Report on Rabaul (Papua New Guinea) — 25 June-1 July 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 June-1 July 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Rabaul (Papua New Guinea). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 25 June-1 July 2003. Smithsonian Institution and US Geological Survey.
Papua New Guinea
4.271°S, 152.203°E; summit elev. 688 m
All times are local (unless otherwise noted)
There was a noticeable decline in ash eruptions from Rabaul caldera's Tavurvur cone on 22 June through at least 30 June. Around the 19th, ash plumes drifted NW, depositing ash in Rabaul Town and nearby villages. On 19 and 21 June ash emissions occurred within several minutes of each other, but on the 22nd the interval became much longer with no ash emissions occuring for as long as an hour. Ash-laden plumes rose between several hundred and ~1,500 m above the summit. Seismicity decreased on the 22nd, with the occurance of fewer low-frequency earthquakes that are associated with eruptive activity. No significant changes in deformation were recorded.
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.
Source: Rabaul Volcano Observatory (RVO)