Biggest and Hottest Shield Volcano in the World Is Twice As Big As Hawaii's Mauna Loa

The world's biggest and hottest shield volcano has been identified in Hawaii, with researchers discovering Pūhāhonu is twice as big as the previous record holder, Mauna Loa.

A shield volcano is a type of volcano made almost entirely of lava flows. They have a broad dome shape with gentle sloping sides. Mauna Loa, on the Island of Hawaii, covers an area of 2,035 square miles. Until now it was considered the world's biggest volcano—a title briefly held by the extinct, underwater volcano Tamu Massif, until scientists discovered it did not form through a single eruption.

In 1974, scientists suggested that based on limited survey data, Pūhāhonu may be the largest volcano in Hawaii. However, later studies that included the parts of Mauna Loa below sea level meant the latter was named the largest volcano.

In a study published in the journal Earth and Planetary Science Letters, researchers have now analyzed rocks from the volcano, carried out new bathymetric and gravity mapping, and refined models to better estimate its size. Lead author Michael Garcia, from the Department of Earth Sciences, University of Hawai'i at Mānoa, said the team's goal was to survey volcanoes in the Northwest Hawaiian Ridge, which makes up part of the Hawaiian Emperor chain.

Their findings showed Pūhāhonu was far larger than Mauna Loa, at almost twice the size. "Until our study, everyone believed that Mauna Loa was the world's largest volcano—it remains the tallest volcano..." Garcia told Newsweek in an email.

"We were surprised to find the Pūhāhonu was twice the size of Mauna Loa. Marine eruption has removed much of the volcano, so it is no longer as tall or taller than Mauna Loa."

As well as finding Pūhāhonu is the world's biggest shield volcano, they also found it is the hottest. They calculated that an extremely hot mantle is the best explanation for the large volumes of magma that would have been needed to produce such a huge volcano. "The gargantuan size of Pūhāhonu reflects its high melting temperature, the highest reported for any Cenozoic basalt," they wrote, saying a single "wave" from the Hawaiian plume was probably the cause.

"The temperature we calculated is based on the composition of the rock and its minerals was 1700 C," Garcia said. "This is exceptionally hot compared to any known lava in the last 65 million years. The new finding tells us that the Hawaiian mantle plume has pulses of hot material that rise from the lower mantle as solitary waves. These waves are more insulated from the surrounding mantle allowing them to erupt at higher temperatures."

Concluding, the researchers say the Hawaiian Emperor Chain is one of the best-studied mantle plumes, yet we are still learning more about its history through mapping and sampling. Garcia said the seafloor is a "great frontier for science," with many things yet to be discovered. "We have a general idea of what is down there but the details remain elusive for much of the ocean basins."