TAIRIKU KUROSAWA/ Editorial Writer
January 8, 2022 at 18:30 JST
A budding islet created by the eruption of an underwater volcano appears to now be fully submerged due to wave erosion of the lava mass.
The Asahi Shimbun’s Asuka light aircraft on Jan. 6 flew over the Fukutoku-Okanoba underwater volcano just north of Minami-Iwojima island in the Ogasawara island chain that lies about 1,000 kilometers south of Tokyo.
While accumulated lava could be seen just under the waves, Setsuya Nakada, who heads the Center for Integrated Volcano Research at the National Research Institute for Earth Science and Disaster Resilience, observed that even at low tide, when the flight was made, no land mass emerged above the water surface.
Nakada also noted that there was almost no outflow of pumice, welcome news for fishermen forced to abandon their work as pumice clogged fishing ports not only in locations close to the Ogasawara chain, but as far away as Okinawa Prefecture, also about 1,000 km away.
A full-scale eruption at Fukutoku-Okanoba on Aug. 13 sent plumes of smoke and ash to heights of 16 km. It was the largest eruption in about a century, next to the 1914 eruption of Sakurajima in Kagoshima Prefecture.
A flight by the Asuka over Fukutoku-Okanoba in October showed evidence of a layered foundation created by lava. But this time it was nowhere to be seen, having been eroded by the waves.
However, there were signs that volcanic activity was continuing as waters around the underwater volcano were greenish.
Only a very thin band of floating pumice was observed from the air. No pumice was visible after flying about 50 km west of the underwater volcano.
Nakada said the pumice was created by the erosion of the emerging island, but few traces of it exist now.
The Japan Coast Guard confirmed the first appearance of a new island in 35 years. Fukutoku-Okanoba created tiny islets in the past after eruptions in 1904, 1914 and 1986. However, those also eventually submerged through erosion due to the soft nature of the lava.
Pumice was carried by the Kuroshio Current northward toward the coastal areas of western Japan, the Izu island chain and the Kanto region.
“Conjecturing from past examples, another large eruption like the one last year will not likely occur anytime soon,” Nakada said. “But that eruption created a ‘foundation’ on the seabed, so it might become easier to leave behind an island with the next large eruption.”
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