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Report on Rabaul (Papua New Guinea) — August 1992

Bulletin of the Global Volcanism Network, vol. 17, no. 8 (August 1992)
Managing Editor: Lindsay McClelland.

Rabaul (Papua New Guinea) Seismicity decreases; slight subsidence follows inflation

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, 17:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199208-252140.

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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)


"A moderate rise in seismicity accompanied by uplift of the central part of the caldera took place over the last four months. After an increase to 1,089 events in July, the level of seismicity remained moderate throughout August, with 514 recorded events. The located earthquakes originated, as usual, from the annular seismic zone. Levelling measurements showed a steady uplift of the central part of the caldera from mid-May to mid-July (+30 mm), followed by a slight subsidence (-8 mm) since. Tilt and EDM measurements around the caldera . . . showed no significant changes."

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: P. de Saint-Ours and C. McKee, RVO.