Report on Suwanosejima (Japan) — 30 September-6 October 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 September-6 October 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Suwanosejima (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 30 September-6 October 2020. 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 nighttime incandescence at Suwanosejima’s Ontake Crater during 25 September-2 October. Eruptive activity was intermittently recorded along with nine explosions. Ashfall was periodically reported in Toshima village, 4 km SSW. An explosion at 0822 on 26 September generated a gray-white ash plume that rose 2 km above the crater rim. At 2028 on 27 September an explosion ejected blocks 400 m from the crater. The Alert Level remained at 2 (on a 5-level scale).
Geologic Background. 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.