ABOUT 600 MILES northwest of Honolulu, in the middle of the Pacific Ocean, two small pinnacles poke out of the sea. To an observer, the 5 acres of rock known as Puhahonu might seem insignificant, except as a landing pad for weary seabirds. But their presence suggests the existence of something much bigger beneath the surface: what many experts are now calling the largest single volcano on Earth. New seafloor mapping of the Papahanaumokuakea Marine National Monument revealed Puhahonu's full size. Michael Garcia, a volcanolo-gist at University of Hawai'i at Manoa, and his colleagues found that the mostly submerged volcano contains at least 35 cubic miles of rock, according to a study published in 2020 in Earth Planetary Science Letters. That's roughly double the volume of Hawaii's Mauna Loa, the previous record-holder for largest shield volcano on the planet. At its widest point, Puhahonu, which means "turtle surfacing for air" in Hawaiian, spans a remarkable 170 miles.
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