Report on Rabaul (Papua New Guinea) — May 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 5 (May 1986)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Seismicity remains elevated; slight inflation
Please cite this report as:
Global Volcanism Program, 1986. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198605-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"Seismicity remained at a relatively high level in May with 1,532 events. As in April, all of the earthquakes were quite small, the largest being an ML 2.4. In April many shallow events occurred in the middle of the caldera, but May locations show a return to the normal pattern of ring-fault seismicity at depths of 1-3 km.
"Levelling measurements showed 9 mm of uplift at the SE tip of Matupit Island 7-28 May, about half the uplift rate measured in April. Tilt measurements showed small inflationary changes (0-10 µrad) in the Greet Harbour area. Electronic distance measurements 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. Lowenstein, RVO.