Report on Suwanosejima (Japan) — 18 January-24 January 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 18 January-24 January 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, 18 January-24 January 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 16-23 January. No explosions were recorded, though eruption plumes rose as high as 1.2 km above the crater rim and blocks were ejected as far as 300 m from the vent. Ashfall was occasionally reported in Toshima village (3.5 km SSW). JMA noted that the number of explosions began decreasing in mid-October 2022 and the last explosion was recorded on 16 November. Additionally, plume heights had occasionally risen higher than 2 km above the crater rim during October-November 2022, but starting in December the heights had generally been at or below 1 km. Other data had also indicated low levels of activity; the probability of material being ejected more than 1 km away from the crater had decreased. The Alert Level was lowered to 2 (on a 5-level scale) on 24 January, 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.