Report on Suwanosejima (Japan) — 3 March-9 March 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
3 March-9 March 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, 3 March-9 March 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 intermittent eruptive events at Suwanosejima’s Ontake Crater during 26 February-2 March. Bombs were ejected as far as 600 m away from the crater and ashfall was reported in Toshima village (4 km SSW). The number of explosions began increasing on 2 March; the total recorded through 1500 on 7 March was 139, but by 1500 on 8 March there was only one additional explosion. The Tokyo VAAC reported that ash plumes rose 0.9-2.1 km (3,000-7,000 ft) a.s.l. during 3-7 March. An explosion at 0317 on 6 March ejected tephra as high as 500 m above the crater rim and bombs 900 m away. The Alert Level remained at 2 (on a 5-level scale).
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.