Report on Suwanosejima (Japan) — 25 August-31 August 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
25 August-31 August 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, 25 August-31 August 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 15 explosions at Suwanosejima's Ontake Crater produced eruption plumes that rose as high as 3.2 km above the crater rim during 20-27 August. Large volcanic bombs were ejected 300 m from the crater. Crater incandescence was visible nightly and ashfall was often reported in Toshima village (4 km SSW); a large amount of ash fell in the village on 26 August. At 1231 on 28 August an eruption produced an ash plume that rose 4.8 km above the crater; weather clouds prevented clear views, though observations indicated that the event continued at least through 1700. The Alert Level remained at 2 and the public was warned to stay 1 km away from the crater.
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.