Report on Rabaul (Papua New Guinea) — November 1997
Bulletin of the Global Volcanism Network, vol. 22, no. 11 (November 1997)
Managing Editor: Richard Wunderman.
Rabaul (Papua New Guinea) Slow ongoing inflation
Please cite this report as:
Global Volcanism Program, 1997. Report on Rabaul (Papua New Guinea) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 22:11. Smithsonian Institution.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
Slow caldera inflation continued throughout November. Weak emissions of white vapor were produced by Tavurvur cone. The volume of emissions increased at the end of the month in response to rainfall. On 26 November, weak night glow was visible and a brief rumbling sound was heard.
Slow, ongoing inflation has occurred since the last significant lava-producing eruption at Tavurvur on 14 March (BGVN 22:03), despite subsequent minor Strombolian and Vulcanian eruptions on 12 April, 1 June, 11 July, and 17 August (BGVN 22:04, 22:05, 22:07, and 22:08). The inflation mainly affected areas within ~3 km of Tavurvur and the Greet Harbour shallow magma reservoir. Maximum rates of tilt were no more than 4 µrad /month; maximum monthly uplift was no more than 1 cm.
One high-frequency event from the NW was recorded on 14 November; no low-frequency events occurred during the month. SO2 output measured by COSPEC decreased in mid-November from ~800 to ~300 tons/day. Soil CO2 flux, monitored at 14 locations around the bay, was relatively low (<=200 mg/(m2 day)).
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: Patrice de Saint-Ours, Rabaul Volcano Observatory, P.O. Box 386, Rabaul, Papua New Guinea.