Report on Ibu (Indonesia) — February 1999
Bulletin of the Global Volcanism Network, vol. 24, no. 2 (February 1999)
Managing Editor: Richard Wunderman.
Ibu (Indonesia) Eruptions that began on 18 December 1998 continued in January 1999
Please cite this report as:
Global Volcanism Program, 1999. Report on Ibu (Indonesia). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 24:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199902-268030.
1.488°N, 127.63°E; summit elev. 1325 m
All times are local (unless otherwise noted)
Local residents first noticed thick gray ash emissions from the summit on 18 December 1998 (corrected from BGVN 24:01); this information reached the Volcanological Survey of Indonesia (VSI) Gamkonora volcano observatory on the 31st. On 2 January personnel from VSI who went to the island to take COSPEC measurements of the SO2 release observed a loud eruption that caused up to 3 mm of ashfall in and around Tugure Batu Village. The eruption lasted 35 minutes and generated a plume 1,000 m high. Another eruption observed on 5 January 1999 lasted for 60 minutes. Thunderclaps from the summit were heard on 16 January and a night glow from ejecta was evident above the summit area. Residents also reportedly saw lava at the crater rim. The seismometer from Gamkonora (an RTS PS-2) was installed ~2 km from the summit of Ibu on 3 February along with an ARGOS satellite system tiltmeter.
Field observations on 11 March revealed continuing eruptions and rumbling noises, but the larger eruptions (accompanied by booming and thick ash ejection) had decreased to a rate of one every 15-20 minutes. When observed on 2 February larger eruptions occurred every 5 minutes. Seismograph records are still dominated by explosion events; during 9-15 March there were 779 events, increased from 673 events the previous week.
Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.
Information Contacts: R. Sukhyar and Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).