Report on Rabaul (Papua New Guinea) — June 1988
Scientific Event Alert Network Bulletin, vol. 13, no. 6 (June 1988)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Microseismicity increases
Please cite this report as:
Global Volcanism Program, 1988. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198806-252140
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Microseismicity showed a further increase in June with a monthly total of 238 events. All were of small magnitude (ML <1.5) but occurred in swarms, with the highest output on 1 June (23 events) and 26-27 June (62 events). Locatable events were grouped on the NW to NE portion of the . . . caldera seismic zone (Vulcan, Beehives, Greet Harbour) at depths of 1-4 km. All measured parameters of ground deformation (EDM, tilt, levelling, and tide gauges) showed neither inflationary nor deflationary 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: P. de Saint-Ours and P. Lowenstein, RVO.