Report on Rabaul (Papua New Guinea) — September 1989
Scientific Event Alert Network Bulletin, vol. 14, no. 9 (September 1989)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Annual level survey shows changes to 34 mm
Please cite this report as:
Global Volcanism Program, 1989. Report on Rabaul (Papua New Guinea). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 14:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198909-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Background-level activity continued in September. The total number of caldera earthquakes was 99, compared with 202 in August and 119 in July. All of the events were small (ML <1.5), and none were large enough to be located.
"The annual survey of the complete Rabaul Caldera level network began in August and was still in progress at the end of September. Compared with the 1988 annual survey, the 1989 results indicate slight subsidence in the N part of the caldera (5 mm) and between Rabaul township and Matupit Island (9 mm). On Matupit Island, uplift has continued, with the S part of the island rising ~34 mm. Around the N and E shores of Greet Harbour, there was subsidence of between 9 and 30 mm."
Geologic Background. 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, RVO.