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