Report on Rabaul (Papua New Guinea) — September 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 9 (September 1992)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Seismicity declines
Please cite this report as:
Global Volcanism Program, 1992. Report on Rabaul (Papua New Guinea). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 17:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199209-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"There was a decrease in seismic activity . . . during September while ground deformation measurements indicated continued uplift. The number of caldera earthquakes recorded was 394 . . .. Only 25 events were large enough (M >0.5) to be located, the majority from the W part of the caldera seismic zone. The tiltmeters in the N and NE parts of the caldera registered a steady accumulation of a few microradians of inflation during September. Results from the annual levelling survey, which was completed in August, show continued long-term uplift. Over the past year, the S part of Matupit Island has been elevated ~60 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: B. Talai and C. McKee, RVO.