RVO reported that ash plumes from Rabaul caldera's Tavurvur cone rose to altitudes of approximately 1.7-2.7 km (5,600-8,900 ft) a.s.l. and drifted NW on 3 October. Ashfall was reported from areas downwind, including Rabaul Town. Ash plumes on 4 October drifted W and resulted in ashfall in Matupit Island, Malaguna. Incandescent fragments were ejected from the summit. On 5 October, vapor plumes with minor ash content were noted. Rumbling noises occasionally accompanied the ash emissions.

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.

Source: Rabaul Volcano Observatory (RVO)