Report on Suwanosejima (Japan) — 14 October-20 October 2020
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 14 October-20 October 2020
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2020. Report on Suwanosejima (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 14 October-20 October 2020. Smithsonian Institution and US Geological Survey.
Suwanosejima
Japan
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
JMA reported nighttime incandescence and intermittent eruptive activity at Suwanosejima’s Ontake Crater during 9-16 October. Four explosions were recorded during 12-14 October; an explosion at 0100 on 13 October ejected bombs 400 m from the crater and an explosion at 0313 on 14 October produced an ash plume that rose 1.2 km above the crater rim. Ashfall was periodically reported in Toshima village, 4 km SSW. The Alert Level remained at 2 (on a 5-level scale).
Geological Summary. The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. One of Japan's most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits covered 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 an open collapse scarp extending 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.