"Seismic activity . . . showed an increase in December, when 1,090 caldera earthquakes were recorded . . . . This is the highest monthly total since August 1988, although it is only one earthquake more than . . . in July 1992. The December earthquakes occurred mainly in four swarms: on 1, 11, 14, and 17 December. The last of these was the largest, containing 226 events, some of which were felt in the Rabaul area with intensity III-IV. The 36 earthquakes located in December were distributed mainly around the northern end of the caldera seismic zone."

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: H. Patia and B. Talai, RVO.