Scientists identify the source of 7,500-square-mile "pumice island"

Australian Naval officer Tim Oscar called the massive chunk of volcanic rock pictured up top "the weirdest thing [he'd] seen in 18 years at sea." Now, NASA satellite images have revealed the source of the floating raft: a mysterious undersea volcano known as the Havre Seamount.

Everyone knew the mass likely came from an underwater volcano — when lava cools rapidly, it turns to pumice, which, being less dense than water, bobs on the surface of the ocean not unlike the edge of an ice shelf. The general consensus last week was that the pumice had likely emanated from an underwater volcano situated north of New Zealand by the name of Monowai, but as SPACE.com's Jeanna Bryner explains, we now know this to be false:

To finger the source, scientists looked to earthquake records and satellite imagery. New Zealand's GNS Science organization and scientists from Tahiti suggested a connection between the pumice raft and a cluster of earthquakes in the Kermadec Islands on July 17-18. (As magma rises from undersea volcanoes, pushing its way through cracks in the seafloor, the pressure can lead to earthquakes.)

As for imagery, volcanologist Erik Klemetti, an assistant professor of geosciences at Denison University, and NASA visualizer Robert Simmon looked through a months' worth of satellite photos taken by NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra and Aqua satellites. And that's where they gleaned the first evidence of the offending volcano. Images taken on July 19, from 9:50 a.m. to 2:10 p.m. local time, revealed ash-stained water, gray pumice and a volcanic plume.

Scientists identify the source of 7,500-square-mile "pumice island"

Overlaying these images onto topographical maps of the ocean floor revealed a little-studied volcano by the name of Havre Seamount to be the likely source of the pumice raft (according to Klemetti, "Havre doesn't even have an entry in the Global Volcanism Program database or really any information about it," and " doesn't even show up on many maps of the active Kermadec volcanoes"). Additional, nighttime images from MODIS also showed plenty of heat emanating from the volcano's erruption, suggesting it was strong enough to breach the ocean surface. All that being said, Klemetti says research teams will need to observe the seafloor eruption site firsthand to confirm that Havre Seamount is, in fact, the source of the pumice raft.

Read more at Wired Science, NASA Earth Observatory and SPACE.com.

NASA MODIS image courtesy of Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC