Report on Rabaul (Papua New Guinea) — September 1988
Scientific Event Alert Network Bulletin, vol. 13, no. 9 (September 1988)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Seismicity declines but remains above normal
Please cite this report as:
Global Volcanism Program, 1988. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198809-252140
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Seismicity subsided in September but was still above normal levels. A total of 353 events was recorded in September. Most days, less than ~20 events were detected, but 60 were recorded on the 29th. Twelve events could be located, distributed on the NW, NE, and SE portions of the caldera seismic zone. Levelling measurements showed slight uplift (maximum 5 mm) of SE Matupit Island between 16 August and 20 September, and slight subsidence of a few millimeters between Rabaul town and Matupit Island. EDM results indicated little change during the month except at the entrance to Greet Harbour where slight expansion (~10 microstrain) was recorded."
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: C. McKee and P. Lowenstein, RVO.