Report on Suwanosejima (Japan) — 21 August-27 August 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 21 August-27 August 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Suwanosejima (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 21 August-27 August 2002. Smithsonian Institution and US Geological Survey.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
Eruptive activity began to decline at Suwanose-jima in comparison to the previous week. Periods of volcanic tremor occurred on the 19th and 20th. According to the Suwanose-jima office of Toshima Village, rumbling sounds were not as strong as those of the previous week, but were sometimes accompanied by the sounds of large explosions on the 20th. Small amounts of ash fell in inhabited areas about 4 km SSW of the summit on the 20th and 21st. On the afternoon of the 20th ash also fell in Naze city on Amami-oshima Island, about 140 km S of Suwanose-jima. Aerial inspections conducted during the report period by the staff of Kagoshima Meteorological Observatory revealed that an ash-rich cloud rose 1.5 km above the crater and drifted S.
Geologic Background. 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.