Report on Rabaul (Papua New Guinea) — March 2000
Bulletin of the Global Volcanism Network, vol. 25, no. 3 (March 2000)
Managing Editor: Richard Wunderman.
Rabaul (Papua New Guinea) During early 2000, occasional ash clouds and the 1995 vent reactivates
Please cite this report as:
Global Volcanism Program, 2000. Report on Rabaul (Papua New Guinea). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 25:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200003-252140.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
After the emissions of dark gray ash clouds from the 1941 vent on 30 December 1999, through 16 January 2000 activity consisted mostly of thin white and grayish clouds. Occasional pale gray to dark gray ash clouds of moderate volumes were interspersed among the ongoing thin white vapor emissions.
The 1995 lava-producing vent reactivated on 16 January at 1532 with emissions of dark gray ash clouds until the 18th, before going quiet again at month's end. The initial emissions on 16 January occurred frequently (4/minute) during the first 30-45 minutes before decreasing to 1/minute thereafter. The ash clouds rose ~500-1,000 m above the summit and were later blown by high-altitude winds to the N and low-altitude winds to the SE, resulting in ashfalls in those directions.
Seismicity associated with the ongoing activity at Tavurvur was very low in January. A total of 66 low-frequency events were detected, of which most were associated with surface activity. The only harmonic tremor was recorded on the 30th. Nine high-frequency events were recorded during the month. Only two of these events which originated NE of the volcano, were located outside of the caldera. The other seven were too small to locate; however, their arrival times indicated an azimuth of NE.
The eruptive activity remained low throughout February. Gentle emissions of very thin volumes of white vapor continued for most of the period. However, between 7 and 14 February small volumes of pale gray ash clouds were produced at irregular intervals, and seismicity fluctuated. Again between 21st and 22nd small amounts of white-to-brownish ash clouds were produced. Most of the ash emissions during both periods rose to several hundred meters above the summit before they were blown to the SE and occasionally to the N, NW, and SW by variable winds. Very fine ash fell in the same areas.
Event trigger counts were similar to December 1999 and January 2000, with a total of 78 low-frequency events detected. Most of these were associated with the summit activity of Tavurvur. Three high-frequency earthquakes were detected in February. Two were located to the S and NE, outside of the caldera. The other was too small to locate, however, arrival times on the few stations that detected it indicated a NE azimuth.
A slight increase in ash emission associated with sub-continuous non-harmonic tremor was observed in March. Bands of such tremor were recorded on 8, 14-20, and 30-31 March. The tremor occurred only once each day, but at different times of the day. The duration for each episode of tremor ranged from an hour to about 5 hours. During the corresponding period of 15-20 March, Tavurvur's 1995 vent produced occasional gentle puffs of thick gray ash clouds that were blown SE by low-altitude winds and later to the W by high-altitude winds. Similar ash emission was observed on 31st. On that day the ash clouds rose only a few hundred meters at the highest and were later blown N and NW. The 1941 vent remained quiet, releasing only very small volumes of thin white vapor.
March's low-frequency earthquakes continued to fluctuate around normal background. Trigger counts for March were 90. Most of these events were associated with the summit activity of Tavurvur. Seven high-frequency earthquakes were detected in March. Three were locatable. The others occurred outside of the caldera. Ground deformation measurements by the electronic and water-tube tilt instrumentation showed an inflationary trend which began in late February.
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, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.