Report on Rabaul (Papua New Guinea) — December 1989
Scientific Event Alert Network Bulletin, vol. 14, no. 12 (December 1989)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Increase in seismicity; inflation
Please cite this report as:
Global Volcanism Program, 1989. Report on Rabaul (Papua New Guinea). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 14:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198912-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"December showed both a relative increase in seismicity and an accelerated rate of inflation in the central part of the caldera. The moderate rise in seismicity observed since October continued, with 886 caldera events (ML <=2.3) recorded in December. Background seismicity fluctuated between 10 and 40 events/day. Minor swarms occurred on 12 (52 events), 13 (121), 18 (45), and 24 (76) December, alternately from the NW (Beehives), N (Greet Harbour), and E (Blanche Bay) areas of the well-established annular seismic zone.
"Renewed inflation in the central part of the caldera was suggested by rise of the S tip of Matupit Island . . . of 3 mm/month from September to November. Uplift of 20 mm was recorded in December. Only six tilt stations around Greet Harbour and on the Vulcan Headland showed a significant inflationary trend (3-10 µrad/month since mid-October)."
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: P. de Saint-Ours, RVO.