The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) lowered the Alert Level for Ibu to 2 (the second lowest level on a four-level scale) at 1700 on 1 May, based on visual observations and monitoring data that showed decreasing activity since February. Eruptive activity continued to be recorded, though plumes heights were lower and incandescent material was ejected only as far as 200 m from the crater rim. Seismic activity had decreased, and deformation data showed some signs of decreased pressure, or deflation. Daily gray, white-to-gray, or white-to-brown ash plumes rose 300-700 m above the crater rim and drifted in variable directions. Nighttime crater incandescence was visible in some webcam images. The public was advised to stay 2 km away from the active crater and 3.5 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)