Report on Rabaul (Papua New Guinea) — 4 October-10 October 2006
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 4 October-10 October 2006
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2006. Report on Rabaul (Papua New Guinea) (Sennert, S, ed.). Weekly Volcanic Activity Report, 4 October-10 October 2006. 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)
The RVO reported that a large, sustained Vulcanian eruption of Rabaul began at about 0845 on 7 October. An ash column rose to over 5 km (16,400 ft a.s.l.) and had produced thunder and lightning. Sand-sized particles fell to the E. By 1200, windows rattled and doors slammed in the nearby town of Rabaul, N of Tavurvur crater, from semi-continuous air blasts that became rhythmic. Windows in the observatory, 12 km away, blew out from shockwaves. Moderately heavy ash fell in southern Rabaul town. Lapilli ~1 mm in diameter and lithics up to 3 cm in diameter fell in the S and SW parts of the caldera. Residents affected by heavier ashfall and air blasts self-evacuated. The eruption grew to sub-Plinian status throughout the day. Thick ash plumes reached 18 km (59,000 ft a.s.l.) altitude and dispersed N, NW, S, and SW. Ashfall affected the entire Gazelle Peninsula.
At 1415, the eruption style changed to Strombolian, which lasted until about 1730. During the night, moderate to bright incandescence was observed on the N rim of Tavurvur. Explosions and loud roaring noises were occasionally heard.
On 8 October, thick white and blue vapor clouds were accompanied by ash explosions and plumes that drifted N and NW. Lava flows on the W and N flanks were visible from 2 km NW in Rapindik. The lava flow on the W flank reached the sea, causing secondary explosions.
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 asymmetrical 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 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W 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.