CVGHM reported that seismicity from Ibu increased during 6-14 April and remained elevated during 15-20 April. Plumes described as "eruption smoke" rose to altitude of 1.8-2.1 km (5,900-6,900 ft) a.s.l. during 12-21 April and were gray during 18-21 April. The Alert Level was increased to 3 (on a scale of 1-4) on 21 April. Residents and tourists were not permitted within 2 km of the crater.

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.

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