Report on Suwanosejima (Japan) — 15 September-21 September 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
15 September-21 September 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, 15 September-21 September 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 the number of daily explosions at Suwanosejima's Ontake Crater increased on 16 September and remained elevated through 20 September. Eruption plumes rose as high as 2.4 km above the crater rim and material was generally ejected 300 m away from the crater. Notably, explosions at 2014 on 16 September and at 0212 on 17 September ejected material almost 1 km S and SE, respectively. 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.