RVO reported that during 15-23 April white vapor plumes containing some ash rose at most 100 m from Rabaul caldera's Tavurvur cone and drifted SE. Roaring and rumbling noises were less intense than during previous weeks. Based on analyses of satellite imagery, the Darwin VAAC reported that on 18 April an ash plume rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted more than 35 km E. Satellite images later that day showed that the plume had dispersed.

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