Report on Rabaul (Papua New Guinea) — May 1989
Scientific Event Alert Network Bulletin, vol. 14, no. 5 (May 1989)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Seismicity increases slightly; inflation slows
Please cite this report as:
Global Volcanism Program, 1989. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 14:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198905-252140
Papua New Guinea
4.2459°S, 152.1937°E; summit elev. 688 m
All times are local (unless otherwise noted)
"In general, activity remained at background level in May. Seismicity increased slightly, with a total of 164 small caldera earthquakes. The daily earthquake count fluctuated between 0 and 19. The 7 events that could be located occurred in the NW part of the caldera seismic zone.
"Levelling measurements on 26 May showed that the S and SE parts of Matupit Island had risen by ~25 mm since the previous measurements on 30 March. Over the past 1.5 years, uplift has been approximately linear at a rate of ~40 mm/year, considerably less than the 1973-83 (pre-seismo-deformational crisis) rate of ~100 mm/year. No significant tilt changes were recorded in May, and EDM data showed no clear trends."
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: H. Patia and C. McKee, RVO.