During late March through late April 2008, the Center of Volcanology and Geological Hazard Mitigation (CVGHM) described mainly white plumes emitted from Ibu. On at least five days, however, the plumes were gray. During 17-31 March, frequent white plumes rose to an altitude of 1.5 km. On 31 March the plume altitudes increased to 1.6 km.

During 4-5 April 2008, seismicity increased in amplitude and plume altitude increased to 1.8-2.0 km. On 5 April, the eruption plume was gray and material fell around the crater. Residents of nearby communities were not permitted to climb or approach the crater.

Plumes that were possibly gray rose to altitudes between 1.6 and 1.9 km during 6-17 April. Gray plumes rose to altitudes of 2-2.1 km during 18-21 April. On 21 April, CVGHM warned that residents and tourists were not permitted within 2 km of the crater.

Steam plumes rose above the crater during late May to late August 2004 (BGVN 30:03). Thermal anomalies detected by the MODIS instruments triggered MODVOLC thermal alerts (table 1) during that interval and the last quarter of 2004; alerts were also noted during February 2005, but not in 2006 and 2007. Thermal anomalies were again measured by the MODIS instrument in mid-May 2008 and continued to be detected through late October.

Table 1. MODVOLC thermal anomalies over Ibu from late August 2004 to 20 October 2008. Courtesy of the HIGP Thermal Alerts System.

Geological Summary. 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, has contained several small crater lakes. The 1.2-km-wide outer crater is breached on the N, creating a steep-walled valley. A large cone grew ENE of the summit, and 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. The first observed and recorded eruption was a small explosion from the summit crater in 1911. Eruptive activity began again in December 1998, producing a lava dome that eventually covered much of the floor of the inner summit crater along with ongoing explosive ash emissions.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Saut Simatupang, 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) 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/).