Japan Coast Guard officials say the volcanic eruptions on a tiny remote island in the Pacific are expanding Japan's territorial waters and exclusive economic zone.
Volcanic activity began near Nishinoshima Island in November 2013. Lava flows have made the island larger.
The coast guard conducted an aerial radar survey in July to revise nautical charts.
The officials found that the island's western coast had been extended by 320 meters and the southwestern coast by 230 meters since the last survey 2 years ago.
The island's surface area has grown by around 10 percent to 3 square kilometers.
The officials estimate that the eruptions will add 4 square kilometers to Japan's territorial waters, and the EEZ will expand by 46 square kilometers.
The coast guard plans to continue monitoring the island.