Report on Ibu (Indonesia) — 7 September-13 September 2011
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 7 September-13 September 2011
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2011. Report on Ibu (Indonesia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 7 September-13 September 2011. Smithsonian Institution and US Geological Survey.
1.488°N, 127.63°E; summit elev. 1325 m
All times are local (unless otherwise noted)
CVGHM reported mostly clear conditions at Ibu during January-8 September and that white-to-gray plumes were observed rising 200-400 m above the craters. On 20 August observers from the nearby villages of Goin and Duono noted multiple eruptions from the S, E, and N craters. Eruption "smoke" rose 50-250 m above the craters and an avalanche traveled 300 m. Seismicity indicating avalanches occurred on average 45 times per day during January-8 September. Other types of seismic signals fluctuated during the time period but stabilized or decreased towards September. Based on visual observations and seismicity, CVGHM lowered the Alert Level to 2 (on a scale of 1-4) on 8 September.
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.