Report on Suwanosejima (Japan) — 29 April-5 May 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
29 April-5 May 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, 29 April-5 May 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 that at 0432 on 28 April an eruption at Suwanosejima’s Ontake Crater produced a plume that rose 1.6 km above the crater rim and ejected blocks as far as 800 m from the crater. An explosion at 1214 on 29 April caused glass in an office building to vibrate in a village 4 km SSW. There was a total of 64 and 50 explosions recorded on 28 and 29 April, respectively; two explosions were detected on 30 April and one on 1 May. 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.