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Report on Rabaul (Papua New Guinea) — September 1990


Rabaul

Bulletin of the Global Volcanism Network, vol. 15, no. 9 (September 1990)
Managing Editor: Lindsay McClelland.

Rabaul (Papua New Guinea) Seismicity remains at background

Please cite this report as:

Global Volcanism Program, 1990. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 15:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199009-252140



Rabaul

Papua New Guinea

4.2459°S, 152.1937°E; summit elev. 688 m

All times are local (unless otherwise noted)


"Seismicity remained at a low level in September. The total number of caldera earthquakes recorded was 101 (compared to 113 in August, 213 in July, and an average of 215/month since mid-1986). There was a tight clustering of events below the NE part of Greet Harbour, and a broadly scattered group between Vulcan and Matupit Island. All events were of small magnitude (ML <=1.5). No significant changes were observed in levelling, tide gauge, tilt, EDM, and gravity measurements."

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 asymmetrical 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 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W 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: I. Itikarai and C. McKee, RVO.