Based on observations of satellite imagery, the Darwin VAAC reported that a low-level plume from Bagana drifted SW on 10 December and an ash-and-steam plume was observed on 17 December.

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)