Report on Suwanosejima (Japan) — 14 June-20 June 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 14 June-20 June 2023
Managing Editor: Sally Sennert. Written by JoAnna G. Marlow.
Please cite this report as:
Global Volcanism Program, 2023. Report on Suwanosejima (Japan) (Marlow, J G, and Sennert, S, eds.). Weekly Volcanic Activity Report, 14 June-20 June 2023. 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 eruption at Suwanosejima's Ontake Crater continued during 14-19 June. A total of 526 volcanic earthquakes, 26 explosions, and 18 eruptive events were recorded by seismic monitoring stations throughout the week; activity was most notable during 15-16 June with totals of 164 volcanic earthquakes and 10 explosions. Ash plumes were observed daily; the tallest plumes rose 2 km above the crater rim on 15 and 16 June. Continuous emissions during 0936-1355 on 16 June rose as high as 2 km and drifted SE and SW. Some events ejected large volcanic blocks up to 400 m from the crater during 14-18 June. Incandescent ejecta from explosions during the nights of 18-19 June were sometimes visible in webcam images. Occasional ashfall and rumbling noises were reported in Toshima village (3.5 km SSW). The Alert Level remained at 2 (on a 5-level scale) and the public was warned to stay at least 2 km away from the crater.
Geological Summary. The 8-km-long 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. 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 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 open 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.