What happened to the "pumice stone" that washed ashore in large quantities on the coasts of Okinawa and other places last year?
One year has passed since the eruption of the submarine volcano on the Ogasawara Islands that caused it.
As we proceeded with the interview, we found that the pumice stone seemed to spread to places where it had not existed before.
Furthermore, in Okinawa, there are also new issues related to pumice stone.
I will tell you in detail.
(Reporter Goichi Miyahara, Social Affairs Department, Reporter Keisuke Miyahara, Okinawa Bureau)
A large-scale eruption of a submarine volcano that erupted pumice
The eruption occurred from August 13th to 15th last year, exactly one year ago during the Obon period.
For the first time in 11 years, a large-scale eruption occurred at the submarine volcano "Fukutoku Okanoba" in the Ogasawara Islands.
A large amount of "pumice" was ejected by this eruption.
Two months after the eruption, they washed ashore in Okinawa Prefecture and the Amami region of Kagoshima Prefecture.
After that, they washed ashore one after another along the coasts of Kanto and the Izu Islands.
Pumice stone collection from Okinawa is progressing, but “disposal” is a challenge
One year after the eruption, we interviewed Okinawa Prefecture to find out what happened to the pumice stone.
At that time, out of the 87 fishing ports in the prefecture, almost all of them were found to have had pumice washed ashore.
In addition to the impact of voluntary suspension of fishing at 33 fishing ports, it washed ashore on beaches in various places, which had a major impact on tourism.
When I visited the beach in Nakijin Village this time, it was covered with a large amount of pumice last year, but pumice can be seen only in some areas.
Some people were enjoying marine leisure as usual.
According to the prefecture, the collection of pumice stones is progressing at fishing ports and beaches, and the situation is returning to its previous state.
On the other hand, it is said that "disposal" after collection is a problem.
At the temporary storage site in Onna Village, black bags containing pumice stones collected from beaches and fishing ports in the village were piled up.
As of June this year, approximately 97,000 cubic meters have been collected across the prefecture and temporarily stored at temporary storage sites in at least 19 municipalities.
It means that there is already a temporary storage place that is full.
Okinawa Prefecture is using some of the collected pumice stone to refill limestone and other mined sites, and is considering using it to prevent red soil from flowing into the sea and to improve farmland soil.
Where is the "pumice stone" now?
Nationwide simulation
A pumice stone whose impact is limited in Okinawa.
where in Japan is it?
Toru Miyama, senior researcher at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted a distribution simulation based on ocean current and wind data.
We'll see the results.
Specifically, pumice continues to be abundantly distributed around Okinawa and Amami.
Furthermore, according to the estimate, it was distributed over a wide area centering on the Pacific Ocean from the Nansei Islands to the northeastern coast.
It is believed to have spread along the Kuroshio Current, which flows east along the southern coast of Japan.
Furthermore, since the beginning of this year, the pumice stone has been riding the ``Tsushima Current'' and has traveled north on the sea west of Kyushu, and since April it may have drifted to the Sea of Japan side.
Around autumn last year, when pumice caused damage to the fishing industry in various places, it was only washed ashore in the Izu Islands and the Kanto region in addition to Okinawa and Amami. can be
According to senior researcher Miyama, the results of this simulation are generally consistent when compared with eyewitness information on SNS.
Expert ``There is a low possibility of drifting ashore, but don't let your guard down''
Although pumice stones are believed to be more widely distributed than last year, Chief Researcher Miyama is calling for a calm response.
As time passes, the pumice is dispersed widely over the sea, and some of it sinks into the sea, so it is said that there is less possibility that it will be washed up on the coast as much as before.
On the other hand, he said, "It wouldn't be surprising if small amounts of pumice were washed ashore in various coastal areas in the future. There is no need to worry too much, but there is a possibility that pumice will enter the engine cooling system of fishing boats and cause trouble." Also, if there is information on pumice stone, please be careful and stay alert."
Do pumice stones affect marine life?
In addition, a large amount of washed-up pumice had an impact on marine life.
The research results were announced by a research group led by Project Assistant Professor Yoshikazu Ohno of Kitasato University, who specializes in marine biology.
From October to December last year, we conducted a survey in Kunigami Village in northern Okinawa Prefecture to see if a large amount of pumice stone was affecting the natural creatures living along the coast.
As a result, it was confirmed that the fiddler crab, a type of sand crab, was affected by the survey, and was partially weakened in the tidal flat covered with pumice.
Fiddler crabs live in burrows in tidal flats and eat microbes in the sand and mud, but it seems that the burrows were clogged with pumice stones and there was a shortage of food.
In the video taken by Mr. Ohno, it was recorded that fiddler crabs were fighting over some of the remaining burrows, and large fiddler crabs drove out smaller fiddler crabs from their burrows.
In addition, in the sea, it was confirmed that some sunken pumice stones were colliding with the surface of the coral.
Although the effects of pumice on corals are not known in detail, the research group will continue to investigate the effects, etc., as small damage is expected to occur.
Project Assistant Professor Ono said, ``Although it was short-term, changes in the behavior of small individuals such as fiddler crabs were also observed, so I think there was a negative impact of pumice on coastal organisms. There are many things we don't know about the effects of pumice stones in the ocean and those that have sunk to the seafloor, so we need to continue our research."
Active volcanic activity continues at Fukutoku Okanoba
What is happening now to "Fukutoku Okanoba" where a large amount of pumice erupted?
No eruptions have been confirmed since August last year, and the Japan Meteorological Agency said the possibility of another eruption of that scale is unlikely for the time being.
However, recent aerial surveys conducted by the Japan Coast Guard have confirmed the distribution of pale yellow-green discolored water directly above the crater, indicating that active volcanic activity is still continuing.
The Japan Meteorological Agency has issued an eruption warning to the surrounding sea area, calling for vigilance to vessels passing through the area, as well as calling attention to floating objects such as pumice caused by the eruption.