Report on Rabaul (Papua New Guinea) — April 1994
Bulletin of the Global Volcanism Network, vol. 19, no. 4 (April 1994)
Managing Editor: Richard Wunderman.
Rabaul (Papua New Guinea) Seismicity continues to decline; additional uplift at Matupit Island
Please cite this report as:
Global Volcanism Program, 1994. Report on Rabaul (Papua New Guinea). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 19:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199404-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
"There was a further decline in the level of seismicity in April. A total of 397 caldera earthquakes were recorded, down from 458 in March and 580 in February. Of this total, 181 earthquakes occurred during four small swarms that took place on the 13th (33), 17th (73), 19th (38), and 25th (37). Thirty-eight of the caldera earthquakes were located. About half of them were scattered evenly in the N part of the caldera seismic zone. The rest were located in the W part of the seismic zone near Vulcan. Routine levelling . . . on 2 May showed that uplift of ~25 mm had taken place at the S end of Matupit Island since the previous survey on 16 March."
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: I. Itikarai and C. McKee, RVO.