RVO reported that during 3-9 October, eruptions occurred at Rabaul caldera's active Tavurvur cone. Irregular ash emissions rose 800-1,500 m above the volcano (or 4,900-7,200 ft a.s.l.). Incandescent volcanic bombs were visible showering the cone's sides. Seismicity at the volcano was at moderate-to-high levels, with most earthquakes associated with ash emissions and explosions. Ground-deformation measurements fluctuated since stabilizing during the previous week, however the general trend showed slight deflation. People were discouraged from venturing within 1 km of the erupting vent. According to the Darwin VAAC, ash was visible on satellite imagery on 5 October.

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

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.