RVO reported that during 6-8 December Rabaul caldera's Tavurvur cone emitted thick white-to-gray plumes that rose to 1.2-3.2 km (3,900-10,500 ft) a.s.l. and drifted NW and NE. Ashfall was reported from areas downwind (NW) on 6 and 7 December. Roaring noises were heard during 7-10 December. On 11 December, the volcano was quiet and emitted only a diffuse plume that was also visible on satellite imagery. On 12 December, a loud explosion shook houses in Rabaul Town and a gray plume rose to 1.7 km (5,600 ft) a.s.l. and drifted E. When the noise stopped on 10 December, the deformation monitoring equipment recorded an approximate 1-cm rapid uplift that subsided after the explosion on 12 December.

Geological Summary. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the asymmetrical shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Sources: Darwin Volcanic Ash Advisory Centre (VAAC), Rabaul Volcano Observatory (RVO)