PVMBG reported that the eruption at Ibu continued during 5-11 June with occurrences of tall ash plumes. White, gray, and black ash plumes rose as high as 5 km above the crater rim and drifted in multiple directions during 5-6 and 9 June. White steam-and-gas plumes rose 200-1,000 m above the crater rim and drifted in multiple directions during on 29 May and 3 June. White-and-gray ash plumes rose as high as 4 km and drifted in multiple directions on 11 June. The Alert Level remained at 4 (the highest level on a four-level scale) and the public was advised to stay 4 km away from the active crater and 7 km away from the N crater wall opening.

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)