After being knocked from its lofty perch in 2013, Hawaii island’s Mauna Loa is once again king of the mountain as the world’s largest shield volcano.

“We have to hand the crown back to Mauna Loa,” said Will Sager, a professor of marine geophysics at the University of Houston who received his master’s degree and Ph.D. at the University of Hawaii at Manoa. “It’s the world’s largest shield volcano.”

In 2013 Sager’s research of an undersea “anomaly” called Tamu Massif — located about three-quarters of the way between Hawaii and Japan — suggested that Tamu Massif was the world’s largest shield volcano.

“That was the biggest shield volcano that anyone knew of at the time,” Sager said. “It eclipsed Mauna Loa by 50 times. … It’s the size of New Mexico.”

Shield volcanoes take shape as thin, liquid basalt lava surfaces through vents in “flow after flow… building a broad, gently sloping cone of flat, domical shape, with a profile much like that of a warrior’s shield,” according to the U.S. Geological Survey. Shield volcanoes like Mauna Loa build slowly over time from hundreds of eruptions creating layers.

After his team’s original paper was published in Nature Geoscience in 2013, something bothered Sager.

“Nature Geoscience has a really good press department,” Sager said. “The hook was that ‘scientists discover biggest volcano in the world.’ It went viral. You can’t argue with big press. There were over 400 web articles. But there were things that bugged me.”

So in a follow-up article published Monday by Nature Geoscience, Sager’s team said it was premature to call Tamu Massif Earth’s largest shield volcano — or even to compare it to Mauna Loa, because they are so different.

“It’s like putting together a dinosaur with only a tooth and a leg bone,” Sager told the Honolulu Star-Advertiser on Friday. “We’re taking partial information and putting it together with the model we understand. In hindsight that wasn’t right.”

Asked how Tamu Massif should be categorized if it’s not a shield volcano, Sager said, “There is no good volcanic analogy.”

Tamu Massif likely formed when two undersea plates pulled apart — allowing magma to spurt out — before closing again and pulling apart again over time.

All of the activity at Tamu Massif “could form thick crust as it built up and then it got thin again,” Sager said. “It’s one of the biggest volcanic mountains in the world, but it’s not a single shield volcano.”

That distinction now reverts to Mauna Loa.

Janet Babb, a geologist and spokeswoman for the U.S. Geological Survey’s Hawaiian Volcano Observatory, wrote Friday in an email to the Star-Advertiser that Sager’s updated research suggests that Tamu Massif is a “complex of volcanoes on a mid-ocean spreading ridge system, whereas Mauna Loa is a result of hot spot volcanism (a shield volcano above the Hawaiian hot spot).”

Tamu Massif is a rounded dome that measures about 280 by 400 miles, “or more than 100,000 square miles,” Babb wrote. It sits about 6,500 feet below the surface of the ocean, with a base that extends down to about 4 miles deep, she said.

“Tamu Massif dwarfs the largest active volcano on Earth, Mauna Loa in Hawaii, which measures about 2,000 square miles … stands about 1.86 miles tall with its summit about one mile below the surface of the ocean,” Babb wrote.

“When you count all that goes on below the ocean, Mauna Loa is twice as high,” Sager said. While Mauna Loa’s slope sits at about a 5-degree angle, Tamu Massif spreads out at a more gentle 1-degree slope, Sager said.

The data suggests that Tamu Massif is something different, certainly not a shield volcano, Sager said.

“This ocean plateau is a special type of volcano,” he said.

Mike Garcia, a UH professor of earth sciences, knew Sager from Sager’s student days when they did research together.

Sager’s latest research “puts Mauna Loa back in front,” Garcia said.

Perhaps more important, Garcia said that ongoing research “tells us about the processes going on in the Earth’s mantle.”

After Sager’s 2013 paper was published, Babb said the Hawaiian Volcano Observatory wrote a Volcano Watch article titled “Mauna Loa is still the largest ACTIVE volcano on Earth.”

Now the latest research by Sager’s team suggests they were “comparing apples to oranges,” Babb wrote. “Thus, the new research on Tamu Massif may not have any implications for Mauna Loa — other than it proves that we can now drop the ‘ACTIVE’ qualifier — i.e., ‘Mauna Loa is the largest volcano on Earth.’”