Rabaul caldera's active Tavurvur cone continued to emit ash during 15-21 August, although there was a slight decline in the frequency of emissions in comparison to earlier weeks. Ash plumes rose 800-1,500 m above the volcano (or 4,900-7,200 ft a.s.l.) and drifted N and NW, occasionally depositing ash on the E part of Rabaul Town and in areas farther downwind. Projected incandescent lava fragments were visible at night. Seismicity was at moderate-to-high levels, with most earthquakes associated with ash emissions and explosions. Ground-deformation measurements from GPS and tide-gauge instruments fluctuated, however the general trend showed a slow rate of uplift. As a safety precaution, people were discouraged from venturing within 1 km of the erupting vent.

Source: Rabaul Volcano Observatory (RVO) via the Darwin Volcanic Ash Advisory Center

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.