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A massive amount of pumice stone that has drifted ashore in Okinawa Prefecture has been causing headaches for local officials, but geologists are seeing it as a great opportunity to learn more about Mother Nature.

At Okinawa Prefectural Museum and Art Museum, researchers are already starting to gather the stones that have drifted onshore throughout Okinawa, noting the date and place where they were found.

For Ken Usami, one of the curators at the facility, it is a reminder of when he gathered pumice stones on Aka Island, part of the Kerama islands group, in 2017 as part of his research.

“If there are more pumice stones found from underwater volcanic eruptions, we’ll be able to compare the two and see if there have been any changes in the Earth’s activities,” he said.

“Pumice stones are evidence of the Earth’s activities. I want to gather them and hand them over to the next generation,” said Usami, adding that he hopes their arrival will get people interested in geology and petrology.

Pumice stones drift in the sea off mainland Okinawa on Oct. 26. | JAPAN COAST GUARD / VIA THE OKINAWA TIMES
Pumice stones drift in the sea off mainland Okinawa on Oct. 26. | JAPAN COAST GUARD / VIA THE OKINAWA TIMES

Yuzo Kato, professor emeritus at the University of the Ryukus in Okinawa, agrees, saying the stones could lead to a better understanding of ocean currents.

When an undersea volcano erupted in 1924 off Iriomote Island, pumice stones drifted north to Hokkaido, said Kato. That helped researchers understand the Kuroshio Current, the ocean current flowing south of Japan, he said.

In 1986, there was an eruption at the Fukutoku-Okanoba underwater volcano — the same one that erupted earlier this year — causing pumice stones to drift ashore on the coast of Okinawa.

This allowed scientists to confirm the flow of the Kuroshima Countercurrent, said Kato. He has high hopes that he will get a better understanding of the flow of the Kuroshio Current and the Kuroshio Countercurrent from satellite images of the pumice stones.

“It is rare to see this massive amount drifting ashore,” he said. “The flow of the pumice stones is a precious opportunity to learn about Mother Nature.”

Jun Tomiyama, a professor of engineering at the University of the Ryukyus, is more interested in using the stones as construction materials.

Tomiyama has been studying ways to reuse waste material that poses difficulties in disposal. Based on a study by University of Tokyo researchers on manufacturing what is called “botanical concrete” — made of waste logs and waste concrete — Tomiyama had been looking at ways to add bagasse, or the remains of crushed sugarcane, to the mix.

It was then that the pumice stones made headlines.

Even though the stones don’t have the appropriate physical properties to be used as construction material, they can be made into concrete if they are mixed with other materials, said Tomiyama.

“In Okinawa, an island with a closed environment, sustainability is key,” he said. “The study on botanical concrete could lead to using pumice stones that would (otherwise) need to be disposed of.”

This section features topics and issues from Okinawa covered by The Okinawa Times, a major newspaper in the prefecture. The original article was published Oct. 29.

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