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Report on Rabaul (Papua New Guinea) — November 1991

Bulletin of the Global Volcanism Network, vol. 16, no. 11 (November 1991)
Managing Editor: Lindsay McClelland.

Rabaul (Papua New Guinea) Slight increase in seismicity

Please cite this report as:

Global Volcanism Program, 1991. Report on Rabaul (Papua New Guinea). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 16:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199111-252140.

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Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


"There was a slight increase in seismicity in November. The total number of caldera earthquakes for the month was 347 (compared to 200 for October). The daily count fluctuated between 0 and 93. There were three earthquakes strong enough to be felt: a ML 2.0 event on 6 November in the E part of the caldera seismic zone, and events of M 1.4 and 1.9 on 21 and 22 November, respectively, in the W part of the zone. All other events had magnitudes <1.0. Of the 347 earthquakes, only 14 could be located. These clustered in the W, NW, and E parts of the caldera seismic zone."

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.