Report on Rabaul (Papua New Guinea) — July 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 7 (July 1987)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Low level seismicity and deformation
Please cite this report as:
Global Volcanism Program, 1987. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 12:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198707-252140
Papua New Guinea
4.2459°S, 152.1937°E; summit elev. 688 m
All times are local (unless otherwise noted)
A low level of activity continued in July with 107 caldera earthquakes recorded. About 20% were located; normally, only 5-10% of the recorded events are locatable. Most of the July events were distributed in a broad NE-trending zone linking the NE and SW parts of the caldera. Ground deformation rates remained low, although levelling measurements showed an uplift of 8 mm on the S part of Matupit Island . . . between 23 June and 27 July. Tilt changes were very small; the largest measured was 4 µrad of inflation in the NE area of the caldera (Greet Harbour).
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 P. Lowenstein, RVO.