PVMBG reported that the eruption at Ibu was intensifying. At 0158 on 8 May a dense gray ash plume rose 2 km above the summit, produced lightning in the plume, and drifted E and SE. Incandescence from the crater was visible and roaring could be heard in areas as far away as the Ibu observation post (9 km W). Seismicity was at high levels. The Alert Level was raised to 3 (the second highest level on a four-level scale) and the public was advised to stay 3 km away from the active crater and 5 km away from the N crater wall opening. Additional ash plumes that same day were gray-to-white or gray-to-black, rose 1.5-2 km, and drifted NE, E, and SE. Dense gray ash plumes rose 1.2-1.5 km and drifted E on 9 May. At 0024 on 11 May a dense gray ash plume rose 4 km and drifted N and NW and at 0912 a dense gray-to-black ash plume rose 5 km and drifted W.

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)