Report on Rabaul (Papua New Guinea) — March 1999
Bulletin of the Global Volcanism Network, vol. 24, no. 3 (March 1999)
Managing Editor: Richard Wunderman.
Rabaul (Papua New Guinea) Small pyroclastic flows following explosions during 15-20 February
Please cite this report as:
Global Volcanism Program, 1999. Report on Rabaul (Papua New Guinea) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 24:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199903-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
Moderate activity at Tavurvur continued during February with quiet, intermittent emissions of pale gray ash rising 600-1,000 m above the summit. Variable NW winds led to light ashfalls at Talwat and Matupit. A short period of more energetic activity during 15-20 February included moderate explosions ejecting lava blocks and dark gray ash. Small pyroclastic flows were generated down the S flank and ash rose to about 2,000 m. Some light ashfall was reported as far south as Kokopo.
Although the caldera was still restless, leveling, tilt, and GPS showed minor deformation with few significant movements during February. Seismicity was much lower than that previous months; low-frequency events totaled 465, compared with 2,843 in December 1998 and 1,413 in January 1999. Twenty-four explosive events were recorded, on 3, 4, 8, 12-18, 20, 21, 23, and 24 February. Only two high-frequency events were detected NE of the caldera, compared with 28 in that direction during January.
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: Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.