It must have been a strange sight: Passengers on an airplane flying over the Southwest Pacific in July 2012 saw a raft of pumice — light, porous volcanic rock — that would eventually grow to be 150 square miles, more than three times the area of the city of Boston.
It was a telltale sign of the largest underwater volcanic eruption of the past century, according to researchers from Woods Hole Oceanographic Institution, which, along with the University of Tasmania, led the first up-close investigation of the eruption.
Researchers deployed Sentry, an autonomous underwater vehicle, and Jason, a remotely operated vehicle, to explore, map, and collect materials from the volcano, WHOI said in a statement.
Findings from the 2015 expedition to the Havre volcano, which rises from about a mile below the ocean to about 2,100 feet under the surface, were published Wednesday in the journal Science Advances.
“Mapping, observation and sampling by submersibles have provided an exceptionally high fidelity record” of what the volcano ejected, which included lava from 14 vent sites, researchers said in the study.
More than three-quarters of the pumice chunks ejected floated away from the volcano, the study said, while some, including chunks 30 feet in diameter, settled to the seafloor.
The study opened a new window on volcanic activity on the seafloor, where more than 70 percent of all volcanic activity on Earth occurs.
Adam Soule, WHOI associate scientist and chief scientist for the the National Deep Submergence Facility, which operates and maintains the submersibles, said one lesson learned was that researchers looking at the seafloor debris around volcanos that have erupted in the past won’t get a full picture of an eruption’s scale because much of the rock might have floated away.
“There’s a good chance we’re missing a large part,” he said in a telephone interview.
Soule said researchers expected to find signs of an explosive eruption because pumice is associated with such eruptions. But when they arrived at the site they found the eruption had been “largely effusive, meaning kind of gentle,” while still producing pumice.
For years after the eruption, pumice washed ashore in New Zealand and Australia, he said.
The Jason submersible brought samples of dense lava, ash, pumice, and giant pumice to the surface, including one piece 5 feet in diameter that was the first of its kind ever collected, WHOI said.
Scientists are examining the physical and chemical composition of the samples to learn more about the eruption and the materials themselves, WHOI said.
Scientists from WHOI and the University of Tasmania were joined by others from the University of California Berkeley and the University of Otago in New Zealand on board the research vessel Roger Revelle, operated by the Scripps Institution of Oceanography. The study was supported by a grant from the National Science Foundation.