An eruption in 2002 began on 11 May when discolored plumes were noted (BGVN 28:04). Anomalous seismicity began on 14 May 2002, when about 900 events were recorded (table 1). The number of events dropped to very low levels the next day, but then gradually increased to a peak of 967 on the 28th and almost that many on the 29th. During June 2002, seismicity was high on the 2nd (650 events), 3rd (> 300 events), and 8th (~ 240 events). There were also 117 tremor events during the month, 73 of them on the 15th. Plumes and ashfall were reported through 5 June (BGVN 28:04).

Table 1. Summary of seismicity and plume observations at Kikai, May 2002-January 2005. All reported plumes were described as either white (W), light white (LW), grayish white (GW), or gray (G). Data courtesy of JMA.

Activity for the following year consisted of low-level seismicity of less than 200 events per month, and frequent, almost daily, white plumes. Eruptive activity began again on 7-8 June 2003 when 800-1,000 m ash plumes were recorded. Although plumes were not reported, eruptions also occurred during 10-12 June. Additional eruptions were noted by JMA during 7, 14-17, 26, 27, and 30 July, and 12, 13, and 15-18 August 2003. All of the June-August eruptions caused ashfall. The last grayish white eruption plumes in 2003 were seen on 19 and 22 September.

From March to September 2004, Tokyo Volcanic Ash Advisory Center (VAAC) reports indicated a number of small eruptions at Kikai. Three plumes in March 2004 reportedly rose to 1.5 km altitude, but no ash was visible in satellite imagery (table 2). JMA also reported eruptions on those days, but only indicated plumes 700 m high.

Table 2. Date and time of eruptions from Kikai, the direction and altitude of observed plumes, and whether ash was seen on satellite image. Based on information from the Tokyo VAAC.

Another plume on 1 June did have ash visible to satellites. This eruption was not included in the JMA observations. Plumes were seen again on 13 August and 25 September, again with JMA only reporting 700-800 m plumes compared to 1.2 and 1.5 km plumes, respectively, in the VAAC advisory. No seismicity was detected during 25 September-5 October 2004, the period following the eruption of a grayish-white plume to 700 m. Data from JMA through January 2005 indicate continuing volcanic earthquakes (less than 10/day in December) and almost daily white plumes as high as 700 m, but generally 400 m or below.

Geological Summary. Multiple eruption centers have exhibited recent activity at Kikai, a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake (or Iwo-dake) lava dome and Inamuradake scoria cone, as well as submarine lava domes. Recorded eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Satsuma-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Satsuma-Iojima.

Information Contacts: Japan Meteorological Agency (JMA), Volcanological Division 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: http://www.jma.go.jp/); Tokyo Volcanic Ash Advisory Center, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan (URL: https://ds.data.jma.go.jp/svd/vaac/data/).