"Activity remained at a low level in March. A total of 265 caldera earthquakes was recorded. Daily earthquake totals ranged from 0 to 24, with the highest daily total recorded in a small Greet Harbour swarm on 18 March that included two felt events (M_L 2.8 and 2.6). During the month, seismicity was broadly distributed within the caldera seismic zone. Levelling measurements on 26 March indicated deflation of 2 mm at the S tip of Matupit Island since previous measurements on 20 February."

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: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO.