Report on Rabaul (Papua New Guinea) — February 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 2 (February 1987)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Slight increase in seismicity; minor subsidence
Please cite this report as:
Global Volcanism Program, 1987. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:2. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198702-252140
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Seismicity remained at a low level in February [with] 155 recorded events. The earthquakes were concentrated at the NE and NW parts of the caldera seismic zone. Levelling surveys on 19 and 20 February from the town of Rabaul . . . to Matupit Island . . . indicated slight subsidence since October 1986 at all stations, with maximum subsidence of 11 mm on Matupit Island. Tilt showed no clear trend and most changes were <5 µrad."
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 688-m-high asymmetrical pyroclastic 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 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western 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: P. Lowenstein, RVO.