Report on Suwanosejima (Japan) — August 2018
Bulletin of the Global Volcanism Network, vol. 43, no. 8 (August 2018)
Managing Editor: Edward Venzke. Report research and preparation by: Janine Krippner.
Suwanosejima (Japan) Intermittent ash emission continues from January through June 2018
Please cite this report as:
Global Volcanism Program, 2018. Report on Suwanosejima (Japan). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 43:8. Smithsonian Institution.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
Suwanosejima volcano is located in the northern Ryukyu Islands in the south of Japan and has been on Alert Level 2 since December 2007. This report is a summary of activity for the period January to June 2018 and is based on information from the Japan Meteorological Agency (JMA) along with Tokyo VAAC notices.
During the reporting period, the active Ontake crater produced intermittent explosions that scattered ejecta around the crater and ash plumes to an altitude of 1.5-3 km. Ashfall was reported in a village 4 km away on 10 days during January-May 2018 (table 14). Incandescence was visible at night using monitoring equipment. Ash plumes were noted by the Tokyo Volcanic Ash Advisory Center (VAAC) throughout the reporting period (figure 32, table 15).
|Month||No. of explosions||Max plume height (m above crater)||Dates of ashfall in village 4 km SSW||No. of seismic events||Other daily activity detail|
|Jan 2018||0||1,100||27, 31||97||Incandescence at night.|
|Feb 2018||1||1,100||2, 3||100||Incandescence at night.|
|Mar 2018||9||2,200||25, 29||251||Incandescence at night. Ejecta scattered around the crater.|
|Apr 2018||8||2,000||18, 28, 29||62||Incandescence at night.|
|May 2018||2||1,100||14||90||Incandescence at night. Ejecta scattered around the crater.|
|Jun 2018||--||900||--||275||Incandescence at night.|
|Month||VAAs issued||VAA dates||Plume heights|
|Jan 2018||1||15||1.8 km|
|Feb 2018||1||2||1.2 km|
|Mar 2018||22||17, 22(3), 23, 25(2), 26(5), 27(5), 28(3), 29(2)||1.2-3.6 km|
|Apr 2018||16||1, 2, 3, 4(4), 5(2), 8, 11, 24, 27, 28(2)||1.2-2.4 km|
|May 2018||3||1, 4, 15||1-1.8 km|
|Figure 32. An ash plume at Suwanosejima reached 1 km above the crater on 3 February 2018. Image captured by the Kyanpuba webcam, courtesy of JMA (February 2018 monthly report).|
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 of the volcano 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.
Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).