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Report on Rabaul (Papua New Guinea) — March 1998


Bulletin of the Global Volcanism Network, vol. 23, no. 3 (March 1998)
Managing Editor: Richard Wunderman.

Rabaul (Papua New Guinea) Ash emissions, pyroclastic flows, and inflation during March

Please cite this report as:

Global Volcanism Program, 1998. Report on Rabaul (Papua New Guinea) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 23:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199803-252140


Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)

Eruptive activity at Tavurvur persisted during March following the 3 February eruption (BGVN 23:02), producing ash emissions, small pyroclastic flows, and relatively low but fluctuating seismicity. Seismicity peaked around20 March, when eruptions became more energetic, and was probably related to near-surface eruptive activity.

Deformation monitoring indicated steady inflation at Tavurvur. Readings from the Sulphur Creek water tube (3.5 km NW of Tavurvur) revealed a change of ~3 µrad tilt away from the volcano during March. Leveling and real-time GPS also showed continuing inflation.

Tavurvur continued to erupt throughout March and emitted ash at intervals of ~10 minutes to several hours; the rapidly convecting column sometimes rose 2-4 km. After emissions had ceased for more than 10-20 minutes, activity would often recommence with explosions that threw large numbers of blocks from the vent. Blocks up to 1 m in diameter were regularly thrown 1 km S and W of the vent, landing out to sea. Large blocks (~3-4 m across) littered the rim and upper slopes of Tavurvur, probably produced during larger-than-usual explosions on 7 and 8 March.

The 8 March explosion sent red oxide-covered lava blocks and boulders over the S crater rim and down the S flank of Tavurvur, where the flow traveled ~1 km. This mass was described as being "pushed" from the vent immediately prior to the explosion. At other times the ash plume underwent partial column collapse and sent short, billowing flows randomly down the cone's flanks. The flows deposited light gray dust ~50-150 m downslope in well-defined tongues.

During 18-26 March night glow became more evident; occasionally lava fountains sent glowing fragments 200-300 m above the crater rim for up to 5 minutes at a time. During 26-31 March intermittent ash emissions with discrete explosions after longer periods of quiescence resumed.

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: Ben Talai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.