Report on Suwanosejima (Japan) — November 2017
Bulletin of the Global Volcanism Network, vol. 42, no. 11 (November 2017)
Managing Editor: Edward Venzke. Report research and preparation by: Liz Crafford.
Suwanosejima (Japan) Persistent ash plumes, explosions, and Strombolian activity during September 2015-December 2016
Please cite this report as:
Global Volcanism Program, 2017. Report on Suwanosejima (Japan). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 42:11. Smithsonian Institution.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
Suwanosejima, an andesitic stratovolcano in Japan's northern Ryukyu Islands, was intermittently active for much of the 20th century, producing ash plumes, Strombolian eruptions, and ash deposits. Continuous activity since October 2004 has consisted generally of multiple ash plumes most months rising a few hundred meters above the summit to altitudes between 1 and 2 km, and tens of reported explosions. Activity between January and September 2015 included small eruptions in July and August that produced ash plumes rising to 3-4 km altitude. Increased activity beginning in August 2015 included incandescence at the crater and increased explosive activity with incandescence in September; 89 explosions occurred that month, and ash fell in the village 4 km SSW (BGVN 42:01). Eruptive activity for the period of September 2015-December 2016 included intermittent explosions, ash plumes up to 4.3 km altitude, ashfall within a 5-km radius, and Strombolian activity. Information is provided primarily by the Japan Meteorological Agency (JMA), and the Tokyo Volcanic Ash Advisory Center (VAAC).
Activity during September-December 2015. Numerous explosions were reported by the JMA during 24-30 September. The Tokyo VAAC reported a plume at 2.1 km altitude extending SE on 24 September; subsequent reports noted there were no observations of ash emissions or plumes in satellite data during that time, and no further VAAC reports were issued after 30 September (until January 2016).
JMA reported that explosions at the Ontake crater on 2, 13, and 31 October 2015 produced gray-and-white emissions and rose a maximum of 800 m above the summit (at ~800 m elevation). Explosions occurred on 1 and 20 November as well; the plume rose 1 km above the crater rim on 1 November. Ashfall was confirmed in the small village 4 km SSW after both events. There were no explosions reported during December 2015; only steam emissions rose 600 m above the summit crater, and rumbling was heard on 12 December from the nearby settlement. Incandescence was visible with a thermal camera at night during September-December 2015.
Activity during 2016. According to JMA, explosions and intermittent emissions occurred during most months of 2016 (table 12). Ashfall in the village 4 km SSW of the summit was reported during January-April, July-August, and October-November. Steam-and-ash plume heights ranged from 800 to 2,700 m above the crater rim. The number of monthly seismic events was low in January (25), increasing to a maximum of 1,195 in April. It dropped below 200 by July, and below 100 during November and December. Incandescence at night was reported often every month. An overflight on 31 May 2016 revealed a steam plume rising 400 m above Ontake crater (figure 20). Strombolian activity on 15 September and 23 November 2016 ejected incandescent blocks onto the crater rim (figure 21). An ash emission on 25 November sent gray and white ash and steam 1,800 m above the crater rim (figure 22). Incandescent blocks from an explosion were also observed on 17 December.
|Month||No. of explosions||Emission events||Max plume height (m above crater)||Dates of ashfall in village 4 km SSW||No. of seismic events||Other activity detail|
|Jan 2016||1||Yes, small||--||22, 23||25||Occasional incandescence at night; explosion at 2114 on 6 Jan.|
|Feb 2016||0||Occasional small||800 m||22||64||Occasional incandescence at night.|
|Mar 2016||13||1,700 m||7, 20, 21||170||Incandescence at night; shockwaves felt 20-21 Mar.|
|Apr 2016||14||--||1,700 m||11, 15, 18, 19||1,195||Incandescence at night; occasional rumbling; seismicity increased 24-26 Apr.|
|May 2016||5||Steam plumes||1,200 m||None||396||Incandescence at night; overflight (figure 20); steam plume 400 m above crater on 31 May drifted NE.|
|Jun 2016||0||Occasional||1,900m||None||606||Incandescence at night.|
|Jul 2016||0||Occasional||1,900 m||23||142||Incandescence at night.|
|Aug 2016||26||--||2,700 m on 12 and 28||1, 2||171||Incandescence at night; tephra around crater on 12 and 28 Aug; infrasound on 13, 14 Aug; rumbling on 25 Aug.|
|Sep 2016||1||3||Ash to 1,900 m on 17, steam to 2,400 m on 5||None||106||Incandescence almost every day; Strombolian activity and explosion at 2305 on 15 Sep (figure 21).|
|Oct 2016||0||Occasional||1,200 m||6, 30||102||Incandescence almost every day.|
|Nov 2016||11||Occasional ash emissions||1,800 m||5, 6, 26, 29||56||Constant incandescence; Strombolian explosion at 2325 on 23 Nov sent blocks around crater (figure 22).|
|Dec 2016||7||Occasional ash emissions||2,500 m at 1356 on 13||None||33||Incandescence at night; large explosion at 2020 on 13 Dec; incandescent blocks on 17 Dec.|
|Figure 20. Aerial photos of Ontake crater at Suwanosejima on 31 May 2016. Upper image is the close-up view outlined in red below. Courtesy of JMA (Volcanic activity commentary on Suwanosejima, May 2016).|
The Tokyo VAAC also reported information about ash plumes and explosions during 2016 (table 13). Explosions were reported during every month of 2016 except February, and ranged from two in January to 19 in August. Most plume heights were lower than 2.7 km altitude. Exceptions included: an explosion on 1 August produced an ash plume that rose to 3.4 km altitude and drifted S; a plume rose to 3 km on 29 November and also drifted S; and the largest of the year, an ash plume that rose to 4.3 km altitude and drifted E, on 13 December (figure 23).
MODVOLC thermal alerts were reported on 20 April, 4 May (3), and 17 May 2016.
|Month||Explosion Count||Explosion Days||Plume Heights||Drift Directions|
|Jan 2016||2||4, 6||1.5 km||SE|
|Mar 2016||14||2 (2), 4, 6, 7 (2), 10, 21, 22 (2), 23, 26 (2), 30||1.2-2.4 km||SE, W, N|
|Apr 2016||13||5, 10, 14 (2), 15, 17 (2), 18, 19 (3), 20, 21||1-2.4 km||E, W, SE, S, N|
|May 2016||5||3 (2), 4 (2), 18||1.5-2.1 km||E, SE, W|
|Jun 2016||4||13 (3), 14||1.8-2.7 km||E|
|Jul 2016||4||18 (2), 22, 31||1.5-2.7 km||NE, E, N, NW, W|
|Aug 2016||19||1 (3), 10 (3), 11, 12, 14 (2), 17, 25, 26 (2), 27 (2), 28 (2), 31||1.0-3.4 km||SW, SE, W, NW|
|Sep 2016||2||15, 16||2.7 km||W|
|Oct 2016||5||6 (2), 25 (2), 26||1.5-1.8 km||E, S, NE|
|Nov 2016||18||5, 6, 8, 10 (2), 11 (3), 12 (2), 16, 17, 19, 20, 23, 25 (2), 29||1.2-2.1, 3.0 km on 29||E, SW, SE, S, W|
|Dec 2016||4||13 (2), 16, 17||4.3 on 13, 1.8 km||NE, SE, SW, W|
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), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).