Report on Rabaul (Papua New Guinea) — March 1988
Scientific Event Alert Network Bulletin, vol. 13, no. 3 (March 1988)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Increased seismicity but continued deflation
Please cite this report as:
Global Volcanism Program, 1988. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198803-252140
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
Microseismicity increased markedly after the first week in March, and the month's total [of earthquakes] reached 107 events, the highest since July 1987. All of the March events were of small magnitude (ML <2) and some occurred in swarms. The strongest concentration was in the region between Vulcan and Matupit Island, where focal depths were 1-4 km. A few shocks occurred in the Karavia Bay area S and SE of Vulcan.
There was no significant change in the trend of ground deformation. Tide gauges off Vulcan Headland and Matupit Island continued to record slow subsidence (~3 mm/month). On land, levelling between Rabaul town and Matupit Island confirmed the continuing subsidence, which has totaled as much as 15 mm on the island since October 1987. However, levelling of Vulcan Headland suggests a 3-5 mm rise since April 1986. Neither tilt nor EDM data showed any significant changes.
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 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. de Saint-Ours and C. McKee, RVO.