Report on Suwanosejima (Japan) — 23 June-29 June 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
23 June-29 June 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Suwanosejima (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 23 June-29 June 2021. Smithsonian Institution and US Geological Survey.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
JMA reported that eruptive activity at Suwanosejima's Ontake Crater increased during 21-23 June with multiple events. Eruptive events at 2254 on 21 June and 0004 on 23 June ejected large incandescent bombs 900 m NW and SE (respectively) from the crater; eruption plumes rose 1.2 km above the crater rim. The increased activity prompted JMA to raise the Alert Level to 3 at 0015 on 23 June and warn the public to stay at least 2 m away from the active crater. During an overflight on 23 June scientists noted incandescence on the crater floor and that there were several high-temperature deposits scattered in and around the crater. White plumes rose 200-300 m above the crater rim. Multiple eruptive events during 23-28 June ejected bombs 600 m and produced ash plumes that rose as high as 2.3 km.
Geological Summary. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed 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 the horseshoe-shaped Sakuchi caldera, which extends 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.