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 688-m-high asymmetrical pyroclastic 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 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western 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: Rabaul Volcano Observatory (RVO), Darwin Volcanic Ash Advisory Centre (VAAC)