Tavurvur crater activity continued small pale-gray ash emissions at long irregular intervals during March and April. No significant changes in ground deformation were measured during this period. There was a slight increase in the rate of ash emission during mid-March. The emissions contained moderate ash content and rose < 1 km above the summit before blowing to the S and SE with fine ashfall downwind. On 22 March a few moderate explosions were accompanied by loud roaring noises. A similar pattern occurred during April, i.e., a steady increase in the rate of ash emission until 22 April with moderate explosions being accompanied by loud roaring noises.

Seismic activity related to the continuing eruptive activity at Tavurvur was much lower; there were 120 low-frequency events in March and 142 in April, compared with 465 in February and 1,413 in January. A total of 15 explosions were recorded through March, whereas only three occurred in April. Five of the six high-frequency events in March were located; one occurred to the W and the rest NE of the caldera. Only three were recorded in April, one to the E and two NE of the caldera.

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: Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.