Report on Rabaul (Papua New Guinea) — September 1984
Scientific Event Alert Network Bulletin, vol. 9, no. 9 (September 1984)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Seismicity, ground deformation rates decline
Please cite this report as:
Global Volcanism Program, 1984. Report on Rabaul (Papua New Guinea). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 9:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198409-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Declining seismicity and rates of ground deformation were evident in September. The total number of caldera earthquakes for the month was 4048 and the seismic energy released amounted to about [8 x 1014] ergs (compared to 5,285 earthquakes and about [2.4 x 1016] ergs in August).
"Seismicity was concentrated in the N part of the caldera seismic zone. Measured vertical uplift continued to be greatest along the SE coast of Matupit Island. However, the maximum uplift in September was only 14 mm (compared to 35 mm in August). Tilt and horizontal distance measurements continued to indicate slow steady inflation and expansion in the Greet Harbour area."
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.