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Report on Rabaul (Papua New Guinea) — November 1991


Rabaul

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) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199111-252140



Rabaul

Papua New Guinea

4.2459°S, 152.1937°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."

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: B. Talai and C. McKee, RVO.