Report on Suwanosejima (Japan) — July 2011
Bulletin of the Global Volcanism Network, vol. 36, no. 7 (July 2011)
Managing Editor: Richard Wunderman
Suwanosejima (Japan) Many small explosions up to 2 km altitude during mid-2009 to mid-2011
Please cite this report as:
Global Volcanism Program, 2011. Report on Suwanosejima (Japan). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 36:7. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN201107-282030.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
In a previous report (BGVN 34:07) we discussed ash plume data from the Tokyo Volcanic Ash Advisory Center (VAAC) and reports from the Japan Meteorological Agency (JMA) that covered explosive activity based on infrasound measurements and seismicity during October 2008 to July 2009. Many explosions were heard and felt but cloud cover obscured direct observations. From 6 July 2009 to 14 July 2011 the Tokyo VAAC reported 234 explosions; 62 of which produced a measurable ash plume (table 9) from the summit crater, On-take (also called Otake).[Skip text table]
Date Altitude (km) Drift 15-17 Jul 2009 1.5-2.1 NE, W 16-17 Aug 2009 1.8 E 28-29 Aug 2009 1.5-2.4 W 17-18 Sep 2009 1.5 S 01 Oct 2009 1.5 W 10 Oct 2009 1.5 — 04-05 Nov 2009 1.2-1.8 SW, W, NE 26 Nov 2009 3.0 E 14 Dec 2009 1.2-1.5 E 22 Dec 2009 1.5 — 02 Jan 2010 1.8 — 04-05 Jan 2010 1.5-1.8 NE, E 09 Jan 2010 1.8 E 26-27 Jan 2010 1.2-1.5 SE, W 29 Jan 2010 1.8 — 17 Feb 2010 1.2-1.5 E, SE 19 Feb 2010 1.5 SE 21 Feb 2010 1.8 — 15-16 May 2010 1.5-1.8 NW 23 Jul 2010 2.4 NW 26 Jul 2010 1.5 W 22 Sep 2010 1.5-2.1 SE 25 Sep 2010 1.5 E 05 Oct 2010 1.5 E 17 Oct 2010 1.5 SE 10-12 Nov 2010 1.5-2.1 SE, N, SW 18 Nov 2010 1.8 — 21 Nov 2010 2.1 NE 29 Nov 2010 1.2-1.5 — 04 Dec 2010 1.2 SE 13 Jan 2011 1.2 SE 22 Jan 2011 1.5 S 05 Feb 2011 0.6 SW 12 Apr 2011 1.8 — 14 Jul 2011 3.7 —
JMA stated that this volcano has erupted every year since 1956. The activity alert status for Suwanose-jima was Level 2 (on a 1 to 5 scale where 5 is the highest) from December 2007 to July 2011; this status indicates that the crater is too dangerous to visit.
Activity during late 2009. The Tokyo VAAC reported frequent plumes from mid-August through December 2009. The tallest plumes, above 1.5 km altitude, occurred on 16-17 and 29 August, and 5 and 26 November (table 9). According to JMA, a visitor during 29-30 December 2009 saw Strombolian eruptions.
Activity during 2010. Ash plumes up to ~ 2.4 km altitude were reported by the Tokyo VAAC on many days throughout the year (table 9).
Based on the seismic record, JMA was able to infer when explosions occurred within the crater. The number of these explosions decreased from 64 in January to 0 in June; from July to September there were less than 20 monthly explosions, but activity appeared to peak in November when 94 explosions were recorded.
Aerial observations were made in collaboration with the Japan Maritime Self Defense Force (JMSDF) on 14 December (figure 14). The flight confirmed high temperature areas at both the summit crater's center and at the lower, outer rim. Thes results were congruent with those obtained earlier, in December 2009, and JMA concluded that similar conditions prevailed in the crater during this interval.
Activity during 2011. Ash plumes were reported by the Tokyo VAAC for January, February, April, and July; the tallest occurred on July 14 and reached ~ 3.6 km altitude (table 9). From January to July 2011, volcanic earthquakes and tremor remained relatively high (figure 15).
A 2.9-magnitude earthquake centered below Suwanose-jima occurred on 3 February 2011 at 2206. That month, local inhabitants reportedly felt 17 earthquakes. No surface change was observed before or after the earthquakes. Surveillance in February 2011 included visual observations by the Coast Guard.
Immediately after the 11 March 2011 Tohoku Earthquake (M 9.0, located offshore of Honshu, Japan) instruments at Suwanose-jima recorded increases in high-frequency (A-type) earthquakes. A-type earthquakes are generally considered to have shallow focal depths; B-type earthquakes, deeper focal depths.
Ash explosions seemingly rarely occurred through March 2011, but reports from Toshimamura village stated that observers there had seen ballistics thrown from the summit crater. Due to prolonged poor weather, surveillance cameras did not record this activity. JMA reported that plume heights for April, May, and June 2011 remained at background levels, with maximum heights of 0.4?1.0 km. Intermittent incandescence was recorded with surveillance cameras when clear weather allowed observations at night from March through June.
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: Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Yukio Hayakawa, Gunma University, Faculty of Education, Aramaki 4-2, Maebashi 371-8510, Japan.