CVGHM reported that during May through 6 June white-to-gray plumes rose 200-450 m above Ibu's crater rim. Seismicity increased and volcanic tremor was detected. The lava dome contained to grow, especially the N part, and in early June had grown taller than the N crater rim. Based on visual and instrumental observations, as well as the hazard potential, CVGHM increased the Alert Level to 3 (on a scale of 1-4) on 7 June. The public was warned to stay at least 3 km away from the active crater.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

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.