Emissions of light to pale ash clouds from Tavurvur characterized activity during November 2003. Between 10 and 20 November the ash emissions occurred frequently at irregular intervals. During 20-24 November Tavurvur produced only a handful of emissions at very long intervals, but after 24 November the emissions became frequent. Occasional moderate explosions through 14 December produced thick ash plumes that rose 1-2.5 km above the summit. Incandescent lava fragments from some explosions were visible at night and occasional roaring and rumbling noises were heard. After 16 November winds were consistently from the SE, blowing ash plumes N and NW. Ashfall resulted in downwind areas, including Rabaul Town and villages on Tavui Peninsula, Malagura and Matupit; accumulation was heaviest in the area of Rabaul Town. Fine ashfall also occurred to the W, SW, S, and SE.

Seismicity has been low, with some high-frequency earthquakes from the NE. Ground deformation in November remained low. The real-time GPS and electronic tilt site on Matupit Island, in the center of the caldera, continued to indicate a slow gradual uplift. This uplift is part of the long-term trend reported earlier (BGVN 28:03).

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.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.