that travel long distances must destroy magnetic tapes. "

Publish their discoveries in Nature Geoscience, According to the team, Tamu Massif seems to be an oceanic plateau formed by a process called seabed propagation. Instead of adding new material on the top of the volcano, it was built by inflation and deflation of the crust as it thickened and thinned, forming at the top of Ridge. This means that new material is added to the center and older material is removed.

As a result of these discoveries, the title of the world's largest volcano dates back to Mauna Loa, Hawaii. It also means that Tamu Massif is a strange hybrid of volcanism and plaque formation and, to Sager's knowledge, unique. "I'm working on analyzing existing data on other ocean plateaus to see if I can find more evidence of peak formation," he said. "So far, I can not find an example of an ocean shelf that did not form on a ridge, the problem is that the existing data is mediocre (the oceanic plateaus have found a good place to hiding), so for many, I can not say if they formed at the peak. "

This article has been updated to include more information about the research vessel used for the survey.