HONOLULU (KHON2) — Pūhāhonu means “turtle rising for breath” in Hawaiian. It’s also considered the largest and hottest oceanic shield volcano on Earth. A shield volcano is formed of fluid lava flows.

Located within the Papahānaumokuākea Marine National Monument, Pūhāhonu is nearly twice as big as Mauna Loa. Geoscientists had long thought that Mauna Loa was the largest such volcano until 2020 when researchers at the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology (SOEST) shared the discovery. This distinction hasn’t changed.

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“That isn’t a distinction that will change year-to-year,” said Dan McCorkle with the National Science Foundation (NSF). “The 2020 study documented the size of Pūhāhonu and estimated the temperatures deep in the earth at the time Pūhāhonu formed, roughly 12.5 to 14 million years ago. So its title as ‘largest and hottest’ is likely to last.”

While Pūhāhonu is known to be the largest oceanic shield volcano, whether it’s the largest shield volcano on Earth is debatable. According to NSF’s Dr. Kevin Johnson, there are several much larger continental shield volcanoes.

Johnson, based in Hawaii, was a professor at UH Mānoa’s SOEST for over 20 years prior to moving to NSF. His area of research was oceanic volcanoes.

“There are several volcanoes on continents that are similar or much larger in size, such as the Columbia River Basalts in the northwestern U.S. (174,000 cubic km), the Deccan Traps in India (~1,000,000 cubic km) and the Siberian Traps (~955,000 cubic km),” Johnson told KHON2.

He said Pūhāhonu is approximately 148,000 cubic kilometers in volume.

Kamaʻehuakanaloa, formerly known as Lōʻihi Seamount, is another volcano scientists are keeping their eyes on. It’s likely to one day break the surface of the ocean and become a new island, but scientists cannot predict how long that would take. They said it depends on the rate of eruption.

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Johnson shared that a NSF-funded project has recently been approved to study Kamaʻehuakanaloa but is awaiting ship scheduling to proceed. It’s expected to happen within the next couple of years.