Floating pumice stones have washed ashore on a beach in Chiba Prefecture, near Tokyo. Officials have yet to determine whether they are from an underwater volcanic eruption in the Pacific.
Professor Emeritus Hayakawa Yukio of Gunma University posted a photo of a small number of lightweight stones on his Twitter account on Monday. He said he found them on a beach in Tateyama City, Chiba Prefecture.
City and prefectural officials are investigating whether the stones are from the undersea volcano that erupted near the Ogasawara Islands in August.
Since mid-October, such stones have been appearing on coastlines in Okinawa and Kagoshima prefectures in southwestern Japan, affecting local fishing operations and tourism industry.
Tateyama city officials say they have received no reports of damage to local ship navigation and fishing activities.
The prefectural government of Chiba is calling on local residents to report it if they find any such stones.
Pumice stones have also been found washed ashore on Miyakejima and Mikurajima, two of the Tokyo-administered Izu Islands in the Pacific.
On Miyakejima, stones stretching for several tens of meters were found on a beach near a fishing port in the northwestern part of the island. Officials say a large one was measured at 4 centimeters in length. No interference with ships has so far been reported.
The Tokyo Metropolitan Government is working with local municipalities and the Coast Guard to gather information and monitor the situation.