According to the Volcano Observation Report No. 4 on Satsuma-Iwo-jima volcano of JMA (June 6, 2002), intermittently discolored plumes were issued from the summit, being associated with volcanic tremors observed since May 11. The seismic activity of small volcanic earthquakes has been elevated since May 29. According to the local branch of Mishima village in this island, discolored plumes were rising intermittently, and ash falling was observed in the residential area during June 3 to 5.
JMA issued the Observation Report #4 on Satsuma-Iwojima volcano on 23 July 2001. A continuous volcanic tremor event had occurred since 20 July at this volcano. The JMA seismometer installed about 700 m SW of Iwo-dake had caught small volcanic earthquakes since January in 2000. The daily number ranges from 50 to 110. Small volcanic tremor events were sometimes observed. According to the Iwo-jima Branch of the Mishima Village Office, ash fall was observed during 19 to 21 July, following the 9 April, 15 and 29 May, and 12 June events. The white plume was rising as low as 20 m above the crater.
The daily number of earthquakes ranged from 30 to 90 during the period from December 2000 to March 2001. Small volcanic tremors had been observed since December. Faint ash falling was often observed.
Information: JMA_Fukuoka, Naokuni Uchida: email@example.com
ACTIVITY DURING 1997-1998
JMA started the seismic observation in September 1997, and had observed several volcanic earthquakes a day. The number of the earthquakes increased suddenly in April 1998, ranging from 60 to 80 per day, sometimes over 100 per day. Although the daily number decreased once to less than 20 in June 1998, it increased again between 20 and 40 in September, and more than 60 in the late-1998. In May 4-5, 1998, JMA staffs found newly-deposited ash layer as thick as 5 cm around the crater, suggesting eruption in end-April or early-May. Geological Survey of Japan analyzed the ash and concluded that the ash is composed mainly of silicic and altered lava fragments of the Iwodake lava (rhyolite). Local people in this volcanic island witnessed ash falling in August and October 1998. Scientists of Geological Survey of Japan also witnessed volcanic ash intermittently emitted from the crater and found ash deposits in the southeastern middle-flank of the volcano in early-November 1998. JMA issued nine observation reports on this volcano in 1998.
ACTVITY DURING JANUARY-MAY 1999
Volcanic earthquakes occurred 50 to 100 times per day in January and February 1999, and 90 to 130 times a day after February. The hypocenters of the earthquakes locate just below the Iwodake. Local people observed ash falling on January 24 and February 14 1999. JMA issued 5 observation reports this year (as of May 10).
BACKGROUND OF VOLCANO
Satsuma-Iwojima is the volcano island with the dimension of 6 km east-west and 3 km south-north, which rims the Kikai Caldera (formed 6.3 ka, 23x16 km) together with Takeshima island. The main peak, Iwodake, is a rhyolite lava dome (704 m above the sea) with a strong activity of solfatara. Composition of rocks of Satsuma-Iwojima Volcano is bimodal in SiO2 (69-72% and 51-54%). The 1934-35 eruption occurred on the sea floor 2 km east of the volcano, and formed a new island, Iwojima-shinto (Showa-Iwojima). Iwodake smoked in 1936 and 1988. The activity is monitored geophysically by Sakurajima Volcano Observatory, Kyoto University, and JMA, and geochemically by Geological Survey of Japan.
Link to Satsuma-Iwojima of Geological Survey of Japan (in Japanese text, but can look at the image of volcano) or other images of the volcano at the same siteÅD
Information contact: JMA, Geological Survey of Japan, firstname.lastname@example.org; Volcano Research Center, email@example.com.