RVO reported that during 16-25 April, white-to-gray emissions from Rabaul caldera's Tavurvur cone generated plumes that rose a few hundred meters and drifted multiple directions. Based on reports from RVO and satellite imagery, the Darwin VAAC reported that a diffuse plume rose to an altitude of 1.5 km (5,000 ft) a.s.l. on 18 April and drifted SW. Occasionally during 18-23 April, moderately-sized explosions led to darker gray plumes. During 22-25 April, light ashfall was reported in Rabaul town. Weak roaring noises occasionally accompanied the emissions. A slight glow was seen from crater at night and small amounts of incandescent material were rarely ejected from the crater during 16-23 April.

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)