Report on Suwanosejima (Japan) — 2 July-8 July 2025
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 2 July-8 July 2025
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2025. Report on Suwanosejima (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 2 July-8 July 2025. Smithsonian Institution and US Geological Survey.
Suwanosejima
Japan
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
The Japan Meteorological Agency (JMA) reported that eruptive activity at Suwanosejima's Ontake Crater continued during 30 June-7 July. Incandescence was observed nightly in webcam images. Six explosions were recorded during the week, at 0806 on 30 July, at 0752 and 1608 on 1 July, at 0206 on 2 July, and at 1327 and 2038 on 6 July. The explosions produced ash plumes that rose as high as 2 km above the crater rim and drifted W, SE, and E; some of the plumes were not visible. Ashfall was reported by the Suwanosejima Branch of the Toshima Village Office (3.5 km SSW) on 30 June and 6 July. Eruptive events during 30 June and 6-7 July generated ash plumes that rose as high as 2 km above the crater rim and drifted W, SE, and E. The Alert Level remained at 2 (the second level on a five-level scale) and the public was warned to be cautious within 1.5 km of the crater.
Geological Summary. The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. One of Japan's most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits covered residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed, forming a large debris avalanche and creating an open collapse scarp extending to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.