Report on Rabaul (Papua New Guinea) — October 1992
Bulletin of the Global Volcanism Network, vol. 17, no. 10 (October 1992)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Seismicity remains low; minor uplift
Please cite this report as:
Global Volcanism Program, 1992. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:10. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199210-252140
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Seismic activity . . . remained low during October, when 588 earthquakes were recorded . . . . The highest daily total was on the 22nd, when a brief swarm of 149 events was recorded. Three or four of the largest were felt in Rabaul. Over half of the 24 earthquakes located in October were from the swarm, 1-2 km NE of Vulcan on the W side of the caldera ring-fault system. The rest of the located events were scattered around the NW and E sides of the ring fault. Levelling measurements between 8 August and 16 October showed a small amount of uplift (4 mm) at the S tip of Matupit Island. Another round of levelling measurements on 9 November indicated uplift of 13-16 mm along the SE coast of Matupit Island. This uplift may correlate with the seismicity on the 22nd. No significant changes were shown by EDM or dry-tilt 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. Itakarai, R.C. Stewart, and C. McKee, RVO.