PVMBG reported that the eruption at Ibu continued during 22-28 May. White steam-and-gas plumes rose 200-600 m above the crater rim and drifted in multiple directions during on 29 May and 3 June. White-and-gray ash plumes rose 200-800 m and drifted in multiple directions during 30-31 May and 3 June. Taller plumes were visible during 1-2 June. At 0323 on 1 June a dense gray-to-black ash plume rose 6 km above the summit and drifted SW and at 1103 on that same day a dense gray plume rose 5 km and drifted SW. A 10-minute-long eruption that began at 1235 on 2 June produced a dense gray-to-black ash plume that rose 7 km above the summit and drifted W. BNPB noted that tephra fell in areas to the W including at the Ibu observation post (9 km W) and in Gam Ici (8.5 km W). At 0303 on 27 May an eruptive event produced a white, gray, and black ash plume that rose 6 km above the crater rim and drifted SW and W. According to a news article ash fell in residential areas and at the Ibu observation post (9 km W). Incandescent material was ejected as far as 1 km from the vent onto the NW, W, SW, and S flanks. 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)