During 31 August-5 September, Rabaul caldera’s Tavurvur cone remained quiet and no nighttime incandescence was observed. Variable amounts of white vapor were visible rising from the summit as well as traces of blue vapor. A few short-duration rumbling noises were heard during 30-31 August, and seismicity remained very high and dominated by small, low-frequency earthquakes. However, earthquakes decreased from 80 events per hour to 15 events per hour at 0300 on 31 August. Less than 10 earthquakes were detected during 1-2 September; a slight increase in low-frequency earthquakes was detected during 4-5 September.

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)