The Darwin VAAC reported that on 31 July an ash plume from Bagana rose to 4.6 km (15,000 ft) a.s.l. based on a pilot observation. A few hours later steam emissions were identified in satellite images.

Geological Summary. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. 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 frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)