Report on Suwanosejima (Japan) — 15 February-21 February 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 15 February-21 February 2023
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2023. Report on Suwanosejima (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 15 February-21 February 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 13-20 February. Occasional ashfall and rumbling noises were reported in Toshima village (3.5 km SSW). The number of explosions per day increased on 13 February and then gradually decreased beginning on 16 February; a total of about 24 explosions occurred during the week. At 2131 on 15 February an explosion produced an ash plume that rose 1.3 km above the crater rim and ejected large blocks as far as 900 m SE. An explosion around an hour later, at 2237, ejected large blocks as far as 700 m SE. During 18-20 February explosions produced ash plumes that rose as high as 2 km above the crater rim and ejected large blocks as far as 400 m from the vent. Crater incandescence was visible at night. The Alert Level remained at 2 (on a 5-level scale) and residents were warned to stay 1 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.