The Darwin VAAC reported that continuous ash plumes from Bagana were identified in satellite images rising to 2.4-3.7 km (8,000-12,000 ft) a.s.l. and drifting S and SW at 2310 on 16 September and 0150 and 0410 on 17 September.

Geological Summary. Bagana volcano, in a remote portion of central Bougainville Island, is frequently active. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although occasional explosive activity produces pyroclastic flows. Lava flows with tongue-shaped lobes up to 50 m thick and prominent levees descend the flanks on all sides.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)